BIOSOLIDS

Biosolids are stabilized organic wastes, or municipal sewage sludge, as defined in Ont. Reg. 347. Hauled sewage (or septage) is not included in this definition, however, the term ìwaste materialî is commonly used to refer to biosolids or septage wastes.

Biosolids are produced in the municipal sewage treatment plant as part of the treatment process of municipal waste. This includes human waste, storm water (in some instances), industrial processing wastes, washing/cooling wastes, and miscellaneous flows connected to sanitary sewers. The waste material is processed and the solids are separated from the liquid portion, prior to discharge of the effluent to the environment. The solids portion remaining is referred to as sewage sludge, or biosolids.

Sewage treatment plants process this waste material in either aerobic or anaerobic conditions, and the sludge by-product is considered to be stabilized, in that disease-causing organisms are reduced, and the potential for odour is minimized. Septage wastes, or sewage wastes from private on-site sewage systems (septic tank or holding tank wastes) are not necessarily stabilized, in that high numbers of disease causing pathogens may be present, and the potential for odour of such waste is greater.

Traditionally, the disposal of biosolids can range from land filling, disposal in landfills, or incineration. Both of these options can prove to be expensive, in that valuable landfill area is taken up by sludge during disposal, and costs related to incineration makes this option less environmentally sensitive. With the recognition of the benefits of utilization of this waste material in agricultural, the use of biosolids on agricultural land mirrors the 3 R's of Reduce, Reuse or Recycle.

By matching the nutrient content of biosolids with plant growth and agricultural needs, the sludge becomes an integral part of the agricultural industry, while providing an efficient and cost effective means for disposal of the waste material. Biosolids are spread or injected on the disposal plots. The practice of biosolids utilization must be compared to fertilizer application programs, to ensure economical crop production. By involving an agronomist (field crop production and soil management specialist) in the process, the use of specific crops for extraction of the available nutrients can be achieved. Stringent testing and sampling ensures that no degradation of the environment occurs, and control measures such as application rates, clearance distances and spreading restrictions minimize the long-term risk of biosolids utilization to the environment.