Incineration is a method used to reduce the hazardous elements in dry sludge and can be a viable solution to challenges related to scarcity of landfills. Sewage sludge is often recycled into organic fertilizers known as biosolids. However, there are instances where incineration is the best solution. Experts in Canada maintain that it is an environmentally sound method of waste disposal and is used in facilities across the country. Below are some of the main advantages and disadvantages of sewage sludge incineration.
Advantages
Energy Generation
Incineration, also called “mass burn,” utilizes a high temperature furnace that burns any waste. In large treatment plants, high quantities of sludge are used as a source of energy used to produce steam when fed through a turbine. Incineration is more effective when used for combined heat and power (CHP). In a CHP plant, the electricity generated by the hot steam is recaptured and fed through pipelines where nearby facilities can use it for heating.
Control the Spread of Diseases
Residual wastes from hospitals, research facilities and other industries can be hazardous to our health and the environment. These harmful elements may require thermal treatment to control the spread of diseases or toxins. Sewage sludge incineration reduces volume (up to 90%) and weight (up to 75%) and breaks down dangerous substances such as pathogens and toxic chemicals. Flue gases from exhaust pipes must be handled properly by utilizing a complex treatment system to prevent hazardous emissions and ashes from contaminating the environment.
Recovery of Precious Metals
Significant quantities of precious metals may be recovered from urban waste after it goes through the sewage sludge incineration process. These metals can be recycled from sewage ash. Several studies show that high volumes of gold (AU) and silver (AG) have been recovered from wastewater treatment plants around the world. In Palo Alto, California, incinerated ash yielded average values of 30 ppm Au and 660 ppm Ag. In Melbourne, Australia, average values of gold and silver were of 0.77 ppm Au and 18.8 ppm Ag. The highest gold values have been found in the Suwa facility, in Nagano Prefecture in Japan, which includes values of up to 1 890 ppm Au, or more than a kilogramme per tonne of ash.
Disadvantages
Impacts Air Quality
Sewage sludge incineration may impact the surrounding air quality. Combustion of waste materials may result in the production of fine inhalable particles laced with toxic metals. Although the high combustion temperature vaporizes heavy metal compounds, they can condense on the surface of the ash particles. Research has shown that about 78 – 98% of Cadmium (Cd), Chromium (Cr), Copper (Cu), Nickel (Ni), Lead (Pb) and Zinc (Zn) remain in the ash. Fly ash are usually controlled via wet scrubbers, electrostatic precipitators, and bag filters.
Release of Dioxins
Sewage sludges may contain significant concentrations of hazardous metals, depending on their origin and the wastewater treatment. When incinerated, the dry sludge may release dioxins including polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F), which are also called persistent organic pollutants (POPs). These toxic substances can result from incomplete combustion by using deficient technology or operating the incinerator incorrectly. Dioxins are carcinogenic and a serious public health threat. Most governments have set goals of restricting, if not totally eliminating, these substances from human activities.
Mercury Contamination
Mercury that results from incinerating waste occurs mainly via fly ash, bottom ash and filter cake. Almost all mercury compounds are hazardous even at very low concentrations in both aquatic and terrestrial ecosystems. It bio-accumulates in the environment, meaning it can build up in organisms through out the food chain. Specifically, mercury contamination affects the kidneys and neurological systems in complex organisms.
In May 2001, the Canadian Council of Ministers of the Environment (CCME) developed Canada-wide Standards (CWS) for emissions of incinerators. There have been various initiatives to prevent pollution such as limiting the amounts of toxic wastes that go into the incinerators, reduction of toxic substances used in raw materials, educational and training programs, and funding assistance.
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.
Sources:
http://www.cela.ca
https://www.ec.gc.ca
https://www.ecocycle.org
https://www.ccme.ca
Water and Environment Journal