Recycling Treated Municipal Wastewater for Industrial Water Use

TM4: WWTP Effluent Quality
Recycling Treated Municipal Wastewater for Industrial Water Use
2.0 Analysis Background and Results
Data Source
All WWTPs are required to submit discharge monitoring reports in accordance with
their NPDES permit. Historic records of WWTP influent and effluent quantity and
quality are maintained by the Minnesota Pollution Control Agency (MPCA). These
data and the corresponding GIS data were provided by MPCA through the
Environmental Data Access system and used in this analysis (MPCA, 2005).
The discharge monitoring report data are entered into the Environmental Data Access
system as reported by the municipality. Information can be incorrectly listed on the
monitoring reports by the municipality (i.e. misplacement of a decimal point is a
common error). These “incorrect” values are not identified or changed unless the
municipality contacts the MPCA with revised values or if the reported values exceed
permitted limits and MPCA takes enforcement action and inquires about the
exceedance. For this study, all data are presented as contained in the database.
Data Analysis Methods
Monthly discharge data were summarized as annual average flows and concentration
to perform statistical analyses. The 2005 water quality data were linked to the WWTPs
location shapefile and maps were generated to characterize the average annual
effluent quality of Minnesota’s municipal WWTPs. A summary of the data analysis is
presented below. Appendix A presents the detailed data analysis methods.
The constituents of concern evaluated in this study are not monitored in the effluent
of all facilities. This study identifies a constituent as “not measured” if it is not
monitored at these facilities. The term “not measured” is also used to designate
missing data for a specific constituent at an individual WWTP, but this is a rare
occurrence.
Results
CBOD5
The organic concentration in the water supply needs to be kept at a minimum for
most industrial water uses. Organic matter provides a food source for microbial
growth which can lead to biological fouling and related scaling problems.
Consumption of oxygen and reduced oxygen levels could be a concern for some
industries. Also disinfection processes are less stable with higher organic
concentrations. Several states with water reuse regulations require reclaimed water to
meet a CBOD5 limit of 20 mg/L for various uses. CBOD5, or related parameters such
as BOD5 or TOC, are constituents routinely tested in WWTP effluent, with CBOD5 the
most common one for Minnesota’s WWTPs. Higher effluent CBOD5 concentrations
are often indicative of facilities with lower levels of treatment or possibly facilities that
are operating at the capacity limit and are not achieving the performance expected for
critical treatment processes.
2 Craddock Consulting Engineers
In Association with CDM & James Crook
TM4-WWTP Eff Quality_0707.doc