Performance Of Zeolite/Tourmaline-Modified Polyurethane Carriers Enhancing Deammonification Process For Domestic Wastewater And The Action Mechanism

Nitrogen pollution is one of the main causes of water eutrophication.Deammonification,with the combination of the partial nitrification（Pa N）process and anaerobic ammonium oxidation（Anammox）,needs less aeration energy consumption,no extra organic carbon sources and reduced greenhouse gas emissions.However,low ammonium concentrations in domestic wastewater can result in lower anaerobic ammonium-oxidizing bacteria（An AOB）activity and difficulty in inhibiting the nitrite-oxidizing bacteria（NOB）activity and growth,resulting in difficulties in the practical application in domestic wastewater treatment.In very few applications,the Anammox process has been partially achieved in wastewater treatment plants through the application of carriers in the anoxic zone,but its contribution to total nitrogen removal is minimal.However,the enhanced functional bacterial retention through carrier addition showed great potential for achieving mainstream deammonification.In this study,the functional carriers for enhancing biomass and functional bacterial activity were prepared to promote the biofilm formation and deammonification process,and the feasibility of rapid start-up and stable operation of the functional carrier-based deammonification reactor was investigated.Finally,an integrated deammonification process was established to achieve efficient nitrogen removal from domestic wastewater.Zeolite/tourmaline-modified functional（ZTP）carriers were prepared using polyurethane carriers（PU）,zeolite and tourmaline,and enhanced mechanisms of biofilm formation and deammonification were revealed.The surface roughness,specific surface area and Zeta potential of the ZTP carrier increased by 13.6 times,2.24 times and 17.54 m V compared to the PU carrier,and its surface metal element content also increased.The properties of ZTP carriers enhanced biomass retention,which increased PN content,PS secretion and microbial community evenness,thereby facilitating biofilm formation.The ZTP carriers balanced the functional bacteria activity(1.81 mg N·（g VSS·h）^-1and 1.32 mg N·（g VSS·h）^-1for An AOB and AOB respectively).Three-dimensional fluorescence spectroscopy indicated that the increased content of humic acids as electron transfer carriers promoted the bacteria metabolism.The plug-flow fixed-bed deammonification reactor（PFBR）was constructed based on ZTP carriers to reveal the bacterial characteristics and enhanced mechanism for the stable operation of the functional carrier-based deammonification reactor.The start-up time of PFBR_ZTPwas reduced to 21 d,resulting in a final NRR of 0.18 kg N·（m³·d）^-1,with long-term refrigerated deammonification sludge.However,the PFBR_PUwas established within 44 d.The An AOB abundance（Candidatus Brocadia and Candidatus Kuenenia-dominated）reached an abundance of 9.4%,an increase of 77.4%compared to the PFBR_PU（5.3%）,and ammonium-oxidizing bacteria（AOB）（Nitrosomonas）reached an abundance of 4.0%.Fluctuations in influent C/N reduced the PFBR_PUperformance and stability.The negative impact of influent C/N fluctuations was mitigated by effluent return flow.Fluctuations in influent C/N did not have a significant impact on PFBR_ZTPperformance.The redundancy analysis showed that the microbial community structure of PFBR_PUchanged significantly and the dominant effect factor changed to the influent C/N fluctuation amount,which in turn reduced system stability.The ZTP carriers maintained the abundance balance of the main functional bacteria and promoted partial denitrification（0.48%for Thauera）.The HAS-PFBR_ZTPintegrated system was constructed in combination with a high-rate activated sludge reactor to investigate the performance of treating real domestic wastewater.At 16-20°C,the HAS-PFBR_ZTPcould achieve an average NRR of 0.13 kg N·（m³·d）^-1and effluent concentrations meet the primary A discharge standard.The Anammox process of PFBR_ZTPdominated nitrogen removal（64.0±13.2%）.Multiple linear regression analysis showed that the absolute values of the dependent variables coefficients△NO₃^--N/△NH₄⁺-N were 47.7%and 48.4%lower for the influent COD and effluent NH₄⁺-N of PFBR_ZTPcompared to the PFBR_PU,and the coefficient absolute values of the independent variables of the operating parameters were also lower than the PFBR_PU.The PFBR_ZTPcould better maintain system stability facing variations in influent water quality and operating parameter adjustments.The ZTP carriers were more beneficial in maintaining the biofilm structure and functional bacteria metabolic activity(1.23 g INT·（g VSS·h）^-1)in the actual wastewater treatment.The difference between AOB and An AOB activity in PFBR_ZTPand the higher relative abundance of Thauera（0.22%and 0.35%）suggested that partial denitrification is an important nitrogen transformation process that maintains the supply of An AOB substrate.