effect of leaching from filters on laboratory analyses - Environmental ...
effect of leaching from filters on laboratory analyses - Environmental ...
effect of leaching from filters on laboratory analyses - Environmental ...
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EFFECT OF LEACHING FROM FILTERS ON LABORATORY ANALYSES OF<br />
COLLECTIVE ORGANIC CONSTITUENTS<br />
ABSTRACT<br />
Eakalak Khan,* Sindhuja Subramania-Pillai**<br />
*Department <str<strong>on</strong>g>of</str<strong>on</strong>g> Civil Engineering<br />
North Dakota State University<br />
Fargo, North Dakota 58105<br />
**North Dakota State Water Commissi<strong>on</strong>, Bismarck, North Dakota<br />
Membrane and glass fiber <str<strong>on</strong>g>filters</str<strong>on</strong>g> are widely used in <strong>laboratory</strong> water and wastewater <strong>analyses</strong>.<br />
During sample filtrati<strong>on</strong>, some <str<strong>on</strong>g>filters</str<strong>on</strong>g> release organic compounds, which may interfere with<br />
organic <strong>analyses</strong>. This research investigated the interferences due to organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> in the<br />
determinati<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> dissolved organic carb<strong>on</strong>, biodegradable dissolved organic carb<strong>on</strong>, soluble<br />
biochemical oxygen demand, and soluble chemical oxygen demand and the appropriate cleaning<br />
method for the <str<strong>on</strong>g>filters</str<strong>on</strong>g>. Nineteen <str<strong>on</strong>g>filters</str<strong>on</strong>g> studied included 16 membrane <str<strong>on</strong>g>filters</str<strong>on</strong>g> and 3 glass fiber<br />
<str<strong>on</strong>g>filters</str<strong>on</strong>g>. A wide variati<strong>on</strong> was observed <strong>on</strong> the amount and characteristics <str<strong>on</strong>g>of</str<strong>on</strong>g> organics <str<strong>on</strong>g>leaching</str<strong>on</strong>g><br />
<str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g>. Some <str<strong>on</strong>g>filters</str<strong>on</strong>g> showed no organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> while some others had very high<br />
organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g>. Soaking the <str<strong>on</strong>g>filters</str<strong>on</strong>g> in dei<strong>on</strong>ized distilled water (DDW) resulted in more<br />
leachable organics <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> compared with filtering DDW through them. Certain <str<strong>on</strong>g>filters</str<strong>on</strong>g><br />
should be avoided for use in the above <strong>analyses</strong> and soaking in DDW is a more suitable cleaning<br />
method than discarding initial filtrati<strong>on</strong> volumes for most <str<strong>on</strong>g>filters</str<strong>on</strong>g>.<br />
KEYWORDS<br />
Leaching, organics, <str<strong>on</strong>g>filters</str<strong>on</strong>g>, interference, <strong>laboratory</strong> <strong>analyses</strong>.<br />
INTRODUCTION<br />
WEFTEC®.06<br />
Filtrati<strong>on</strong> is used to process water samples in a variety <str<strong>on</strong>g>of</str<strong>on</strong>g> science and engineering fields<br />
(Horowitz et al., 1996). In the field <str<strong>on</strong>g>of</str<strong>on</strong>g> water quality, it is mainly employed to distinguish<br />
between suspended and dissolved c<strong>on</strong>stituents (Otsuki and Fuwa, 1977; Daniels<strong>on</strong>, 1982; Aiken<br />
and Leenheer, 1993; Burgess et al., 1996). Filtrati<strong>on</strong> is carried out mainly using either membrane<br />
<str<strong>on</strong>g>filters</str<strong>on</strong>g> or glass fiber <str<strong>on</strong>g>filters</str<strong>on</strong>g>. The <str<strong>on</strong>g>filters</str<strong>on</strong>g> used should neither introduce any artifacts to the analysis<br />
nor affect the analytical procedure. Some problems associated the use <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>filters</str<strong>on</strong>g> are as follows:<br />
<str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> organic carb<strong>on</strong> and ultraviolet (UV) absorbing comp<strong>on</strong>ents, absorpti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> dissolved<br />
and colloidal matter, and clogging <str<strong>on</strong>g>of</str<strong>on</strong>g> membrane surface because <str<strong>on</strong>g>of</str<strong>on</strong>g> the build up <str<strong>on</strong>g>of</str<strong>on</strong>g> the particulate<br />
matter (Karanfil et al., 2003).<br />
The operati<strong>on</strong>al definiti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> dissolved c<strong>on</strong>stituents in water is the porti<strong>on</strong> that passes through a<br />
0.45 μm pore size filter (APHA et al., 1998; U.S. Envir<strong>on</strong>mental Protecti<strong>on</strong> Agency, 1999). Only<br />
membrane <str<strong>on</strong>g>filters</str<strong>on</strong>g> are available with a uniform absolute pore size (Retenti<strong>on</strong> efficiency <str<strong>on</strong>g>of</str<strong>on</strong>g> 100%<br />
for rated pore size) <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.45 μm. The smallest nominal pore size (Retenti<strong>on</strong> efficiency 60 to 98%<br />
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2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
901
WEFTEC®.06<br />
for rated pore size) <str<strong>on</strong>g>of</str<strong>on</strong>g> glass fiber <str<strong>on</strong>g>filters</str<strong>on</strong>g> is larger than 0.45 μm. As a result, they are not<br />
appropriate for use in dissolved c<strong>on</strong>stituent measurements. However, membrane <str<strong>on</strong>g>filters</str<strong>on</strong>g> because<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> their organic compositi<strong>on</strong> suffer <str<strong>on</strong>g>from</str<strong>on</strong>g> organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g>. In order to avoid the possible organic<br />
c<strong>on</strong>taminati<strong>on</strong> <str<strong>on</strong>g>from</str<strong>on</strong>g> membrane <str<strong>on</strong>g>filters</str<strong>on</strong>g>, some researchers (Dubruiel et al., 1997; Khan et al., 1998)<br />
used glass fiber <str<strong>on</strong>g>filters</str<strong>on</strong>g> for dissolved organic carb<strong>on</strong> determinati<strong>on</strong> while some other researchers<br />
used the membrane <str<strong>on</strong>g>filters</str<strong>on</strong>g> after dec<strong>on</strong>taminating them. Rinsing the <str<strong>on</strong>g>filters</str<strong>on</strong>g> with dilute nitric acid,<br />
dilute hydrochloric acid followed by distilled water, or dei<strong>on</strong>ized distilled water (DDW) have<br />
been reported as the dec<strong>on</strong>taminati<strong>on</strong> methods (Buffle et al., 1992; Baeyens et al., 1998; Karanfil<br />
et al., 2003).<br />
Hwang et al. (1979) examined the c<strong>on</strong>centrati<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> total organic carb<strong>on</strong> (TOC), chemical<br />
oxygen demand (COD) and nitrate in the filtrates <str<strong>on</strong>g>of</str<strong>on</strong>g> a Millipore mixed cellulose acetate and<br />
cellulose nitrate membrane filter. Moderate to significant amounts <str<strong>on</strong>g>of</str<strong>on</strong>g> TOC, COD, and nitrate<br />
were released <str<strong>on</strong>g>from</str<strong>on</strong>g> the filter. Norrman (1993) used pre-packed and membrane <str<strong>on</strong>g>filters</str<strong>on</strong>g> for<br />
dissolved organic carb<strong>on</strong> (DOC) determinati<strong>on</strong>. The filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> the membrane <str<strong>on</strong>g>filters</str<strong>on</strong>g> showed<br />
severe c<strong>on</strong>taminati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> DOC. Kaplan et al. (1993) reported that polyvinylidene difluoride and<br />
mixed cellulose ester <str<strong>on</strong>g>filters</str<strong>on</strong>g> used for sterilizing incubati<strong>on</strong> water leached significant amounts <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
DOC and assimilable organic carb<strong>on</strong> (AOC) and that polysulf<strong>on</strong>e and nyl<strong>on</strong> <str<strong>on</strong>g>filters</str<strong>on</strong>g> released DOC<br />
even after copious washing with dei<strong>on</strong>ized water. Their study also indicated that AOC<br />
c<strong>on</strong>centrati<strong>on</strong>s were significantly higher with membrane filtrati<strong>on</strong> than with glass fiber filtrati<strong>on</strong>.<br />
Shaw et al. (2000) found that as much as 2 mg/L <str<strong>on</strong>g>of</str<strong>on</strong>g> biodegradable dissolved organic carb<strong>on</strong><br />
(BDOC) is released <str<strong>on</strong>g>from</str<strong>on</strong>g> a 0.22 μm pore size cellulose acetate membrane filter. Details<br />
regarding the amount <str<strong>on</strong>g>of</str<strong>on</strong>g> sample filtered were not provided by the authors. Khan et al. (1998)<br />
studied the organics released <str<strong>on</strong>g>from</str<strong>on</strong>g> the same type <str<strong>on</strong>g>of</str<strong>on</strong>g> filter. The <str<strong>on</strong>g>filters</str<strong>on</strong>g> released about 0.40 to 0.50<br />
mg <str<strong>on</strong>g>of</str<strong>on</strong>g> TOC. The organics leached <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> were about 50% to 85% biodegradable. The<br />
