There are various ways of processing wastewater to produce biosolids and the following describes just one in simple terms.There are four key stages in the production of biosolids:
1. Mechanical screening – which removes large objects, sand grit and organic solids.
2. Biological breakdown and stabilisation – which utilizes microorganisms to breakdown the sewerage converting it to organic solids.
3. Extensive anaerobic digestion - which produces a stabilised organic matter and methane gas as a byproduct.
4. The final product is dewatered through the addition of a polymer which results in a soft textured substance with an earthy, distinctive odour.
Dewatering is commonly used to remove the moisture content of biosolids and provide the following advantages:
- Reduction of costs associated to the transport to ultimate disposal site;
- Easier handling;
- Better calorific value for incineration;
- Reduction of bulking agents and amendments when used for composting;
- Reduction of odor;
- Prevention of potential of putrefaction; and
- Reduction of leachage when disposed at landfill site.
Interesting fact: In Perth, Western Australia, approximately 200 tonnes of biosolids are produced every day. That is around ten large truck loads!