In the summer of 2004, IFM was approached by a local food manufacturer to help evaluate the performance of the polishing lagoon at this facility.
The wastewater treatment plant is permitted to discharge 10 MGD directly into the Maumee River. The plant consists of roughing towers, sedimentation basins, Dissolved Air Flotation Systems (DAF's) and secondary trickling filters. The polishing lagoon has a 25 million gallon capacity and typically has a two to four day detention time.
It was observed by plant personnel that ammonia levels from the polishing lagoon were above their NPDES Permit limits. After initial review of the system, it was determined that ammonia levels were typically non-detectable out of the secondary trickling filters, but increasing through the lagoon.
It was likely that the lagoon was creating ammonia as the result of the lack of clarifiers or other solids separating devices following the secondary trickling filters. Sloughings from the filters were allowed to settle in the polishing lagoon, where those solids experience septicity and produce ammonia.
Initially, IFM initiated a bioaugmentation program utilizing our General Wastewater Microbes (GWM 2010) to help reduce the organics contributing to the formation of ammonia through the 25 MG lagoon. Over the course of two months, this bioaugmentation program proved to help reduce ammonia levels in the discharge. However, these favorable ammonia levels were not being met as consistently as the plant and Ohio EPA would like.
After reviewing the entire system through field and laboratory analysis, IFM determined the following:
-Sloughings and TKN in the secondary filter effluent led to the formation of ammonia in the lagoon. -pH, dissolved oxygen and alkalinity were below optimum nitrification conditions. -Based on sludge judge readings, sludge accumulation was not the problem. -Aeration in the polishing lagoon consisted of floating aerators and several coarse bubble diffusers on the bottom, resulting in largely ineffective aeration.
Based on these observations, IFM suggested aeration improvements as a proper course of action. IFM along with its parent company, Poggemeyer Design Group, designed a fine bubble aeration system for the lagoon.
This system was installed in the lagoon and started up in August 2005. To achieve nitrification, the food manufacturer had to inoculate the lagoon with nitrifying and heterotrophic bacteria and increase the lagoon's alkalinity. Since this time, ammonia levels have ranged from non-detectable to 0.5 mg/l.
Biological products continue to be added to the lagoon. Additionally, bioaugmentation is being trialed at other locations of the wastewater treatment plant to reduce future loadings on the lagoon.