Wastewater contains many forms of energy since its most abundant component is organic waste, containing many chemical and organic fertilizer ingredients. It also has many other minerals and compounds that can be useful after being extracted from the influent to a WWTP (Wastewater Treatment Plant). The water also contains heat as it enters the plant and retains most of it, or it may even be warmer, upon leaving the plant as treated water. So there are abundant materials useful for producing energy and for other industrial and agricultural purposes, as well as direct sources of energy in wastewater and around its treatment processes. Not only are we failing to recover much of this material and energy for productive use, but we also expend energy to separate the contaminants from the feedwater. So wastewater treatment is energy negative; that is, it uses more than it produces. Can we find ways to turn this around and make wastewater treatment energy-positive? Many researchers think this is possible. Transcend Water, a leader in the design of wastewater treatment systems, constantly strives to design improved systems that are more efficient energy users and potentially energy producers as they become viable options. This article explores the pros and cons of extracting useful products and energy from treating wastewater and employing them in other productive enterprises.
The Costs of the Wastewater Treatment Process
Wastewater treatment plants perform an essential service to society by removing contaminants to a sufficient degree to make the effluent compatible with the environmental waters into which it’s discharged.
While performing this service, WWTPs worldwide consume 1,000 TWh (Trillion Watt-hours) of energy every year. That’s the equivalent of 200 nuclear power reactors, 90 million tons of oil burned in thermic power plants, or 20,000 large wind turbines. Since only about half of the world’s wastewater is treated, and it’s projected that the world will have 3 billion more people by 2050, these energy costs could double or more by mid-century.
Finding ways to recover some of that energy from wastewater is a worthy initiative.
What’s Useful in Wastewater?
Here’s a list of common components of municipal, i.e., household, wastewater. A wastewater treatment plant removes most of these materials from the feedwater, so they’re contained in the sludge from the various wastewater treatment processes.
Many components of agricultural fertilizer are found in wastewater treatment plant sludge – credit Ryan Thorpe on Unsplash.com
The list:
- Carbonaceous organic matter 280 mg/L
- Protein compounds up to 350 mg/L
- Carbohydrates 28 mg/L
- Chlorides 100 mg/L
- Calcium carbonate (alkalinity) 100 mg/L
- Oil and grease 100 mg/L
- Potassium and compounds 50 mg/L
- Phosphorus and compounds 30 mg/L
- Nitrogen and compounds 10 mg/L
- Salmonella and other pathogens > 7K mg/L
These materials have value as feedstocks, fuels, or catalysts for agricultural, industrial or if nothing else, research use.
Additionally, wastewater contains heat, it has mass, and when it’s moving, it has kinetic energy. Extracting heat energy and using the heat and kinetic energy are additional ways of capitalizing on wastewater as a resource.
Sounds Great! Is This a Free Resource?
Not exactly!
Filtering or settling can separate a few of the minerals and compounds, making them reasonably accessible. Many though are combined physically or chemically in the sludge from a treatment plant, and the processes to separate them can be expensive.
In retail markets, people might be squeamish about products that come from a wastewater treatment plant.
The engineers at Transcend Water continually explore options to design more sustainable WWTPs. Aerobic digesters are among the process design options that can generate electricity and are already included in the tool. Transcend’s goal is to extend the Design Generator with more technologies that recover energy from wastewater treatment plant wastes and effluents.
In summary, wastewater treatment plants consume significant amounts of energy to make our water clean enough to avoid serious negative impacts on the environment. Wastewater contains many elements and compounds that can be useful in industrial and agricultural processes.
Transcend Water’s engineers stay abreast of the possibilities for economic methods of recovering the materials and energy available from wastewater and treatment plant effluents. When these options gain viability, they’re added to the Transcend Design Generator. Learn more about the design generator and discuss your water engineering and energy recovery needs with the expert engineers at Transcend.
