Advances in Biological Odor Control — Why Science Matters

Odorous compounds in municipal wastewater could broadly be divided into two categories: inorganic and organic. While the majority of inorganic odor is caused by hydrogen sulfide and ammonia, the list of organic odorous compounds is much broader and not well defined. The most common compounds include a generic list of reduced organic sulfur compounds, such as carbonyl sulfide, carbon disulfide, dimethyl sulfide, dimethyl disulfide and methyl mercaptan. While most of these are present in relatively low concentrations, their respective odor thresholds are also very low, and thus they often are a key contributor to wastewater treatment plant odor issues.The conventional approach to treating organic odors is either through adsorption to an activated media, chemical oxidation or biological removal. Most sources that generate organic odors require significant ventilation, resulting in large airflows, thus making conventional biofilters or adsorption technologies expensive due to large capital and/or operational expense.Moreover, biological removal of reduced organic sulfur compounds (ROSC) is complicated and not well understood. Currently accepted solutions require very long Empty Bed Retention Times and are designed based on trial-and-error methods rather than on sound science. This often results in very large system footprint, and system performance that is not well predictable and does not meet expectations.This paper summarizes the current knowledge on biological removal of organic odors as well as proposes new research to further the science of biological removal of organic odors. One of the main challenges with biological removal of ROSCs is the physical-chemical properties of these compounds; most of them have very low solubility in water and do not freely dissociate. These properties are thought to make mass transfer of these ROSCs the limiting rate factor during biological oxidation. Furthermore, current oxidation models and molecular studies indicate multi-microorganism consortia including heterotrophic and autotrophic microorganisms involved in the degradation of ROSCs. Recent research further suggests single-species autotrophic degradation of ROSCs, often believed to be degraded by heterotrophic bacteria only. Therefore the use of biotechnology to oxidize ROSCs is almost virgin research territory and provides for ample opportunity for improvement.In order to further the science of biological ROSC removal, an innovative Mobile Research Center (MRC) was developed to study the effect of different media or combinations thereof, mass transfer optimization, process optimization through improved process control on the treatment of ROSCs. The MRC also allows for validation of existing scientific literature and to test new hypotheses to further the understanding of new biochemical processes to make biological ROSC removal more efficient, reliable and cost-effective.