Odors produced from biosolids are a major impediment to beneficial reuse of wastewater residuals in many treatment plant operations. As a nuisance, they also erode public support for land application practices. The main intend of my research is to investigate the reasons of odor generation in digested biosolids and to develop optimal control strategies as a contribution to make the land application of wastewater biosolids a preferred and efficient way in waste management.
The chemicals responsible for odors from biosolids are well known. They can be divided into three groups: ammonia and organic amines; reduced sulfur compounds (including organic types); and volatile organic acids.
Since proteins and certain amino acids contain organic forms of both nitrogen and sulfur, they may lead to increased odor emanation. Proteins are a major constituent in all digested biosolids, so other factors may be responsible for the variability in odor levels with respect to time and location. One potentially important factor is instability and even upsets in digester conditions, such as temperature, salinity, or recalcitrant substrate concentrations. Severe odors are produced most commonly under anaerobic conditions and primarily when specific transient conditions arise. Microbial populations use an adaptation mechanism consisting of the intracellular accumulation of certain solutes, termed osmolytes or osmoregulators, to restore the internal pressure and cell volume (turgor) within the cells. These osmolytes, such as choline, betaine and dimethylsulfoniopropionate (DMSP), may also serve as the precursors of odorous compounds from biosolids, explaining why upset conditions lead to odors
In my study, headspace samples of incubated biosolids are analyzed by SPME (solid phase micro-extraction) GC-MS. So far, results showed that odor production is associated with anaerobic system imbalance such as increased salinity. The NaCl exacerbated odorant production, shortening the onset time and increasing the concentrations of both dimethyl sulfide (DMS) and methanethiol (MT). NaCl inhibited gas production, but acclimation was aided by the added amino acids, which also led to significant sulfurous odor production from biosolids.
My results hopefully will contribute to explain odor production mechanisms from digested biosolids with additional supportive experiments, such as measurement of dimethylsulfopropionate (DMSP) in biosolids to determine optimum time for controlled addition of osmolytes to the biosolids to be able to help cells to restore their osmotic balance fromtoxicity and indirectly decrease the production of odor precursors. In addition, using appropriate inhibitors to stop the certain microbial population from using osmolytes is planned to be another future experiment. Results from proposed experiments are expected to help to determine the effectiveness of these chemical inhibitors, the conditions under which they are most effective, odorants that can be inhibited and the best time of application for optimal odor control.