| Tannery industry is one of the most important industrial sources of conventional pollution and toxic pollutants.At present,after the traditional biological treatment,most discharge standards of pollution indicators can be reached,but ammonia and total chromium concentrations are difficult to meet the standard.It is more difficult to dispose ammonia because the ammonia in tannery wastewater can be released during the process of treatment.The nitrogen removal of anaerobic ammonium oxidation（anammox）,a novel biotechnology of nitrogen removal from wastewater,is much higher than the traditional process.Based on research results in the field of treatment of high-strength ammonia nitrogen wastewater,such as landfill leachate,supernatant of sludge digestion and semiconductor processing wastewater,the application of anammox process into the integrated tannery wastewater treatment is also highly promising.In this paper,the acute toxic effects of heavy metal Cr（Ⅵ）and Cr（Ⅲ）on anammox granular sludge were evaluated,and the short-term effects of Cr（Ⅵ）on anammox and the related mechanism were investigated by pre-exposure and starvation tests.Then two laboratory-scale anammox reactor were used to investigate the long-term effects of Cr（Ⅵ）on the reactor performance and recovery process,and the spatial distribution of chromium in reactor and in anammox granular sludge was monitored.Moreover,the resistant function of extracellular polymeric substances（EPS）when the biogranules suffered the Cr（Ⅵ）stress and its mechanism also were analyzed deeply.The main results are as follows:Batch test showed that Cr（Ⅵ）inhibited the anammox reaction,and the 50% inhibition concentration（IC50）was calculated to be 296.5 mg L-1 by simulation of the noncompetitive inhibition model.The effect of Cr（Ⅲ）on specific anammox activity（SAA）of the granular sludge was not obvious,and most Cr（Ⅲ）tested precipitated due to the strong interference of alkalinity.Short-term stavation（lasting within 48 h）could alleviate the inhibitory effect of Cr（Ⅵ）,but with the increase of starvation time or Cr（Ⅵ）concentration,the residual SAA decreased.The activity of granular sludge after longterm starvation is more sensitive to the toxicity of Cr（Ⅵ）,cause secrious inhibition,and accompanied with subsequent NO2--N inhibition.The inhibition of Cr（Ⅵ）is more severe in continuous-flow test operation,and nitrogen removal efficiency and sludge activity decreased rapidly,resulting in operational instability.The upper tolerance limit of chromium load for the anammox reactor was 0.05 kg m-3 d-1.Reactor performence could recoverd after a long-term regulation period,and secondary tolerance was significantly increased,and the average removal of Cr（Ⅵ）and total nitrogen were 58.0% and 91.7%,respectively.Based on the multilayer structure of the EPS,spatial distribution of chromium in granular sludge was monitored.With the increase of exposure duration,the Cr（Ⅵ）in granular sludge gradually migrated from the EPS to the cells;with the increase of Cr（Ⅵ）concentration,the main contribution region accommodating Cr（Ⅵ）was shifted inward.The Cr（Ⅵ）stress process is complex,and significantly increased EPS played a dual role against the invasion and self-detoxification.The lipid carbon chains and carboxyl groups in the EPS may be the main functional groups for anammox granule to relieve the Cr（Ⅵ）inhibition. |
