Effectiveness of biological treatment of textile wastewater followed by chemical treatment

Abstract

Untreated or poorly treated effluent from textile industries is severely polluting the water courses of Bangladesh. Regular operation of well designed emuent treatment plant is necessary to reduce the pollution problem of Bangladesh. This study represents an attempt to evaluate the efficiencies of two most widely used treatment methods; physicochemical treatment followed by biological treatment method and Biological Treatment followed by Chemical Treatment and also to evaluate the efficiencies of an advanced treatment method of attached growth activated sludge biological treatment followed by electromagnetic coagulation process. The study also tried to identify simple and cost effective treatment method for the treatment of textile liquid waste based on the laboratory test results and as well as to assess present water treatment and ETP condition in Textile Industry. Raw liquid waste was collected from a textile industry. Physico-chemical, Electromagnetic coagulation process and biological treatment processes were applied in the laboratory by varying different design parameters such as coagulant-dose, aeration time, Electrolysis time. Chemical coagulation with ferric chloride was used for physicochemical treatment and conventional activated sludge process and advanced attached growth activated biological treatment process was used for biological treatment. Electro coagulation process was done using iron plate with customized 48V DC power supply and current flow through the circuit was maintained by variable resistance. A little attempt was taken to compare the removal efficiency between attach growth activated sludge biological treatment process and conventional activated sludge process and to compare the efficiency of chemical coagulation process and electromagnetic coagulation process. Treatment efficiencies were determined using post treatment pollutant concentration and were represented as percent of raw concentration of pollutant. BOD" COD, TDS, TSS, color and turbidity, Alkalinity and Electrical Conductivity was taken as indicators in the assessment of treatment efficiencies of different treatment options. Conventional activated sludge biological process followed by chemical coagulation process can remove color up to 80.26 percent, Turbidity up to 91.89 percent, TSS up to 80.31 percent, TDS up to 17.27 percent, COD up to 84.5 percent and BOD up to 78.02 percent, Electrical conductivity up to 4.24 percent ofraw wastewater concentration. Introduction of advanced attached growth activated sludge biological process followed by electromagnetic process can remove color up to 98.2 percent, Turbidity up to 86.5 percent, TSS up to 100 percent, TDS up to 25.4 percent, COD up to 95 percent and BOD up to 97.5 percent, Electrical conductivity up to 13.56 percent of raw wastewater concentration. A comparative study among the conventional chemical coagulation process followed by activated sludge process, the conventional activated sludge process followed by chemical coagulation process, and advanced attached growth activated sludge process followed by electromagnetic coagulation process was carried out. The study focused on the requirement of land, treatment efficiencies and operational cost aspects of those three processes. The study result showed that the advanced attached growth activated sludge process followed by electromagnetic coagulation process is more economical than the conventional chemical coagulation process followed by activated sludge process and the conventional activated sludge process followed by chemical coagulation process in terms of area requirement, treatment time and chemical consumption. Because the latest treatment method attached growth activated sludge process followed by electromagnetic coagulation process requires less area for aeration tank, requires less aeration time and also requires less operational cost than that of the others two treatment method.