Study On The Solid Aerobic Fermentation Of The Mixture Of Excess Sludge And Wetland Mowing Phragmites Australis

As China’s industrialization level continues to increase,population density continues to increase,the problem of water pollution is becoming more and more serious,the construction of sewage treatment plant has become an indispensable measure to control water pollution.The construction and operation of a large number of sewage treatment plants plays a great role in preventing and controlling the water pollution in China,but at the same time,a large number of solid wastes,namely excess sludge,will inevitably be produced in the process of wastewater treatment.At present,the treatment and disposal of excess sludge has become one of the urgent environmental problems in China.On the other hand,the annual popularization of artificial wetland wastewater treatment technologies,including urban wetland parks,advanced sewage treatment,and distributed small artificial wetlands,etc.,produces a large amount of large-scale wetland plants such as Phragmites australis,Irises,Canna and other biomass every year.A large number of wetland plants after mowing have an urgent need for treatment and disposal.Therefore,Phragmites australis,a typical wetland plant,was selected as the representative in this study.Phragmites australis was used as the bulking agent and carbon source provider in the sludge composting process.The changes of physical and chemical indexes in the composting process of the mixture of excess sludge and mowed Phragmites australis were measured and analyzed,aiming to provide a solution of waste resource utilization for both excess sludge and mowing Phragmites australis.Aerobic composting process is very complex,involving physical,chemical and biological changes,which is affected by temperature,water content,carbon to nitrogen ratio,particle size and other factors.Composting experiment is a necessary means to study the composting process,determine the best composting process conditions,and improve the composting efficiency and quality.The actual large-scale composting experiment needs a lot of manpower,material resources and time,and the experimental process is difficult to control,so the laboratory composting reactor is widely used because of its small size,short composting cycle,easy to achieve automatic control,simple operation and other advantages.However,due to its small size and limited number of organic substrates,the laboratory composting reactor has the problems of insufficient fermentation caused by excessive heat dissipation,poor thermal insulation,short high-temperature period or low ambient temperature,which makes its operation parameters and composting status greatly different from the actual project.Therefore,the thermal insulation conditions and measures of the system must be thoroughly discussed in laboratory composting reactor experiments.In this study,through the design of a certain aerobic fermentation device,the heat and mass transfer process in the core area of aerobic fermentation is reduced by a small volume of organic solid waste material under the condition of a large number of materials.The real-time temperature compensation reactor system is adopted,which is guided by the core temperature of the reactor,so that the wall temperature of the reactor changes with the change of the core temperature of the reactor,so as to achieve more accurate and real temperature compensation To simulate the thermal effect observed in a large reactor.The effects of different temperature compensation methods on composting(R1: room temperature,R2: a thermostat incubator at30 oC,R3–R5: real-time temperature compensation strategies with maximum heating thresholds of 30 oC,50 oC,and 70 oC,respectively)were compared to find the best temperature compensation method and threshold setting conditions,and further provide more stable and reliable basic data and technology to support the actual operation of aerobic fermentation system.The system was applied to the experiment of aerobic fermentation of excess sludge and mowing Phragmites australis.During the composting process,the temperature,oxygen and carbon dioxide emissions of the compost were monitored in real time.The physical and chemical properties of the compost materials were evaluated by the determination and analysis of the organic content,carbon nitrogen ratio,total organic carbon,three-dimensional fluorescence spectrum,Fourier infrared spectrum and scanning electron microscope.Nutrient composition and safety of compost were evaluated by germination index,p H,conductivity,total nitrogen,total phosphorus and total potassium.The 16 S rDNA high-throughput sequencing method was used to quantitatively analyze the changes of composting bacterial community,and the interaction between microbial community succession and environmental conditions was further constructed.The research results show that the thermal insulation strategy has a significant impact on the compost behavior.Real-time temperature compensation oriented to the core temperature of the compost can increase the maximum temperature of the compost,extend the high-temperature period of the compost,and improve the consistency of the core and edge temperature of the compost.Reactor R5 with real-time temperature compensation and a heating threshold of 70 oC works best.The real-time temperature compensation strategy can effectively improve the temperature of the heap,so as to improve the activity of Firmicutes(mainly Bacillus),so as to promote the degradation of compost organic matter,promote compost maturity.The C/N ratio,germination index,p H,EC,conductivity,total nitrogen,total phosphorus and total potassium content of the five compost products all meet the requirements of composting and have non-toxic effects on plants and reached complete maturation.The results of three-dimensional fluorescence spectrum and Fourier infrared spectrum can also directly see this conclusion.The results above showed that the feasibility of solid-state aerobic fermentation with the mixture of excess sludge and mowed Phragmites australis.