Enhancement On The Nitrate Removal Using Rice Bran As Carbon And Microbial Sources In Groundwater

The nitrate pollution was serious in China.The lack of bioavailable carbon source in groundwater has become an important limiting factor for improving the denitrification performance.Therefore,the selection of cost-effective solid-phase carbon sources was a research hotspot in denitrification.This study used rice bran,an agricultural waste,as carbon and microbial source to enhance groundwater denitrification performance.In batch studies,the physicochemical properties and denitrification properties of rice bran were investigated and the optimum dosage of rice bran and the microbial community structure in rice bran were determined.In addition,the effect of pH on the denitrifying bacteria in rice bran was discussed.In column studies the effects of biofilm carriers'types,filling modes and hydraulic retention time?HRT?on denitrification performance of rice bran packed bed bioreactor were investigated.Physicochemical analysis showed that the carbon content of rice bran in this study was as high as 46.52%±0.98%.Rice bran contained trace elements,vitamin B₁and B12,which could promote microorganisms'growth and improve microbe resistance.Nitrate removal rate increased as the rice bran increase.However,the highest total nitrogen removal efficiency of 96.2%was achieved with 1.50 g rice bran.Microorganism analysis indicated that biodegradation?Massilia,Sphingomonas,Chryseobacterium and Sorangium?and bio-denitrifying bacteria?Pseudomonas,Flavobacterium,Delftia and Comamonadace-ae?were coexisted in rice bran denitrification system.In addition,the organic acids produced by rice bran fermentation were citric acid?20%?and acetic acid?15%?,which were the main degradation products of biodegradable bacteria in rice bran and the main substrate of denitrifying bacteria.The optimum pH of nitrate-reducing bacteria in rice bran were7.00,but nitrate could be completely degraded in the range of 6.00⁹.50.However,the optimum pH of nitrite-reducing bacteria were 7.00⁸.00.When pH?6.00 or pH?8.00,the nitrite-reducing bacteria in rice bran were more sensitive to variation of pH than nitrate-reducing bacteria.In addition,a continuous flow experiment was carried out via a series of rice bran-packed denitrifying bioreactors.The results demonstrated that zeolites were more suitable for biofilm carriers than ceramics.Therefore,the rice bran-zeolites-packed mixed filling reactor had the shortest set-up period and more stable.Simultaneously,filling method also affected the performance of denitrification.The rice bran was wrapped in degreased gauze to avoid the rice bran wastage and blockage of reactor.In addition,gauze surface was conducive to biofilm formation,which made the denitrification performance more stable in the rice bran-gauzes segmented reactor?RGS?.The highest nitrate removal rate of 262.20g·m^-3·d^-1 and removal efficiency of 98.5%±1.2%were obtained when HRT was 12 h.The results indicate that rice bran was an economical and effective carbon and microbial sources to improve the denitrification performance of groundwater.A new approach was provided for the treatment of nitrate contaminated groundwater.