2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P81 DETERMINATION OF SuRFACTANTS
INCLuDED IN SEwAGE wATER
MILADA VáVROVá a,b , LEnKA LAnGOVá a ,
KRISTýnA KUBíČKOVá b , HELEnA ZLáMALOVá
GARGOŠOVá a , MICHAELA STOUPALOVá b and
VLADIMíR VEČEREK b
a Brno University of Technology, Faculty of Chemistry,
Purkyňova 118, 612 00 Brno,
b University of Veterinary and Pharmaceutical Sciences Brno,
Faculty of Veterinary Hygiene and Ecology,
vavrova@fch.vutbr.cz
Introduction
Surfactants or detergents belong to a group of organic
substances that adsorb at a low concentration in the interface,
thereby decreasing interfacial or surface energy. Detergents
therefore show surface activity which manifests itself by the
formation of foam in aqueous solutions 1 . Such properties
facilitate the wetting of surfaces and the removal of impurities
2 .
Detergents can be divided according to their dissociation
properties into the following groups: anionic detergents, cationic
detergents, ampholytic detergents, and non-ionogenic
detergents 2 . There are many kinds of individual detergents.
During wastewater treatment, detergents account for
a high percentage of chemical oxygen demand. Detergents
are also able to increase the solubility of other toxic organic
components in water and soil. When adsorbed in sludge, they
may impair sludge dewatering. Generally, the concentration
of detergents at the outflow from a wastewater treatment
plant depends on the efficiency and technological parameters
of the facility.
Wastewater usually contains different kinds of detergents.
For biological treatment, the level of detergents in
wastewater should not exceed 1,000 mg dm –3 (ref. 4 ). In countries
where the consumption of washing powders and cleaning
agents is high, the concentration of anion-active detergents
in municipal wastewater varies in a range of 10–20 mg dm –3 .
Increased concentrations of detergents can be detected in
wastewater from textile industry, the production of washing
and cleaning agents and cosmetic production plants, and
may exceed 100 mg dm –3 . High levels of detergents are also
present in wastewater originating from laundries and car
washes 5 . The limit concentration of anion-active detergents
in drinking water is 0.2 mg dm –3 . This parameter is used to
indicate the level of pollution in underground water or treated
surface water with sewage 2 .
Experimental
The samples of wastewater to be analysed were collected
at both the inflow and outflow of the wastewater treatment
plant of the University of Veterinary and Pharmaceutical
Sciences (VFU Brno). The samples of wastewater taken at
the outflow were collected before chlorination to prevent the
distortion of the results. The sample of water was measured
s501
immediately after collection; the transfer of the sample took
approximately 10 minutes.
Detergents were determined using Merck spectrophotometric
cuvette tests. The method for the determination of
anion-active detergents can be used for concentrations ranging
from 0.05 to 2.0 mg dm –3 . This method is similar to
EPA 425.1, US Standard Methods 5540 and En 903. Cationactive
detergents are determined using a spectrophotometric
method in a concentration range of 0.05–1.5 mg dm –3 . The
determination of non-ionogenic detergents was carried out in
a range of 0.1–7.5 mg dm –3 .
Results
The levels of anion-active, cation-active and non-ionogenic
detergents were measured at both the inflow and outflow
of the wastewater treatment plant during one week. It
follows from the overview of the results provided in Table I
that the samples of wastewater contain mainly anion detergents
whose level is three orders higher than that of other
detergents. The results in the table also demonstrate that the
level of detergents in water – particularly anion-active detergents
– decreased significantly as a result of wastewater treatment;
the highest level detected was 0.97 mg dm –3 and was
determined on Friday while the lowest level (0.29 mg dm –3 )
was found on Tuesday. The highest concentration of cationic
detergents (0.24 mg dm –3 ) was detected on Monday and
decreased markedly on other days (0.025 mg dm –3 ). The presence
of highly toxic cationic detergents is alarming.
Table I
Comparison of the levels of anion-active detergents in the
inflow and outflow [mg dm –3 ]
Inflow Outflow
1 20.00 0.40
2 12.90 0.29
3 18.30 0.49
4 13.90 0.49
5 14.00 0.97
Table II
Comparison of the levels of cation-active detergents in the
inflow and outflow [mg dm –3 ]
Inflow Outflow
1 0.400 0.240
2 0.020 0.025
3 0.690 0.025
4 0.025 0.025
5 0.025 0.025
The levels of non-ionogenic detergents in wastewater
collected at the outflow were the same in all cases
– 0.05 mg dm –3 . The differences between individual findings
(the highest and the lowest levels) are difficult to explain; it is