Inhibitory Effect Of Cadmium On Nitrogen Removal And Microbial Community Structure By Anammox System

Some high-strengh ammonium wastewater such as industrial wastewater and landfill leachate contains a large amount of heavy metals.Cadmium is one of the common heavy metals in high-strengh ammonium wastewater,which has strong toxicity to microorganisms.The anaerobic ammonium oxidation?Anammox?process,as a new type of cost-effective nitrogen removal process,it has the advantages of no additional carbon source,low sludge production and no secondary pollution.When the Annamox process is used to treat high-strengh ammonium wastewater containing cadmium,cadmium may affect the stable operation of the Anammox reactor.However,there are few reports on the effects of cadmium on the nitrogen removal performance and microorganism diversity of the Anammox process.In this study,the simulation of cadmium-containing ammonium wastewater was treated as the object of treatment,The short-term batch experiments investigate the effect of cadmium on anaerobic ammonia oxidation,to determine the dose-effect relationship between different concentrations of cadmium and anaerobic ammonia oxidation activity,and by analyzing the sludge extracellular polymer?EPS?and related enzyme activity changes to explore the reaction of anaerobic ammonia oxidation sludge under short-term exposure to different cadmium concentrations.The long-term experiments explore the effect of cadmium on the nitrogen removal performance,sludge characteristics and microbial community of the reactor,it provides a theoretical basis for the application of the Anammox process in the treatment of wastewater containing cadmium.The main findings are as follows:The short-term toxicity exposure test results show that the half maximal inhibitory concentration(IC₅₀)of cadmium on Anammox was 2.49 mg/L,and low concentrations of cadmium will stimulate anaerobic ammonia oxidation sludge to secrete more EPS.The long-term toxicity exposure test?140 days?showed that when the cadmium concentration was 1 mg/L,the nitrogen removal performance of the reactor increased slightly,and when the concentration increased to 5 mg/L,the reactor gradually lost its nitrogen removal capacity.60 days after stopping the addition of cadmium the nitrogen removal performance of the reactor was restored.During the process,the specific anammox activity?SAA?of the sludge showed a trend of increasing first and then decreasing as the concentration of cadmium increased.When the concentration of cadmium was 1 mg/L,the SAA was the highest at 78.4±2.4mg N/?g VSS·d?.Cadmium will affect the secretion of extracellular polymer?EPS?from the reactor sludge,especially protein EPS.The heme c content continued to decrease with increasing cadmium concentration.The cadmium adsorption rate of the reactor increased with the increase of cadmium concentration,and the EPS-bound cadmium content in the sludge was significantly positively correlated with the cell-bound cadmium content.The analysis of the microbial community structure in the reactor under long-term toxic exposure showed that at the concentration of 3 mg/L cadmium,the growth and reproduction of microorganisms in the reactor had been inhibited and the number of OTUs began to decrease.The anaerobic ammonia-oxidizing bacteria detected in the reactor was Candidatus Kuenenia,and there was no significant change in its relative abundance during the cadmium exposure period.The genus of bacteria with denitrification function in the reactor increased a lot,compared with the denitrification bacteria?Denitratisoma?and Theromomonas increased by 350.3%and41.8%respectively during the stable operation of the reactor.