biodegradability <str<strong>on</strong>g>of</str<strong>on</strong>g> the organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> other types <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>filters</str<strong>on</strong>g> has not been reported.<br />
Karanfil et al. (2003) tested seventeen different <str<strong>on</strong>g>filters</str<strong>on</strong>g> for their interferences in DOC and<br />
ultraviolet absorbance at 254 nm (UV254) measurements. For all seventeen <str<strong>on</strong>g>filters</str<strong>on</strong>g> tested, UV254<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> the first 100 mL extract was less than 0.0045 cm -1 . For UV scans between 200 and 800 nm <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
the 100 mL filtrate, there were no light absorbing impurities detected. Hydrophilic<br />
polyethersulf<strong>on</strong>e <str<strong>on</strong>g>filters</str<strong>on</strong>g> followed by hydrophilic polypropylene <str<strong>on</strong>g>filters</str<strong>on</strong>g> exhibited the least organic<br />
<str<strong>on</strong>g>leaching</str<strong>on</strong>g> and thus interference with DOC analysis. To minimize the interferences, the <str<strong>on</strong>g>filters</str<strong>on</strong>g><br />
should be rinsed with a minimum <str<strong>on</strong>g>of</str<strong>on</strong>g> 30 mL distilled and dei<strong>on</strong>ized water per cm 2 <str<strong>on</strong>g>of</str<strong>on</strong>g> filter surface<br />
area or at least 500 mL <strong>on</strong> a 47-mm diameter filter to make the filtrate free <str<strong>on</strong>g>of</str<strong>on</strong>g> DOC and UV<br />
absorbing comp<strong>on</strong>ents.<br />
Filtrati<strong>on</strong> through a filter is an essential step for determining DOC, soluble COD (SCOD),<br />
soluble biochemical oxygen demand (SBOD) and BDOC <str<strong>on</strong>g>of</str<strong>on</strong>g> a water sample. The interference<br />
due to filter <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <strong>on</strong> DOC measurement was thoroughly investigated (Karanfil et al., 2003)<br />
while its <str<strong>on</strong>g>effect</str<strong>on</strong>g>s <strong>on</strong> SCOD and BDOC measurements were studied <strong>on</strong>ly for <strong>on</strong>e type <str<strong>on</strong>g>of</str<strong>on</strong>g> filter<br />
(Hwang et al., 1979; Khan et al., 1998; Shaw et al., 2000). The interference <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> <strong>on</strong><br />
SBOD measurement has not been studied.<br />
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2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
902
This paper presents a detailed investigati<strong>on</strong> <strong>on</strong> the interferences c<strong>on</strong>tributed by filter <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <strong>on</strong><br />
DOC, SCOD, SBOD, and BDOC measurements for comm<strong>on</strong>ly used <str<strong>on</strong>g>filters</str<strong>on</strong>g>. The interference <strong>on</strong><br />
DOC measurement was investigated to c<strong>on</strong>firm the results <str<strong>on</strong>g>from</str<strong>on</strong>g> a previous study (Karanfil et al.,<br />
2003) and to select the <str<strong>on</strong>g>filters</str<strong>on</strong>g>, that have substantial organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g>, for SBOD and BDOC tests.<br />
The variati<strong>on</strong>s in organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> generated by different filter manufactures and pore sizes were<br />
examined. In additi<strong>on</strong>, the <str<strong>on</strong>g>effect</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> filter soaking in DDW <strong>on</strong> the leachable organics was studied<br />
and compared with a comm<strong>on</strong> filter cleaning practice by discarding initial volumes <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrate<br />
to determine an appropriate method for minimizing the interference caused by organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g>.<br />
METHODOLOGY<br />
Filters<br />
Nineteen different <str<strong>on</strong>g>filters</str<strong>on</strong>g> made <str<strong>on</strong>g>of</str<strong>on</strong>g> 11 different materials were studied (Table 1). The selecti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
filter materials was based <strong>on</strong> a survey by Karanfil et al. (2002), which was c<strong>on</strong>ducted am<strong>on</strong>g<br />
drinking water practiti<strong>on</strong>ers and researchers to determine current practices for measuring DOC<br />
and UV absorbance in water samples. The <str<strong>on</strong>g>filters</str<strong>on</strong>g> tested in this study covered all filter materials<br />
reported in Karanfil et al. (2002) except for glass fiber <str<strong>on</strong>g>filters</str<strong>on</strong>g> with binders. Glass fiber <str<strong>on</strong>g>filters</str<strong>on</strong>g><br />
with binders were not studied as Standard Methods (APHA et al., 1998) explicitly recommends<br />
using glass fiber <str<strong>on</strong>g>filters</str<strong>on</strong>g> without binders for UV absorbance measurements. This study included<br />
hydrophilic nyl<strong>on</strong> <str<strong>on</strong>g>filters</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.45 µm pore size manufactured by four different manufacturers in<br />
order to determine the differences in the organics <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> the same pore size<br />
and filter material but produced by different manufacturers. Filters made <str<strong>on</strong>g>of</str<strong>on</strong>g> the same material,<br />
manufactured by the same manufacturer but <str<strong>on</strong>g>of</str<strong>on</strong>g> different pore sizes were included to determine<br />
the differences in organics <str<strong>on</strong>g>leaching</str<strong>on</strong>g> caused by pore size. They were hydrophilic polyethersulf<strong>on</strong>e<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> pore sizes 0.20 µm, 0.45 µm and 0.80 µm, cellulose acetate filter <str<strong>on</strong>g>of</str<strong>on</strong>g> pore sizes 0.20 µm and<br />
0.45 µm and glass fiber <str<strong>on</strong>g>filters</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> pore sizes 0.70 µm and 1.5 µm.<br />
Water Samples<br />
Laboratory grade DDW was used as water samples. It was prepared using electrically heated<br />
stills (Barnstead/Thermolyne, Model A1013–B, Dubuque, Iowa) and the E-pure<br />
(Barnstead/Thermolyne, Model D4631, Dubuque, Iowa) water purificati<strong>on</strong> system, which<br />
c<strong>on</strong>sisted <str<strong>on</strong>g>of</str<strong>on</strong>g> the following three cartridges in sequence: macropure, ultrapure, and organic free.<br />
Only DDW, that had higher than 17 MΩ resistivity, was collected and stored for use in high<br />
density polyethylene carboys (Nalgene Co., Rochester, New York). The DDW was always<br />
checked for its organic carb<strong>on</strong> c<strong>on</strong>centrati<strong>on</strong> before using it and always had less than 0.1 mg<br />
TOC/L.<br />
Experimental Setup and Procedure<br />
WEFTEC®.06<br />
The experimental setup and procedure was divided in to two parts: filtrati<strong>on</strong> test and soak test.<br />
Two different types <str<strong>on</strong>g>of</str<strong>on</strong>g> tests were c<strong>on</strong>ducted <strong>on</strong> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> in order to determine the behavior <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
the <str<strong>on</strong>g>filters</str<strong>on</strong>g> with respect to <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> organics, when subjected to different test c<strong>on</strong>diti<strong>on</strong>s.<br />
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2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
903
904<br />
Copyright ©<br />
2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
Table 1 - Filters Used in the Study<br />
Filter Type Filter Material<br />
Gelman<br />
Versapor<br />
Gelman GN-6<br />
Gelman FP-<br />
Vericel<br />
Gelman HT-<br />
Tuffryn<br />
Gelman<br />
Nylaflo<br />
Millipore<br />
Nyl<strong>on</strong><br />
Osm<strong>on</strong>ic<br />
Magna Nyl<strong>on</strong><br />
Whatman<br />
Nyl<strong>on</strong><br />
Gelman Supor<br />
200<br />
Gelman Supor<br />
450<br />
Gelman Supor<br />
800<br />
Whatman<br />
(WCN)<br />
Hydrophilic acrylic<br />
polymer<br />
Hydrophilic mixed<br />
cellulose ester<br />
Hydrophilic<br />
polyvinylidene<br />
fluoride<br />
Hydrophilic<br />
polysulf<strong>on</strong>e<br />
Pore Size<br />
(µm)<br />
0.45<br />
0.45<br />
0.45<br />
0.45<br />
Applicati<strong>on</strong> Manufacturer Informati<strong>on</strong><br />
Prefiltrati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> difficult to filter soluti<strong>on</strong>s and<br />
serum<br />
Microbiological analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> potable, waste, process<br />
and natural waters<br />
HPLC sample preparati<strong>on</strong>, mobile phase<br />
filtrati<strong>on</strong>/degassing and solvent filtrati<strong>on</strong><br />
Sterlizati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> culture media and other aqueous<br />
soluti<strong>on</strong>s<br />
Hydrophilic nyl<strong>on</strong> 0.45 Aqueous and solvent based applicati<strong>on</strong>s<br />
Hydrophilic nyl<strong>on</strong> 0.45<br />
Hydrophilic nyl<strong>on</strong> 0.45<br />
Used in clarifying aqueous or organic soluti<strong>on</strong>s<br />
prior to HPLC analysis<br />
Aqueous filtrati<strong>on</strong> without wetting and organic<br />
