Research On The Coupled Bioelectrochemical Hydrogen Autotrophic Denitrification With Sulfur Autotrophic Denitrification Technology And The Microbial Community Structure

In recent years,due to the heavy use of fertilizers and pesticides in agricultural production,the nitrate content in surface water and groundwater exceed the standard badly,which forms a serious threat to water environment and human health.Therefore,it is important to find a nitrate removal technology of high efficiency and low energy consumption in today’s water treatment industry.Study found that the coupled bioelectrochemical hydrogen autotrophic denitrification with sulfur autotrophic denitrification technology not only makes denitrification efficiency significantly improved,but also has realized the clean and pollution-free autotrophic denitrification process.Therefore,facing the increasingly severe situation of nitrate pollution,it has great theoretical significance and application prospect to carry out the coupled bioelectrochemical hydrogen autotrophic denitrification with sulfur autotrophic denitrification technology.After the coupled membrane reactor has worked stablely,the effects of influent pH,influent concentration of NaHCO3,influent nitrate concentration,current intensity,and hydraulic retention time are assessed throughout this trial.At the same time,we use the high-throughput sequencing technology to research the influence of microbial community structure by different current intensity.In addition,by using push flow reactor dynamics equation,we build a relationship between hydraulic retention time and influent nitrate concentration in the optimal operating condition.Finally,the energy consumption is studied to analyse the operation economy of the coupled reactor.The results show that the coupled bioelectrochemical hydrogen autotrophic denitrification with sulfur autotrophic denitrification has great effect,and there is almost not ammonia nitrogen in the system.The bioelectrochemical hydrogen autotrophic denitrification accounts for a large proportion in it.For sulfur autotrophic denitrification,it also makes certain contribution to the whole system,which accounts for above 20%of the denitrification system.The influent pH,influent concentration of NaHCO3,influent nitrate concentration,current intensity,and hydraulic retention time all have certain influence to the coupled reactor.The coupled system are greatly influenced by the influent pH.The optimal pH for sulfur autotrophic denitrification is 8.5,and the optimal pH for bioelectrochemical hydrogen autotrophic denitrification is 7.5.Because the bioelectrochemical hydrogen autotrophic denitrification accounts for a large proportion in coupled system,the optimal pH for the coupled system is 7.5;Compared with sulfur autotrophic denitrification,bioelectrochemical hydrogen autotrophic denitrification is more influenced by influent concentration of NaHCO3.With the influent concentration of NaHCO3 rising,the nitrate nitrogen removal rate increases,but when the influent concentration of NaHCO3 reaches to 3 g/L,the nitrate nitrogen removal rate does not significantly increase;The influent nitrate concentration affects the denitrification efficiency of the coupled system.When nitrate nitrogen concentration in the influent water is not more than 200 mg/L,the nitrate nitrogen degradation rate of coupled system increases with the rising concentrations of nitrate nitrogen,but when influent water nitrate nitrogen concentration reaches 250 mg/L,nitrate nitrogen degradation rate begins to drop,mainly because high nitrate concentration inhibits the bacteria activity of bioelectrochemical hydrogen autotrophic denitrification;Current intensity has great influence on denitrification efficiency of the coupled system.Weak current stimulation can improve the activity of microorganism and increase its ability to denitrify.Sulfur autotrophic denitrification ability increases with rising current intensity in the section of bioelectrochemical hydrogen autotrophic denitrification.When the current intensity is low,the production of hydrogen is less,so the bioelectrochemical hydrogen autotrophic denitrification ability is weak.The best effect of denitrification is achieved when the current is added to 200mA.However,if the current intensity increase continuously to 300mA,the bioelectrochemical hydrogen autotrophic denitrification is suppressed and the denitrification efficiency of the coupled system is also influenced.Hydraulic retention time has big influence to both section of the coupled system.If the hydraulic retention time is short,hydraulic scour is larger,so denitrification effect of the coupled system is poorer.The increase of hydraulic retention time can improve the removal rate of nitrate,but the increment of removal rate reduces gradually.We use the high-throughput sequencing technology to research the influence of microbial community structure by different current intensity.The analysis results show that the dominant bacterial phylum is Firmicutes and class is Clostridia and genus is Proteiniclasticum.Current intensity of 200mA is beneficial to the growth of the dominant bacteria in the coupled system,so denitrification effect is best at the same time.When the current intensity increases to 300mA,growth of theProteiniclasticum is restrained,which leads the debasing of denitrification efficiency.Other bacteria also played an important role for denitrification,and due to competition between the bacteria,growth of other bacteria are restrained by the dominant bacteria.Especially,we find bacterial phylum Proteobacteria and Actinobacteria,bacterial class Betaproteobacteria,Alphaproteobacteria,Actinobacteria and Epsilonproteobacteria,bacterial genus Thauera,Acetoanaerobium,Sulfurovum,Azoarcus and Thiobacillus have higher tolerance for current,and they can better adapt to the current intensity of 300mA.When influent pH,influent concentration of NaHCO3,influent nitrate concentration,and current intensity are fixed,we establish a dynamical model between hydraulic retention time and influent nitrate concentration(C0/C= 0.7432e0.2527T),which can well reflect the actual operation condition of the coupled reactor.Finally,energy consumption analysis shows that tthe greater efficiency of energy utilization is achieved at the smaller current intensity.