Study On The Thermodynamic Properties And The Mechanism Of Sludge Reduction Of A+OSA Combination Process

With the development of national economy and the modernization of the city, the city's environment and ecological balance requirements, energy saving and lower consumption has become a major concern. In sewage treatment process, energy saving including optimization of exterior energy conversion and interior energy transfer. The sludge reduction technologies are optimizing internal energy utilization of the area.This paper studied on the A+OSA combined process which can achieve nitrogen removal and sludge reduction synchronically. In order to apply this technology to provide theoretical guidance for engineering practice, the methods of thermodynamic analysis had been introduced, the mass transfer and energy conversion characteristics of A+OSA combined process had been studid, and also the mechanism of sluge reduction of this process had been discussed.The sludge reduction ablility under different hydraulic retiontion time (HRT) of A+OSA system had been studied. The results show that, under the undisturbed conditions, the sludge reduction rate of A+OSA system are 21%, 27% and 13% respectively when HRT are 7.14h, 5.56h and 3h. The sludge reduction rate has been increased when HRT is shortened. But when HRT is less than 5.56h, the sludge reduction effectiveness has been declined sharply.The element contents of sewage and sludge samples of A+OSA system had been studied. The results show that, taking the molar concentration of nitrogen as a base, the elemental composition of influent samples is C9H18O9N, of sludge samples is C5H7O3N, and of effluent samples is C3H8O8N. Carbon and hydrogen are the main elements to provide the heat value of sewage and sludge samples.The carbon equilibrium equations had been established through the analysis of carbon balance model. The results show that, the carbon mass balance equation of A+OSA system is Q1X1=Q3X3+Q5X5+rV,SV2+M. In the total output of carbon quality in A+OSA system and AO system, the averge carbon quality contained in effluent are 24.53% and 27.10% respectively, in excess sludge discharge are 11.69% and 14.47%, and in gas are 63.78% and 58.43%. At the conditions of the same external environment and effluent quality, the more the carbon quality contained in gas, the less the excess sludge production. Through the analysis of the carbon loss amounts in different units in A+OSA system, the conclusion which the sludge reduction of A+OSA system is based on the sludge decay in sludge holding tank and the sludge compensatory growth in main reaction zone is get. The sludge reduction amount is equal to difference value between the sludge decay value and compensatory growth value. The sludge reduction variation of A+OSA system is proposed. The best condition where the sludge reduction amount is the most is in the vicinity of 5.56h.After the analysis of of energy balance model, the enthalpy balance computations of A+OSA system and AO system were established. The results show that, in the total energy output of the two systems, the averge energy contained in effluent are 5.09% and 6.62%, in excess sludge discharge are 16.37% and 21.18%, and in power and heat are 78.55% and 72.19%. At the conditions of the same external environment and effluent quality, the more the energy has loss, the less the excess sludge production. Through the analysis of the energy loss in different units in A+OSA system, the same conclusion which confirms the carbon balance analysis is get.In the bio-oxidation process, the flow of energy contained in substrate can be represent to the formula: E _in - E_eff=E_m+E_bio+E_h+E_s. The results show that, during the operation of A+OSA system, the values of E _in - E_eff are essentially the same, and the values of E bio which is the energy used for biological synthesis have decreased. The increased energies include the lost energy since power and heat and energy spilling. The biological metabolic uncoupling which reduces the biosynthesis has exsit in the A+OSA system, and has a contribution to the sludge reduction of this system.The removal rateη_C and the power and heat dissipationη_d can both reflect the extent of degradation of organic matter and energy enriched conditions. These can be used to estimate the effection of sludge reduction of A+OSA system. The larger theη_C andη_d value are, the better the effect of sludge reduction of the system is, and vice versa.