solvent filtrati<strong>on</strong>s such as HPLC, for<br />
microbiological work<br />
Hydrophilic nyl<strong>on</strong> 0.45 Biotechnology and chromatography applicati<strong>on</strong>s<br />
Hydrophilic<br />
polyethersulf<strong>on</strong>e<br />
Hydrophilic<br />
polyethersulf<strong>on</strong>e<br />
Hydrophilic<br />
polyethersulf<strong>on</strong>e<br />
0.20<br />
0.45<br />
0.80<br />
Cellulose nitrate 0.45<br />
Biological, pharmaceutical and sterlizing filtrati<strong>on</strong><br />
requirements<br />
Biological, pharmaceutical and sterlizing filtrati<strong>on</strong><br />
requirements<br />
Biological, pharmaceutical and sterlizing filtrati<strong>on</strong><br />
requirements<br />
Routine applicati<strong>on</strong>s involving particles and cells<br />
<str<strong>on</strong>g>from</str<strong>on</strong>g> 0.1 to 5.0mm<br />
Pall corporati<strong>on</strong>,<br />
Ann Arbor, MI, USA.<br />
Pall corporati<strong>on</strong>,<br />
Ann Arbor, MI, USA.<br />
Pall corporati<strong>on</strong>,<br />
Ann Arbor, MI, USA.<br />
Pall corporati<strong>on</strong>,<br />
Ann Arbor, MI, USA.<br />
Pall corporati<strong>on</strong>,<br />
Ann Arbor, MI, USA.<br />
Millipore corporati<strong>on</strong>,<br />
Bedford, MA, USA.<br />
Osm<strong>on</strong>ics Inc.,<br />
Minnet<strong>on</strong>ka, MN, USA.<br />
Whatman Internati<strong>on</strong>al<br />
Ltd., Maidst<strong>on</strong>e, UK.<br />
Pall corporati<strong>on</strong>,<br />
Ann Arbor, MI, USA.<br />
Pall corporati<strong>on</strong>,<br />
Ann Arbor, MI, USA.<br />
Pall corporati<strong>on</strong>,<br />
Ann Arbor, MI, USA.<br />
Whatman Internati<strong>on</strong>al<br />
Ltd., Maidst<strong>on</strong>e, UK.<br />
WEFTEC®.06
905<br />
Copyright ©<br />
2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
Table 1 - Filters Used in the Study (C<strong>on</strong>tinued)<br />
Filter Type Filter Material<br />
Whatman<br />
Nucleopore<br />
Gelman GH<br />
Polypro<br />
Polycarb<strong>on</strong>ate 0.40<br />
Hydrophilic<br />
propylene<br />
Pore Size<br />
(µm)<br />
0.45<br />
Advantec Cellulose acetate 0.45<br />
Advantec Cellulose acetate 0.20<br />
Whatman<br />
GF/F<br />
Applicati<strong>on</strong> Manufacturer Informati<strong>on</strong><br />
Medical, industrial filtrati<strong>on</strong>, fluid analysis, water<br />
testing, chemical assay, solvent filtrati<strong>on</strong> and<br />
bacteria m<strong>on</strong>itoring<br />
Filtrati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> aqueous soluti<strong>on</strong>s and aggressive<br />
solvents<br />
Tissue culture media, protein, enzyme, biological<br />
media sterilizati<strong>on</strong>,<br />
Tissue culture media, protein, enzyme, biological<br />
media sterilizati<strong>on</strong>,<br />
Glass fiber 0.70 Filtrati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> dilute aqueous soluti<strong>on</strong>s<br />
Gelman A/E Glass fiber 1.00<br />
Whatman 934-<br />
AH<br />
For dissolved and suspended solids testing in<br />
sanitary water analysis procedures<br />
Glass fiber 1.50 Suspended solids in water analysis<br />
Whatman Internati<strong>on</strong>al<br />
Ltd., Maidst<strong>on</strong>e, UK.<br />
Pall corporati<strong>on</strong>,<br />
Ann Arbor, MI, USA.<br />
Advantec MFS Inc.,<br />
Pleas<strong>on</strong>t<strong>on</strong>, CA, USA.<br />
Advantec MFS Inc.,<br />
Pleas<strong>on</strong>t<strong>on</strong>, CA, USA.<br />
Whatman Internati<strong>on</strong>al<br />
Ltd., Maidst<strong>on</strong>e, UK.<br />
Pall corporati<strong>on</strong>,<br />
Ann Arbor, MI, USA.<br />
Whatman Internati<strong>on</strong>al<br />
Ltd., Maidst<strong>on</strong>e, UK.<br />
WEFTEC®.06
WEFTEC®.06<br />
Filtrati<strong>on</strong> Test. The filtrati<strong>on</strong> test apparatus c<strong>on</strong>sisted <str<strong>on</strong>g>of</str<strong>on</strong>g> 300 mL capacity glass funnel, stainless<br />
steel support screen for the filter, glass base for the stainless steel support, silic<strong>on</strong>e stopper,<br />
polytetrafluoroethylene support screen gaskets, aluminum clamp, and graduated Erlenmeyer<br />
flask with a side arm to attach to vacuum. The vacuum (25 in mmHg) was applied by using<br />
lubricated reciprocating <strong>laboratory</strong> pumps (Model No. 0522-V4B-G18ODX, Gast Manufacturing<br />
Corporati<strong>on</strong>, Bent<strong>on</strong> Harbor, Michigan).<br />
The filtrati<strong>on</strong> test for DOC measurement was carried out in 50 mL increments. The filtrates were<br />
collected in separate vials for each 50 mL increment and then analyzed for TOC. Filtrati<strong>on</strong> was<br />
c<strong>on</strong>tinued up to a cumulative volume <str<strong>on</strong>g>of</str<strong>on</strong>g> 300 mL for all <str<strong>on</strong>g>filters</str<strong>on</strong>g> studied except for Gelman FP-<br />
Vericel and Gelman HT-Tuffryn. For these two <str<strong>on</strong>g>filters</str<strong>on</strong>g>, the filtrati<strong>on</strong> was carried out up to a<br />
cumulative volume <str<strong>on</strong>g>of</str<strong>on</strong>g> 1000 mL because both were found to be highly c<strong>on</strong>taminated in a previous<br />
study (Karanfil et al., 2003). For each type <str<strong>on</strong>g>of</str<strong>on</strong>g> filter, in order to determine the average DOC<br />
<str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g>, 3 to 4 <str<strong>on</strong>g>filters</str<strong>on</strong>g> were tested. For each type <str<strong>on</strong>g>of</str<strong>on</strong>g> filter, a clean setup was used.<br />
The setup was tested for any organic c<strong>on</strong>taminati<strong>on</strong> by passing 50 mL <str<strong>on</strong>g>of</str<strong>on</strong>g> DDW through it twice<br />
without the filter and testing the passing water for TOC.<br />
For COD determinati<strong>on</strong>, according to Standard Methods (APHA et al., 1998), the maximum<br />
volumes <str<strong>on</strong>g>of</str<strong>on</strong>g> sample are 10 mL and 50 mL for the closed and open reflux methods, respectively.<br />
Since the objective <str<strong>on</strong>g>of</str<strong>on</strong>g> this study was to determine the organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g>, and to<br />
find its interference in the organic parameter determinati<strong>on</strong>, COD was determined for the first 50<br />
mL filtrate <strong>on</strong>ly. The sample for COD was withdrawn <str<strong>on</strong>g>from</str<strong>on</strong>g> the 50 mL filtrate before it was<br />
analyzed for DOC.<br />
SBOD and BDOC measurements were studied for the <str<strong>on</strong>g>filters</str<strong>on</strong>g> whose 100 mL filtrate had DOC ≥<br />
0.3 mg/L. This cut<str<strong>on</strong>g>of</str<strong>on</strong>g>f initial DOC was chosen to be high enough for the method detecti<strong>on</strong> limit<br />
(MDL) <str<strong>on</strong>g>of</str<strong>on</strong>g> the BDOC procedure (or DOC difference before and after incubati<strong>on</strong>), which is 0.10<br />
to 0.15 mg/L (Khan et al., 1999).<br />
Biochemical oxygen demand (BOD) analysis can be carried out in 60 mL or 300 mL BOD<br />
bottles. For BDOC measurement, there is no standard method. BDOC is the measure <str<strong>on</strong>g>of</str<strong>on</strong>g> DOC<br />
depleti<strong>on</strong> in the sample after inoculati<strong>on</strong> with microorganisms. Assuming that the DOC<br />
measurement requires 40 mL, the volume <str<strong>on</strong>g>of</str<strong>on</strong>g> sample required for BDOC is at least 80 mL. As a<br />
result, for BDOC measurement, 100 mL is probably a minimum volume that would be filtered.<br />
In this study, 300 mL BOD bottles were used for simultaneous SBOD and BDOC<br />
determinati<strong>on</strong>s, and the minimum volume required was 340 mL: 40 mL for initial DOC<br />
measurement (for BDOC determinati<strong>on</strong>) and 300 mL for incubati<strong>on</strong>.<br />
The BDOC and SBOD measurements for each filter type were c<strong>on</strong>ducted in four replicates. To<br />
obtain sample for two replicate <strong>analyses</strong>, eight 100 mL filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> 8 different <str<strong>on</strong>g>filters</str<strong>on</strong>g> were<br />
combined. Then, the mixture was transferred to a 1 L pyrex bottle. After that, 800 µL <str<strong>on</strong>g>of</str<strong>on</strong>g> BOD<br />
nutrient salt soluti<strong>on</strong> was added to the sample. The sample was then aerated for 20 to 30 minutes<br />
using Kimble glass diffusers to attain dissolved oxygen (DO) saturati<strong>on</strong> in the sample for BOD<br />
measurement. Then, the sample was transferred into two 40 mL vials for initial DOC<br />
measurement and two BOD bottles, which c<strong>on</strong>tained 0.25 mL <str<strong>on</strong>g>of</str<strong>on</strong>g> washed mixed liquor suspended<br />
solids (MLSS) as a seed.<br />
Copyright ©<br />
2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
906
The MLSS was obtained <str<strong>on</strong>g>from</str<strong>on</strong>g> an activated sludge municipal wastewater treatment plant. The<br />
sample for two more replicates was obtained following the same procedure.<br />
BDOC was based <strong>on</strong> 5 days <str<strong>on</strong>g>of</str<strong>on</strong>g> incubati<strong>on</strong>. For FP-Vericel, HT-Tuffryn, Millipore Nyl<strong>on</strong>, and<br />
GH Polypro <str<strong>on</strong>g>filters</str<strong>on</strong>g>, DOC c<strong>on</strong>centrati<strong>on</strong> remaining after 5 days <str<strong>on</strong>g>of</str<strong>on</strong>g> incubati<strong>on</strong> was high. In order<br />
