Study On Microwave Drying And Resource Utilization Of Sewage Sludge

Sewage sludge is the product of the municipal sewage treatment plants.With the increase of population and the progress of environmental standards,the production of municipal sewage in China was more than 40 million tons per year.Sludge treatment and disposal has become a urgent problem to be solved for the development of cities.Drying is the first step to treat and dispose sewage sludge.It is important to develop a quick and high-efficiency method to dry the sludge.Sewage sludge is also a king of biomass,which can be pyrolyzed as a resource to produce useful gas.In order to explore a economic and environmental friendly method to dispose sewage,three kinds of differeent municipal sewage sludge were the study object in this paper.Thin-layer drying characteristics and condensate water quality when using microwave drying were studied.Pyrolysis of dried sludge using conventional heating and microwave-induced heating to produce combustible gas had been studied.The main content and conclusions of this study are summarized as follows:Microwave drying of sludge is fast,uniform and high efficiency.It only took 3 minutes to dry the sludge from moisture content 76.89% to less than 10% when microwave power was 1200 W and the thickness of sludge was 4mm.The Midilli model represented the microwave thin-laying drying characteristics better than the other models.The unit energy consumption could only be 265.58J/g while the average energy consumption of thermal drying was more than 2000 J/g.The condensate of sludge microwave drying was mainly alkalic,and the COD and NH₄⁺-N content were lower than than of thermal drying.The pyrolysis of dried sludge using conventional heating to produce pyrolysis gas was conducted.The results showed that isothermal heating pyrolysis of sludge had a higher gas yield and heat value than programmed heating.The pyrolysis gas yiled,concentration of CO,CH₄,H₂ and the heat value of pyrolysis gas were increased with temperature while CO₂ content reduce with temperature.The concentration of CO,CH₄,H₂ was 21.3%,23.2% and 26.6% respectively and pyrolysis gas yiled was 366 m3/?t.dried sludge?when the temperature was 800?.Microwave pyrolysis of dried sludge experiment showed that higher microwave power was in favour of improving gas production and the concentration of CO and H₂.The combustible gas percentage could be 81.13%,and pyrolysis gas yiled was 1106 m3/?t.dried sludge?.Small sludge particle size was in favour of pyrolysis gas production.The pyrolysis gas productivity was 1063 m³/?t.dried sludge?when the sludge particle size was less than 1mm and the microwave power was 2000 W.The concentration of CO₂ and CH₄ increased with sludge particle size while CO and H₂ reduce with particle size.