No abstract

This paper deals with an almost 1-year long pilot study of a nitritation-denitritation process that was followed by anammox polishing. The pilot plant treated real municipal wastewater at ambient temperatures. The effluent of high-rate activated sludge process (hydraulic retention time, HRT=30 min, solids retention time=0.25 d) was fed to the pilot plant described in this paper, where a constant temperature of 23 °C was maintained. The nitritation-denitritation process was operated to promote nitrite oxidizing bacteria out-selection in an intermittently aerated reactor. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia and nitrate+nitrite concentrations. The unique feature of this aeration control was that fixed dissolved oxygen set-point was used and the length of aerobic and anoxic durations were changed based on the effluent ammonia and nitrate+nitrite concentrations. The anaerobic ammonia oxidation (anammox) bacteria were adapted in mainstream conditions by allowing the growth on the moving bed bioreactor plastic media in a fully anoxic reactor. The total inorganic nitrogen (TIN) removal performance of the entire system was 75±15% during the study at a modest influent chemical oxygen demand (COD)/NH4+-N ratio of 8.9±1.8 within the HRT range of 3.1-9.4 h. Anammox polishing contributed 11% of overall TIN removal. Therefore, this pilot-scale study demonstrates that application of the proposed nitritation-denitritation system followed by anammox polishing is capable of relatively high nitrogen removal without supplemental carbon and alkalinity at a low HRT.

As nitrogen discharge limits are becoming more stringent, short-cut nitrogen systems and tertiary nitrogen polishing steps are gaining popularity. For partial nitritation or nitritation-denitritation systems, anaerobic ammonia oxidation (anammox) polishing may be feasible to remove residual ammonia and nitrite from the effluent. Nitrogen polishing of mainstream nitritation-denitritation system effluent via anammox was studied at 25°C in a fully anoxic moving bed bioreactor (MBBR) (V = 0.45 m(3) ) over 385 days. Unlike other anammox based processes, a very fast startup of anammox MBBR was demonstrated, despite nitrite limited feeding conditions (influent nitrite = 0.7 ± 0.59 mgN/L, ammonia = 6.13 ± 2.86 mgN/L, nitrate = 3.41 ± 1.92 mgN/L). The nitrogen removal performance was very stable within a wide range of nitrogen inputs. Anammox bacteria (AMX) activity up to 1 gN/m(2) /d was observed which is comparable to other biofilm-based systems. It is generally believed that nitrate production limits nitrogen removal through AMX metabolism. However, in this study, anammox MBBR demonstrated ammonia, nitrite, and nitrate removal at limited chemical oxygen demand (COD) availability. AMX and heterotrophs contributed to 0.68 ± 0.17 and 0.32 ± 0.17 of TIN removal, respectively. It was speculated that nitrogen removal might be aided by denitratation which could be due to heterotrophs or the recently discovered ability for AMX to use short-chain fatty acids to reduce nitrate to nitrite. This study demonstrates the feasibility of anammox nitrogen polishing in an MBBR is possible for nitritation-denitration systems.

Highlights1) Short-cut nitrogen removal was demonstrated in a two-sludge NO2 --shunt process followed by AMX polishing at 25 ºC 2) An aeration control strategy was developed and implemented in the NO2 --shunt phase to produce an effluent with equal NOx-N and NH4 + -N 3) NOB suppression was realized in a single CSTR and maintained without using any external inhibitors at 25 ºC 4) Mainstream AMX polishing was demonstrated in an un-aerated MBBR 5) Mainstream NOB out-selection strategies and mechanisms have been suggested AbstractMainstream deammonification is regarded as a paradigm shift from the conventional aerobic wastewater treatment that is capable of promoting more sustainable nitrogen removal. It is understood that for deammonification to be successful in mainstream wastewater treatment, the suppression of NOB in the cold and dilute conditions associated with mainstream applications needs to be resolved. While NOB suppression in low C/N sidestreams is generally well understood, the mainstream application remains elusive. Since known factors that favor NOB suppression in sidestream such as high free NH3, high temperature, and free HNO2 are not available in mainstream, it has been recognized that operational strategies based on a different set of parameters are needed to suppress NOB. The prospect of mainstream deammonification in treatment plants that lack anaerobic digestion (e.g., incinerator plants) and therefore the potential for sidestream-generated ammonia oxidizing bacteria (AOB) bioaugmentation (without NOB) beckons an entirely different approach that might include separating the nitritation and anaerobic ammonia oxidation (AMX) steps. To prove the viability of mainstream NOB suppression and deammonification, a pilot study was conducted. The pilot study incorporates two unique stages operated in series, known as an A/B process. The A-stage included a low solids retention time (SRT), high-rate activated sludge (HRAS) process targeted at 30-60% influent chemical oxygen demand (COD) removal. The B-stage included a two-sludge deammonification process incorporating a Nitritation-Denitritation through Modulating Aeration (NiDeMA) CSTR with a clarifier followed by a fully-anoxic AMX moving bed bioreactor (MBBR). This paper considers the B-Stage, which includes the NiDeMA CSTR operated under cyclical dissolved oxygen (DO) conditions based on a control strategy applying on-line in-situ NH4 + , NO2 -, and NO3 -1959 WEFTEC 2013 measurements and an unaerated AMX MBBR. This aeration scheme combined with aggressive SRT limitation provided NOB suppression which was confirmed through weekly nitrogen processing rate measurements coupled with targeted qPCR of the bacterial community. The fully anoxic AMX MBBR has demonstrated near complete removal of NO2 -. Consequently, NOB suppression mechanisms have been postulated, and an operational framework has been put forward paving the way for mainstream deammonification in treatment plants that do not have anaerobic digestion.