Biogas availability and its energy use in combined wastewater treatment plants (CWWTP)

Abstract

CWWTP are sanitation facilities formed by the coupling of an aerobic post-treatment (i.e. activated sludge, extended aeration, etc.) with a primary anaerobic treatment (i.e. UASB). In these combined arrangements, usually biogas produced in the UASB units is used to drive mechanical energy for aeration requirements in the secondary treatment (i.e. Activated Sludge, AS). Quality of effluents from CWWTP is similar to those from AS processes but combined treatments could become completely self-sufficient in energy consumption. In this manner, CWWTP improve the carbon-sequestration potential in the sanitation sector by increasing the capture of methane-rich biogas and its energy utilization. This study show how effluent quality parameters and energy demand in the AS unit can be influenced by control, sludge external recirculation and aeration strategies. Modelling and simulation tests, have allowed identifying operational conditions for potential energy savings and rational use of the biogas energy available in a full-scale CWWTP treating municipal sewage.

Applications of Activated Sludge Models

“…Furthermore, coupling activated sludge and anaerobic digestion models can be a promising approach towards optimising the wastewater and sludge treatment processes and evaluating potential upgrade options in developing countries in a cost-effective manner (Salem et al 2002). So far, successful practical applications of such an approach, involving a municipal wastewater treatment plant from developing countries, are fairly limited (Fall et al 2009;Meneses et al, 2011). Therefore, it is interesting from both a practical and a modelling perspective to further investigate the interactions between the wastewater treatment and the sludge treatment lines such as (i) the effects of modifying the return sludge flows and/or sludge wasting rate, (ii) the impact of upgrading the plant to perform N-removal on the anaerobic sludge digestion and (iii) the influence on high strength return flows from sludge treatment on the activated sludge system.…”