The primary objective of wastewater treatment is to process domestic sludge before recycling it into productive materials such as fertilizers or feeding it back into the water system. Based on the wastewater quality, biosolids are classified into Class A and Class B. Class A is a type of sterilized sludge that is used for land application as organic fertilizers. Class B biosolids typically end-up in landfills or are incinerated. Class B biosolids can also be used to produce biogas as a byproduct of the anaerobic digestion of wastewater sludge. Biogas has a huge potential as a source of renewable energy for heat and electricity.
The development of the thermal hydrolysis process has greatly improved sludge treatment efficiency. This innovative technology utilizes life steam injection that breaks down cell structures leading to higher availability of volatile organic compounds and lowering overall viscosity. Thermal hydrolysis is a two-stage process combining pressure cooking followed by a rapid decompression. This entails that the thickened sludge is heated up to between 150 and 165 degrees Celsius, at a pressure of around seven bars, then held for about 20 to 30 minutes before transferring to anaerobic digestion.
There are several benefits to utilizing the Thermal Hydrolysis Process:
– It breaks down the organic matter in the sludge making it more digestible for the microbes used in the anaerobic digester.
– Because sterilization destroys pathogens, thermal hydrolysis can be used to comply with the most stringent requirements for land application such as the U.S. Environmental Protection Agency criteria for land application as a fertilizer.
– Results in better dewaterability of the biosolids producing drier biosolids cake
– Increases biogas production by up to 35%. Biogas can be used to produce green electricity or be injected in the gas grid reducing utilities costs
– The resulting sludge cake has lower odour levels.
– Since global phosphorus resources are limited, recycling phosphorus through land application is a sound, environmentally sustainable practice.
– Presents a cost advantage for farmers who spend a lot of money on nitrogen and phosphorus fertilizers. Utilizing biosolids as a fertilizer reduces production costs
The first full-scale application of thermal hydrolysis process was done by a company called Cambi in the city of Hias in Norway. Since then, there have been over 30 additional installations globally. Black & Veatch, an engineering and construction company in the United Kingdom has developed the largest thermal hydrolysis plant in the world. It provides farmers with a high quality soil conditioner as well as generates renewable electricity from the biogas of up to 122 gigawatt hours in a year.
According to Martin Jolly, Black & Veatch UK Technical Director, some facilities have realized the cost advantage of thermal hydrolysis in the end-use and disposal costs of biosolids through the reduction of volatile solids and better dewaterability. “In Europe and some regions of the U.S., revenue from energy production can provide a significant additional consideration, due to high electricity costs and credits associated with green energy production,” he added.
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.