to check whether the BDOC at 5 days (BDOC5) was a major porti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> total biodegradable<br />
leached organics, the incubati<strong>on</strong> was c<strong>on</strong>tinued for these <str<strong>on</strong>g>filters</str<strong>on</strong>g> until 28 days and BDOC was<br />
determined (BDOC28). When the filtrate <str<strong>on</strong>g>from</str<strong>on</strong>g> the FP Vericel filter was tested for BOD without<br />
any diluti<strong>on</strong>, the final DO after 5 days <str<strong>on</strong>g>of</str<strong>on</strong>g> incubati<strong>on</strong> was below 1 mg/L. The criteria for BOD<br />
measurement are the depleti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> DO ≥ 2 mg/L and the final DO ≥ 1 mg/L. This filtrate was later<br />
diluted at a 1:2 ratio (1 porti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the sample and 2 porti<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> DDW) for the BOD and BDOC<br />
tests.<br />
Soak Test. Wide-mouthed, 500 mL Erlenmeyer flasks were used. The <str<strong>on</strong>g>filters</str<strong>on</strong>g> were individually<br />
placed inside the flasks with 100 mL DDW. The <str<strong>on</strong>g>filters</str<strong>on</strong>g> were allowed to be in the DDW for 24<br />
hours, and then, 40 mL <str<strong>on</strong>g>of</str<strong>on</strong>g> the water were taken for DOC analysis. Then, the remaining water<br />
was drained and refilled with a new batch <str<strong>on</strong>g>of</str<strong>on</strong>g> 100 mL DDW and the DOC analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> samples<br />
was performed after 24 hours. This was c<strong>on</strong>tinued until there was no <str<strong>on</strong>g>leaching</str<strong>on</strong>g> observed <str<strong>on</strong>g>from</str<strong>on</strong>g> the<br />
<str<strong>on</strong>g>filters</str<strong>on</strong>g> (when the DOC was less than 0.10 mg/L). The soak test <strong>on</strong> <str<strong>on</strong>g>filters</str<strong>on</strong>g> would provide a<br />
reas<strong>on</strong>able estimati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the maximum <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g>. Results <str<strong>on</strong>g>from</str<strong>on</strong>g> the soak test could<br />
be used to determine how much organics leach during the filtrati<strong>on</strong> test compared with the<br />
maximum <str<strong>on</strong>g>leaching</str<strong>on</strong>g> and to provide informati<strong>on</strong> <strong>on</strong> the possibility <str<strong>on</strong>g>of</str<strong>on</strong>g> using a different filter<br />
cleaning method. The soak test samples were analyzed <strong>on</strong>ly for DOC as DOC is the most<br />
accurate and precise parameter am<strong>on</strong>g the four parameters measured in the filtrati<strong>on</strong> test.<br />
Moreover, the soak test does not represent the way the filter is used for measuring SCOD,<br />
SBOD, and BDOC, so there is no necessity to get the informati<strong>on</strong> <strong>on</strong> the other parameters for the<br />
soak test samples. DOC is a good enough parameter to serve the purpose <str<strong>on</strong>g>of</str<strong>on</strong>g> the soak test.<br />
Glassware Cleaning<br />
All the glassware used for this study except the filtrati<strong>on</strong> funnel and filtrati<strong>on</strong> base was cleaned<br />
by the following procedure. First, all the glassware was washed with hot water and a <strong>laboratory</strong><br />
grade cleaning soluti<strong>on</strong> (7X, ICN Biomedicals Inc., Aurora, Ohio). Then, it was rinsed pr<str<strong>on</strong>g>of</str<strong>on</strong>g>usely<br />
with DDW, soaked in 10% nitric acid overnight and again rinsed pr<str<strong>on</strong>g>of</str<strong>on</strong>g>usely with DDW,<br />
respectively. The 10% nitric acid used for the soaking was prepared <str<strong>on</strong>g>from</str<strong>on</strong>g> a 70% reagent grade<br />
soluti<strong>on</strong> (Mallinckrodt Baker, Inc., Phillipsburg, New Jersey). Lastly, the cleaned glassware was<br />
baked at 550°C in a muffle furnace for 30 minutes. The cleaning <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrati<strong>on</strong> funnel and<br />
filtrati<strong>on</strong> base included all cleaning steps but baking.<br />
Analyses and Measurements<br />
WEFTEC®.06<br />
DOC was determined according to Standard Methods (APHA et al., 1998) using a TOC analyzer<br />
(Phoenix 8000, Emers<strong>on</strong> Process Management: Tekmar-Dohrmann Divisi<strong>on</strong>, Mas<strong>on</strong>, Ohio,<br />
USA). The COD for the samples were analyzed by using the closed reflux colorimetric method<br />
(APHA et al., 1998) using a spectrophotometer (Hach, DR/4000V, Loveland, Colarado, USA)<br />
and the Hach digesti<strong>on</strong> vials (Hach, Loveland, Colarado, USA) with a c<strong>on</strong>centrati<strong>on</strong> range <str<strong>on</strong>g>of</str<strong>on</strong>g> 0<br />
Copyright ©<br />
2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
907
to 40 ppm. BOD and BDOC <str<strong>on</strong>g>of</str<strong>on</strong>g> the samples were measured simultaneously following the<br />
procedure by Khan et al. (1999). The <strong>on</strong>ly modificati<strong>on</strong>s to the procedure were the usage <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.25<br />
mL MLSS instead <str<strong>on</strong>g>of</str<strong>on</strong>g> 2 mL and eliminati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the initial filtrati<strong>on</strong> step using a 0.7 µm pore size<br />
glass fiber filter. Only 0.25 mL <str<strong>on</strong>g>of</str<strong>on</strong>g> MLSS was used as inoculum, as it resulted in the DO<br />
depleti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> < 1 mg/L in the blank (Criteri<strong>on</strong> for depleti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> DO in the blank, APHA et al.,<br />
1998). The initial filtrati<strong>on</strong> step was eliminated because the samples for SBOD and BDOC<br />
<strong>analyses</strong> were likely to be particulate free as they were the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> different <str<strong>on</strong>g>filters</str<strong>on</strong>g> and<br />
DDW was used to generate them. DO was measured using a meter (Ori<strong>on</strong> model 850A Plus,<br />
Thermo Ori<strong>on</strong>, Beverly, Massachusetts, USA).<br />
Statistical Analyses<br />
The data were analyzed using the Tukey-Kramer multiple comparis<strong>on</strong>s, t-test, and paired t-test.<br />
The statistical <strong>analyses</strong> were performed using the Micros<str<strong>on</strong>g>of</str<strong>on</strong>g>t Excel XP and Statistical Analysis<br />
S<str<strong>on</strong>g>of</str<strong>on</strong>g>tware (SAS® 1999 versi<strong>on</strong> 8, Cary North Carolina, USA).<br />
RESULTS AND DISCUSSION<br />
Filtrati<strong>on</strong> Test<br />
WEFTEC®.06<br />
DOC Results. The DOC <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> all <str<strong>on</strong>g>filters</str<strong>on</strong>g> until a cumulative filtrati<strong>on</strong> volume <str<strong>on</strong>g>of</str<strong>on</strong>g> 300 mL is<br />
shown in Figure 1. It is evident that in all <str<strong>on</strong>g>filters</str<strong>on</strong>g> except for Gelman FP-Vericel and Gelman HT-<br />
Tuffryn the DOC <str<strong>on</strong>g>leaching</str<strong>on</strong>g> ceased within the first few initial incremental volumes. Gelman FP-<br />
Vericel had the highest organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> c<strong>on</strong>tinuing until a cumulative filtrati<strong>on</strong> volume <str<strong>on</strong>g>of</str<strong>on</strong>g> 1000<br />
mL (data not shown) followed by Gelman HT-Tuffryn, which had DOC <str<strong>on</strong>g>leaching</str<strong>on</strong>g> until a<br />
cumulative filtrati<strong>on</strong> volume <str<strong>on</strong>g>of</str<strong>on</strong>g> 500 mL (data not shown). The DOC values <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrates<br />
reported in this study compares well with those reported by Karanfil et al. (2003) for all <str<strong>on</strong>g>filters</str<strong>on</strong>g><br />
except for Gelman GH Polypro. The reas<strong>on</strong> for observing the difference for this filter is not<br />
clear. It might be because <str<strong>on</strong>g>of</str<strong>on</strong>g> the lot or batch variati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> tested.<br />
Statistical analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> the mass <str<strong>on</strong>g>of</str<strong>on</strong>g> carb<strong>on</strong> <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> hydrophilic nyl<strong>on</strong> <str<strong>on</strong>g>filters</str<strong>on</strong>g> using the<br />
Tukey-Kramer procedure indicated significant difference am<strong>on</strong>g the manufacturers (p = 0.05<br />
criteri<strong>on</strong>, data not shown). The difference am<strong>on</strong>g the manufacturers could be because <str<strong>on</strong>g>of</str<strong>on</strong>g> the<br />
differences in the manufacturing processes and/or the additives. For the polyethersulf<strong>on</strong>e <str<strong>on</strong>g>filters</str<strong>on</strong>g><br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> different pore sizes, there was no significant difference in the mass <str<strong>on</strong>g>of</str<strong>on</strong>g> carb<strong>on</strong> <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g><br />
