Study On The Multistage Contact Oxidation Technology Treatment Of Hypersaline Organic Wastewater And Its Microbiological Characteristics

Sodium saccharin is a sweetener widely used in electroplate,food,medicine,daily chemical industries,it would generate a large amount of sodium saccharin wastewater during its production process.Sodium saccharin wastewater,which contains a large quantity of organic substances and high concentrations of inorganic salts,is a typical hypersaline organic wastewater that is difficult to treat.Nowadays,physical-chemical methods have been employed for the treatment of saccharin sodium wastewater,but these methods have significant drawbacks including high operation costs and secondary pollution.Biological treatment with the advantage of energy-efficient,cost-effective and environment-friendly is proposed as the promising option to treat the sodium saccharin wastewater,but few studies have been conducted.Therefore,the sodium saccharin wastewater was treated by the activated sludge process and multistage contact oxidation technology in this study,exploring the microbial community characteristics in multistage contact oxidation system,revealing the succession of microbial community structure in hypersaline organic wastewater biological treatment system.These results provided a theoretical basis for the stable operation and optimization of biological systems for the treatment of hypersaline organic wastewater.Method?1?Activated sludge process and the multistage contact oxidation technology both were used to treat the sodium saccharin wastewater,investigating the variation of COD,TN,NH₄⁺-N,NO₂^--N,NO₃^--N,pH,SS,MLSS and DHA,and revealing the treatment efficiency and maximum salt tolerance,respectively.?2?Microbiological characteristics during multistage contact oxidation system were explored.The shift of microbial community structure was investigated by high-throughput sequencing technology;the microorganisms were isolated and screened by the traditional isolation method,and the isolated microorganisms were identified from the molecular biology level;the salt-tolerant bacteria which were capable of efficiently degrading the organic matter in the sodium saccharin wastewater were further screened,and the optimal degradation conditions of salt-tolerant bacteria were optimized by single factor test and response surface method.Results?1?Activated sludge process was used to treat the sodium saccharin wastewater,when the COD in influent was 791?4533 mg/L and the sludge loading was 0.03?0.15 kg COD/?kg MLSS·d?,the average removal efficiencies of COD and NH₄⁺-N were about 77.6%?84.7%and 63%?92.7%respectively at the influent salinity of 1.0%?3.0%;When the influent salinity increased to3.5%?5.0%,the average removal efficiencies of COD and NH₄⁺-N decreased to 42.9%?64.2%and 50.3%?60.3%respectively,MLSS increased rapidly,and settling performance of sludge deteriorated.?2?Multistage contact oxidation technology was further applied to treat the sodium saccharin wastewater,when the COD in influent was 791?7540 mg/L and the sludge loading was 0.03?0.24kg COD/?kg MLSS·d?,the average removal efficiencies of COD and NH₄⁺-N are about71.5%?91.2%and 83.7%?92.7%at the influent salinity of 1.0%?3.0%respectively.As the influent salinity increased to 3.5%?5.0%,the average removal efficiencies of COD and NH₄⁺-N were 87.7%?91.5%and 58.3%?85.6%,which increased 30%and 25%respectively compared with activated sludge process.The average removal efficiencies of COD and NH₄⁺-N reduced to60%and 20%as the influent salinity further increased to 5.5%?8.0%,these results indicated that multistage contact oxidation technology is more tolerant to salinity than activated sludge process.In addition,as the influent salinity increased,the dehydrogenase activity?DHA?gradually decreased,and the SS decreased first and then increased.The yield of sludge reduced when compared with the activated sludge process.?3?High-throughput sequencing results revealed that the microbial diversity in the multistage contact oxidation system decreased gradually,and the microbial abundance increased first and then decreased as the influent salinity increased.Proteobacteria,Bacteroidetes and Acidobacteria were the primary phyla in the inoculated sludge;the abundances of Proteobacteria and Firmicutes went up as the influent salinity increased,while the abundances of Bacteroidetes and Acidobacteria were rapidly reduced with increasing salinity.In addition,Pseudomonas,Fusibacter and Hydrogenophaga enriched when the influent salinity was 3.5%,but gradually eliminated at salinity of 7.0%;the abundances of Marinobacterium,Methylophaga and Halomonas increased at salinity of 3.5%and 7.0%.CCA analysis indicated that salinity was a major factor driving the changes of microbial community structure in multistage contact oxidation system.?4?The microorganisms in the multistage contact oxidation system were separated and screened,bacteria screened from the original inoculated sludge were mainly belonging to Bacillus,Acinetobacter and Pseudomonas;when the influent salinity increased to 3.5%,the number of bacteria belonging to Pseudomonas,Halomonas and Hydrogenophaga increased dramatically;the bacteria of Pseudomonas and Halomonas dominated when the influent salinity further increased to 7.0%.?5?The aforementioned bacteria were further screened to obtain the strains which can effectively degrade the organic matter in sodium saccharin wastewater:A20,A29 and A32.The COD removal efficiencies of the three strains were above 60%when the salinity of sodium saccharin wastewater was 5%,inoculum concentration was 15%,pH value was 8 and temperature was 30?.The results of response surface methodology revealed that the optimal degradation conditions of the three strains were as follows:pH=8.0,temperature was 30.3?,inoculum concentration was 14.1%?A20?;pH=8.2,temperature was 30.1?,inoculum concentration was15.9%?A29?;pH=8.3,temperature was 31.4?,inoculum concentration was 12.5%?A32?.The actual COD removal efficiencies of the strains A20,A29 and A32 under these conditions were65.4%,66.2%and 69.4%,respectively.Conclusions?1?The performance of multistage contact oxidation technology for sodium saccharin wastewater treatment is obviously better than that of activated sludge process.?2?The microbial community structure in the multistage contact oxidation system was shifted by salinity,Proteobacteria and Firmicutes enriched with the increase of influent salinity,and played an important role in the removal of pollutant in sodium saccharin wastewater.?3?The microorganisms isolated from the multistage contact oxidation system were mainly belonging to Pseudomonas and Halomonas.?4?Through single factor experiment and response surface methodology optimization,the COD removal efficiencies of salt-tolerant bacteria for sodium saccharin wastewater were more than65%.