Enhancing Nitrogen Removal Efficiency Of Low Carbon Source Influent By A New Slow-release Carbon Source Carrier

At present,the low carbon source of urban sewage inhibits the denitrification and total nitrogen removal of sewage plants,resulting in excessive total nitrogen in tailwater and causing harm to the ecosystem.Compared with the traditional liquid carbon source,the artificially prepared slow-release carbon source has the characteristics of stable and controllable carbon release rate.Besides,the dosage is easy to control,which will not cause secondary pollution or incomplete denitrification,thus can effectively treat the wastewater from the low-carbon source.In recent years,the research on the preparation of solid slow-release carbon source with low cost and excellent denitrification performance has become a hot topic.The purpose of this thesis is to study the denitrification of a new type of slow-release carbon source filler.Glucose and starch were used as carbon sources to modify the polyvinyl formal?PVF?packing in order to enhance the denitrification efficiency and microbial growth with of low-carbon source influent.The results showed that under the condition of aeration intensity of 4.0±0.2 L·min^-1,inlet COD of259.33±5.14 mg·L^-1,inlet NH₄⁺-N concentration of 27.03±0.24 mg·L^-1and HRT of 8h,the TN removal rates of dse-coupled PVF?GP?packing and starch-coupled PVF?SP?packing were 86.77%and 87.03%,respectively.In the control group with unmodified filler,the removal rate of TN was only 54.22%.The experimental results showed that the carbon release rates of GP and SP fillers were 196.56 mg·g^-1·d^-1and 166.74mg·g^-1·d^-1,respectively.The DO distribution of biofilm was determined by dissolved oxygen microelectrode method.The results showed that the mass transfer depths of DO in GP and SP fillers were 907.3?m and 959.1?m,respectively,while the dissolved oxygen in unmodified fillers could permeate to more than 1247.6?m,which limited the formation of anoxic zone and the denitrification effect.It was found that as carbon sources,glucose and starch increased oxygen consumption during mass transfer and inhibited the excessive penetration of DO in the filler,thus creating an anoxic environment suitable for denitrification and conducive to the growth of denitrifying bacteria.Among them,Comamonas.sp and Dokdonella.sp play the role of denitrifying organics in anoxic environment.Meanwhile,it is pointed out that glucose is easy to be eluted when it is used as carbon source coupling,resulting in excessive COD in the effluent while the coupling degree of starch and filler is good,which can maintain stable and enhance denitrification effect.In the regeneration effect experiments,after determining the starch as the dominant carbon source,the last stage of the packing was cleaned and modified with starch as the material to prepare slow-release carbon source.The experimental results show that the new type of slow-release carbon source packing SP-2 and SP-3concentration of carbon source,respectively for 2656 mg and 2678 mg,and carbon release rate were 171.78 mg·g^-1·d^-1and 173.04 mg·g^-1·d^-1,indicates that it has good regenerative effect.After the regeneration of starch coupled PVF?SP?,the removal rate of NH₄⁺-N was nearly 100%,the TN concentration was 4.92±0.15 mg·L^-1and 5.31±0.09 mg·L^-1,respectively,and the removal rate reached 78.79%and 77.11%,respectively.The effluent COD was stable,which could be used as an effective slow-release carbon source to enhance the biological denitrification effect under the influent condition of oligocarbon-carbon source.In the experiment of using the packing shell to improve the new slow-release carbon source,after replacing the sandwich carbon source on the 20th day,the TN concentration of the reactor effluent was 2.48±0.06 mg·L^-1and the TN removal rate was 89.31%,achieving the high-efficiency and stable denitrification effect in a short time after the start-up.