The following paper is a comparison of an organic media biofilter and 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 system compared was an in-ground, header/lateral system operated in a forced draft, up flow, open top configuration. The biofilter system consists of a 72,000 m /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 composed of organics and reduced sulphur compounds such as dimethyl sulphide (DMS), dimethyl disulphide (DMDS), and methyl mercaptan (MM). These compounds, with low water solubility and high molecular weights are difficult to degrade biologically to meet stringent Ministry of the Environment (MOE) odor emission guidelines.
This paper describes the dewatering process, the generation and characterization of odors, and compares the odor removal characteristics of softwood bark organic media against a mineral based, permanent inorganic 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.