Enhancing The Anammox Performance In Low Temperature By Adding Montmorillonite Or Loofah Sponge

As a promising biological nitrogen removal technology,Anaerobic Ammonia oxidation（Anammox）for wastewater treatment has the advantages of low oxygen demand,less excess sludge production,and low operating costs.However,the low nitrogen removal rate of this technology under conditions of temperature less than25℃is a bottleneck restricting its application in municipal wastewater nitrogen removal.In order to enhance the low-temperature tolerance of Anammox consortia,the feasibility of using the Anammox batch reactor with montmorillonite as carrier and the Anammox upflow continuous-flow reactor with a loofah as a filler was investigated in this study.The influence of these carriers on the agglomeration performance of Anammox sludge during the start-up of the reactor was investigated.The nitrogen removal performance of the reactor under low temperature（25℃¹0℃）was investigated through gradual cooling,Scanning electron microscopy（SEM）,high-throughput sequencing and metabolomics methods were used to explore the mechanism how the carriers enhanced the low-temperature tolerance of Anammox consortia.The main conclusions are as follows:（1）The addition of montmorillonite and loofah carrier can successfully start the Anammox reactor,and both can improve the nitrogen removal performance of the Anammox reactor under low temperature.The total nitrogen removal efficiency（NRR）of the batch reactor with montmorillonite was maintained at 0.3-0.35kg-N/（m³·d）under low temperature（25℃¹0℃）,which was significantly higher than that of the blank non-addition reactor.The NRR of upflow continuous-flow reactor with loofah reached up to 3 kg-N/（m³·d）.（2）Montmorillonite as a carrier has a good ability to adsorb bacteria and NH₄⁺,thereby promoting the growth of Anammox,and increasing the agglomeration performance of anaerobic ammonia oxidation sludge to resist low temperatures.Moreover,the presence of montmorillonite can increase the low-temperature metabolic activity of the Anammox consortia and promote the growth of Candidatus Brocadia which is reported to have strong low-temperature tolerance ability,thereby strengthening the tolerance of Anammox consortia to low temperature.（3）The loofah is loose and porous,and can be used as a sustained-release carbon source.It has high biological affinity,promoting adsorption of anammox bacteria on the surface and forming stable biofilm to resist cold stress.Moreover,loofah can promote the growth of Anammox bacteria.The cooperation of denitrifying bacteria and Anammox bacteria in the system played an important role in the process of nitrogen removal under low temperature.In conclusion,both montmorillonite and loofah carriers helped Anammox consortia resist cold stress and enhance nitrogen removal.This study has provided a solution to increase the nitrogen removal efficiency of urban wastewater with low temperature.