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Assessment Of Sludge Resource Utilization Potential Of Typical Wastewater Treatment Plants In Jiangsu Province

Posted on:2023-08-12Degree:MasterType:Thesis
Country:ChinaCandidate:L Y QuFull Text:PDF
GTID:2531307061963029Subject:Architecture and civil engineering
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With the promotion of carbon peak and carbon neutral target,the "Opinions of the CPC Central Committee and State Council on the complete and accurate implementation of the new development concept of carbon peak and carbon neutral work" put forward the ecological priority and green low-carbon development path.The implementation of policies such as sound resource recycling system and promotion of resource utilization of sewage sludge also means that the sludge industry will see stricter regulation and the value chain of resource recycling needs to be opened up.The future sludge treatment and disposal will further emphasize energy saving and energy resource recovery and reuse,and sludge resource utilization is bound to play a significant role in the future sludge treatment and disposal arena,and the sludge heat value as an important indicator to assess the sludge energy recovery potential should not be ignored.There are few studies on the overall sludge characteristics in Jiangsu Province,and there is a lack of research on its resource utilization.A thorough understanding of the physicochemical properties of sludge and a systematic basic investigation is essential to assess the potential of sludge for resource utilization,and only by first understanding sludge at its source can we accurately assess its energy recovery potential and find appropriate resource utilization methods for it.This study aims to provide a scientific basis for the future resource utilization of sludge in Jiangsu Province,and to provide a reference for the establishment of corresponding standards and specifications.In this study,dewatered sludge from 25 representative municipal wastewater treatment plants in Jiangsu Province is used as the research object,and its basic characteristics and pyrolysis properties are studied experimentally,and the qualitative factors affecting the heat value of sludge are explored by multivariate analysis.Secondly,a linear model of sludge heat value prediction based on empirical heat value prediction model and principal component analysis-linear regression method is constructed and compared with the nonlinear model of sludge heat value prediction constructed based on BP neural network method.Finally,the energy recovery potential of sludge is evaluated based on the sludge pyrolysis characteristics,and a multi-factor combination mathematical(SWOT-FAHP)model for the best decision of sludge resource utilization method is constructed.The basic and pyrolytic properties of dewatered sludge are experimentally investigated by field sludge sampling and The experimental study of the basic characteristics of the sludge showed that68% of the sludge samples had a p H distribution in the suitable range of 6.5 ~ 8.5,87.5% of the sludge samples had a moisture content that could meet the requirement of less than 80% of the ex-factory sludge,and the sludge organic matter content ranges from 35.6% ~ 73.4%,with an average value of 50.38%.Experimental studies on the pyrolysis characteristics of the dewatered sludge show that for industrial analysis,the ash content of the sludge ranges from 24.39% ~ 61.95%,the volatile content ranges from 29.38% ~ 67.16%,and the fixed carbon content ranges from 6.04%~ 9.50%.For ultimate analysis,the carbon content ranges from 35.41% ~ 49.68%,hydrogen content ranges from 8.23% ~ 11.57%,oxygen content ranges from 25.53% ~ 41.15%,nitrogen content ranges from 6.91% ~ 13.35%,and sulfur content ranges from 0.37% ~ 0.98%.In terms of heat value analysis,the dry basis high heat value is in the range of 5328 ~ 15069 k J/kg,and the average value is 9883 k J/kg.Based on the sludge data from the status survey of sludge treatment and disposal in Jiangsu Province in 2011 and the sampled sludge data in this study,the effects of qualitative factors wastewater type,flocculant type,sludge dewatering method and drainage system on the heat value of sludge are analyzed.The study shows that for the sludge sampled in this study,the influence of effluent type and flocculant type on the calorific value is high,while for the 2011 sludge sample,the flocculant type shows a significant influence on the calorific value of the sludge.The results of the reclassification of the sludge according to the influencing factors and the in-depth study of its characteristics show that the type of flocculant has a significant effect on the water content and the type of effluent has a significant effect on the organic matter,volatile matter,carbon content and calorific value.Linear and non-linear models are constructed to predict the sludge heat value based on the pyrolysis characteristics of sludge.It is shown that the modified empirical model for heat value prediction is significantly improved in prediction accuracy compared with the previous empirical model,while the linear model constructed based on principal component analysis is further improved in prediction accuracy compared with the modified empirical model for heat value.Finally,to compare the fitness of linear and nonlinear models for sludge calorific value prediction,BP neural network method is used to build a nonlinear model,and the results show that the model has good stability and learning effect.Comparing the quantitative evaluation indexes of the prediction models constructed based on the three different research methods,the prediction model constructed by applying the BP neural network method has higher precision and accuracy,which indicates that the sludge calorific value model constructed by applying the nonlinear model has a higher degree of fitness.However,it is undeniable that the linear model constructed based on the empirical model of calorific value as well as the principal component analysis also has a certain degree of accuracy and fitness.The average energy recovery potential of anaerobic digestion is about 1482 k Wh/t dry sludge and the average energy recovery potential of incineration is about 549 k Wh/t dry sludge based on the characteristics of sludge pyrolysis.Since the energy recovery potential of sludge incineration is positively correlated with the heat value of sludge in the assessment model,it is inferred that the low heat value of sludge is one of the main reasons for the low energy recovery potential of incineration,and the co-resource of sludge mixed with biomass can have the feasibility of improving the energy conversion efficiency of sludge resource utilization by increasing the organic matter content and heat value of raw materials,thus achieving efficient energy recovery.The SWOT-FAHP model is developed to explore the best decision for sludge resource utilization in Jiangsu Province.The assessment model of the resource utilization approach from economic,social,environmental and technological perspectives is established with problem solving,ecological environment,technological development and laws and regulations as assessment criteria.The weight calculation results show that the weights of the four criteria are in decreasing order as problem solving,ecological environment,technological development,and laws and regulations,and the evaluation of the resource utilization methods based on the criteria results in the decreasing weights of the four methods as pyrolysis,anaerobic digestion,incineration,and gasification,thus determining pyrolysis as the best method of sludge resource utilization in Jiangsu Province at present.Based on this conclusion,it is proposed that sludge mixed with biomass co-pyrolysis carbonization or anaerobic digestion is expected to be an important development direction of sludge resource utilization method in Jiangsu Province in the future.
Keywords/Search Tags:Municipal dewatered sludge, Resource utilization, Pyrolysis characteristics, Heat value prediction, Energy potential assessment
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