N2O production and emission pathways in anammox biofilter for treating wastewater with low nitrogen concentrations

Insights into carbon-neutral treatment of rural wastewater by constructed wetlands: A review of current development and future direction

In recent years, with the global rise in awareness regarding carbon neutrality, the treatment of wastewater in rural areas is increasingly oriented towards energy conservation, emission reduction, low-carbon output, and resource utilization. This paper provides an analysis of the advantages and disadvantages of the current low-carbon treatment process of low-carbon treatment for rural wastewater. Constructed wetlands (CWs) are increasingly being considered as a viable option for treating wastewater in rural regions. In pursuit of carbon neutrality, advanced carbon-neutral bioprocesses are regarded as the prospective trajectory for achieving carbon-neutral treatment of rural wastewater. The incorporation of CWs with emerging biotechnologies such as sulfur-based autotrophic denitrification (SAD), pyrite-based autotrophic denitrification (PAD), and anaerobic ammonia oxidation (anammox) enables efficient removal of nitrogen and phosphorus from rural wastewater. The advancement of CWs towards improved removal of organic and inorganic pollutants, sustainability, minimal energy consumption, and low carbon emissions is widely recognized as a viable low-carbon approach for achieving carbon-neutral treatment of rural wastewater. This study offers novel perspectives on the sustainable development of wastewater treatment in rural areas within the framework of achieving carbon neutrality in the future.

Enhanced nitrogen removal via partial nitrification/denitrification coupled Anammox using three stage anoxic/oxic biofilm process with intermittent aeration

Pre-capturing organics in municipal wastewater for biogas production, combined with Anammox-based nitrogen removal process, improves the sustainability of sewage treatment. Thus, enhancing nitrogen removal via Anammox in mainstream wastewater treatment becomes very crucial. In present study, a three-stage anoxic/oxic (AO) biofilm process with intermittent aeration was designed to strengthen partial nitrification/denitrification coupling Anammox (PNA/PDA) in treatment of low C/N wastewater, which contained chemical oxygen demand (COD) of 79.8 mg/L and total inorganic nitrogen (TIN) of 58.9 mg/L. With a hydraulic retention time of 8.0 h, the process successfully reduced TIN to 10.6 mg/L, achieving a nitrogen removal efficiency of 83.3 %. The 1st anoxic zone accounted for 32.0 % TIN removal, with 10.3 % by denitrification and 21.7 % by PDA, meanwhile, the 2nd and 3rd anoxic zones contributed 19.4 % and 4.5 % of TIN removal, primarily achieved through PDA (including endogenous PD coupling Anammox). The 1st and 2nd intermittent zones accounted for 27.2 % and 17.0 % of TIN removal, respectively, with 13.7 %-21.3 % by PNA and 3.2 %-5.3 % by PDA. Although this process did not pursue nitrite accumulation in any zone (< 1.5 mg-N/L), PNA and PDA accounted for 35.1 % and 52.1 % of TIN removal, respectively. Only 0.21 % of removed TIN was released as nitrous oxide. The AnAOB of Candidatus Brocadia was enriched in each zone, with a relative abundance of 0.66 %-2.29 %. In intermittent zones, NOB had been partially suppressed (AOB/NOB = 0.73-0.88), mainly due to intermittent aeration and effective nitrite utilization by AnAOB since its population size was much greater than NOB. Present study indicated that the three-stage AO biofilm process with intermittent aeration could enhance nitrogen removal via PNA and PDA with a low N2O emission factor.

Analyzing greenhouse gas emissions and influencing factors of 247 actual wastewater treatment plants in China using emission factor and operational data integrated methods (ODIM)

In response to China's policies on pollution control and carbon emission (CE) reductions, more stringent regulations have been implemented to evaluate CE in wastewater treatment facilities. In this study, we have analyzed CE from China's wastewater treatment plants (WWTPs) and influencing factor. Emission factor (EF) and operational data integrated methods (ODIM) were utilized to measure emissions, using data collected from 247 WWTPs over a 1-year period across seven regions in China. The average CE intensity was 0.45 kgCO2-eq/m3, affected by region, season, influent water quality, treatment processes, effluent discharge standards, and facilities. The scale effect was obvious only in the range of 2 × 105 m3/day. Underground WWTPs exhibited significantly higher CE compared to aboveground WWTPs. In summary, the assessment of CE in 247 actual WWTPs not only identifies emission reduction potential but also provides a scientific basis for formulating targeted emission reduction measures.