Fecal matter found in sludge and biosolids have been used as fertilizer for agriculture for many years. But before it is applied, it must pass strict regulatory guidelines to limit the number of coliform organisms or pathogens in sludge. This is important because if these biosolids are not treated properly, it could contaminate crops and become detrimental to humans. Sewage sludge received little to no treatment in the early 1970s and the main concern was focused on odour control and volume reduction.
Wastewater treatment plants today have come a long way in understanding the significance of disease-causing organisms in sludge and they have developed several techniques through the years to reduce pathogens in sludge to safe levels.
Below is a list of the common pathogens found in sludge and biosolids and the diseases that they can cause. Of the listed organisms, the highest risk of infection and spread of disease would come from Helminths, followed by the medium risk posed by bacteria, and finally the lowest risk are from viruses.
Among the more common bacteria found in biosolids are Shigella sp. (bacillary dysentery), Salmonella sp. (gastroenteritis), Salmonella typhi (typhoid fever), and E. coli (gastroenteritis).
Some of the diseases that viruses can potentially bring are Hepatitis A, acute gastroenteritis, poliomyelitis, and non-specific flu-like symptoms.
These can also be found in biosolids and examples of these include Entamoeba histolytica (amoebic dysentery), Giardia lamblia/Cryptosporidium sp./Balantidium coli (gastroenteritis).
Parasitic worms are another organism that can be found in biosolids and include Ascaris sp. (roundworms), Taenia sp. (tapeworms), Necator americanus (hookworms) and Trichuris trichuria (whipworms).
Wastewater treatment plants have an array of technologies and methods that help reduce pathogens. Below is a list of processes eliminate pathogens from sludge treatment.
Heating all the sludge particles to a temperature of >80ºC and drying to > 90% solids.
Heating a fluid sludge in a well-mixed container to a temperature of > 70ºC for > 30 minutes.
Placing in an aerated static pile system required for 3 days at 55ºC and in windrows heating to 55ºC for 15 days to 3 weeks with up to 5 turnings in the 15 day period.
Thermophilic Aerobic Digestion
Must operate in a batch mode and have 2 reactors in series during which the temperature is 55ºC for > 20 hours, or 60ºC for > 4 hours.
Thermophilic Anaerobic Stabilization
Maintain at 55°C for > 20 hours without addition of untreated sludge.
Aside from minimizing the pathogens in wastewater through various treatment processes, natural methods such as heat, sunlight, drying, appropriate pH levels and predation by native soil microorganisms, may further reduce pathogens.
Biosolids that have undergone the prescribed treatment processes will have significantly less odours and have minimal biodegradable material. These processes have been refined through the years to ensure that the biosolids that are used in agriculture will not affect the health of the vegetation and the human population. As part of environmental protection legislation, most provincial and territorial governments have developed specific regulations that deal with solid waste management. Some pathogens are subject to federal/provincial/territorial standards, requirements or guidelines which provide maximum pathogen or pathogen indicator concentrations for land application programs.
If you are a municipality in Ontario and in need of a biosolids management solution, please feel free to contact us at 1 (877) 479-1388.