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The following paper describes the comparison of an organic media biofilter against a synthetic media biofilter for the treatment of residual odors emanating from the operation of a biosolids dewatering and truck loading system at the City of Toronto˙s Ashbridges Bay Treatment Plant.
The systems under comparison were in ground, header/lateral systems operated in a forced draft, up flow, open top
configuration. The biofilter system consists of a 73,000 m3/hr four cell arrangement, consisting of a pre-humidification system, supplementary moisture addition through a surface irrigation system and variable frequency controlled ventilation fans. The odor control system was constructed with a chemical scrubber system using sodium hypochlorite and sodium hydroxide, followed by the biofilter. Odor testing revealed that the biofilter was sufficient to treat the odors without pre-treatment from the scrubber system. The scrubber system was removed from operation, and the biofilter maintained its exceptional performance. The scrubbers have yet to be re-commissioned.
Biosolids dewatering facilities are typically characterized by persistent residual nuisance odors that are typically composed of organics and reduced sulphur compounds such as DMS, DMDS, and MM. These compounds, with low water solubility and high molecular weights have typically been very difficult to degrade biologically to the stringent MOE odor guideline performance required.
This paper describes in detail the dewatering process, the generation and characterization of odors, and compares the odor removal characteristics of a softwood bark media against a mineral based, permanent media. Practical operating experiences are discussed in detail and performance under a variety of conditions is examined using theoretical models. These kinetic models are used to describe the degradation characteristics of the process and can be used to predict the performance of the systems under a variety of operating conditions.
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