Supor 450 filter (0.45 µm pore size) when compared with those <str<strong>on</strong>g>from</str<strong>on</strong>g> Supor 200 (0.20 µm pore<br />
size) and Supor 800 (0.80 µm pore size), but there was a difference between those <str<strong>on</strong>g>from</str<strong>on</strong>g> Supor<br />
200 and Supor 800 (Tukey-Kramer procedure, p = 0.05 criteri<strong>on</strong>, data not shown). This suggests<br />
that when the difference in pore size between the <str<strong>on</strong>g>filters</str<strong>on</strong>g> compared is large, the difference in<br />
organics <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> them becomes significant. This observati<strong>on</strong> was c<strong>on</strong>firmed by no<br />
significant difference in mass <str<strong>on</strong>g>of</str<strong>on</strong>g> carb<strong>on</strong> <str<strong>on</strong>g>leaching</str<strong>on</strong>g> between the cellulose acetate <str<strong>on</strong>g>filters</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> two<br />
different pore sizes (0.20 µm and 0.45 µm) and a significant difference in mass <str<strong>on</strong>g>of</str<strong>on</strong>g> carb<strong>on</strong><br />
<str<strong>on</strong>g>leaching</str<strong>on</strong>g> between the Whatman GF/F and 934-AH glass fiber <str<strong>on</strong>g>filters</str<strong>on</strong>g> (pore sizes <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.70 µm and<br />
1.50 µm) based <strong>on</strong> two tailed t-test at p = 0.05.<br />
Copyright ©<br />
2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
908
Figure 1 - DOC Results <str<strong>on</strong>g>from</str<strong>on</strong>g> Filtrati<strong>on</strong> Test <strong>on</strong> all 19 Filters<br />
DOC (mg/L)<br />
20<br />
15<br />
10<br />
5<br />
0<br />
Versapor<br />
GN-6<br />
FP Vericel<br />
HT Tuffryn<br />
Nylaflo<br />
Millipore nyl<strong>on</strong><br />
Magna nyl<strong>on</strong><br />
Whatman nyl<strong>on</strong><br />
Supor 200<br />
Supor 450<br />
Supor 800<br />
WCN<br />
Polycarb<strong>on</strong>ate<br />
GH Polypro<br />
Cellu.ace. (0.45)<br />
Cellu. ace. (0.20)<br />
GF/F<br />
A/E<br />
934-AH<br />
Filter type<br />
WEFTEC®.06<br />
50 mL<br />
100 mL<br />
150 mL<br />
200 mL<br />
250 mL<br />
300 mL<br />
For all three filter materials tested for the <str<strong>on</strong>g>effect</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> pore size, organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> tended to increase<br />
with decreasing pore size. The higher organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> <str<strong>on</strong>g>filters</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> smaller pore size can be<br />
because <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>on</strong>e or more <str<strong>on</strong>g>of</str<strong>on</strong>g> the following reas<strong>on</strong>s. The <str<strong>on</strong>g>filters</str<strong>on</strong>g> with smaller pore sizes had more<br />
amounts <str<strong>on</strong>g>of</str<strong>on</strong>g> membrane materials that were tightly packed than the <str<strong>on</strong>g>filters</str<strong>on</strong>g> with larger pore sizes.<br />
There were more membrane surface areas available for c<strong>on</strong>tact with DDW in the smaller pore<br />
sized <str<strong>on</strong>g>filters</str<strong>on</strong>g> than the larger pore sized <str<strong>on</strong>g>filters</str<strong>on</strong>g>. In additi<strong>on</strong>, the c<strong>on</strong>tact time <str<strong>on</strong>g>of</str<strong>on</strong>g> DDW filtered <strong>on</strong> the<br />
filter was higher for the smaller pore sized <str<strong>on</strong>g>filters</str<strong>on</strong>g> compared to that <str<strong>on</strong>g>of</str<strong>on</strong>g> the larger pore sized <str<strong>on</strong>g>filters</str<strong>on</strong>g>.<br />
As a result, more <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> the smaller pore sized <str<strong>on</strong>g>filters</str<strong>on</strong>g> was observed.<br />
SCOD Results. The COD <str<strong>on</strong>g>of</str<strong>on</strong>g> the first 50 mL filtrate <str<strong>on</strong>g>from</str<strong>on</strong>g> all 19 <str<strong>on</strong>g>filters</str<strong>on</strong>g> is shown in Figure 2. The<br />
error bars represent standard deviati<strong>on</strong>. FP-Vericel filter, which had the highest DOC<br />
c<strong>on</strong>taminati<strong>on</strong>, also showed highest COD in its filtrate. Average COD <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> four<br />
different FP-Vericel was 48 ± 3 mg/L. FP-Vericel filter was followed by HT-Tuffryn in the<br />
amount <str<strong>on</strong>g>of</str<strong>on</strong>g> DOC c<strong>on</strong>taminati<strong>on</strong> and so was COD. The average COD <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> HT-<br />
Tuffryn filter was 35 ± 4 mg/L. The COD <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> the other <str<strong>on</strong>g>filters</str<strong>on</strong>g> were less than 8<br />
mg/L which should not be c<strong>on</strong>cerned as Standard Methods (APHA et al., 1998) states that COD<br />
values less than 25 mg/L would be qualitative than quantitative.<br />
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2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
909
Figure 2 - COD C<strong>on</strong>centrati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the First 50 mL Filtrate<br />
<str<strong>on</strong>g>from</str<strong>on</strong>g> all 19 Filters<br />
COD (mg/L)<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
Gelman Versapor<br />
Gelman GN-6<br />
Gelman FP-Vericel<br />
Gelman HT-Tuffryn<br />
Gelman Nylaflo<br />
Millipore Nyl<strong>on</strong><br />
Osm<strong>on</strong>ic Magna Nyl<strong>on</strong><br />
Whatman Nyl<strong>on</strong><br />
Gelman Supor 200<br />
Gelman Supor 450<br />
Gelman Supor 800<br />
Whatman (WCN)<br />
Corning<br />
Gelman GH Polypro<br />
Cellulose Acetate (0.45 )<br />
Cellulose Acetate (0.2 )<br />
Whatman GF/F<br />
Whatman A/E<br />
Whatman 934-AH<br />
Filter type<br />
SBOD Results. The results <str<strong>on</strong>g>of</str<strong>on</strong>g> SBOD analysis are shown in Table 2. Only the types <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>filters</str<strong>on</strong>g>,<br />
that met the DOC criteri<strong>on</strong> specified above in the Experimental Setup and Procedure subsecti<strong>on</strong>,<br />
are presented except 0.20 µm pore size cellulose acetate filter. The filtrate <str<strong>on</strong>g>from</str<strong>on</strong>g> 0.20 µm pore<br />
size cellulose acetate filter was not included for BOD and BDOC <strong>analyses</strong>, since the mass <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
carb<strong>on</strong> <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> it was not statistically different <str<strong>on</strong>g>from</str<strong>on</strong>g> that <str<strong>on</strong>g>from</str<strong>on</strong>g> 0.45 µm pore size cellulose<br />
acetate filter. Moreover, for SBOD and BDOC determinati<strong>on</strong>s, the pore size <str<strong>on</strong>g>of</str<strong>on</strong>g> the filter required<br />
is <strong>on</strong>ly 0.45 µm (the cut-<str<strong>on</strong>g>of</str<strong>on</strong>g>f for soluble or dissolved fracti<strong>on</strong>). The filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> Gelman FP-<br />
Vericel, Gelman HT-Tuffryn and Gelman GH Polypro had BOD c<strong>on</strong>centrati<strong>on</strong> greater than the<br />
MDL <str<strong>on</strong>g>of</str<strong>on</strong>g> 2 mg/L while for the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> the other <str<strong>on</strong>g>filters</str<strong>on</strong>g>, their BOD c<strong>on</strong>centrati<strong>on</strong>s were<br />
below 2 mg/L. The BOD c<strong>on</strong>centrati<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> Gelman FP-Vericel and HT-Tuffryn<br />
were high and proper cleaning <str<strong>on</strong>g>of</str<strong>on</strong>g> these <str<strong>on</strong>g>filters</str<strong>on</strong>g> should be carried out before using them for SBOD<br />
determinati<strong>on</strong>. The BOD c<strong>on</strong>centrati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the sample is determined using the following equati<strong>on</strong>:<br />
BOD = [(DOi – DOf)sample - (DOi – DOf)blank]F<br />
WEFTEC®.06<br />
where DOi is the initial dissolved oxygen c<strong>on</strong>centrati<strong>on</strong>, DOf is the final dissolved oxygen<br />
c<strong>on</strong>centrati<strong>on</strong>, blank refers to DDW with just the seed, and F is the diluti<strong>on</strong> factor.<br />
Copyright ©<br />
2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
910
911<br />
Copyright ©<br />
2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
Table 2 - SBOD and BDOC Results<br />
Filter Type<br />
Average<br />
BOD<br />
(mg/L)<br />
Average<br />
Initial<br />
DOC<br />
(mg/L)<br />
Average<br />
BDOC5<br />
(mg/L)<br />
Average<br />
Percent<br />
Biodegradable<br />
Average<br />
BDOC28<br />
(mg/L)<br />
Average<br />
Percent<br />
Biodegradable<br />
Significant<br />
Difference<br />
between<br />
BDOC5 and<br />
BDOC28<br />
95 Percent<br />
C<strong>on</strong>fidence<br />
Interval <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
Total BDOC<br />
(mg/L)<br />
Gelman GN-6 0.59 ± 0.29 0.36 ± 0.06 0.23 ± 0.04 63 ± 7 - - - 0.28 – 0.29<br />
Gelman FP-<br />
Vericel<br />
14.48 ± 0.53 7.14 ± 0.03 4.59 ± 0.06 64 ± 1 6.20 ± 0.04 87 ± 1 Yes 6.14 – 6.26<br />
Gelman HT-<br />
Tuffryn<br />
5.11 ± 0.49 2.51 ± 0.07 1.86 ± 0.16 74 ± 8 2.00 ± 0.17 80 ± 9 No 1.72 – 2.27<br />
