Novel Integrated High-Rate Filtration and Fixed-Film Biological Reactor Demonstrates Simultaneous TSS and BOD Removal in Wet Weather Peak Flows

Wet weather poses significant risks to WRRFs, especially when increased flows cause plants to exceed design capacities. This paper presents results from a 13-month pilot of a new technology for rapid treatment of excess flows. The pilot, performed at a blending permit plant in Genesee County, Michigan, tested two distinct configurations of the Proteus™ up-flow media filter: a primary filtration (PF) reactor for removal of suspended solids (TSS) and particulate biological oxygen demand (BOD), and a biological (B) reactor equipped with aeration for biofilm growth and oxidation of BOD. Both utilize a new, X-shaped polypropylene media designed specifically to filter high-solids primary influent. In both reactors, sensors tracked flow rate, TSS, bed pressure, reactor DO, and temperature. Composite samples tracked a range of water quality factors including BOD, TSS, COD, nutrients, microbiological indicators and chlorine demand. To emulate the variability of wet weather flows, some weeks of testing diluted raw water while others amended influent with primary sludge. When processing plant influent, the PF reactor processed up to 133 gpm, achieving average TSS removal of 78%, BOD removal of 69% and COD removal of 67% at empty bed contact times (EBCTs) of 5-13 minutes. When processing primary effluent, the same reactor removed 71% of TSS, 51% of BOD and 56% of COD. The biological (B) reactor processed up to 64 gpm, achieving TSS removal of 84%, BOD removal of 81% and COD removal of 78% at EBCTs of 10-30 minutes in screened raw water. Treatment of primary effluent yielded equivalent TSS removal, but reduced BOD and COD removals of 60% and 58%, respectively. BOD removal improved with increasing EBCTs and higher loadings. The biological configuration also showed improved removal performance for total and fecal coliforms, chlorine demand and nutrients. In Spring 2020, the pilot captured a real wet weather blending event. Despite two weeks of minimal feeding prior to wet weather, the biological reactor maintained effluent TSS/BOD below 22/20 mg/L. These results demonstrate that a combined primary/biological filter can provide rapid treatment of excess flows, providing a new treatment option for utilities dealing with challenging wet weather conditions.