Researcher's waste-to-energy technology moves from the lab to the marketplace

April 20, 2012
Ruihong Zhang, a UC Davis professor of biological and agricultural engineering, has been working on her anaerobic digester technology for the past decade. (Karin Higgins/UC Davis photo)

( -- Technology invented by a University of California, Davis, researcher that converts solid waste into renewable energy is debuting today as the first commercially available, high-solid anaerobic digestion system in the United States.

Ruihong Zhang, a UC Davis professor of biological and agricultural engineering, has been working on her anaerobic digester technology for the past decade, bringing it from the laboratory to the pilot stage in 2006. When Clean World Partners, a Sacramento-based startup that licensed the technology from UC Davis, unveils the biodigester today at a Sacramento, Calif., packaging company, it will mark the first time her research has reached the market.

“I applaud Professor Zhang for this tremendous accomplishment," said UC Davis Chancellor Linda P.B. Katehi. "Scientists like Professor Zhang are helping UC Davis address the most pressing global problems of our time. Her work brings us a giant step closer to the sustainable future we all hope for.”

The anaerobic digestion system is located at American River Packaging. It will convert 7.5 tons per day of food waste from regional food producers, including Campbell’s Soup Company, and a half ton each day of unrecyclable corrugated material from ARP into natural gas. The system will generate roughly 1,300 kWh of per day, meeting about 37 percent of ARP’s electricity needs and preventing an estimated 2,900 tons of waste from entering landfills each year. The project has created about 22 jobs.

“This kind of project and technology is actually changing how societies treat and view waste as a resource, which, overall, leads to a better world, a cleaner environment and new jobs,” said Zhang.

Anaerobic digestion relies on bacteria to break down biodegradable waste material in the absence of oxygen. Zhang’s system turns that waste into such valuable byproducts as renewable energy, compost, water, and natural fertilizer. While anaerobic digestion is not a new technology in itself, operational and material-handling limitations had prevented its commercial adoption.

Unlike most other digesters that primarily treat liquid waste, such as manure from dairy farms and municipal wastewater, Zhang’s high-rate digester technology can convert both liquid and , including food waste, yard waste, plant residues, paper and cardboard.

Zhang also sought to overcome two key barriers to the widespread use of anaerobic digesters: time and money. The new technology makes such waste conversion systems replicable, with many components prefabricated, reducing the time it takes to build them. For example, the Clean World Partners system at ARP went from bare ground to energy production within 90 days and cost about $2 million to $3 million.

Zhang’s system also turns waste into energy in half the time of other digesters and produces more gases that can be turned into clean energy. These efficiency improvements are expected to drive down cost and maximize the amount of energy produced and the volume of waste diverted from the landfill.

Clean World Partners formed in 2009 to commercialize Zhang’s anaerobic digestion technology and bring it to a wider market. The company plans to open a second conversion facility using Zhang’s technology at Sacramento County’s south area transfer station in June.

“Ruihong’s contributions continue to be critical to our success as a key adviser,” said Clean World Partners CEO Michele Wong, a UC Davis alumna. “We are proud to work with UC Davis and Ruihong to commercialize these technologies.”

The anaerobic digestion facility was first developed and tested as a pilot plant at UC Davis. The university is currently working with Clean World Partners to bring a full-scale biodigester to campus. Though still in the planning stages, that biodigester is expected to help UC Davis West Village, the nation’s largest planned zero-net-energy community achieve its goal of generating as much power as it consumes in the course of a year.

Explore further: Cost-effective farm waste-to-energy technology focus of research

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5 / 5 (3) Apr 20, 2012
54.2kw generator...from garbage...and producing compost as a side effect.

If you play your cards right, you could get someone to actually pay you to take their garbage away, just like the landfill companies do...just charge less money than the landfill does, and you'll get your garbage for free energy, and get paid too.
2.3 / 5 (3) Apr 20, 2012
Thank Goodness for Obama and his foresight and leadership.
not rated yet Apr 20, 2012
As a Davis resident (and UC Davis scientist), I'm very proud of this achievement. Turning trash into 22 jobs, clean(ish) energy, compost for improving soil... this is where civilization needs to go.
1 / 5 (1) Apr 20, 2012
It remains to be seen whether this form can either out compete, or coexist with, other strategies like pyrolysis. Pyrolysis has some strong advantages like being able to handle many different forms of waste while recovering things like glass and metal. And at least one company has claimed to be able to effectively "dial up" the conditions needed to get specific fuels and chemicals at high purity instead of having to separate random products. But this method may be more useful in certain markets depending on factors like population density and waste production paterns.
1 / 5 (1) Apr 20, 2012
Thank Goodness for Obama and his foresight and leadership.

