Startup and Pilot Testing of MBBR and IFAS Partial Denitrification/Anammox Processes

Partial denitrification/anammox (PdNA) is an emerging biological nutrient removal (BNR) process that can be used to remove ammonia (NH3) and NOx from wastewater. This process is a combination of partial denitrification (PdN), which serves to reduce nitrate (NO3) to nitrite (NO2), and anaerobic ammonia oxidation, or anammox (AMX), which uses the nitrite as an electron acceptor to oxidize ammonia. PdNA provides significant aeration and external carbon savings when compared to the conventional nitrification/denitrification biological removal process for nitrogen but has been difficult to implement in mainstream treatment conditions due to many factors. One of these factors is the slow growth rate and startup time of anammox bacteria. This research first focused on determining the required startup time and startup optimization methods for a proposed mainstream polishing PdNA MBBR at Hampton Roads Sanitation District's James River Treatment Plant (JRTP). These two MBBRs were started with either virgin carriers or carriers coated with a preliminary biofilm and were fed secondary effluent The MBBRs were dosed with glycerol based on a feedforward carbon control approach and were not seeded with anammox at any point. Anammox activity was detected in the preliminary biofilm and virgin media MBBRs approximately 52 and 86 days after startup, respectively. Based on these results, starting up a mainstream PdNA reactor without seed is possible, and using preliminary biofilm carriers can speed up startup by approximately one month. A second experiment was conducted to determine the carbon demand and nitrogen removal capabilities of a glycerol fed PdNA MBBR and AMX MBBR in series. A nitrifying MBBR was also added to the MBBR train to test how well residual nitrite leaving the MBBRs could be polished off to limit ozone/disinfectant demand downstream. Additionally, a methanol-fed PdNA integrated fixed-film activated sludge (IFAS) reactor was also operated to determine the carbon demand and nitrogen removal capabilities for a PdNA process in an IFAS reactor. The PdNA and AMX MBBRs had average effluent TIN concentrations of 3.75 ± 1.25 and 2.81 ± 1.21 mg TIN/L, respectively, with a COD dosed per TIN removed ratio (COD/TIN) of 2.42 ± 0.77 g COD/g TIN for the entire process. The PdNA IFAS reactor had average effluent TIN concentrations of 4.07 ± 1.66 mg/L and 3.30 ± 0.96 mg/L at hydraulic retention times (HRTs) of 30 and 25 minutes. At these two HRTs, the PdNA IFAS process had a COD/TIN ratio of 1.08 ± 0.38 and 2.18 ± 0.99 g COD/g TIN, respectively. Overall, this indicated that both the PdNA MBBR and IFAS processes could reach low effluent TIN limits in mainstream conditions with low demand for COD, even with relatively low and unstable PdN efficiencies. Additionally, the nitrifying MBBR managed to keep the effluent nitrite concentration consistently below 0.5 mg/L at ammonia and nitrite influent loadings rates of 0.055 ± 0.035 and 0.379 ± 0.112 g N/m2/day. This research demonstrated that starting a PdNA process in mainstream conditions, without seed, can be accomplished within a reasonable timeframe and provides knowledge that can help engineers better understand the advantages of PdNA and design and startup mainstream polishing PdNA MBBRs and IFAS reactors.