Alkaline stabilization
Alkaline stabilization involves adding alkaline materials, such as lime or kiln dust, to sewage biosolids to increase pH, reduce pathogen levels and control odours. The process can be used for treating septage and is used to treat sewage biosolids in some municipalities. There are also systems operating in Ontario that use thermal alkaline stabilization.
Composting
Although composting sewage biosolids has not been a common practice in Ontario, there are numerous methods for doing this. Typically the process involves aerobic, thermophilic, biological stabilization in a windrow, aerated static pile or in-vessel composting. Composting biosolids kills pathogens and produces a rich humus-like material which has excellent soil-conditioning properties, but it contains less plant-available nitrogen than other forms of biosolids.
Another option is to manage sewage biosolids through vermicomposting, a process using worms that produces an organic material that is stable and has minimal levels of pathogens and other contaminants.
Dewatering
Dewatering biosolids involves separating water and solids though the use of various methods, such as vacuum filters, centrifuges, geomembrane filtration, filter and belt fibre presses. Depending on the method, the dewatering process removes 15 to 45 per cent of the water. Dewatering reduces the sludge volume, which makes it easier for haulers to handle the material and can greatly lower transportation costs for municipalities.
Pelletization
Pelletization of sewage sludge or biosolids involves heat drying technologies, which kill pathogens, remove water to reduce volume and weight, preserve nutrients and organic matter and eliminate odour. A variety of heat sources can be used including heat from engines, boilers, kilns and power facilities.
The process produces pea-sized pellets that are easier to handle and spread and that can be blended with commercial fertilizers. Toronto, Windsor and Smith Falls currently use pelletization treatment.