Millipore Nyl<strong>on</strong> 0.91 ± 0.69 0.60 ± 0.03 0.34 ± 0.10 56 ± 15 0.57 ± 0.03 95 ± 2 Yes 0.52 – 0.62<br />
Osm<strong>on</strong>ics Magna<br />
Nyl<strong>on</strong><br />
0.68 ± 0.27 0.35 ± 0.03 0.00 ± 0.00 0 - - - 0.00 – 0.00<br />
Whatman Nyl<strong>on</strong> 0.81 ± 0.38 0.81 ± 0.02 0.65 ± 0.05 80 ± 4 - - - 0.57– 0.72<br />
Whatman (WCN) 1.40 ± 0.16 0.40 ± 0.02 0.18 ± 0.02 42 ± 11 - - - 0.10 – 0.24<br />
Gelman GH<br />
Polypro<br />
2.97 ± 0.32 1.49 ± 0.08 0.84 ± 0.11 56 ± 5 0.95 ± 0.10 64 ± 3 No 0.80 – 1.11<br />
Cellulose Acetate<br />
(0.45 µm)<br />
0.13 ± 0.10 0.30 ± 0.00 0.20 ± 0.01 66 ± 3 - - - 0.18 – 0.21<br />
Whatman A/E 0.94 ± 0.22 0.49 ± 0.05 0.43 ± 0.03 88 ± 9 - - - 0.39 – 0.47<br />
WEFTEC®.06
WEFTEC®.06<br />
With interference <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g>, the DOf <str<strong>on</strong>g>of</str<strong>on</strong>g> the sample will be less because <str<strong>on</strong>g>of</str<strong>on</strong>g> the additi<strong>on</strong>al BOD<br />
exerted by the organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> and this will result in SBOD overestimati<strong>on</strong>. For<br />
samples <str<strong>on</strong>g>of</str<strong>on</strong>g> which the SBOD determinati<strong>on</strong> requires diluti<strong>on</strong>, the interference <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> will be<br />
amplified by the diluti<strong>on</strong> factor if the diluti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the sample is performed before filtrati<strong>on</strong>. If the<br />
diluti<strong>on</strong> is performed after filtrati<strong>on</strong>, depending <strong>on</strong> the diluti<strong>on</strong> factor, the interference <str<strong>on</strong>g>from</str<strong>on</strong>g> the<br />
<str<strong>on</strong>g>filters</str<strong>on</strong>g> in the SBOD determinati<strong>on</strong> either remains unchanged (because <str<strong>on</strong>g>of</str<strong>on</strong>g> the inclusi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the diluti<strong>on</strong><br />
factor) or becomes too low to be detected.<br />
BDOC Results. The BDOC results <str<strong>on</strong>g>of</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> tested are shown in Table 2. BDOC5 <str<strong>on</strong>g>of</str<strong>on</strong>g> the<br />
filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> Gelman GN-6, Whatman (WCN) and cellulose acetate (0.45 µm) <str<strong>on</strong>g>filters</str<strong>on</strong>g> were close<br />
to the MDL <str<strong>on</strong>g>of</str<strong>on</strong>g> the BDOC procedure <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.15 mg/L. These results indicate that the interference in<br />
BDOC measurement <str<strong>on</strong>g>from</str<strong>on</strong>g> these <str<strong>on</strong>g>filters</str<strong>on</strong>g> is minimal when compared with the other <str<strong>on</strong>g>filters</str<strong>on</strong>g>.<br />
The filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> Gelman FP-Vericel filter, which had the highest organics <str<strong>on</strong>g>leaching</str<strong>on</strong>g>, had the<br />
highest BDOC c<strong>on</strong>centrati<strong>on</strong> am<strong>on</strong>g the <str<strong>on</strong>g>filters</str<strong>on</strong>g> tested. There was a significant difference (t-test, p<br />
= 0.05 criteri<strong>on</strong>, n = 4) in the BDOC c<strong>on</strong>centrati<strong>on</strong> obtained after 5 and 28 days <str<strong>on</strong>g>of</str<strong>on</strong>g> incubati<strong>on</strong><br />
suggesting that when sufficient amount <str<strong>on</strong>g>of</str<strong>on</strong>g> incubati<strong>on</strong> is provided all <str<strong>on</strong>g>of</str<strong>on</strong>g> the organics <str<strong>on</strong>g>leaching</str<strong>on</strong>g><br />
<str<strong>on</strong>g>from</str<strong>on</strong>g> it will be biodegradable (p = 7.77×10 -9 ). The BDOC <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> Gelman HT-<br />
Tuffryn filter was also high. The c<strong>on</strong>tinuati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> incubati<strong>on</strong> until 28 days for this filter did not<br />
show BDOC c<strong>on</strong>centrati<strong>on</strong> significantly different <str<strong>on</strong>g>from</str<strong>on</strong>g> that obtained after 5 days <str<strong>on</strong>g>of</str<strong>on</strong>g> incubati<strong>on</strong><br />
(t-test, p = 0.05 criteri<strong>on</strong>, n = 4) indicating that the <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> this filter has both<br />
biodegradable and n<strong>on</strong>-biodegradable organics (p = 0.28). Similar results were obtained for the<br />
filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> Gelman GH Polypro. There was no significant difference (p = 0.18) between the<br />
BDOC c<strong>on</strong>centrati<strong>on</strong>s obtained after 5 and 28 days <str<strong>on</strong>g>of</str<strong>on</strong>g> incubati<strong>on</strong>.<br />
The BDOC <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> the three hydrophilic nyl<strong>on</strong> <str<strong>on</strong>g>filters</str<strong>on</strong>g> tested were different as seen in<br />
Table 2. Most <str<strong>on</strong>g>of</str<strong>on</strong>g> the organics <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> Whatman nyl<strong>on</strong> <str<strong>on</strong>g>filters</str<strong>on</strong>g> were biodegradable after 5<br />
days <str<strong>on</strong>g>of</str<strong>on</strong>g> incubati<strong>on</strong> and about 50% <str<strong>on</strong>g>of</str<strong>on</strong>g> the organics <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> Millipore nyl<strong>on</strong> were<br />
biodegradable after 5 days. The incubati<strong>on</strong> when c<strong>on</strong>tinued until 28 days for the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g><br />
Millipore nyl<strong>on</strong> <str<strong>on</strong>g>filters</str<strong>on</strong>g> indicated that there was no significant difference between the initial DOC<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> the leached organics and BDOC28 (t-test, p = 0.19). All <str<strong>on</strong>g>of</str<strong>on</strong>g> the <str<strong>on</strong>g>leaching</str<strong>on</strong>g> organics <str<strong>on</strong>g>from</str<strong>on</strong>g> them<br />
were biodegradable if sufficient time was allowed. For the other hydrophilic nyl<strong>on</strong> filter, namely<br />
Osm<strong>on</strong>ics nyl<strong>on</strong>, the <str<strong>on</strong>g>leaching</str<strong>on</strong>g> organics were not susceptible to biodegradati<strong>on</strong>.<br />
Although the membrane material <str<strong>on</strong>g>of</str<strong>on</strong>g> Osm<strong>on</strong>ics magna nyl<strong>on</strong> filter is same as that <str<strong>on</strong>g>of</str<strong>on</strong>g> the Whatman<br />
and Millipore nyl<strong>on</strong> <str<strong>on</strong>g>filters</str<strong>on</strong>g>, the biodegradability <str<strong>on</strong>g>of</str<strong>on</strong>g> the leached organics was completely<br />
different. No BDOC exerti<strong>on</strong> in the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> Osm<strong>on</strong>ics magna nyl<strong>on</strong> <str<strong>on</strong>g>filters</str<strong>on</strong>g> could be<br />
because either the organics <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> them are in fact biorefractory/n<strong>on</strong>biodegradable or the<br />
leachate c<strong>on</strong>tains some toxic compounds that affect the microbial activity <strong>on</strong> the DOC. There<br />
will be no interference when using Osm<strong>on</strong>ics magna nyl<strong>on</strong> filter for BDOC measurement if the<br />
reas<strong>on</strong> for no BDOC is because they are not biodegradable. On the other hand, if toxicity is the<br />
reas<strong>on</strong> for having no biodegradability, the usage <str<strong>on</strong>g>of</str<strong>on</strong>g> this filter will impose an error in the BDOC<br />
measurement. The interference <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> during BDOC measurement varies for different<br />
types <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>filters</str<strong>on</strong>g>. However, the exact magnitude <str<strong>on</strong>g>of</str<strong>on</strong>g> interference in BDOC measurement <str<strong>on</strong>g>from</str<strong>on</strong>g> the<br />
<str<strong>on</strong>g>filters</str<strong>on</strong>g> cannot be determined <str<strong>on</strong>g>from</str<strong>on</strong>g> this study al<strong>on</strong>e as there are several factors, such as volume <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
sample filtered, type and volume <str<strong>on</strong>g>of</str<strong>on</strong>g> inoculum, and incubati<strong>on</strong> time, that can affect the BDOC<br />
Copyright ©<br />
2006 Water Envir<strong>on</strong>ment Foundati<strong>on</strong>. All Rights Reserved<br />
912
esult.<br />
Soak Test<br />
WEFTEC®.06<br />
The DOC data <str<strong>on</strong>g>of</str<strong>on</strong>g> the samples <str<strong>on</strong>g>of</str<strong>on</strong>g> all 19 <str<strong>on</strong>g>filters</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> the soak test are shown in Table 3. In 18 <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
the 19 <str<strong>on</strong>g>filters</str<strong>on</strong>g>, the soak test samples showed that DOC stopped <str<strong>on</strong>g>leaching</str<strong>on</strong>g> (DOC ≤ 0.10 mg/L)<br />
within four days. Gelman FP-Vericel filter, exhibited the <str<strong>on</strong>g>leaching</str<strong>on</strong>g> until 10 days (data not<br />
