New digesters to turn Sacramento food waste into energy

Clean World Partners (CWP) and Atlas Disposal Industries, both of Sacramento, California, have just broken ground on a $13 million (€10.4 million) anaerobic digester and renewable natural gas fuelling station in south Sacramento.

This is said to be the US’ largest commercial solid waste digester and phase one will be complete in the next few months.

Atlas Disposal will collect 9,100 tonnes a year of waste from local food-processing companies, restaurants and supermarkets and convert it into natural gas, electricity and heat, as well as fertiliser and soil amendments for agriculture.

In 2013, CWP plans to expand the plant to process 36,500 tonnes a year. It will be the company’s second commercial digester, joining one launched at American River Packaging in North Natomas in March.

CWP was formed in January 2009 to commercialise a new anaerobic digester technology developed by Ruihong Zhang of UC Davis.  

In January 2011, the company was acquired by Synergex Ventures, a subsidiary of Synergex International, a software and professional services company based in Gold River. Synergex president and CEO Michele Wong also serves as CEO of Clean World Partners.

Zhang's research focused on reducing the amount of time required to convert waste material into usable gaseous products. Zhang still serves as the company's technology adviser.

CWP's organic waste recycling plant at American River Packaging's headquarters was the first commercial high-solid anaerobic digestion system in the US. It was the product of a public-private partnership including the packaging company, Campbell Soup, Atlas Disposal, Otto Construction, UC Davis and Sacramento Municipal Utility District (SMUD).

CWP is sole owner of the plant, which it paid for with private financing and a federal grant. A $1.31 million grant from the California Energy Commission helped with pre-development work.

The $2.9 million plant co-digests 7.5 tonnes of food scraps – collected and delivered daily by Atlas – and unrecyclable corrugated material from the packaging plant, diverting 2,900 tonnes of waste annually from area landfills.

It generates 1,300 kilowatt-hours of green energy each day – about 37% of American River Packaging's needs – and produces an estimated 1,000 tonnes a year of compost and soil amendments for regional farming and gardening operations.

The new digester in south Sacramento will produce natural gas to fuel part of Atlas Disposal's truck fleet.

Eventually, the fuel could be used by local school districts, transit and distribution companies. Sikich envisions the center in five years fueling 100 to 150 trucks and up to 80 school buses.

Diesel prices are at $3.80 a gallon, while an equivalent amount of CNG costs around $2.25.

And natural-gas-powered heavy-duty vehicles reduce smog-causing emissions by more than 80%  and reduce greenhouse gas emission by 10 to 15% over a comparable diesel vehicle.

They are also as much as 90% quieter.

When complete, the new centre will replace 1 million gallons of diesel per year with renewable natural gas, produce 2 million kilowatt-hours of electricity per year and divert 37,000 tonnes of waste annually from landfills, CWP officials say.

Roughly 90% of the electricity produced will be used to power the digester and refuelling station, and the balance will be sold to SMUD though a net metering agreement.

The state energy commission gave CWP a $6 million grant, and Atlas a $300,000 grant, to build and run the new site. The rest of the cost was covered by Synergex Ventures, through cash and securities.

CWP hopes to start making money from the plants by early next year.

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