Akron Water Pollution Control Station No Feasible Alternative

Akron WPCS personnel performed two in-house stress tests prior to the Facilities Plan 98 6 to
evaluate the secondary treatment performance and capabilities. The first stress test was
performed between December 1992 and January 1994 (Activated Sludge Plant Stress Test,
1994 3 ). A second stress test was mandated by the July 17, 1995 Consent Decree. The second
stress test was performed from March 1997 to September 1997 (Activated Sludge Plant Stress
Test, 1997 4 ).
A third stress test was performed in November/December 2006 and is being reported as part of
this Report. All three stress test reports are provided in Appendix A. The following is a summary
of the three stress test results.
1993 Stress Test
The Akron WPCS secondary treatment (activated sludge plant) facility was operated at higher
than normal flow rates on 18 separate occasions in 1993 to intentionally stress the performance
of these facilities. These stress test events ranged from a 1.75 hours duration to a maximum of
34.5 hours. Target flow rates were 110, 115, 120 and 130 MGD. The complete stress test report
is provided in Appendix A.
The following is a synopsis of test observations:
• Observations of “severe degradation” were made at sustained flows of 110 MGD. Short
“upsets” were experienced. Sludge blankets were within 6 inches of the effluent launders.
However, discharge permit parameters were being met.
• Total Suspended Solids (TSS) effluent concentrations of 38 mg/l were seen at a 115 MGD
test flow after only two hours. Plant personnel were unable to restart the test. TSS
concentrations exceeded permit limits on forty-four occasions over the next five months;
they were believed to have resulted from a loss of biomass and nitrifiers during the cold
weather stress test.
• The CBOD5 and TSS concentrations were at or above permit limits during two, 120 MGD
stress test events in November 1993.
“Plant personnel proposed the following additional conclusions based on their 1993 stress test
experience:
• the recovery phase for the secondary treatment (activated sludge) plant after an event of
110 MGD requires at least a three mean cell residence time (MCRT) duration for proper
recovery before continuation of stress testing (experiencing additional high flow events);
• continued and/or frequent storm events will degrade the activated sludge treatment level for
any extended period of flows over 100 MGD;
• physical flooding of the aeration tanks occurs at flows over 110 MGD;
• flooding (weir submergence) of the final settling tanks occurs during extended high flow
events;
• hydraulic capacity of the aeration basins is limited;
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