Dual roles of odor cleaners and pollutant producers for chemical scrubbing and biological treatment: Evidence in a food waste anaerobic digestion plant

The odor generated during municipal solid waste and wastewater treatment is a major source of public complaints worldwide. Chemical scrubbing and biological treatment are commonly used to control the odor. However, in this study, such odor control measures were found to produce derived odorous compounds and greenhouse gases, leading to reduced efficiency or uncertainty in odor treatment. In a food waste anaerobic digestion plant, a series of site and lab investigations were conducted on the odor control performance and mechanisms, as well as secondary pollutants of chemical scrubbing and biotrickling. Methanethiol, hydrogen sulfide (H 2 S), propanethiol, and acetaldehyde were identified as the top four odor contributors to the gas collected in the plant. The mechanisms of acetaldehyde and propanethiol removal in the chemical scrubbers were studied using gas-washing bottles. Acetaldehyde was mainly removed via physical absorption, whereas propanethiol could be completely removed via oxidation by sodium hypochlorite (NaClO). However, acetaldehyde was desorbed from the absorption solution and generated from the oxidation of ethanol by NaClO in the chemical scrubbers, leading to low, or even negative removal efficiency. H 2 S, methanethiol, propanethiol, and acetaldehyde could be abated by the biotrickling filters. However, H 2 S, methanethiol, propanethiol, and greenhouse gases could be also produced under anaerobic conditions, particularly when the packings were compacted. Furthermore, acetaldehyde could be produced from ethanol by bacteria possessing dehydrogenase under aerobic conditions. Both chemical scrubbers and biotrickling filters demonstrated the dual roles of odor removal and pollutant production.