Study On Small Towns Wastewater Treatment Process Alternative Selection Based On Fuzzy Borda Method

Due to the lack of relevant technical guidance and planning,the construction of sewage treatment facilities in small towns is faced with the problem of blindly following the urban sewage treatment model,which is difficult to adapt to the actual needs of sewage treatment in small towns.In order to cope with the increasing pressure of sewage treatment in small towns,it is necessary to establish a set of systematic and objective evaluation system,make the decision-making process more scientific and reasonable,and provide more sufficient and reliable evidence for the construction of sewage treatment projects,so as to select the most suitable sewage treatment technology in small towns.In this paper,according to small towns wastewater characteristics,small towns sewage disposal difficulties,development of small towns in our country and small town sewage treatment requirements,A/O,A/A/O,oxidation ditch,CASS,SBR,biological contact oxidation,BAF,artificial wetland and MBR process was selected as alternative process.The evaluation index system was set up through literature research and consulting experts.The comprehensive weight of index was obtained by combining subjective weights and objective weights.The evaluation value and ranking of alternative processes were obtained by using fuzzy Borda method.The comprehensive evaluation method was revised based on the classification of different types of small towns.Different small towns selected for example application and suggestions on the development of wastewater treatment process in the future were made.The conclusions of this dissertation are summarized as follows:(1)The evaluation index system of four kinds sixteen indicators was set up from economic cost,technical performance,environment effect and operation management aspects.The indexs include construction cost,floor area,operation cost,pollutant removal rate,shock resistant load capacity,climate adaptation capacity,solid waste production rate,energy consumption,operation stability,technology maturity and operational management difficulty.(2)The analytic hierarchy process was used to determine the subjective weight,entropy weight method was used to determine the objective weight.At last comprehensive weight was got in the case of subjective and objective weight preference was equal to the weighted comprehensive.The index weighting results was as follows:economic cost index weighted 0.3916,technical performance index weighted 0.4643,environmental effect index weighted 0.0500,and operation management index weighted 0.0941.(3)Three single evaluation method,fuzzy integral,grey correlation analysis and TOPSIS method,was used to evaluate alternative process.Fuzzy Borda me thod was used to combine the evaluate results after consistency check.The res ults were shown as follows.From the point of view of economic cost index,t he order was: constructed wetland>CASS>SBR>oxidationditch>BAF>biologicalco ntactoxidation>A/O>A/A/O>MBR;From the point of view of technical perform ance index,the order was: MBR> oxidationditch>CASS>SBR>BAF>A/A/O>A/O>biologicalcontactoxidation>constructed wetland;From the point of view of en vironmental effect index,the order was: artificial wetland>biological contact oxi dation> BAF>SBR>A/O>A/A/O>MBR>CASS>oxidation ditch;From the point o f view of management and operation index,the order was: A/O>constructed w etland>oxidation ditch>MBR>CASS>A/A/O>SBR>biological contact oxidation>B AF;From the point of view of total evaluation value,the order was: construct ed wetland>CASS>oxidation ditch>SBR>MBR>A/O>BAF>biological contact oxi dation>A/A/O.(4)Small towns in our country were divided into different types from five economic developed,land tense situation,the control temperature,water scarcity and emissions standards aspects.Index weight was revised depending on the type of small towns.The applicable processes in gaojia town were determined to be constructed wetland,oxidation ditch process and CASS process and the applicable processes in meixi town were MBR process,CASS process,oxidation ditch process and SBR process.(5)Suggestions were made on the development of wastewater treatment process in the future from the four directions of the evaluation index system.