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

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.