Treatment of Biogas Produced in Anaerobic Reactors for Domestic Wastewater: Odor Control and Energy/Resource Recovery
Anaerobic municipal wastewater treatment in developing countries has important potential applications considering their huge lack of sanitation infrastructure and their advantageous climatic conditions. At present, among the obstacles that this technology encounters, odor control and biogas utilization or disposal should be properly addressed. In fact, in most of small and medium size anaerobic municipal treatment plants, biogas is just vented, transferring pollution from water to the atmosphere, contributing to the greenhouse gas inventory. Anaerobic municipal sewage treatment should not be considered as an energy producer, unless a significant wastewater flow is treated. In these cases, more than half of the methane produced is dissolved and lost in the effluent so yield values will be between 0.08 and 0.18 N m3 CH4/kg COD removed. Diverse technologies for odor control and biogas cleaning are currently available. High pollutant concentrations may be treated with physical-chemical methods, while biological processes are used mainly for odor control to prevent negative impacts on the treatment facilities or nearby areas. In general terms, biogas treatment is accomplished by physico-chemical methods, scrubbing being extensively used for H2S and CO2 removal. However, dilution (venting) has been an extensive disposal method in some small- and medium-size anaerobic plants treating municipal wastewaters. Simple technologies, such as biofilters, should be developed in order to avoid this practice, matching with the simplicity of anaerobic wastewater treatment processes. In any case, design and specification of biogas handling system should consider safety standards. Resource recovery can be added to anaerobic sewage treatment if methane is used as electron donor for denitrification and nitrogen control purposes. This would result in a reduction of operational cost and in an additional advantage for the application of anaerobic sewage treatment. In developing countries, biogas conversion to energy may apply for the clean development mechanism (CDM) of the Kyoto Protocol. This would increase the economic feasibility of the project through the marketing of certified emission reductions (CERs).