Forecast Of Urban Wastewater Discharge And COD Emission Based On Modified Gray And Markov Model

The forecast work of urban wastewater discharge and chemical oxygen demandemission was important. Based the investigation on research progress of urbanwastewater discharge and pollution gross control, this paper analysed thedisadvantages of conventional model and established a modified Gray Markov Modelwhich then applied to the forecast work of urban wastewate discharge and chemicaloxygen demand emission.After analysing the advantages and disadvantages of traditional Gray MarkovModel based the Gray Model and Markov Model knowledge, this paper established amodified Gray Markov Model. The modified model had high accuacy as it optimizedthe Markov process, it incresed the weight of high probable state considering allpossible states. The modified Gray Markov Model had following characteristics:needing less data, having simple calculation process, improving the simulationaccuracy for data sequences with great random fluctuation and can avoid the worstresult obttained by conventional Gray Markov Model.Based the domestic sewage discharge and industrial wastewater discharge inTianjin from2001to2009, modified Gray Markov Models were established toforecast them respectively. The results showed that: the forecast results of modifiedGray Markov Model had higher accuracy than Gray Model, and the modified Modelcould avoid the worst results of conventional Model. In the period from2010to2015,the domestic sewage discharge had an increase trend and would be654.1241milliontons in2015, the industrial wastewater discharge had a decreased trend and would be187.0769million tons in2015, the urban wastewater dischage had an increased trendand would be841.2010million tons in2015, the percentage of domestic sewagecharge in urban wastewater discharge had an increased trend as time went on andwould be77.76%in2015.According to the chemical oxygen demand emission of domestic sewage andindustrial wastewater in Tianjin from2001to2009, modified Gray Markov Modelwas established to forecast the total chemical oxygen demand emission. The resultsshowed that forecast value of modified Model was the same with the conventionalGray Markov Model and had high accuracy. In the period from2010to2015, the totalchemical oxygen demand emission had a decreased trend and would be110.4 thousand tons in2015, so it could reach the goal of reducing chemical oxygendemand emission in the “12th of five-year plan” of Tianjin. During the period of“11th of five-year plan” in Tianjin, the domeistic chemical oxygen demand emissionhad an inceased trend and the value would be increased by22.8thousand tonscmpared with the year2005, the industrial chemical oxygen had a decreased trend andthe value would be reduced by36.9thousand tons cmpared with the year2005, thetotal chemical oxygen demand emission had a decresed trend and the value would bereduced by14.1thousand tons cmpared with the year2005, so the reducing work ofchemical oxygen demand total emission depended mainly on industry.