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Abstract
Odours from wastewater treatment facilities can cause nuisance impacts in the community and erode public acceptance, while odorous emissions from biosolids can limit opportunities for their beneficial reuse via land application. The aim of this research was to understand how odour emissions throughout wastewater treatment plants are affected by the configuration and operation of biosolids processing. Odour emissions can be more effectively managed if reasons for the presence of different types of odorants and their sensorial impacts are known.
Odorants in emissions throughout the biosolids processing at eight wastewater treatment plants were quantified using methods specifically targeting volatile sulfur compounds (VSCs), which are thought to be key odorants in wastewater treatment. In addition, a range of volatile organic compounds (VOCs) and their sensorial properties were studied using gas chromatography coupled with an odour detection port (GC-MS/O). Intra and inter site variations in emissions were compared to the different biosolids processing operations over the eight sites.
VSCs such as hydrogen sulfide, methyl mercaptan and dimethyl sulfide were identified as dominant odorants due to their high concentrations and low odour detection thresholds. In addition, certain VOCs such as p-cresol, trimethylamine and volatile fatty acids were detected at sensorially perceptible levels. Anaerobic digestion and dewatering were studied to determine their influence on nuisance emissions from the biosolids product. Temporal variations in biosolids emissions were studied over an eight week period at one WWTP showing significant variations in biosolids iron, aluminium and sulfur content which appeared to be related to certain emissions. Optimisation of a full scale dewatering centrifuge showed weir plate height and feed flow affected emissions of ammonia and dimethyl sulfide as the biosolids aged.
GC-MS/O analysis was used to identify odorants based on their sensorial properties; which highlighted the range of human variability in odour perception. While models were produced for the prediction of odour concentration based on odorants, limitations to this approach were identified. Alternatively, the odorants identified throughout the eight sites formed the basis of biosolids processing Odour Wheels. The use of Odour Wheels links odour perception to odorants and process conditions, which can assist onsite odour management.