shown). For most <str<strong>on</strong>g>of</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g>, the DOC <str<strong>on</strong>g>leaching</str<strong>on</strong>g> was found <strong>on</strong>ly in the samples obtained after<br />
soaking the <str<strong>on</strong>g>filters</str<strong>on</strong>g> for <strong>on</strong>e day in DDW. The DOC data <str<strong>on</strong>g>of</str<strong>on</strong>g> the soak test samples had less<br />
variability when compared with the DOC data <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrati<strong>on</strong> test samples.<br />
The comparis<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> mass <str<strong>on</strong>g>of</str<strong>on</strong>g> carb<strong>on</strong> <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> different <str<strong>on</strong>g>filters</str<strong>on</strong>g> when subjected to filtrati<strong>on</strong> and<br />
soak tests is shown in Table 4. Significant difference between the mass <str<strong>on</strong>g>of</str<strong>on</strong>g> carb<strong>on</strong> <str<strong>on</strong>g>from</str<strong>on</strong>g> the<br />
filtrati<strong>on</strong> and soak tests was determined statistically using t-test at p = 0.05. The difference in the<br />
mass for <str<strong>on</strong>g>filters</str<strong>on</strong>g>, which had DOC c<strong>on</strong>centrati<strong>on</strong> less than 0.1 mg/L in either the filtrati<strong>on</strong> test or<br />
soak test, was not determined. From the table, it is observed that in all <str<strong>on</strong>g>filters</str<strong>on</strong>g> except for<br />
Whatman GF/F filter, the mass <str<strong>on</strong>g>of</str<strong>on</strong>g> carb<strong>on</strong> <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> when subjected to the soak<br />
test was statistically either not different <str<strong>on</strong>g>from</str<strong>on</strong>g> or greater than the mass <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> the filtrati<strong>on</strong><br />
test indicating that soaking the <str<strong>on</strong>g>filters</str<strong>on</strong>g> would result in removing most <str<strong>on</strong>g>of</str<strong>on</strong>g> the leachable organics<br />
<str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g>. The possible reas<strong>on</strong> for the different results <str<strong>on</strong>g>from</str<strong>on</strong>g> the two tests could be because<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> the presence <str<strong>on</strong>g>of</str<strong>on</strong>g> less soluble organics in the <str<strong>on</strong>g>filters</str<strong>on</strong>g>. The less soluble organics were less<br />
susceptible to <str<strong>on</strong>g>leaching</str<strong>on</strong>g> during the filtrati<strong>on</strong> test because <str<strong>on</strong>g>of</str<strong>on</strong>g> less c<strong>on</strong>tact time with DDW.<br />
Guidelines for the Use and Cleaning <str<strong>on</strong>g>of</str<strong>on</strong>g> Filters<br />
Table 5 summarizes the interference caused by organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> <str<strong>on</strong>g>filters</str<strong>on</strong>g> <strong>on</strong> organic <strong>analyses</strong><br />
and the recommended filter cleaning method. The interference with DOC analysis was found in<br />
14 out <str<strong>on</strong>g>of</str<strong>on</strong>g> the 19 <str<strong>on</strong>g>filters</str<strong>on</strong>g> tested. The interference in SCOD analysis was observed <strong>on</strong>ly in 2 <str<strong>on</strong>g>filters</str<strong>on</strong>g>.<br />
The interference in SBOD analysis was found in 3 out <str<strong>on</strong>g>of</str<strong>on</strong>g> the 10 <str<strong>on</strong>g>filters</str<strong>on</strong>g> tested. Although the BOD<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> other <str<strong>on</strong>g>filters</str<strong>on</strong>g> was less than the MDL <str<strong>on</strong>g>of</str<strong>on</strong>g> 2 mg/L, the interference will be<br />
amplified by the diluti<strong>on</strong> factor if the sample is filtered through the filter after diluti<strong>on</strong>. This<br />
amplificati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the interference by the diluti<strong>on</strong> factor is applicable to all the organic parameters<br />
studied. The BDOC <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrates was greater than the MDL <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.15 mg/L in 9 out <str<strong>on</strong>g>of</str<strong>on</strong>g> the 10<br />
<str<strong>on</strong>g>filters</str<strong>on</strong>g> tested. For the other filter (Osm<strong>on</strong>ics Magna Nyl<strong>on</strong>), the organics leached were not<br />
biodegradable at all. However, it cannot be c<strong>on</strong>cluded that there is no interference <str<strong>on</strong>g>from</str<strong>on</strong>g> this filter<br />
since the exact reas<strong>on</strong> for no biodegradability in the leached organics is not known. Thus,<br />
interference <str<strong>on</strong>g>from</str<strong>on</strong>g> this filter in BDOC analysis is reported as inc<strong>on</strong>clusive in Table 5.<br />
Table 5 reveals that in most <str<strong>on</strong>g>filters</str<strong>on</strong>g> which showed interference in organic analysis, the suggested<br />
cleaning method is to soak the <str<strong>on</strong>g>filters</str<strong>on</strong>g> in DDW. In <str<strong>on</strong>g>filters</str<strong>on</strong>g>, which either had no organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> or<br />
had no statistical difference in the total mass <str<strong>on</strong>g>of</str<strong>on</strong>g> carb<strong>on</strong> <str<strong>on</strong>g>leaching</str<strong>on</strong>g> when subjected to filtrati<strong>on</strong> and<br />
soak tests, the suggested cleaning method is discarding initial filtrati<strong>on</strong> volumes, as it c<strong>on</strong>sumes<br />
less time than the cleaning by soaking. It is clear <str<strong>on</strong>g>from</str<strong>on</strong>g> Table 5 that the soak time and the<br />
filtrati<strong>on</strong> volume to be discarded differ <str<strong>on</strong>g>from</str<strong>on</strong>g> filter to filter.<br />
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Table 3 - Soak Test Results<br />
Filter Type<br />
Average DOC <str<strong>on</strong>g>of</str<strong>on</strong>g> Soak Samples (mg/L)<br />
Day 1 Day 2 Day 3 Day 4<br />
Average Total<br />
Mass <str<strong>on</strong>g>from</str<strong>on</strong>g><br />
Soak Test<br />
(µg)<br />
95 Percent C<strong>on</strong>fidence<br />
Interval Estimate <str<strong>on</strong>g>of</str<strong>on</strong>g> the<br />
Total Mass <str<strong>on</strong>g>of</str<strong>on</strong>g> Carb<strong>on</strong><br />
(µg)<br />
Gelman Versapor 0.70 ± 0.02 0.04 ± 0.04 - - 70 ± 2 67 – 74<br />
Gelman GN-6 1.32 ± 0.16 0.06 ± 0.04 - - 132 ± 12 106 – 158<br />
Gelman FP-Vericel 21.8 ± 1.40 3.47 ± 0.55 1.49 ± 0.12 1.07 ± 0.05 3076 ± 124 1 2878 – 3274 1<br />
Gelman HT-Tuffryn 5.24 ± 0.34 0.63 ± 0.02 0.35 ± 0.00 0.06 ± 0.02 623 ± 33 569 – 676<br />
Gelman Nylaflo 0.09 ± 0.00 - - - 9 ± 0.4 9 – 11<br />
Millipore Nyl<strong>on</strong> 0.84 ± 0.03 0.04 ± 0.04 - - 84 ± 3 79 – 89<br />
Osm<strong>on</strong>ic Magna Nyl<strong>on</strong> 0.40 ± 0.07 0.01 ± 0.01 - - 40 ± 7 29 – 51<br />
Whatman Nyl<strong>on</strong> 0.91 ± 0.03 0.08 ± 0.02 - - 91 ± 3 86 – 96<br />
Gelman Supor 200 0.29 ± 0.02 0.23 ± 0.04 0.01 ± 0.02 - 52 ± 6 43 – 61<br />
Gelman Supor 450 0.12 ± 0.05 0.13 ± 0.02 0.09 ± 0.00 - 24 ± 3 19 – 30<br />
Gelman Supor 800 0.23 ± 0.01 0.03 ± 0.02 - - 23 ± 1 21 – 26<br />
Whatman (WCN) 0.66 ± 0.08 0.14 ± 0.02 0.05 ± 0.01 - 80 ± 9 66 – 95<br />
Whatman Nucleopore 0.05 ± 0.01 - - - 5 ± 0.8 4 – 6<br />
Gelman GH Polypro 1.46 ± 0.15 0.11 ± 0.02 0.04 ± 0.03 - 157 ± 16 131 – 183<br />
Cellulose acetate (0.20 µm) 0.57 ± 0.03 0.04 ± 0.00 - - 57 ± 3 52 – 62<br />
Cellulose acetate (0.45 µm) 0.28 ± 0.04 0.07 ± 0.03 - - 28 ± 4 22 – 34<br />
Whatman GF/F 0.11 ± 0.02 0.03 ± 0.01 - - 11 ± 2 8.0 – 14<br />
Gelman A/E 0.82 ± 0.11 0.08 ± 0.01 - - 82 ± 12 64 – 100<br />
Whatman 934-AH 0.07 ± 0.00 - - - 7 ± 0 6 – 9<br />
1 Based <strong>on</strong> 10 days <str<strong>on</strong>g>of</str<strong>on</strong>g> soaking (data not shown).<br />
WEFTEC®.06
Table 4 - Comparis<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Mass <str<strong>on</strong>g>of</str<strong>on</strong>g> Carb<strong>on</strong> <str<strong>on</strong>g>from</str<strong>on</strong>g> Filtrati<strong>on</strong> and Soak Tests<br />
Filter Type<br />
Mass <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
Carb<strong>on</strong> <str<strong>on</strong>g>from</str<strong>on</strong>g><br />
Filtrati<strong>on</strong> Test<br />
(µg)<br />
WEFTEC®.06<br />
Mass <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
Carb<strong>on</strong> <str<strong>on</strong>g>from</str<strong>on</strong>g><br />
Soak Test<br />
(µg)<br />
Gelman Versapor 18.5 ± 2.6 70± 2 26<br />
Percent<br />
Mass <str<strong>on</strong>g>from</str<strong>on</strong>g><br />
Filtrati<strong>on</strong><br />
Test<br />
Significant<br />
Difference<br />
between Soak and<br />
Filtrati<strong>on</strong> Tests<br />
Yes (p = 8.79E-<br />
08)<br />
Gelman GN-6 94 ± 21 132 ± 12 71 Yes (p = 0.278)<br />
Gelman FP-Vericel 1063 ± 32 3076 ± 124 35 Yes (p = 7.3E-08)<br />
Gelman HT-Tuffryn 390 ± 44 623 ± 33 63 Yes (p = 0.0002)<br />
Gelman Nylaflo 3 ± 3 1 9 ± 0 1 - -<br />
Millipore Nyl<strong>on</strong> 81 ± 6 84 ± 3 96 No (p = 0.38)<br />
Osm<strong>on</strong>ic Magna Nyl<strong>on</strong> 32 ± 5 40 ± 7 80 No (p = 0.09)<br />
