Technical Study On Enhancement Of Biological Denitrification In Wastewater By Microbial Electrochemical System

Traditional biological denitrification has played an important role in eutrophic wastewater treatment.However,denitrification requires supplement of electron donors?e.g.methanol?and alkalinity.SANI process has preferably solved the above two problems by using heterotrophic sulfate-reducing bacteria and autotrophic denitrifiers.Sulfur sources serve as electron donors,and a minimum sulfide sulfur to nitrate nitrogen ratio of 1.6 is required in this process.High concentration of sulfide is toxic to microbes,and the pre-anerobic technology stinks,so at present SANI process is only applicable to the treatment of wastewater with low ammonia nitrogen concentration.In this paper,bioelectrochemical system?BES?and SANI process were integrated together.Microbial electrolysis cells?MEC?and electrochemical active denitrifiers were introduced into SANI process,aiming at the efficient treatment of wastewater with high ammonia nitrogen concentration by the coupled technology.After the successful construction of BES-SANI coupled biological denitrification system,we changed the reflux ratio,pH of the waste water,applied voltage and other operating conditions to optimize the performance of the system.The research results showed that:when TOC and ammonia nitrogen concentration were 600 mg/L and 214.6 mg/L in the wastewater,respectively,the optimal reflux ratio was 3:1,the optimal pH was 8.0,and the optimal applied voltage was 0.3 V.Under the optimal operating condition,the fastest denitrification rate of BES-SANI coupled denitrification system was 46.5 g r-3 day-1,48.1%higher than SANI process(31.4 g m^-3 day-1),which proved that BES-SANI coupled technology could significantly improve the efficiency of denitrification.By changing the sulfate concentration of feed wastewater several times,we macroscopically studied on the performances of BES-SANI coupled biological denitrification system under different S/N ratio.The research results showed that:Under the operating conditions of TOC,ammonia nitrogen concentration and applied voltage were 600 mg/L,214.6 mg/L and 0.3V,respectively,when the S/N ratio was approximating the theoretical S/N ratio of SANI process,the best total nitrogen removal ratio was about 41.0%,and the excess sludge was effectively controlled;When the S/N ratio was 0.6 times of the theoretical S/N ratio,the best total nitrogen removal ratio was about 43.9%,and the excess sludge slightly increased;When the S/N ratio was 0.3 times of the theoretical S/N ratio,the best total nitrogen removal ratio was about 56.8%,however,the excess sludge accumulated obviously in denitrification process.It was proved that cathode electrode in BES can partly take the place of sulfide to work as electron donor,assist SANI process to improve the efficiency of denitrification,and reduce the dosage of sulfate.The mechanism of BES-SANI coupled biological denitrification system proved that:in the treatment of high concentration ammonia nitrogen wastewater,when S/N?1.5,denitrification rate was mainly dependent on the autotrophic denitrification using sulfur sources,but high sulfur concentration poisoned the microorganisms,which prevented the improvement of denitrification efficiency.When S/N?1.0,a large portion of nitrate was removed by autotrophic denitrification using sulfur sources and electrode as electron donors.With the decrease of sulfate in influent,SANI process faced the problem of lacking in electron donors for autotrophic denitrification.Instead,the electrode in BES could serve as electron donor.When S/N?0.5,dnitrification rate was mainly dependent on heterotrophic denitrification,and the main electron donor was organic carbon source,and as a result,autotrophic denitrification in SANI was inhibited.In conclusion,with the assist of BES,SANI process can be applied to efficient treatment of wastewater with high ammonia nitrogen concentration.