Onsite Power Systems’ biogas energy project on track for commercial use
by Irwin Rapoport
Onsite Power Systems Inc., based in Davis, California, has completed a major test of its anaerobic phased solids digester at UC Davis, which is home to the demonstration facility that is converting food scraps, grass and garden waste (organic materials) into biogas that can be used to generate power and energy, produce compost and reclaim water.
The test was key to Onsite’s plan of offering a commercial product by the beginning of 2008.
The Biogas Energy Project, a partnership that brought together industry, academia and government, began in 2000 and the construction of the first commercial demonstration began two years ago. This project has received major funding support from the California Energy Commission.
“It was primarily to test some of the mechanical loading and hydraulic mixing sections,” says Dave Konwinski, Onsite’s CEO. “We have computer controls in place and it allowed us to fine tune and test the automated systems. The biological side works well.”
The next step, which is ongoing, is to complete systems improvements construction and continuously run the digester for six months.
The Biogas Energy Project is the first large-scale demonstration in the United States of a new technology developed by Ruihong Zhang, a UC Davis professor of biological and agricultural engineering. The technology has been licensed from the university and is being adapted for commercial use by Onsite.
The system consists of the feeding and loading equipment, circulation system, gas collection and clean-up system, material and water recovery system and the tanks.
Onsite’s goal is to target food processing industries and municipalities.
“The equipment is very scalable and we could build plants on-site at food processing plants to access their waste stream and at municipal centralized collection sites,” he says. “We can transfer the energy back into the plants, substantially offsetting buying natural gas or electricity from the grid. Instead of getting rid of that waste, it can be turned into a revenue stream.”
According to the United States Department of Agriculture, there are approximately 29,000 food processing and related operations in the country, of which between 6,000 and 10,000 would be candidates for digesters.
“We are looking at the larger plants because they have a huge waste stream and the digesters can run full time,” says Konwinski.
Municipalities and counties that currently have specific collections for compostable materials such as those in California and parts of the Canadian province of Ontario, would also be perfect candidates for digesters.
“Even if we were to collect it regionally, we could easily set up a system instead of the material going into landfills,” says Konwinski. “There is a lot of material if we start collecting it. California has about 27 million tons of organics a year that still go into landfills that we can’t utilize for composting or other products.
“A city of 100,000 people can generate enough material to feed a generator,” he adds. “It depends on what the small cities and towns do and if there are small food processing operations in the area.”
In rural agricultural areas, parts of plants from biomass crops that cannot be used in the production of ethanol can be used for anaerobic digestion, as well as straw, bedding and the remains from the harvest of crops.
However, unless there is a year-round supply of materials, locating a digester in an agricultural area with one or two crops would not be sustainable.
“What you have to do is incorporate areas that can handle bigger digesters with a variety of materials throughout the year,” says Konwinski. “We are working with several municipalities that have a waste stream that varies year-round and because the digester is flexible, you can use grass clippings in the summer and fall and for a continuous supply, food scraps from hotels, restaurants and recovery programs.
“We will be testing a design with four tanks for loading organic materials in the high seasons – spring, summer and fall and in the winter, when the amount of feedstock drops off,” he adds, “you just take a couple of tanks off-line and reduce the digester size so that you can operate year-round.”
The percentage of organics in the waste stream depends upon the specific area. Some areas have levels below 10% and areas such as California, with a year-long growing season, have percentages above 40 percent.
Shipping this material to landfills costs money, even in areas where tipping fees are low. In areas such as California, tipping fees range between $20 and $150 per ton. California ships much of its garbage to Arizona and New Mexico and Hawaii ships its garbage to the mainland, with a final destination in Idaho.
“Organics are typically 60 to 70 percent moisture, so you are paying to transport water,” says Konwinski. “In California you are basically paying to transport water out-of-state, when California is facing a water shortage. With a digester, we recover that water.”
A ton of food scraps or grass, when broken down, provides between 100 and 200 gallons of water and 2,200,000 BTUs of biogas. The remainder is compost, fertilizer or similar materials. The basic formula is 70 percent water and biogas and 30 percent compost.
“We have tested this in the lab on a sustained basis and we can produce biohydrogen without having to reform it,” says Konwinski. “The water that we reclaim is not going to clean up to the level of food grade water, but it can be gray water to offset for purple waterlines and offset irrigation water potentially. If you clean it up somewhat, you can use it for industrial grade process water.”
“You get into areas of California and you could be paying as high as $500 to $700 an acre foot for water,” says Konwinski, who notes that Las Vegas is considering using digesters to recover water. “We have so many inquiries about the technology.”
Terry Tamminen, who previously worked for California Governor Arnold Schwarzenegger, recently published a book that quoted a report issued by the California Energy Commission and the California Integrated Waste Management Board, which stated: “If we would utilize the organic resources in California, we could offset our petroleum (usage) in California by 25 percent.”
Onsite uses existing commercially available components - those used in the waste water, dairy and food processing industries.
“We put all these pieces together,” says Konwinski. “One of our advantages is using hydraulic mixing. We don’t have any mixing in the tanks. During the May test, we found that it does what it was designed to do. However, we found that we can improve on this by putting in a larger pump. We are still doing hydraulic mixing, but we are able to achieve much more intense mixing while reducing the run time for the pumps and this saves energy.
“By running the digester non-stop with a steady daily load,” he adds, “we can really monitor and document the performance, energy balance – material in and out and energy in and out, how much gas is being produced and at what cost we are producing it. Once we have that validated data, we could go onto the market. We want to know what we can produce for our customers.
Konwinski says that the cost of digester set-ups ranges between $1.5 and $10 million.
“If a food processing plant or municipality is already collecting organics,” he says, “taking in all the costs, you are looking at a three to five year safe payback on the investment. There won’t be a basic price because we could have plants that deal with 200 tons a day and another that handle 20 tons.”
Waste Management has spoken favorably, says Konwinski, about anaerobic digestion technology at recent hearings and workshops sponsored by the California Energy Commission.
“They are realizing that there is economic value here,” he says. “You can get energy out of landfills, but if you put the organic stream into a digester, you have controlled biogas and biogas is much cleaner than landfill gas.”
“Portland, Oregon has phenomenal food collection from hotels and restaurants and it has grown beyond belief,” says Konwinski. “They are collecting around 35,000 tons a year now. We are looking at a scenario where we are the owner/operator of the digester and we contract out a company to manage the maintenance of it. We have remote monitoring systems – both mechanically and biologically. We’ll be able to make changes through the computer to increase production and improve efficiencies.”
With collection models such as those in California and Portland, it just requires other jurisdictions to initiate similar programs.
“You don’t need to be a big city or metropolitan area to do this,” says Konwinski. “Portland has put out an RFP for digester technology. Companies responding had to have their technology operating for two years already. That is one hurdle we have to overcome. Some places have lowered the bar. It really helps that we kept the testing at UC Davis campus, which is internationally renowned for its agricultural work.”
Prof. Zhang recently received the EPA’s Western Regional Leadership Award for her work and at the presentation ceremony, was referred to as “the Einstein of waste.”