Recycling Treated Municipal Wastewater for Industrial Water Use

TM4: WWTP Effluent Quality
Recycling Treated Municipal Wastewater for Industrial Water Use
Craddock Consulting Engineers 23
In Association with CDM & James Crook
TM4-WWTP Eff Quality_0707.doc
Fecal Coliforms
Fecal coliforms are commonly used as indicator organisms of pathogenic organisms
found in treated wastewater. The presence of coliform organisms is taken as an
indication that pathogenic organisms may also be present, and the absence of coliform
organisms is taken as an indication that the water is free from disease-producing
organisms. The only constituent regulated by the California Water Recycling Criteria
(the regulations Minnesota uses for administering permits for water reuse) for
industrial water uses is an indicator organism, total coliforms. For uses that are not
likely to contact humans, the total coliform limit is 23/100 ml. For uses with potential
for human contact, the total coliform limit is 2.2/100 ml. Most WWTPs in Minnesota
are permitted to meet a fecal coliform limit of 200. Fecal coliforms are a subset of total
coliforms.
Figure 29 presents the frequency of occurrence of fecal coliforms in the effluent of all
Minnesota WWTPs. Similar information is shown in Figure 30 for WWTPs with
design capacities greater than 1 mgd. The variability of effluent fecal coliforms is also
characterized for the following ranges: 100/100
mL.
The average WWTP effluent fecal coliform concentrations are depicted by location
and facility capacity in Figure 31 and further detailed in Figures 32-35. Minnesota
facilities produce a high quality effluent in terms of fecal coliforms. There were 170
facilities with fecal coliform counts less than 10/100 mL, accounting for 150 mgd of
the WWTP capacity in the state. Nearly 300 facilities with a design capacity totaling
535 mgd have effluent fecal coliform concentrations in the 10-100/100 mL range. Over
40 WWTPs, with a combined capacity of 70 mgd, produce an effluent with a fecal
coliform count greater than 100/100 mL.