COMPUTER AIDED DESIGN OF ACTIVATED SLUDGE PROCESS TREATMENT PLANT

Abstract

Activated sludge process (ASP) is a widely used aerobic biological wastewater treatment process. The activated sludge process is very flexible and can be adopted to almost any type of biological waste treatment problem. The most common problem encountered in the operation of an activated sludge plant is bulking sludge. Because few plants have escaped the problem of bulking sludge, the factors which favour bulking of sludge, the rules which govern bulking and the methods of bulking control are incorporated in the present study. As the expenditures involved in the design and construction of activated sludge plants are considerable, both in terms of capital, operation and maintenance costs, even a few per cent saving at the design stage would be of significant value. In the present study, an attempt is made to develop a rational approach. to the design of component units of ASP viz, the reactor (aeration task), secondary clarifier and the sludge recycle taking into account the cost considerations and their interactions. Cost of anaerobic digestor is also included in the cost function to accont for the production of excess sludge. Aerator design is based on microbial kinetic concepts and continuous culture of microorganism theory. The design. of secondary clarifier is based on both surface loading rate and solid loading rate. The cost function is framed as the sum of capital and operating costs subject to the constraints determined by effluent quality criteria and process variables affecting the performance. The effect of the process variable on the cost is determined by performing the sensitivity analysis. Results suggest that the cost first decreases with the increase in recirculation ratio and after reaching the minimum, it starts increasing. Cost also increases with the increase in mean-cell residence time and overall efficiency. t