Study On SANI Process Enhanced By Bio-electrochemical System In Treating High-strength Ammonia Wastewater Containing Sulfate

The discharge of high-strength ammonia wastewater containing sulfate would cause eutrophication of natural water,which is seriously harmful for the ecological environment and human health.A sulfate reduction,autotrophic denitrification and nitrification integrated(SANI)process has a great potential in treating municipal wastewater for it's high nitrogen removal efficiency and less secondary pollution.It still has some limitations for treating high-strength ammonium industrial wastewater containing sulfate,i.e.,severe acidification in nitrification process,high denitrification efficiency and high concentration of sulfate needed.In this work,the coupling of microbial-electrochemical system(MES)technology and SANI process was used to realize the application of SANI process in treating high-strength ammonia wastewater containing sulfate.The coupling mechanism between the MES and the SANI system was clarified,and the operating conditions were optimized.Firstly,a sole SANI system was built to treat high ammonia nitrogen wastewater containing sulfate,and the effect of SO42-concentration on the nitrogen removal efficiency of the SANI system was investigated.The results showed that the total nitrogen removal efficiency was?20,25 and 35%with S/N(SO42--S/NH4+-N)=0.47,0.70,and 0.93 in the influent,respectively,indicating that the nitrogen removal efficiency was restricted by low S/N ratio.Besides,low pH value also had an inhibitory effect on the nitrogen removal effciency.To solve the inhibition effect of low pH on nitrification process,this work introduced a hydrogen autotrophic denitrification biocathode to SANI system.The water splitting and hydrogen autotrophic denitrification reaction were coupled on the biocathode.The hydrogen-evolution reaction based on water splitting elevated the pH of electrolyte and the acidification of nitrification process was neutralized.The nitrogen removal efficiency was enhanced by the hydrogen autotrophic denitrification reaction.The biocathode potentials were controlled at-0.8,-0.9,-1.0 V(vs.Ag/AgCl,saturated),the pH of nitrification chamber were increased to?6.5,7.0,and 7.5,respectively.Accordingly,the nitrification efficiency was raised to more than 99%.In the meanwhile,the total nitrogen removal efficiency was increased to?42.7,50.6 and 56.9%,which was 7.7,15.6 and 21.9%higher than that of sole SANI system,respectively.In addition,the anode of the system was used to oxidize residual S2-in the effluent(?30.7 drops to?2.6 mg/L),avoiding secondary pollution.The results of high-throughput gene sequencing confirmed that Desulfovibrio,Thiobacillus,Bacteroides and Nitrospira were the main functional genus of sulfate reduction,sulfide autotrophic denitrification,hydrogen autotrophic denitrification and nitrification chamber,respectively.To relieve the inhibitory effect of low S/N on denitrification process,a hydrogen autotrophic SO42-reducing biocathode was further built to enhance the S cycle(SO42--S2--SO42-)in the SANI system.The SO42-produced in sulfide autotrophic denitrification chamber was reduced to S2-by the biocathode,and the obtained S2-was recirculated to the sulfide autotrophic denitrification chamber to improve the efficiency of sulfide autotrophic denitrification.With the enhancement of the S cycle,under the condition of cathode current of-45 mA and S/N=0.7,the total nitrogen removal efficiency reached?85%,which was nearly 60%higher than that of sole SANI system.At the same time,the total sulfur recovery efficiency was raised from 65%to nearly 95%.The problem of low S/N inhibition effect on the denitrification process was effectively relieved.The study on the mechanism of S cycle enhancement revealed that the sulfur deposition decreased and the S utilization efficiency was improved due to the formation of polysulfide.The relevant results of this work can not only provide an effective way for the treatment of high-strength ammonia wastewater containing sulfate but also provide theoretical basis and technical support for broad application of the SANI process.