A Pilot Study for Treating Facultative Lagoon Effluent Utilizing a Fixed Bed Biofilm Reactor

Facultative lagoons have been widely used in the United States for at least 100 years. There were more than 7,000 facultative lagoons in operation in 2002 (US EPA). As the discharge limits for bio-chemical demand (BOD), ammonia and total suspended solids (TSS) become more stringent, these lagoons need to be upgraded to meet these new requirements. A pilot study was done at the Guntown WWTP in Mississippi utilizing a fixed bed biofilm reactor (FBBR) with structured sheet media (SSM) as a post lagoon unit to polish the lagoon effluent BOD and ammonia. The pilot study was conducted from June 2011 to October 2012. As expected, the effluent BOD, ammonia-N and TSS concentrations from the facultative lagoon varied widely during the study (BOD: 4.0 – 153.0 mg/L, TSS: 18 – 360 mg/L, ammonia-N 0.2 – 70.0 mg/L), which affected the FBBR performance significantly. Detailed analyses indicate that when the influent BOD concentration to the FBBR was lower than 23.0 mg /L, the effluent ammonia concentration from the FBBR would be less than the required 2.0 mg/L. When the in fluent BOD concentration is higher than 23.0 mg/L, the effluent ammonia concentration would exceed the 2.0 mg/L limit. Ammonia loading variations also significantly affected the FBBR performance. TSS concentration however, did not show an apparent effect. The results from this pilot study provides valuable information for understanding the effluent characteristics of this and hundreds of other similar facultative la goons in the region and designing post lagoon polishing FBBRs for facultative lagoons. Based on the results, a series of design recommendations were provided to facilitate future project design.