Experimental Study On The Filtrate Of Thermal Hydrolysis Of Sludge As An Additional Carbon Source For Sewage Denitrification

Insufficient carbon source seriously affects the denitrification effect of sewage treatment plants,resulting in excessively high TN in the effluent,thereby causing nitrogen pollution to the water body.So the sewage treatment plants will add carbon sources,such as acetic acid,sodium acetate,etc.,in the denitrification process,but the disadvantage of high cost limits the application of these carbon sources.Therefore,new types of carbon sources have been extensively studied,including industrial waste water,kitchen waste and waste activated sludge(WAS).WAS is used as a carbon source,which not only solves the problem of insufficient carbon source in sewage treatment plants,but also solves the problem of difficult treatment and disposal of WAS.In this study,the filtrate of thermal hydrolysis of sludge(FTHS)was used as the research object to explore its feasibility as a carbon source for denitrification and its carbon and nitrogen conversion characteristics in the process of denitrification.First,carry out the denitrification batch test to explore the feasibility of FTHS as a carbon source,and determine the optimal C/N ratio of FTHS and sodium acetate as the denitrification carbon source;Continuous tests were carried out using a SBR reactor operating in a two-stage A/O process to compare the denitrification performance of FTHS and sodium acetate as a carbon source for sewage denitrification.Finally,the changes of the two carbon sources on MLSS,MLVSS,EPS of activated sludge,microbial activity and microbial species were analyzed,and the effects of carbon sources on the characteristics of activated sludge and microbial population structure were discussed.The main results of this paper are as follows:(1)Carry out the denitrification batch tests to analyze the denitrification rate of FTHS under different C/N,and compare with the traditional carbon source sodium acetate.The best C/N ratios of FTHS and sodium acetate as denitrification carbon sources are 8 and 4,respectively,and their denitrification rates are 14.81 mg/(gVSS·h)and 15.39 mg/(gVSS · h),respectively.The denitrification capacity of the two carbon sources is 0.24 g N/g COD.According to the denitrification rate and denitrification capacity,it can be seen that FTHS has good biodegradability,so it can be used as the denitrification carbon source in the sewage treatment process.(2)The SBR reactor was used to carry out the continuous denitrification experiment with external carbon source.Adding 6 mL of FTHS per liter of influent water can reduce the TN concentration of effluent from 27.34 mg/L to 12.05 mg/L.It shows that FTHS can effectively improve the denitrification effect of sewage and strengthen the denitrification process;while sodium acetate can reduce the effluent to 7.98 mg/L under the same COD dosage.Although the denitrification effect of FTHS is lower than that of sodium acetate,it can maintain the effluent TN at a low level,so FTHS can be used as an effective carbon source in the sewage denitrification process.(3)In order to analyze the effect of adding FTHS on the denitrification process,the carbon and nitrogen balance analysis in the denitrification process was carried out.Although the addition of FTHS increases the nitrogen load of the sewage treatment system by 13.3%,it can increase the TN removal rate of the sewage treatment system by 33.5%,and FTHS can remove most of its own TN.The essence of using FTHS as a carbon source is the reuse of influent COD.19.6% of the COD in the influent is reused as sewage denitrification carbon source by FTHS.Therefore,FTHS as a carbon source for denitrification can recycle the influent COD to improve the efficiency of nitrogen removal,so it is a good external carbon source.(4)The influence of FTHS as a carbon source on the properties of activated sludge was discussed and compared with the traditional carbon source sodium acetate.Both FTHS and sodium acetate will increase the MLSS and MLVSS of the activated sludge,resulting in an increase in sludge production;In addition,the EPS of activated sludge also increased to varying degrees after adding two carbon sources,resulting in a decrease in sludge settling performance.Compared with sodium acetate,FTHS has less influence on the sludge yield and settling performance,so it can be a carbon source for denitrification of sewage treatment process.(5)The microbial communities when FTHS and sodium acetate are used as the carbon source are analyzed,and the biological diversity when FTHS is used as the carbon source is relatively high.The analysis of denitrifying bacteria shows that the types of denitrifying bacteria also change when different carbon sources are added,indicating that the types of carbon sources will affect the population structure of denitrifying bacteria.In addition,compared with sodium acetate,although the abundance of denitrifying bacteria using FTHS as a carbon source decreased,the denitrification activity was not affected.Using FTHS as the carbon source,although the microbial communities structure in the system has changed,it does not affect the sewage treatment capacity,so it can be used as the denitrification carbon source.