Study On Heterotrophic Denitrification Of High-Salt And High-Nitrate Wastewater

A large amount of high-salt and high-nitrate wastewater will be produced in industrial production such as chemical fertilizer and explosive production,iron and steel processing and landfill leachate treatment.Biological heterotrophic denitrification has become the first choice for the treatment of high nitrate wastewater because of its high efficiency,simple operation and good economy.However,biological heterotrophic denitrification will lead to the problem that the effluent total nitrogen(TN)can not meet the discharge standard in the treatment of landfill leachate membrane concentrate(LLMC).At the same time,for other high-salt and high-nitrate wastewater,microorganisms in activated sludge will lead to plasmolysis due to high salt stress,which will lead to microbial death,resulting in low efficiency of denitrification.Therefore,this paper takes LLMC and simulated high nitrate wastewater from a landfill in Hunan as research objects to carry out heterotrophic denitrification.The main contents and results are as follows:(1)Taking the LLMC of a landfill in Hunan Province as the research object,the changes of nitrogen elements in the process of heterotrophic denitrification of LLMC before and after Fenton oxidation were studied.The structural changes of organic compounds in LLMC before and after Fenton oxidation were analyzed by three-dimensional fluorescence spectroscopy,and the effect of simulated LLMC(purified commercial humic acid,PCHA)on heterotrophic denitrification was investigated.The results showed that after heterotrophic denitrification,the effluent TN of1 LLMC was 100.25 mg/L(in which organic nitrogen was 85.08 mg/L),which could not meet the discharge standard.After Fenton oxidation,the TN of LLMC denitrification effluent was reduced to 24.38 mg/L,which met the TN discharge requirement of GB16889-2008.The main dissolved organic compounds in LLMC are HA-like and microbial metabolic by-products.After Fenton oxidation,the relative content of HA-like in LLMC decreased most obviously,and the content of organic nitrogen decreased,the content of ammonia nitrogen increased,and some organic nitrogen was transformed into ammonia nitrogen.For simulated LLMC,the effluent TN of heterotrophic denitrification increased gradually with the increase of PCHA concentration.When the PCHA concentration reached 2500 mg/L,the TN of heterotrophic denitrification effluent was86.74 mg/L,which could not meet the discharge standard.The possible reason for the substandard TN of LLMC denitrification effluent is that LLMC contains a large number of refractory dissolved nitrogen-containing organic compounds such as humus.(2)Taking simulated high nitrate wastewater as the research object,glucose as organic carbon source,using sequencing batch reactor(SBR),the effects of salinity(0～50 g/L)and compatible solutes Glycine betaine(GB)on heterotrophic denitrification performance and the performance of activated sludge were investigated.The results show that(1)the activated sludge in the SBR reactor can withstand salinity of 0-40 g/L after domestication,and the average removal rate of TN is higher than 98.66%;when the salinity continues to increase to 50 g/L,due to the microbial activity Inhibited,the TN removal rate gradually decreased to 77.56%.With the increase of salinity,the content of extracellular polymer(EPS)in activated sludge increased linearly,among which the loosely bound extracellular polymer(LB-EPS)and the tightly bound extracellular polymer(TB-EPS)increased linearly.The content of protein(PN)and polysaccharide(PS)had a greater effect,and the content of PS was significantly higher than that of PN.(2)When the dosage of GB was 0.5mmol/L,the TN removal rate could reach 89.29%;when the dosage of GB increased to 1.0 and 1.5 mmol/L,due to the inhibition of microbial activity,the TN removal rates in a typical cycle were respectively decreased to 39.06% and 23.48%;the sludge settling performance gradually deteriorated,and the EPS content gradually increased to1023.77 mg/g MLSS.In order to further explore the internal mechanism of the effect of GB addition on heterotrophic denitrification of simulated high nitrate wastewater under high salt condition,high throughput sequencing technique was used to analyze the microbial community structure of activated sludge(named S1,S2 and S3)with GB dosage of0,0.5,1.5 mmol/L respectively.The results showed that the relative abundance of dominant bacteria in S1,S2 and S3 changed obviously,compared with S1,the relative abundance of denitrifying bacteria such as Thauera,Piscicoccus,Lentimicrobium and Marinobacter in S2 and S3 decreased gradually,while the relative abundance of Breoghania,norank-f-lzemoplasmataceae and Nitratireducter increased gradually,among which Breoghania and Nitratireducter were new genera.Therefore,it is speculated that the gradual decrease of the relative abundance of denitrifying bacteria in the system may be the internal reason for the deterioration of denitrifying nitrogen removal efficiency when the dosage of GB is increased to 1.0 mmol/L.