Control of dissolved CH₄ in a municipal UASB reactor effluent by means of a desorption - Biofiltration arrangement

The direct anaerobic treatment of municipal wastewater represents an adapted technology to the conditions of developing countries. In order to get an increased acceptance of this technology, a proper control of dissolved methane in the anaerobic effluents should be considered, as methane is a potent greenhouse gas. In this study, a pilot-scale system was operated for 168 days to recover dissolved methane from an effluent of an upflow anaerobic sludge blanket reactor and then oxidize it in a compost biofilter. The system operated at a constant air (0.9 m³/h ±0.09) and two air-to anaerobic effluent ratio (1:1 and 1:2). In both conditions (CH₄ concentration of 2.7 ± 0.87 and 4.3% ± 1.14, respectively) the desorption column recovered 99% of the dissolved CH₄ and approximately 30% ± 8.5 of H₂S, whose desorption was limited due to the high pH (>8) of the effluent. The biofilter removed 70% ± 8 of the average CH₄ load (60 gCH₄/m³h ± 13) and 100% of the H₂S load at an empty bed retention time of 23 min. The average temperature inside the biofilter was 42 ± 9 °C due to the CH₄ oxidation reaction, indicating that temperature and moisture control is particularly important for CH₄ removal in compost biofilters. The system may achieve a 54% reduction of greenhouse gas emissions from dissolved CH₄ in this particular case.