Chemical assessment of emissions from sewage collection facilities

Abstract

Sewage consists of a wide range of organic and inorganic constituents originating from domestic and trade waste discharges. Of particular interest are the range of odorous volatile organic compounds (VOCs) and volatile sulfur compounds (VSCs) produced by anaerobic reactions (such as fermentation and sulfate respiration) in the sewage, sediments and biofilms on the sewer walls. Complaints due to sewage odour are a major issue for wastewater utilities because the repeated release of unpleasant odours from a sewer network constitutes both a public nuisance and possible regulatory violation. However, the complex nature of sewer odours provides many challenges with regards to the management and control of these emissions.

This thesis aims to improve understanding of the emissions of compounds and odorants from sewage collection facilities by developing and benchmarking analytical methodologies. A highly sensitive and reliable method using gas chromatograph was developed and evaluated for the analysis of full spectra of compounds that present at the headspace of sewer air. While identifying the emitted chemical species provides useful information, the key to understanding the odour is establishing which of the chemical species odorants are. The use of gas chromatograph with simultaneous mass spectrometer and olfactory detection port (GC-MS/ODP) provides a method of prioritising the chemical species present along with their odour potential. The VOCs identified within emissions included alkanes, aromatics, halogenated hydrocarbon and terpenes, esters, aldehydes and alcohols whiles non-H2S VSCs related were: methyl methanethiol (MeSH), dimethyl sulfide (DMS), Carbon disulfide (CS2), dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS). The spatial-temporal variability of VOCs and VSCs were clearly identified and evaluated.

A similar range of VOCs and VSCs have been identified in sewer headspace air across diverse countries and climatic regions, demonstrating that the data and conclusions presented in this present work would extend to context out of Australia and is useful for identifying the odour implications of sewer headspace VOCs for the wider industry. However, measured VSC concentrations from the Perth sampling sites were significantly higher than those at the Melbourne and Sydney sites. This indicates the possibly important role of climatic conditions played for VSCs emission at sewer networks.