New Technology Could Double Energy Generation Potential at Wastewater Treatment Plants

Researchers from the University of Nevada, Reno just completed a successful pilot run of a new technology that allows wastewater treatment plants to produce significantly more energy from sewage sludge through a process of drying and gasifying the sludge after it has gone through biogas digesters. The research team believes their renewable energy technology will reduce greenhouse gas emissions and cut energy and waste disposal costs at treatment plants.

On this blog we’ve been doing our best to point out how wastewater treatment plants can be converted from large energy consumers to energy producers. By viewing waste as a resource, it is possible to begin designing closed-loop systems in which wastewater treatment plants play a central role by producing energy from the organic matter in sewage, fertilizer from leftover sludge, and water by treating it to an appropriate standard and reusing it.

Many plants already produce renewable energy from sewage by harnessing the biogas produced while bacteria break the sewage down. But there are plenty of other ideas floating around. A few examples of wastewater treatment plants being used energy include:

• Portland Oregon’s Columbia Boulevard Wastewater Treatment plant produces over 12 million kilowatt hours of electricity per through a 1.7 megawatt cogeneration system. The heat from the system is used to warm the digesters while the electricity provides about 40% of the plant’s daily power needs. Excess biogas is sold to a nearby metal roof manufacturing company, generating an additional $60,000 for the wastewater treatment plant.

• The False Creek Energy Center in Vancouver B.C. uses wastewater from nearby homes for a district heating system – the first of its kind in North America. Prior to being sent to a large wastewater treatment plant, wastewater is run through a boiler that uses the energy to heat water and homes in the neighborhood. Wastewater heat recovery out of the plant will account for 70% of the neighborhood’s annual energy requirements and reduce greenhouse gas emissions by 50%.

• The North Head Sewage Treatment plant in Sydney, Australia captures energy from treated wastewater falling down a 60 meter shaft within the wastewater treatment facility. This onsite hydroelectric system will generate enough energy to power up to 1,000 homes and reduce greenhouse gas emissions by 12,000 metric tons per year – the equivalent of removing 3,000 cars off the road. In addition, the North Head plant also has a cogeneration system that meets about 15% of the plants energy needs, and a wastewater reuse facility that recycles approximately 400,000 gallons of water per year.

The technology being developed by the team at the University of Nevada, Reno has the potential to allow wastewater treatment plants to squeeze far more energy from wastewater than they currently do, while also cutting down or eliminating the sizeable costs of disposing of the sludge each day. Any of the plants mentioned above – which already generate quite a bit of energy through cogeneration, district heating or hydroelectric systems – could generate even more energy by processing and burning the sludge leftover after digestion.

Although still in the demonstration phase, the research team believes this technology could be commercially available worldwide in about two years. According to a UNR press release:

Like the little engine that could, the University of Nevada, Reno experiment to transform wastewater sludge to electrical power is chugging along, dwarfed by the million-gallon tanks, pipes and pumps at the Truckee Meadows Water Reclamation Facility where, ultimately, the plant’s electrical power could be supplied on-site by the process University researchers are developing.

“We are very pleased with the results of the demonstration testing of our research,” Chuck Coronella, principle investigator for the research project and an associate professor of chemical engineering, said. “The process to dry the sludge to make it burnable for a gasification process, which could then be transformed into electricity, is working very well. This is an important step for our renewable energy research, processing about 20 pounds an hour of sludge in a continuous-feed system to produce about 3 pounds an hour of dried powder.”

The team of researchers custom built the processing machine in a lab at the University and brought it to the plant for testing. It uses an innovative process with relatively low temperatures in a fluidized bed of sand and salts to economically produce the biomass fuel from the gooey sludge.

The new patent-pending, low-cost, energy-efficient technology is an experimental carbon-neutral system. The solid fuel it produces will be analyzed for its suitability to be used for fuel through gasification, and the refrigerator-size demonstration unit will help researchers determine the optimum conditions for a commercial-sized operation.

“The beauty of this process is that it’s designed to be all on-site, saving trucking costs and disposal fees for the sludge,” Victor Vasquez, a University faculty member in chemical engineering and collaborator, said. “It uses waste heat from the process to drive the electrical generation. It also keeps the sludge out of the landfill.”

Estimates, which will be further refined through the research, show that a full-scale system could potentially generate 25,000 kilowatt-hours per day to help power the local reclamation facility.

For a much better description of the process used to convert sludge into a burnable fuel, check out this Youtube video:

The only possible tradeoff that I can think of is that sludge, which in some places gets trucked off to be used as a nutrient-rich fertilizer, will now be used to produce energy, not fertilizer. But since far from all wastewater treatment facilities recycle their sludge as fertilizer – and even those that do often have to pay people to take it – the tradeoff should be minimal.

It will be interesting to see how this technology matures and if, in fact, we will begin seeing large scale commercial applications in the next couple of years. If, as the researchers suggest, you can produce as much energy from the gasified sludge as you can from the biogas emitted during digestion, then wastewater treatment plants already running cogeneration systems could potentially double their renewable energy generation. There is a lot of sludge out there which means energy and cost savings abound. Again from the UNR press release:

“Economically, this makes sense,” Coronella said. “Treatment plants have to get rid of the sludge, and what better way than to process it on-site and use the renewable energy to lower operating costs. This demonstration gives the University an opportunity to involve students in development of waste-to-energy technology, which ultimately will benefit the community. It’s a win-win for everyone involved.”

“Our next step is to do exactly what this dryer is doing on a much larger scale,” he added. “We plan to demonstrate the technology at a scale 100 times larger, to convince investors and plant operators of the technology’s viability.”

The University’s Technology Transfer Office, with assistance from the College of Business, is supporting the project with plans to make the system available to hundreds of communities around the country that operate water-treatment plants.

For example, there are approximately 700,000 metric tons of dried sludge produced annually in California municipalities, which would sustainably generate as much as 10 million kilowatt-hours per day.