Study On The Denitrification Performance Of Corncob-based Solid Phase Denitrification System In Flow Field Environment

With the wide application of fertilizers in modern agriculture,nitrate pollution has attracted great attentions.The remediation methods for nitrate pollution include physical,chemical and biological methods,biological remediation has the advantages of high efficiency and low cost,as well as denitrification is especially suitable for in-situ remediation of nitrate contaminated groundwater.The traditional external carbon source for denitrification is liquid carbon source,which has low molecular weight and high bioavailability.However,because of its strong water solubility,it is easy to lose with the flow of groundwater,and its degradability can also cause its rapid consumption.In contrast,solid phase denitrification?SPD?process has corresponding advantages.Solid substrates can not only provide electron donors for denitrifying microorganisms,but also serve as a growth carrier for biofilm attachment.Typically,it is suitable for in-situ permeable reactive barriers?PRB?facility.Corncob,a typical agricultural waste,is studied as the carbon source for solid phase denitrification under dynamic flow conditions using 1-D column experiment.The results show that the hydraulic retention time has significant effect on the denitrification rate and transformation between the nitrogen species.The increase of hydraulic retention time can improve the denitrification rate,however,it can cause accumulation of nitrite when it is in a proper range or ammonium if it is too large.C/N ratio is also an important factor affecting solid phase denitrification.Appropriate C/N ratio can improve nitrate removal rate and inhibit the production of nitrite and ammonium.The results show that the optimal hydraulic retention time of the system is 16 h,and the proper nitrate concentration for the system to treat is 50mg·L^-1.The results of carbon release performance of corncob granules showed that corncob has good application potential as the packing material of permeable reactive barrier for solid phase denitrification,as it can steadily release water-soluble TOC to provide electron donor,the concentration of TOC released steadily at the later stage was 20 mg·L^-1.The results of EDS showed that the relative carbon content of corn cob particles did not change much before and after the experiment.During the whole dynamic column experiment period,the carbon release of corncob particles was slow and no structural collapse occurred.The SEM results shows that its surface structure also favors microbial adhesion and growth,FTIR result shows that the chemical bonds are stable.And the result indicates that Pseudomonas sp might be the main bacteria in the corncob-based denitrification system.