Study On Technology And Energy Conversion Of Excess Sludge Reduction By Energy Uncoupled Metabolism

Sludge production of conventional activated sludge processes is high, the cost of treatment of these sludge accounts for a large part of the total cost of wastewater treatment. The treatment and disposal of excess sludge has become a heavy burden of many wastewater treatment plants at home and abroad. The final disposal situation of excess sludge is very grim due to the increase in sludge amount. So, economically rational solution to the problem of sludge has become an important task of The Municipal Industry and the Environmental Protection Industry. Conventional sludge treatment and disposal technologies have only concentrated in the post-treatment of the sludge produced, which can not solve the problem of high sludge production fundamentally. Sludge Reduction technology is an ideal way to solve sludge-associated problems, which requires under the premise of wastewater discharge meet the water quality requirements, the whole system discharges the least amount of biosolids.In the paper, based on the OSA process with low energy consumption and no side effects on the environment, the author introduce the sludge holding tank of OSA process into anoxic/oxic(AO) reactor, in order to achieve sludge reduction and nitrogen removal at the same time,and research the mechanism and energy conversion of AO+OSA sludge reduction system.In this test, we studied sludge reduction capability of the AO+OSA process in different hydraulic retention time in sludge holding tank by changing hydraulic retention time in sludge holding tank. The results shows that when the hydraulic retention time in sludge holding tank are 5.56h, 7.14h and 9h, the reduce of sludge production are 31%,22% and 20%. When the hydraulic retention time in sludge holding tank is 5.56h,the low sludge yield rate in main reaction zone and sludge decay(caused by hydrolysis, etc) in sludge holding tank are all contribute to sludge reduction of AO+OSA system, and the contribution of the latter is more; When the hydraulic retention time in sludge holding tank are 7.14h and 9h, main reason of sludge reduction are sludge decay(caused by hydrolysis, etc) in sludge holding tank.When hydraulic retention time in sludge holding tank are 5.56 h and 7.14 h, the introduction of uncoupling tank bring the ability of AO process to remove nitrogen and COD on no significantly impact; when hydraulic retention time in sludge holding tank is 9h, COD remove ability of the system has not had a noticeable impact too, but its nitrogen remove ability was reduced, and specific reasons are pending further study. The ultimate aim of sludge reduction is reducing the energy consumption of sewage treatment. Reduce energy consumption in wastewater treatment including optimization of exterior energy consumption and optimization of interior energy transfer. Sludge reduction is within the scope of optimization of interior energy use. So, thermodynamic analysis is used to study energy conversion feature of sludge reduction system in this test, with the hope of seeking a new point of integration for studies in the field.The author measured the heat value of influent sludge and effluent sludge of sludge holding tank. The results shows that when the hydraulic retention time in sludge holding tank are 5.56h,7.14h and 9h, the heat value between sludge from different hydraulic retention time or different batches have some difference. When the hydraulic retention time in sludge holding tank is 5.56h, the heat value of influent sludge and effluent sludge of sludge holding tank have no difference; when the hydraulic retention time in sludge holding tank are 7.14h and 9h, the heat value of effluent sludge are higher than the heat value of influent sludge. The longer hydraulic retention time in sludge holding tank, the higher the heat value of effluent sludge than influent sludge. When the hydraulic retention time in sludge holding tank is 7.14h, the result of element analysis shows that content percentages of carbon and nitrogen in effluent sludge of sludge holding tank are higher than content percentages of carbon and nitrogen in influent sludge, there is organic enrichment in sludge holding tank; content percentages of hydrogen in effluent sludge is lower than that in influent sludge. The content of element in effluent sludge and influent sludge lead to changes in the heat value of effluent sludge and influent sludge.When the hydraulic retention time in sludge holding tank is 5.56h, without considering plus energy ( aeration, agitation, etc. ), about 4.16% and 3.10% of the total energy input is taken off by effluent of reference system and sludge reduction system respectively; about 38.48% and 27.09% is captured by dehydrated sludge of reference system and sludge reduction system; about 57.36% and 69.81% is transformed into heat and work during wastewater biological treatment of reference system and sludge reduction system. For the part of energy dissipation in the form of power and heat, sludge reduction system is 12.4% more than reference system. And this 12.4% may be mainly from the main reaction zone and sludge holding tank of sludge reduction system.