Study On The Utilizing Potential And The Strategy Of Distribution Of Influent Carbon Source In Urban Sewage Treatment Plant

Because the traditional urban sewage treatment plant pretreatment system only undertakes the removal function of some organic matter,a large amount of non-dissolved organic matter needs to be removed in the aerobic unit,resulting in a higher biological treatment loading and increasing the operating energy consumption of the sewage treatment plant.At the same time,insoluble organic matter generally cannot directly and effectively meet the demand for carbon source in biological nitrogen and phosphorus removal.In order to improve the efficiency of biological nitrogen and phosphorus removal,especially the removal efficiency of TN,it is often necessary to add a large amount of easily degradable carbon sources such as methanol or sodium acetate,which further increases the operating cost of the sewage treatment plant.In addition,the traditional sludge anaerobic digestion system has low organic matter degradation rate and low methane production,which is not conducive to the degradation of potential energy in the sludge.In view of the above problems,this paper took the inflow of Qingdao Haibohe Wastewater Treatment Plant as the research object.Firstly,the chemically enhanced primary treatment(CEPT)process was used to efficiently intercept the insoluble organic matter in the influent of the sewage treatment plant.A part of the chemically enhanced primary sludge that had been intercepted was converted into high-quality carbon sources by hydrolyzed acidification to the biological nitrogen and phosphorus removal unit and the other part produced methane by anaerobic digestion to recover biomass energy.On this basis,based on the quality of the sewage studied and the results of the experiments,the strategy of the distribution of the insoluble organic matter intercepted by CEPT according to the above two routes was discussed.Due to the limited experiments time,some experiments in which chemically enhanced primary sludge was converted into high-quality carbon source by hydrolysis and acidification were completed by other students in the research group.This paper mainly studied the potential of anaerobic digestion and the carbon source allocation strategy of chemically enhanced primary sludge.The main conclusions were as follows:(1)The preferred test of the CEPT coagulant was carried out using ferric chloride,aluminum sulfate and polyferric sulfate as coagulants.The results showed that the best coagulant was ferric chloride.The results of the effects of coagulant dosage on organic matter retention showed that the optimal dosage of Fe Cl3 in CEPT was 20 mg Fe3+/L.In this condition the rejection rate of COD was 60.1%,the removal rates of SS,PO43--P and TN were 65.3%,87.4% and 23.1%,respectively.The experiments results of other factors affecting the interception effect of organic carbon source showed that the stirring time was the most important factor affecting the coagulation test effect.The optimal level conditions of COD rejection were as follows: ferric chloride dosage was 20 mg Fe3+/L,stirring rate was 60r/min,and stirring time should be controlled above 8min.(2)The results of chemically enhanced primary sludge anaerobic digestion test showed that under the conditions of the mesosphilic and thermophilic anaerobic digestion,the cumulative methane production per VSS of the chemically enhanced primary sludge was higher than that of the ordinary primary sludge.Under the condition of mesophilic anaerobic digestion: the cumulative methane production per VSS in the 30 mg Fe3+/L group of chemically enhanced primary sludge was the highest,reaching to 397.63 m L/g VSS,which was 51.1% higher than that of ordinary primary sludge;The maximum rate of specific methane production of chemically enhanced primary sludge was higher than that of ordinary primary sludge.The maximum rate of specific methane production of chemically enhanced primary sludge in the 20 mg Fe3+/L group was the highest,which was 30.7% higher than that of ordinary primary sludge.Under the condition of thermophilic anaerobic digestion: the cumulative methane production per VSS in the 20 mg Fe3+/L group of chemically enhanced primary sludge was the highest,reaching to 350.93 m L/g VSS,which was 25.3% higher than that of ordinary primary sludge;The maximum rate of specific methane production of chemically enhanced primary sludge was lower than that of ordinary primary sludge.The maximum rate of specific methane production of chemically enhanced primary sludge in the 40 mg Fe3+/L was 38.59 m L/(g VSS·d),which decreased by 19.9% compared with ordinary primary sludge.The results of the comparison of mesophilic and thermophilic anaerobic digestion test showed that the methane production and VSS removal rate of chemically enhanced primary sludge under mesophilic anaerobic digestion were significantly higher than that of thermophilic anaerobic digestion;Compared with thermophilic anaerobic digestion,the mesophilic anaerobic digestion chemically enhanced primary sludge in the 30 mg Fe3+/L group cumulative methane production per VSS and VSS removal rate increased by 24.8% and 11.6%,respectively.Therefore,the chemically strengthened primary sludge was suitable for the mesophilic anaerobic digestion process under the test conditions.(3)The analysis results of the carbon source allocation strategy of sewage treatment plant indicate that the proportion of chemically enhanced primary sludge distribution strategy was as follows: 41.8% for anaerobic hydrolysis acidification and 58.2% for anaerobic digestion.The condition can maximize the energy recovery of anaerobic digestion under the premise of meeting the requirements of biological nitrogen and phosphorus removal carbon sources.