Biorem has successfully demonstrated its high rate odour control system for biosolids exhausts at Ashbridges Bay sewage treatment plant in Toronto, Ontario. The demonstration used XLD™, a biofiltration media engineered specifically for biosolids odours. The system has achieved 95% odour removal in less than 20-s Empty Bed Residence Time (EBRT) despite high concentration of organic sulphur compounds (OSC), and has proven its effectiveness over more than 2 years of operation. OSC removal efficiencies were measured to be 95% and higher at EBRTs of 15 s or less. Biorem’s experience with organic media and other inorganic media shows this to be a significant performance improvement, reducing EBRT by as much as 50% for equivalent or better performance. A novel horizontal flow approach was used, which permitted the use a 2.8m high biofilter bed and incorporation of humidifier in the same vessel, resulting in up to 70% footprint reduction. However, the more common vertical flow approach is just as valid, and the key to superior performance is selecting processes and biofiltration media suited to a given application.
Odours in exhausts from biosolids processing and handling are caused primarily by organic sulphur compounds (OSCs), although at some locations, high hydrogen sulphide levels may also be present. OSCs are more difficult to biodegrade than hydrogen sulphide and conventional biofilters used long residence times with organic media in a simple, single stage configuration. Biorem was the first to introduce in the North American market an inorganic coated media, Biosorbens®, which was tailored for the removal of both H2S and organic sulphur compounds at a significantly higher rate and shorter residence time than organic biofilters. Biosorbens® continues to be used in a broad range of sewage and industrial odour control applications. For biosolids application, Biosorbens biofilters are typically designed for 40 s EBRT for guaranteed odour removal of 90%, although actual design may vary to suit site specific conditions.
Since that time, biotrickling filtration technology has been accepted as the most effective process for treating high concentrations of H2S. This has created the opportunity to achieve advancements in biofiltration media specifically for the treatment of more recalcitrant OSCs, and XLD™ is the result of such an initiative by Biorem. This paper presents a case study of biosolids odour treatment at Toronto’s Ashbridges Bay sewage treatment plant using XLD™ and a novel horizontal flow process.