| As an energy-efficient nitrogen process,anaerobic ammonia oxidation（anammox）is now widely used to remove nitrogen in various wastewaters,some of which might contain high salinity.Yet,there are many uncertainties in the treatment of saline wastewater by anammox.In this study,the effect of salinity on the anammox nitrogen removal process was revealed by data analysis from literature and experimental validation.Specifically,it can be divided into two parts:response effect analysis and mechanism analysis of salinity on anammox nitrogen removal process.Response effect analysis includes the following four parts.（1）Firstly,statistical analysis was used to study the changes of nitrogen removal rate（NRR）and specific anammox activity（SAA）of freshwater anammox bacteria（FAB）and marine anammox bacteria（MAB）.The results showed that the nitrogen removal effect of FAB was the best when the salinity was 1.5%,and the activity of FAB was significantly inhibited when the salinity was 5%,But MAB can adapt to higher salinity（7.5%）.（2）Next,the collected data were simulated by kinetic model.It was found that Edwards model can best describe the effect of salinity on Anammox process（R2 was greater than 0.90）,and maximum nitrogen removal rate(NRRmax)was between 0.079 and 4.189 kg/（m3·d）.（3）Then SVM model,ANN model and GPR model were used to simulate and predict the impact of salinity on anammox process.The prediction effect of ANN model was the best and SVM model was the worst.Moreover,with different input variables,the effect of the model was different,and the variables should be considered comprehensively.（4）Finally,we prepared two kinds of self-made anammox biological carriers（biofilm and gel film）,and carried out batch experiments with these two carriers.It was found that with the increase of salinity,the nitrogen removal effect was obviously worse,and the nitrogen removal effect of gel film was stronger than that of biofilm.At the same time,the Edwards model and ANN model could be better fitted to the experimental data.Mechanism analysis mainly includes Spearman correlation analysis,gene analysis,and functional bacteria analysis and nitrogen pathway calculation.Firstly,the Spearman correlation was carried out by SPSS software to compare the correlation between NRR of MAB and FAB and other factors.Secondly,the correlation between main functional bacteria and salinity was analyzed.Then,the relationship between salinity and main functional genes was discussed by RDA analysis.Finally,the calculated parameters were used to analyze the nitrogen pathway.According to the above mechanism analysis results,for FAB,1.5%salinity promoted the activities of AOB gene amo A and anammox gene hzs A,and 1.5%salinity could promote both partial nitrification and anammox.However,salinity had little effect on NOB in freshwater environment.MAB system was different from FAB system.The activities of AOB gene amo A and anammox gene hzs A were not affected by salinity（3%-7.5%）.However,the activity of NOB gene nxr B increased under salinity.In short,through the mathematical modeling and experimental verification of this subject,the response effect and mechanism of the anammox nitrogen removal process of two different types of anammox bacteria to salinity were clarified,which provided a scientific basis and theoretical guidance for the low-energy nitrogen removal process of saline wastewater. |
