These days one hears a lot about biosolids; but what exactly are they?
Biosolids are produced at wastewater treatment plants by recovering and treating organic material. They are rich in plant nutrients and can be applied as a fertilizer and soil conditioner. They contain about 70 per cent water, 20 per cent organic matter, and 10 per cent fine silt and sand. Attached to the organic matter and silt are plant nutrients and small concentrations of trace elements and other substances originating from domestic and industrial sources.
Biosolids do contain small concentrations of trace metals. Plants, animals and humans require certain metals, but excessive amounts can be toxic.
The organic matter in the biosolids absorb and store moister, and tend to bind the metals so that they don’t leach into groundwater. Through its Organic Matter Recycling Regulation, the Province of B.C. sets limits on the amount of trace metals allowed in biosolids.
In a typical sample, the dry-weight percentages of nutrients and trace elements from the Annacis Island WTP are: nitrogen 4.9 per cent, phosphorus 3 per cent, potassium .1 per cent, iron 3.8 per cent, calcium 2.9 per cent, aluminum 1.8 per cent, magnesium .45 per cent, copper .17 per cent, sodium .07 per cent, sulphate .06 per cent, manganese .04 per cent, and other trace elements .08 per cent.
Metro Vancouver biosolids come from the Annacis Island Wastewater Treatment Plant, and are used to reclaim mines to advance re-vegetation; form a soil used in municipal and regional landscaping in the Lower Mainland; enhance growth of poplar trees used in pulp production; and create an effective soil cover used to close landfills and reduce greenhouse gas emissions.
Biosolids production methods, quality and use are all regulated under the B.C. Organic Matter Recycling Regulation, which specifies the types of processes that can be used in its production, and the limits for metals and pathogen concentrations in the end result.
The regulation ensures that as a fertilizer and soil conditioner, biosolids supply plant essential nutrients and organic matter in a manner that protects human health and the environment, and that their application is beneficial to the environment.
If you have further questions about biosolids, please contact Don May (TNRD) at 250-377-8673.
