Role of air scouring in anaerobic/anoxic tanks providing nitrogen removal by mainstream anammox conversion in a hybrid biofilm/suspended growth full‐scale WWTP in China

Abstract

A full‐scale wastewater treatment plant in China experienced unintentional anammox bacterial enrichment on biofilm carriers placed in the anaerobic and anoxic zones of an anaerobic/anoxic/oxic process under ambient temperatures and without bioaugmentation. Here, we show that microaerophilic conditions resulting from air scouring needed for biofilm carrier suspension in the anaerobic/anoxic zones can support a robust nitritation/anammox process. Results from an in situ on/off air scouring test showed that air scouring strongly induced both ammonia and total inorganic nitrogen removal in the anaerobic/anoxic zones. Ammonium concentration in the anaerobic and anoxic tanks remained constant or even slightly increased when air scouring was off, indicating that air scouring made a noticeable difference in nitrogen profiles in the anaerobic/anoxic zones. Various batch tests further indicated that partial denitrification is not likely to generate nitrite for anammox bacteria. Robust nitritation, and anammox on the carriers, can occur at low dissolved oxygen conditions, as measured in the full‐scale facility. The observations show that mainstream deammonification without sidestream bioaugmentation at moderate temperature is feasible and further optimization by a more dedicated design can result in improved nitrogen removal in cases when chemical oxygen demand is limited in mainstream wastewater treatment. Practitioner points Microaerophilic conditions in a full‐scale IFAS reactor caused mainstream anammox in moderate temperate area. Robust nitritation, and anammox on the carriers, can occur at low dissolved oxygen conditions in anaerobic/anoxic tanks with air scouring. Anammox can function well with conventional nitrification and denitrification process at mainstream conditions for stable nitrogen removal.

Novel Use of a Ferric Salt to Enhance Mainstream Nitrogen Removal from Anaerobically Pretreated Wastewater

“…Here, the proposed nitrogen removal A/O system can be upgraded from the current A/A/O system without significant capital costs. On the one hand, anoxic biofilms that were added to the A zone have been achievable at full scale, reported recently. − On the other hand, the added unit for iron dosing only has a volume of 7.5% of the anaerobic zone in the conventional A/A/O process, meaning that it can be directly re-fitted. Moreover, despite dosing into the return sludge, the average iron dosage in terms of treated wastewater was calculated to be 20 mg Fe/L, which is close to the typical range of iron salt dosed (10–40 mg Fe/L-treated wastewater) in many WWTPs. ,, Doing of FeCl 3 slightly reduced the pH of wastewater (Figure S2), which indicates that the alkalinity within wastewater is sufficient to buffer the proton produced in the Fe 3+ hydrolytic process.…”

Sustainable approach of biological treatment of landfill leachate by Anaerobic Ammonium Oxidation: A review

“…The application of Anammox in urban wastewater systems has the potential of optimizing energy recovery by redirecting organic carbon from the nitrogen removal process and redirecting it towards anaerobic digestion. This phenomenon occurs due to the autotrophic nature of Anammox bacteria [33]. The actual implementation of Anammox systems at pilot and industrial sizes is challenging due to the dependence of nitrogen removal efficiency and Anammox activity in landfill leachate treatment on many operational factors [34].…”

How to Provide Nitrite Robustly for Anaerobic Ammonium Oxidation in Mainstream Nitrogen Removal

“…PN means half of the influent ammonium is oxidized to nitrite, and the stable anammox relies on the coupling to PN . It is also the preferred route to supply nitrite for anammox reactions due to its oxygen and carbon savings. ,,, Typically, the distinct niche of ammonia-oxidizing bacteria (AOB) and NOB, such as activity, growth rate, biomass decay rate, and activity recovery rate, as well as their differential tolerance to specific inhibitors, are the foundation of effective controlling strategies for achieving mainstream PN. Previous studies have proven that an unstable nitrite supply is the primary hurdle hindering the widespread adoption of mainstream anammox .…”

“…24,167,182 For example, in Xi'an No. 4 WWTP (Xi'an, China), both PD and PN contributed to the nitrite generation, which then was stimulated to anammox occurrence in an anoxic tank where the carrier was packed; 32,65,80 even when the influent TN and wastewater temperature varied as 20.3−40.8 mg/L and in 11−23 °C, respectively, NRE was enhanced from 68.1% to 77.0% with the average effluent TN concentration less than 8.0 mg N/L. 32,80 This result proved that the nitrite supply via a PD-based process can be a feasible way to achieve mainstream anammox.…”