When and how? This was a lab project in 2006. Are you saying that Obama was involved in American River Packaging or Clean World Partners?
1 / 5 (1) Apr 21, 2012
$2 million to $3 million? Do they even know how much they spent? To get 1300KWh per day?

If you ran the thing 24/365 for 10 years, and assume a build cost of $2 Million, you are paying 42 cents per KWh for the build cost alone! That's 4X the average US electric rate.

Solid waste recycling fees are about $81 per ton, and the system can handle 8 tons per day, producing an income of $648 per day. You have to pay the workers the federal minimum wage of $7.25 per hour, and assuming 8 hrs per day for 22 workers, that comes to $1276 per day, or a net income of -$628 per day. This adds 48 cents per KWh, bringing the average KWh cost for 10 years to $.90 per KWh, or 9X average US electric rates.

That assumes you work 24/365 for 10 years. Any time you take off (like weekends) drives up the KWh cost of the initial investment. The compost will not make up the difference and the workers will soon be out of work when it goes bankrupt.

Nice tech. Not cost effective.
4.2 / 5 (5) Apr 21, 2012
^Bacteria don't take days off and there are normally costs in handling the waste and its off gassing by the landfills also. You know the bulldozers and all those people at the landfill earning a wage? Wonder how much that bulldozer costs? How much did the landfill land cost? Somehow I don't think the math comes out the way you are picturing it and I just saw a discovery program of a guy in college that was getting all the agri waste in his city and doing this same thing and making a very good profit selling the manure.
1 / 5 (2) Apr 21, 2012
Landfills and recycling operations handle 100s of tons of waste per day with fewer employees. Yes, they have capital equipment costs that have to be factored in. The difference is, they can tell you exactly what they paid for it and they made sure that their investment could operate at a profit.

While bacteria may not take time off, you don't just walk away and leave power generation systems unattended - that's just foolish. I gave them only $81 per per ton because any smart business is not going to pay pure disposal rate for recyclable waste. However, even if I gave them the pure disposal rate of $120 per ton for solid waste it still runs a deficit of $316 per day. I also took the lower install cost figure just to give them the benefit of the doubt. The case gets worse if I take the $3 million figure.

I saw the same program. He did not have $2-$3 million in capital equipment investment, only has a few employees, and handles way more tons per day.
1 / 5 (2) Apr 21, 2012
But the by product is BURNED!
How can AGWites tolerate a device that creates a combustible green house gas?
1 / 5 (1) Apr 21, 2012
Pluton, poor baby, giving me 1s doesn't change the math.

What does it take to pay for itself in 10 years?

Assuming a linear relationship of 162.5KWh/ton of waste and an average US electric rate of $.10/KWh, you can make $16.25 of electricity/ton. Assuming you charge a price of $81/ton for disposal, you can make $97.25/ton. Paying 22 employees Fed. min wage 8 hrs/day for 10 years working 365 days/year comes to $4,657,400. Adding the $2M investment brings the total to $6,657,400 over 10 years. If you make $97.25/ton, then you need 68456 tons of waste to break even. This is 18.75 tons/day.

Increase capacity to 18.75 tons/day, with same number of employees and initial investment, you will be making competitive electricity at a rate of 3047KWh per day with a 10 year payback.

I don't know the compost recovery rate, or it's quality for commercial use, nor do I know what other operating costs there will be (taxes, maintenance, etc...). I assume the compost will provide some income.
not rated yet May 03, 2012
Code_Warrior, can you please read again carefully? It says the PROJECT has created 22 jobs, not that it takes 22 people to run the digester. Try your math tricks somewhere else please.
not rated yet May 03, 2012
Well BuddyEbsen, I guess you got me there eh? But there is just one more thing...

I never said it takes 22 people to run the digester, I just assumed that the digester runs 24/365 and employs 22 people per day.

I assumed 3 8-hour shifts running the digester with the 22 people distributed across the shifts with 6 people per shift required to run the digester and 4 collection drivers on day shift. On each shift I assumed 1 operator who monitors the digester controls, 2 people who load refuse into the digester and clean out the waste, 2 people who sort the collected refuse for undigestible materials prior to loading, and 1 person who disposes of the undigestible refuse material.

Of course I can't be certain of how the people are actually employed since that wasn't covered in the article, but a 6 person operation doesn't seem unreasonable to me, nor does having 4 collection drivers given the amount of waste needed per day.

Buddy, perhaps you should think before you type.

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