Application Research On GA-BPNN In Cyclic Activated Sludge System Model

In order to protect the limited freshwater resource of our country, we should develop the work of sewage water treatment. Cyclic Activated Sludge System (CASS) is one of advanced sewage water treatment processes and it suits the conditions of our country. Sewage disposal is a complex process, which is often affected by many factors such as the quality of water supply. Water quality changes have the non-linear feature and nondeterministic features. Artificial Neural Network has self-adaptive, self-learning and fault-tolerant capacity as well as large-scale concurrent operation, which is particularly applicable for inaccurate and fuzzy information processing with many factors and conditions involved. So it has especially essential realistic value to study the modeling of wastewater process.Adopted Matlab 7.0 as computational platform, the paper studied the modeling methods in CASS by GA-BP neural networks, and tried to find the dominant and optimum input factors. The main conclusions are as follows:(1) The results(determination coefficient) are good. Forη_COD ,the results are R = 0.8356 ..Forη_NH3-N,the results are R = 0.8195.The wastewater treatment models by GA-BPNN is feasible. It's provide a new method to study wastewater bio-treatment.(2) Based on GA-BPNN,the method of partitioning connection weights (PCW) was adopted to analyze quantitatively the connection weights between neurons in the different layers of network. The relative importance of input factors are 29.28% (COD_Cr),20.74% (NH4⁺-N),31.79% (TP)and 18.19% (pH) respectively.TP is the dominant factors.(3) Based on GA-BPNN,the method of partial derivatives (PaD) was adopted to analyze the carbon removal. The PaD values ofη_COD with respect to COD_Cr, NH₄⁺-N and pH are all positive ,η_COD increases with the increase of COD_Cr, NH₄⁺-N or pH. When the TP concentration of less than 1.6mg/l, TP influent concentration promotes organic removal; When the influent concentration is greater than 1.6mg/l, TP influent concentration will inhibit organic removal. Forη_COD,precedence for the order of relative importance: pH,TP, NH₄⁺-N and COD_Cr.(4) Based on GA-BPNN,the method of PaD was adopted to analyze the nitrogen removal. The PaD values ofη_NH3-N with respect to COD_Cr and NH₄⁺-N are all positive ,η_NH3-N increases with the increase of COD_Cr or NH₄⁺-N. The PaD values ofη_NH3-N with respect to TP and pH are negative,η_NH3-N decreases with the increase of COD_Cr or NH₄⁺-N. Forη_NH3-N,precedence for the order of relative importance: TP,pH, NH₄⁺-N and COD_Cr.(5) Genetic algorithms to model the optimal operating parameters study shows that: When the influent concentration of 202.87mg/l COD_Cr, 22.00mg/l NH₄⁺-N, 0.93mg/l TP, pH 7.15, organics, ammonia removal increase to 60.82%,64.36% respectively. Improving sludge load,TP pretreatment or buliting hydrolysis pool before CASS pool can promote pollutants removal.