Whatman Nyl<strong>on</strong> 80 ± 8 91 ± 3 88 Yes (p = 0.04)<br />
Gelman Supor 200 17 ± 9 52 ± 6 33<br />
Yes (p = 2.03E-<br />
05)<br />
Gelman Supor 450 7 ± 4 1 24± 3 29 -<br />
Gelman Supor 800 5 ± 1 1 23 ± 1 22 -<br />
Whatman (WCN) 30 ± 7 80 ± 9 38 Yes (p = 0.0001)<br />
Whatman Nucleopore 4 ± 1 1 5 ± 1 1 - -<br />
Gelman GH Polypro 87 ± 30 157 ± 16 55 Yes (p = 0.024)<br />
Cellulose acetate (0.20 µm) 39 ± 5 57 ± 3 68 Yes (p = 0.002)<br />
Cellulose acetate (0.45 µm) 32 ± 7 28 ± 4 114 No (p = 0.28)<br />
Whatman GF/F 21 ± 5 11 ± 2 190 Yes 2 (p = 0.024)<br />
Whatman A/E 56 ± 16 82 ± 12 68 Yes (p = 0.035)<br />
Whatman 934-AH 2 ± 2 1 7± 1 1 - -<br />
1<br />
Values below the DOC cut-<str<strong>on</strong>g>of</str<strong>on</strong>g>f <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.1 mg/L and therefore not included in comparis<strong>on</strong>.<br />
2<br />
Only filter which showed statistically higher carb<strong>on</strong> mass in filtrati<strong>on</strong> test than soak test.<br />
Gelman FP-Vericel and Gelman HT-Tuffryn <str<strong>on</strong>g>filters</str<strong>on</strong>g> should be avoided for dissolved organic<br />
<strong>analyses</strong> because <str<strong>on</strong>g>of</str<strong>on</strong>g> their high organic c<strong>on</strong>taminati<strong>on</strong> and cleaning difficulty. The 0.45 µm pore<br />
sized, Gelman Versapor, Gelman GN-6, Millipore Nyl<strong>on</strong>, Whatman Nyl<strong>on</strong>, Osm<strong>on</strong>ics Magna<br />
Nyl<strong>on</strong>, Gelman Supor 450, Whatman Cellulose Nitrate, Gelman GH Polypro, and Cellulose<br />
acetate <str<strong>on</strong>g>filters</str<strong>on</strong>g> can be used for dissolved organics <strong>analyses</strong> after appropriate cleaning. Gelman<br />
Nylaflo, does not introduce any artifacts to organic <strong>analyses</strong>, and thus can be used for organic<br />
<strong>analyses</strong> without any pretreatment. However, because <str<strong>on</strong>g>of</str<strong>on</strong>g> the possible variati<strong>on</strong> am<strong>on</strong>g <str<strong>on</strong>g>filters</str<strong>on</strong>g><br />
<str<strong>on</strong>g>from</str<strong>on</strong>g> lot to lot, they should be tested for c<strong>on</strong>taminati<strong>on</strong> before use. Although some <str<strong>on</strong>g>of</str<strong>on</strong>g> the other<br />
<str<strong>on</strong>g>filters</str<strong>on</strong>g>, which are not listed above, had minimal or no organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g>, they were not <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.45 µm<br />
pore size, and thus their use in dissolved organic <strong>analyses</strong> should be avoided. It should also be<br />
noted that the interference estimated in this study is based <strong>on</strong> DDW, but in real water samples<br />
the interference <str<strong>on</strong>g>from</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g> might be or might not be the same. This is because the<br />
characteristics <str<strong>on</strong>g>of</str<strong>on</strong>g> the real water sample such as the chemical compositi<strong>on</strong>, pH, and particle size<br />
distributi<strong>on</strong> may not be the same as those <str<strong>on</strong>g>of</str<strong>on</strong>g> DDW. These characteristics could affect the<br />
interacti<strong>on</strong> between the sample and the filter material resulting in different degrees <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
interference.<br />
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Table 5 - Summary <str<strong>on</strong>g>of</str<strong>on</strong>g> Interference Caused by Organic Leaching From Filters <strong>on</strong> Analyses and Suggested Cleaning Method<br />
Filter Type<br />
Interference in the Analysis <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
DOC COD BOD BDOC<br />
Suggested Cleaning Method<br />
Gelman Versapor Yes N 1 N 1 Soak in 100 mL DDW for 24 hours<br />
Gelman GN-6 Yes Yes Soak in 100 mL DDW for 24 hours<br />
Gelman FP-Vericel Yes Yes Yes Yes Soak in 100 mL DDW for 10 days<br />
Gelman HT-Tuffryn Yes Yes Yes Yes Soak in 100 mL DDW for 72 hours<br />
Gelman Nylaflo N 1 N 1 Requires no pretreatment, however filter at least 100 mL <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
DDW before use for analysis<br />
Millipore Nyl<strong>on</strong> Yes Yes Filter at least 150 mL <str<strong>on</strong>g>of</str<strong>on</strong>g> DDW before use for analysis<br />
Osm<strong>on</strong>ic Magna Nyl<strong>on</strong> Yes I 2 Filter at least 100 mL <str<strong>on</strong>g>of</str<strong>on</strong>g> DDW before use for analysis<br />
Whatman Nyl<strong>on</strong> Yes Yes Soak in 100 mL DDW for 24 hours<br />
Gelman Supor 200 Yes N 1 N 1 Soak in 100 mL DDW for 48 hours<br />
Gelman Supor 450 N 1 N 1 Requires no pretreatment, however filter at least 100 mL <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
Gelman Supor 800 N 1 N 1<br />
DDW before use for analysis<br />
Requires no pretreatment, however filter at least 100 mL <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
DDW before use for analysis<br />
Whatman (WCN) Yes Yes Soak in 100 mL DDW for 48 hours<br />
Whatman Nucleopore N 1 N 1 Requires no pretreatment, however filter at least 100 mL <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
DDW before use for analysis<br />
Gelman GH Polypro Yes Yes Yes Soak in 100 mL DDW for 48 hours<br />
Cellulose acetate (0.20 µm) Yes Yes Soak in 100 mL DDW for 24 hours<br />
Cellulose acetate (0.45 µm) Yes Yes Filter at least 150 mL <str<strong>on</strong>g>of</str<strong>on</strong>g> DDW before use for analysis<br />
Whatman GF/F Yes N 1 N 1 Filter at least 150 mL <str<strong>on</strong>g>of</str<strong>on</strong>g> DDW before use for analysis<br />
Gelman A/E Yes Yes Soak in 100 mL DDW for 24 hours<br />
Whatman 934-AH N 1 N 1<br />
1 N-Not tested.<br />
2 I-Inc<strong>on</strong>clusive.<br />
Requires no pretreatment, however filter at least 100 mL <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
DDW before use for analysis<br />
WEFTEC®.06
CONCLUSIONS<br />
This research determined the interference caused by the organics <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g> 19 comm<strong>on</strong>ly<br />
used <str<strong>on</strong>g>filters</str<strong>on</strong>g> in the <strong>analyses</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> organic matter and compared the amount <str<strong>on</strong>g>of</str<strong>on</strong>g> organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> <str<strong>on</strong>g>from</str<strong>on</strong>g><br />
the <str<strong>on</strong>g>filters</str<strong>on</strong>g> when subjected to two different c<strong>on</strong>diti<strong>on</strong>s namely soak and filtrati<strong>on</strong> tests. Five <str<strong>on</strong>g>filters</str<strong>on</strong>g><br />
had negligible or no organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> (DOC < 0.1 mg/L) while two <str<strong>on</strong>g>filters</str<strong>on</strong>g>, Gelman FP-Vericel<br />
and Gelman HT-Tuffryn, had very high organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> (DOC > 5 mg/L) and should not be<br />
used without proper cleaning. Different amounts <str<strong>on</strong>g>of</str<strong>on</strong>g> organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> were observed in the <str<strong>on</strong>g>filters</str<strong>on</strong>g><br />
made <str<strong>on</strong>g>of</str<strong>on</strong>g> the same material but <str<strong>on</strong>g>from</str<strong>on</strong>g> different manufacturers and in the <str<strong>on</strong>g>filters</str<strong>on</strong>g> made <str<strong>on</strong>g>of</str<strong>on</strong>g> the same<br />
material, manufactured by the same manufacturer but <str<strong>on</strong>g>of</str<strong>on</strong>g> substantially different pore sizes. The<br />
SCOD c<strong>on</strong>centrati<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> the filtrates <str<strong>on</strong>g>from</str<strong>on</strong>g> 17 <str<strong>on</strong>g>filters</str<strong>on</strong>g> were much lower than the quantitative level<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> c<strong>on</strong>cern established by Standard Methods (APHA et al., 1998). Only Gelman FP-Vericel and<br />
Gelman HT-Tuffryn <str<strong>on</strong>g>filters</str<strong>on</strong>g> interfered with the COD test. These two <str<strong>on</strong>g>filters</str<strong>on</strong>g> also leached BOD<br />
c<strong>on</strong>tributing substances above the detecti<strong>on</strong> limit al<strong>on</strong>g with Gelman GH Polypro. Due to higher<br />
sensitivity <str<strong>on</strong>g>of</str<strong>on</strong>g> the parameter, several more <str<strong>on</strong>g>filters</str<strong>on</strong>g> interfered with the BDOC test compared to the<br />
SBOD test. The soak test showed higher organic <str<strong>on</strong>g>leaching</str<strong>on</strong>g> than the corresp<strong>on</strong>ding filtrati<strong>on</strong> test<br />
for most <str<strong>on</strong>g>of</str<strong>on</strong>g> the <str<strong>on</strong>g>filters</str<strong>on</strong>g>. The guidelines for the applicati<strong>on</strong> and cleaning <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>filters</str<strong>on</strong>g>, which are useful<br />
for water quality <strong>laboratory</strong> practiti<strong>on</strong>ers and researchers, were generated based <strong>on</strong> the results <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
this study.<br />
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