Submerged Structured Sheet Media (SSM) IFAS and SSM Fixed-Film Only Systems for Simultaneous Carbon Oxidation, Nitrification and Denitrification and Implications

Submerged fixed media has been utilized in wastewater treatment as either a hybrid system in conjunction with returned activated sludge (RAS) or a fixed-film only system without RAS in both Europe and the United States since the 1980s (Schlegel 1998, Muller 1998; Schlegel and Koeser 2007, Flamming et al. 2011, Ye et al. 2010, Zhu et al. 2012a). The benefits of submerged fixed media systems include, but are not limited to, plant capacity increase without requiring new construction, enhanced nitrification at both normal and low temperatures, treatment capacity protection during both hydraulic and loading surges and improved sludge settling characteristics, etc. Most of these systems were designed to specifically target carbon oxidation and/or nitrification. The simultaneous denitrification capability of an aerobic integrated fixed-film activated sludge (IFAS) system or an aerobic fixed-film only system have not been adequately explored even when evidence of significant simultaneous carbon oxidation, nitrification and denitrification (i.e. SND) exists in many of these media systems (Muller 1998, Zhu et al. 2012b).Pilot studies were conducted to evaluate the SND capability of various processes at the City of Reading Wastewater Treatment Plant utilizing PVC structured sheet media (SSM) as the fixed film carrier and the plant's primary effluent as the pilot influent. The pilot influent had an average soluble chemical oxygen demand to soluble total nitrogen (SCOD:TN) ratio of approximately 10.0 and an SCOD to soluble biological oxygen demand (SBOD) ratio of approximately 1.7. A schematic of the pilot set up is shown in Figure 1. The pilot study consisted of five phases. Phase I was a two stage aerobic activated sludge process (ASP) without media. Phase II was a two stage aerobic IFAS process with media in both stages. Phase III was a two stage aerobic fixed-film only process without RAS. Phase IV was a three stage (anoxic for stage 1, aerobic for stages 2 and 3) fixed-film process with media in all three stages but without RAS. Phase V was a three stage (anoxic for stage 1, aerobic for stages 2 and 3) IFAS process with media in all three stages and RAS. Various HRTs were tested. The testing conditions and results are shown in Table 1.