Importance of Musty Odour Character in the Emissions from Anaerobically Stabilized Dewatered Biosolids. Towards the Identification of Unknown Odour Components

Odours from stabilized anaerobically digested wastewater sludge – biosolids can cause local community odorous impact. Contributions from some volatile organic compounds (VOCs) to nuisance odours are not well understood. The analytical identification of compounds with low odour detection thresholds (ODTs) at low concentrations, are challenging. The knowledge about the odour composition from biosolids emission is still limited. In this study thirty-six biosolids samples were taken after anaerobic stabilisation and dewatering at a wastewater treatment plant in Sydney, Australia to investigate the musty type of odorous events during gas chromatography (GC) coupled with mass spectrometer detector (MSD) and an olfactory detection port (ODP) analysis. Biosolid cake samples were stored under aerobic conditions in loosely covered trays for a period of 35 days. Emissions were collected onto Tenax TA sorbent tubes using a U.S. EPA flux hood method at storage days 1, 3, 7, 10, 14, 21 and 35. GC-MS/ODP was used to identify musty type odorous events in the biosolids emissions as potential chemical compounds, however without its chemical detection via MSD. Measured odour intensities, classified on a scale from 1 to 4, and odour characters were specified by three ODP assessors. Two musty type odorous events were identified in all biosolid cake emissions. The measured odour intensities of the musty type odorant(s) did not significantly alter as the biosolids were aged, however varied between biosolids cakes. Due to its odour intensity, similarity with biosolids odours, frequency of detection and its likely low ODT two musty odorous events should be considered as a potential odorant(-s) of concern in biosolids emissions.