Effect Of The Rapid Increase Of Salinity On The Nitrification Capacity Of Biofilm

With the rapid development of the industry,agriculture,and animal husbandry,the discharge of the high salt and ammonia-nitrogen（NH₄⁺-N）wastewater is increasing.It will cause the eutrophication and destroy the aquatic ecological balance.The use of biological methods to replace high-cost physical and chemical methods for treat NH₄⁺-N in high-salt wastewater still face the two bottlenecks of long salt-tolerant acclimation time and worse the treating effect.In this study,the feasibility of reducing the salt-tolerance acclimation time of biological methods was studied to solve the bottlenecks.Three anoxic/oxic biofilm reactors with different strategies for rapid increase salinity were used;specifically,the salinity was increased to 60 g/L over 6,13 and 22 days,respectively.The pollutant removal capacity,biofilm characteristics,and microbial community structures of the three reactors were compared.After the best strategy was selected,it was further compared with slow strategies used in other studies in terms of the above three aspects.（1）The rapid and slow strategies have the same nitrification capacity,and the capacity of the R1 to degrade organics was severely inhibited.Under the environment with high salinity,the denitrification capacity of biofilms less inhibited than the nitrification capacity.The removal efficiency of ammonia-nitrogen exceeded 95%after optimizing the operating conditions of the reactor.（2）A rapid increase in salinity would inhibit the dehydrogenase activity of the biofilm.The key factor that determined the content of extracellular polymeric substances of the biofilm was its capacity to remove organics.The capacity of anaerobic bacteria to rapidly adapt to the high salinity environments was stronger than that of aerobic bacteria.The R3 strategy had the best salt tolerance.（3）Sulfate-reducing bacteria were enriched in the anoxic tank of R1,sulfate-oxidizing bacteria were enriched in the oxic tank of R1,and a sulfur cycle in the R1reactor.The rapid increase in salinity led to the enrichment of heterotrophic nitrifying in the biofilm.