Emergency By-Pass Systems

Use of a Collection System as a Plug Flow Reactor to Lower the BOD in Sewage, by treating with AquaClean

A large municipality in Ohio was evaluating strategies for treating their sewage during situations when it might be necessary to bypass the Wastewater Treatment Plant (WWTP) due to a plant wipeout resulting from a hydraulic surge or other catastrophic shut-down situations.

In order to reduce the impact on the Ohio River from sewage that was not processed through the WWTP, one strategy tested was to treat the collection drainage with a liquid bacterial culture allowing the collection system to be converted to a plug flow reactor by establishing bacterial populations in the sewage stream and on the walls of the collection system pipes, thus forming a biofilm for bioaugmentation within the drainage system itself.

To do this, a lift station was fitted with a battery operated composite sampling pump and bacterial reservoir. The pump was operated in reverse so that rather than taking a sample every hour it discharged a dose of bacteria every hour. Application rate was 4 mg/L based on flow, targeted at 10 ppm during the first week and 2 ppm thereafter. Water samples were taken for BOD analysis coming into the manhole and 250 feet further down in the collection line on a weekly basis.

After several weeks of inoculating the line, an average reduction in BOD of 65% was observed between the two sampling points, indicating that the application was indeed quite successful. Based on this information, it was determined that if the WWTP had to be bypassed, it would be possible to significantly reduce the BOD in the collection system by inoculating the sewage stream with bacteria at a number of strategic points in the collection system that would maximize retention time and result in introduction of bacteria to the entire sewage stream prior to discharge.

In addition, the WWTP would need to take steps to restart the system as quickly as possible. Under normal circumstances, sludge would be brought in from a neighboring facility, but this can take several weeks to effectively restart the system. Again, working with AquaClean, the time for restarting a system was shown to be possible within 5 to 7 days, depending on the specifics of the WWTP. Clearly this is a tremendous cost saving measure, and provides the best short-term solution to protect against sever environmental impact during by-pass and start-up situations.