Foul Air Contaminant Removal in Sewer Odour Control Systems

Odour control systems in wastewater collection systems are typically designed to remove hydrogen sulfide (H2S); however other compounds in sewer related foul air also lead to odour complaints. Methyl mercaptan and dimethyl sulfide are rarely investigated for performance in these treatment systems despite being key odorants. Volatile organic compounds readily occur and rarely contribute substantially to odour impact, but could affect the removal of other more odorous compounds.The most common odour control systems are biologically based (biofilters or biotrickling filters) or adsorption based (predominantly activated carbon). Samples on the inlet and outlet of 10 activated carbon systems, 5 biofilters and 3 biotrickling filters across Sydney, Melbourne and Perth in Australia were taken approximately every month for 18 months. Samples were analysed for a wide range of volatile organic and sulfurous compounds as well as H2S. The collected data were filtered for warm and non-warm periods, wet weather, and for those where data points were greater than three times the standard deviation over the average (known as ‘spikes’). Performance oftreatment systems were analysed under these conditions.An analysis of the most common volatile organic and sulfurous compounds on the inlet samples found that there was no clear relationship between any compounds, meaning that when sampling sewer foul air, all key odorants needed to be tested.All treatment system types perform well at H2S removal. Activated carbon systems exhibited the poorest and most variable treatment of non-H2S based compounds, particularly halogenated volatile organics; however treatment of most compounds improved during spike conditions. Biofilters generally showed the most stable and greatest removal of non-H2S based compounds; however treatment deteriorated during spike conditions.In selecting an odour treatment technology, the concentration and variability of contaminants, treatment required and the space available, allow the most efficient technology selection to be made. Two stage processes are generally required for high level treatments whilst single stages are appropriate for lower treatments. Biofilters are generally preferred as the first (or only) stage, with biotrickling filters used where space is constrained. Activated carbon is suitable for low load scenarios or as a polishing filter