Nitrogen recovery from wastewater as nitrate by coupling mainstream ammonium separation with side stream cyclic up-concentration and targeted conversion

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

“…Currently, reducing carbon emissions and achieving carbon neutrality have become urgent targets in wastewater treatment plants (WWTPs). , Compared with conventional nitrification and denitrification, anammox is a revolutionary biological nitrogen removal process with the advantages of reducing oxygen demand (60%), saving carbon sources (100%), decreasing wasted sludge production (80%) and lessening greenhouse gas (GHG) emissions. ,− Anammox can achieve highly efficient nitrogen removal from wastewater, and act as a cost-effective alternative to the conventional nitrification and denitrification processes. , As an autotrophic nitrogen removal biotechnology, anammox is often coupled with a carbon capture process, such as high-rate activated sludge (HRAS), chemically enhanced primary treatment (CEPT), and anaerobic membrane reactor (AnMBR). − Such configuration can minimize energy consumption and maximize the capture of organic carbon for bioenergy (i.e., methane) production, propelling WWTPs to transform from energy-consumers to energy-exporters. ,, So far, however, critical challenges remain for the stable mainstream anammox in practical application.…”

“…Indeed, although more than 200 full-scale partial nitrification-anammox (PN/A) facilities have been applied worldwide in treating nitrogenous wastewater to date, such as digestate, reject water, and landfill leachate, − only rare instances of pilot- or full-scale anammox engineering implementations have been reported in treating mainstream characterized by a low-strength (20–50 mg N/L), high flow rate (360 billion m 3 /year, globally), and large nitrogen discharge amount (9.25–23.13 billion kg ammonium/year, globally). ,,, Researchers and practitioners are wondering whether PN/A is suitable for mainstream treatment, because the low ammonium concentrations and low temperatures of a mainstream would generally reduce the biological activity of anammox bacteria (AnAOB) and restrict the effective washout of nitrite-oxidizing bacteria (NOB). − Nevertheless, AnAOB have been widespread found in WWTPs, and have shown adaptation to low temperature (10–20 °C) in WWTPs of nontropical regions. ,, Also, the prevalence of the warm side stream anammox treatment would favor mainstream anammox by providing substantial amounts of active anammox biomass. ,, Therefore, it might be the unstable nitrite supply rather than anammox biomass availability that had greatly limited the implementation of mainstream anammox.…”