Optimal Design for Anaerobic Pretreatment of Municipal Wastewater

In recent years the advent of the anaerobic expanded bed reactor (AEBR) has made possible the treatment of wastewaters of comparatively lower strength than have been treated traditionally by anaerobic means. However, regardless of any benefits presented by its use, the process must be shown to be cost effective relative to other options before it will gain acceptance. This paper reports on the results of a series of optimization exercises in which the costs of the AEBR as an expansion alternative for organically overloaded treatment plants are compared with costs for more conventional remedies. The optimization model developed includes the unit processes of primary clarification, AEBR, trickling filtration, secondary clarification, activated sludge, gravity thickening, anaerobic digestion, and vacuum filtration. Several constraint parameters were varied to determine the cases for which the AEBR would be the cost-effective option. These parameters were primary effluent chemical oxygen demand (COD), hydraulic loading, temperature, cost of labor, cost of power, cost of sludge disposal, and amortization interest rate. The results suggest that the AEBR may be a competitive solution for organically overloaded facilities under selected conditions.