Simultaneous Treatment of Biogas Desulfurization and Wastewater Denitrification Based on Autotrophic Denitrification

Author:Liu Yong Jie

Supervisor:feng chuan ping


Degree Year:2019





Water and energy are indispensable resources in human production and life.Unreasonable development and utilization methods of resources have led to widespread deterioration of water pollution and energy shortage around the world.Biological treatment technology based on autotrophic denitrification with reduced sulfur compounds can combine the biogas desulfurization with wastewater denitrification,which is of great significance for the treatment of nitrate pollution in water and the promotion and utilization of biogas.However,in the biogas-based denitrification system,the interactions between gas phase,liquid phase and microbial phase are complicated,and the role and influence of biogas components in denitrification and desulfurization process are not clear.In this study,the effects of biogas components on denitrification and desulfurization performance will be investigated.On this basis,methods for the enhancement of biological denitrification and desulfurization performance will be explored.The bioreactor for denitrification and desulfurization will be constructed.Main results obtained in this study were as follows:Nitrate-and sulfate-dependent methane-oxidizing organisms were cultivated.By evaluating their performance,the feasibility of treating nitrate-and sulfate-contaminated wastewater with the cultivated organisms was verified.Results showed that with sufficient nutrients,the NO3- removal rate by nitrate-dependent methane-oxidizing organisms was only 0.55 mg-N/(L·d),while sulfate reduction rate by sulfate-dependent organisms could only reach as high as 4.1 mg-S/(L·d).Besides,typical methane-oxidizing bacteria accounted for a lower proportion(less than 3%)in the cultivated organisms.The function of CH4 in the treatment process was negligible.Gaseous H2S of high concentration was used as sulfur source to investigate its influence on simultaneous denitrification and desulfurization.It was found that high concentration H2S(2%,v/v)could also be utilized by microorganisms.With S/N molar ratio increasing from 0.38 to 1.52,the lag phase of SO42-generation increased while the maximum increase rate of SO42-decreased,which promoted the accumulation of sulfur oxidation intermediates.With the increase of H2S ventilation duration from 2 to 20 min(aeration rate of 100 mL/min),the NO3-removal rate constant decreased from 0.1231 to 0.0302 d-1,which inhibited the denitrification process.CO2 could be supplied as carbon source in the replacement of NaHCO3 to support the growth metabolism of the denitrification and desulfurization bacteria,while denitrification and desulfurization activities worsen.The pH decrease caused by gaseous CO2 dissolution might be the main reason for the deterioration of nitrogen and sulfur removal performance.In order to improve the pH conditions,activated carbon,medical stone and phosphate rock were used as pH adjusting materials.All the materials were found to have the ability of pH adjustment and could improve microbial activities.And phosphorus ore showed the best adjustment ability among the materials by increasing pH from 5.5 to above 6.3,NO3-removal rate from 0.0319 to above 0.0784 mg-N/(L·h)and maximum SO42-increase rate from 0.07 to above 0.22 mg-S/(L·h).Based on the microbial activity(ATP)analysis and the dissolution characteristics of each material,it was inferred that the dissolution of substances containing Ca and Mg was the main reason for pH increase of systems with medical stone and phosphate ore,at the same time,they could improve the microbial activity directly.The microbial community structure was analyzed by high-throughput sequencing technology.It was found that when NaHCO3 was used as carbon source,the dominant genera were mainly Thiobacillus and Sulfurimonas,which could use reduced sulfur compounds for denitrification.When CO2 was supplied as carbon source,a genus belonging to the PHOS-HE36 family with heterotrophic denitrification function and the genus Thiobacillus were the main functional organisms.The heatmap,inter-group difference analysis and redundancy analysis were used to compare the microbial communities with different carbon source.The results demonstrated that pH showed greater influence on microbial community structure with different carbon sources,while the addition of pH adjusting material had relatively weaker effect.The reactor for simultaneous treatment of biogas and denitrification was constructed with cotton wire as carrier and particle phosphate ore as pH adjusting material.When running under SBR or continuous inlet mode with initial NO3-of 20mg-N/L,both NO3-and NO2-were not detected in the effluent,and the pH of the effluent increased.At the same time,more than 88%of H2S in the vent gas was removed.When applying continuous water inlet mode,the CH4 concentration in the intake and outlet gases fluctuated within the range from 59% to 66%,and the loss of CH4 was barely observed.The microbial communities were well-distributed in the reactor.Thiobacillus and Azospira were the main functional genera for denitrification and desulfurization process,while a variety of microorganisms existed within the reactor including sulfur-based autotrophic denitrifying,heterotrophic denitrifying,sulfur oxidizing and organic degrading bacteria.The realization of the nitrogen and sulfur removal in the reactor was result from the interaction of these microorganisms.In this study,the interaction between biogas components and biological nitrogen and sulfur removal processes was explored,and it could provide effective theoretical and technical support for synchronous treatment for biogas desulfurization and wastewater denitrification.