Influence Of Salinity On Short-cut Nitrification Process And Biofilm Characteristics Under Autotrophic And Heterotrophic Conditions

Nitrogen pollution is one of the major reasons causing water eutrophication,Wastewater biological nitrogen removal technology research has also been a hot topic in recent years.Salt is generally considered to be one of the important factors that inhibited notrigen removal efficiency,especially in industrial wastewater,landfill leachate,and mariculture wastewater treatment.At present,salt was significantly affected the short-cut nitrification during biological nitrogen removal process.Thus,effects of the relationship between salinity and the efficiency of ammonia nitrogen conversion in the process of short-cut nitrification,the rules of nitrification,structural characteristics of biofilms and microbial population structure under salt stress will have important guiding significance to development of new nitrogen removal technology on salt containing wastewater.This paper uses the techniques of molecular biology,with nitrifying biofilm nitrogen removal efficiency by focusing on autotrophic and heterotrophic nitrification biofilm and the relationship between nitrogen efficiency and salinity,reveal the effect of salt stress on the structure characteristics of the biofilm and the microbial population structure.The main conclusions are as follows:1.The short-cut nitrification rules under autotrophic and heterotrophic conditions were studied and the biofilms that developed under autotrophic and heterotrophic conditions were characterized.After 6 months operation without salt addition,the nitrogen conversion rates and nitrosation rates under autotrophic and heterotrophic conditions were 85%,88%and 80%,86%,respectively.The analysis on biochemical components and biofilm structure showed that total extracellular polymeric substances?EPS?content in heterotrophic biofilm was higher than that in autotrophic biofilm,and the ratios of PN/PS in the two different biofilms were 0.96 and 0.69,respectively.The images of three-dimensional excitation-emission matrix?EEM?revealed the ratio differences between two different biofilm of the protein-like substances and humic substances,and the confocal laser scanning microscope?CLSM?results showed the different distribution of EPS contents in the two biofilms.2.The nitrification efficiencies of autotrophic and heterotrophic short-cut nitrification under salt shocking loads were studied,and were compared with the nitrification efficiencies of reactors operated for 7 months under stepwise elevated salinity loading.The results showed that NH₄⁺-N removal efficiency of autotrophic and heterotrophic systems were 4.3%and 4.1%,respectively when the salt shocking loads of 35g·NaCl·L^-1 and 45 g·NaCl·L^-1,respectively.Both systems have been almost completely inhibited.After the reactors long-term salinity domestication,NH₄⁺-N removal efficiency were 40%and 28%at 70 g·NaCl·L^-1 for autotrophic and heterotrophic reactors,respectively.The nitrification systems of two reactors still have a certain activity.About 75%ammonia removal efficiency and above 80%of nitrosation rate were achieved in the two biofilm reactors when concentration of salt was under 40g·NaCl·L^-1.The results suggested that both autotrophic and heterotrophic systems have higher tolerance to salt after long-term domesticated,and the salt tolerant ability of autotrophic biofilms was higher than that of heterotrophic biofilms.3?The EPS components were extracted and analyzed from the autotrophic and heterotrophic short-cut nitrification biofilms under salt stress,and the appearance and structure of biofilm were analyzed by scanning electron microscopy?SEM?and CLSM images.The results showed that under salt stress,the contents of EPS in autotrophic biofilm increased first and then decreased with the increase of salt concentration.The contents of EPS were 112.60,136.18,129.07 and 61.43mg·g^-1·VSS^-1 with the salt concentration at 0,20,50,70 g·NaCl·L^-1,respectively.While the contents of EPS in heterotrophic biofilm were 171.75?151.17?128.2 and 81.79 mg·g^-1·VSS^-1 respectively,showed different change rules with autotrophic biofilm.SEM and CLSM images revealed the structures of autotrophic and heterotrophic biofilms were gradually reduce fragmentation,density,?-polysaccharides on the layer attaching bulk liquid,and extracellular DNA?eDNA?increased.Contents and distribution of protein,lipids and dead cells displayed different changes in autotrophic and heterotrophic biofilms,which affected nitrification characters of biofilms,resulting in different performances for autotrophic and heterotrophic reactors.4?The diversity and abundance of Ammonia Oxidizing Bacteria?AOB?in autotrophic and heterotrophic biofilms were analyzed by High-throughput Sequencing technology.Under the condition of 0 g·NaCl·L^-1,Nitrosomonas of p-proteobacteria possessed the highest abundance in both biofilms.However,the predominant AOB was different in the two biofilms with salinity increased.When salinity was increased to 70g·NaCl·L^-1,the predominant AOB was Nitrosococcus of ?-proteobacteria in autotrophic biofilms,while other AOB descreased a small percentage.However,the predominant AOB of heterotrophic biofilm were Nitrosomonas,except for a small amount of Nitrosococcus.All the other bacteria were not detected,and diversity of AOB was disappeared.This results revealed that the conversion rate of ammonia nitrogen in heterotrophic system was lower than that of autotrophic system under concentration of 70 g·NaCl·L^-1,and heterotrophic reactor was severely inhibited.