Mechanism Of Nitrogen Removal From Marine Aquaculture And Aquatic Products Processing Wastewater Based On Mixotrophic Denitrification Process

With the rapid development of society and economy,the scale of seafood farming and processing industry is expanding,and discharge of wastewater is increasing gradually.This kind of high-salt wastewater contains a large number of nitrogenous pollutants and organic compounds.In this study,the mixotrophic denitrification process was introduced to the seawater high-salt environment by microorganism strengthen method.The artificially strengthen seawater system was utilized to treat nitrogenous compounds and organics in aquaculture and aquatic products processing wastewater.The continuous stirred reactor(CSTR)was used to domesticate heterotrophic denitrifying bacteria,and the treatment loadings were enhanced by adjusting the hydraulic retention time.The carbon and nitrogen degradation metabolism under the no-salt to high-salt environments was analyzed.The effect of C/N on the heterotrophic denitrification reaction was also studied.The degradation characteristics of autotrophic microorganisms to degrade sulfur and nitrogen under no-salt to high-salt environments were investigated,as well as the effect of salinity on autotrophic desulfurization and denitrification reaction.The artificially enhanced seawater treatment system with cyclic flow was adopted to remove nitrogenous and organic contaminants in marine aquaculture and aquatic products processing wasterwater,which based on the heterotrophic and autotrophic desulfurization denitrification reactions.The high-throughput sequencing method was used to analyze the microbial community structure.Its result was analyzed with the removal of carbon,nitrogen,sulfur to reveal the metabolic mechanism of carbon,nitrogen and sulfur.The main research results were shown as follows:(1)Among three methods for activated sludge domestication,the domesticated efficiency of high-salt(30 g/L)was higher than low-salt to high-salt(2 g/L-30 g/L)and no-salt to high-salt(0 g/L-30 g/L).Under the mixotrophic environments,the high-salt domestication of activated sludge was efficient to obtain the microorganisms with high salt-tolerant denitrification ability.(2)In the heterotrophic denitrification system with C/N=5,the removal efficiencies of NO2-and COD were the highest of 99.9%and 99.0%,respectively.The autotrophic desulfurization and denitrification system could withstand salinity up to 80 g/L,and the removal efficiency of NO2-reached 99.4%.When HRTs were 8 h and 32 h,the removal efficiencies of contaminants in heterotrophic denitrification system and autotrophic desulfurization denitrification system were the highest,and NO2-removal loading reached 0.4 kgN/(m3·d)and 0.044kgN/(m3·d),respectively.The former treatment efficiency was higher than the latter.Thus,the low HRT was adopted for the mixotrophic denitrification system.(3)The artificially enhanced seawater treatment system was started up in a low-load method.In the initial stage of operation,the removal efficiencies of NO2-and S2-were high.The concentration of SO42-was also high because of autotrophic denitrification reaction.With increasing of influent loadings,the activities of heterotrophic denitrification bacteria increased and substrate-competition inhibited the activities of autotrophic denitrification bacteria.The removal efficiency of S2' fluctuated.With the generation of high abundances of SRB in the system,more SO42-were reduced to S2-,which exceeded the amounts of S2-used by autotrophic desulfurization denitrification,resulting in the accumulation of S2-in the effluent.At this time,there is no need to add extra S2' to maintain the activity of autotrophic desulfurization denitrification bacteria.Along the water flow,the inlet substrate continued to be degraded,making the dominant genera at adjacent positions were partly same and the dominant genera at start and end were different.The main four dominant genera were Desulfuromusa,Litoreibacter,Thermovirga and Hyphomicrobium.According to the consumption of various pollutants and the characteristics of microbial community,when NO2-and SO42-coexisted in water,the organic matter reacted with SO42-firstly and when S2-and organic matter coexisted,NO2-reacted with S2' firstly.