Letter: Steps toward 100 percent renewable energy

Graphic by Lori Deaton

What’s clean and green, produces 11 megawatts of electricity, and saves the city of Oakland $3 million a year while decreasing the amount of solid waste? What decreases contamination of ground and surface water and minimizes odor while generating electricity and creating sellable fertilizer? What has none of the environmental hazards involved in fracking for gas?

The answer is: biogas digesters utilizing microorganisms. They can handle both human and animal waste, food waste and other agricultural waste. As of 2012, the Oakland plant became the first in the U.S. to sell extra electricity produced entirely from waste back to the grid. Of the 11 MW it produces, it uses 6 MW, so 5 MW are left to sell. It treats 60 million gallons of wastewater daily and uses sewage, food scraps from restaurants, winery and poultry farm wastes [avl.mx/5ph].

In Ohio, a sewage treatment plant using biogas digesters generates enough electricity to power 1,600 homes and also generates revenue from its safe, high-quality fertilizer.

AgStar estimates that biogas recovery systems are technically feasible at over 8,000 large dairy and hog operations, with the potential for generating 13 million megawatt-hours per year. Side benefits: substantial decrease in uncaptured methane emissions from the animal wastes, and the protection of the groundwater and surface water, with greatly decreased odors. Adding 25 percent food waste to sewage sludge in digesters increased biogas production by 60 percent, they found [avl.mx/5pi].

Has Asheville or Buncombe County considered using biogas digesters for municipal waste treatment? What could be better than using waste to generate the energy we need and saving money in the process?

— Cathy Holt
Asheville

Editor’s note: Xpress checked in with the local public agencies that handle municipal waste with the letter writer’s question. We received the following response from Buncombe County Solid Waste Director Dane Pedersen: “Buncombe County operates a bioreactor landfill. The bioreactor landfill works to rapidly transform and degrade organic waste. This increased waste degradation and stabilization are accomplished through the reintroduction of liquid and, in our case, is recirculated leachate that enhances microbial processes. This provides opportunity to recapture air space due to the rapid stabilization of the waste mass, and we are able to harness the biogas that is generated through the organic waste decomposition process and power a 1.4-megawatt generator system that produces enough electricity to power 1,100 homes.

“We enjoy bragging about this waste-to-energy program and place a great deal of value in how we are able to create environmental utility from the services that we provide every day. Implementing practices to create beneficial uses of landfill biogas is and will continue to be a primary objective for our solid waste department. To learn more about the benefits of recirculating leachate visit [avl.mx/5pj].”

Xpress also received a response from Thomas E. Hartye, general manager of the Metropolitan Sewerage District of Buncombe County: “For many years, MSD has utilized digestion of its municipal sludge by anaerobic microorganisms. The byproducts of this digestion system are digested solids and methane gas. MSD would recover this gas and recover heat to generate heat/electricity. The sludge would then have to be lime-stabilized up to a pH of 14, and then could be used as an agricultural supplement or taken to the landfill.

“In the late 1990s, MSD did a cost-benefit analysis of the entire system. Due to lack of efficiency, cost of maintenance and the overall carbon footprint of treating and eliminating sludge byproduct, along with running that process, MSD moved to a different process. The current process utilizes intermediate process solids pumped to gravity thickeners; the thickened solids are pumped to high-performance belt-filter presses, which provide a drier, more BTU-laden sludge so that it can be thermally converted. This reduces the overall cost and carbon footprint.”

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6 thoughts on “Letter: Steps toward 100 percent renewable energy

  1. Jim

    100%? What about all those trucks that pick up and transfer it to the “green facility”? More BS.

    • cecil bothwell

      The world truck fleet is poised to shift to electric vehicles. The City of Asheville just put 5 electric buses into service. The country of Chile recently received 100 Chinese electric buses. Several years ago Asheville began examining electric garbage trucks as possible replacements. Tesla introduced its semi version set to begin production in the not distant future, with a 300 to 500 mile range. So the question of trucks operating on renewable energy isn’t an issue. It’s a question of when, not if.

      • Ron Patton

        Current electric vehicles (like Teslas and Asheville’s 5 new electric buses) aren’t green – they’re greenwashed. Their emissions are just pushed further upstream to the coal and gas power plants where they’re hidden from the end-user. They make people feel good about doing something for the environment but they are FAR from green – especially when you factor in the lifecycle of the batteries from the massive raw material mining operations to disposal of the toxic spent cells. Again, all that is hidden from the end-user. Yes, perhaps someday, we’ll have 100% solar, biomass, nuclear (yes nuclear), hydro, and wind, but until then please don’t promote current electric vehicles as green.

      • Ron Patton

        I looked up some statistics and crunched some numbers:

        It takes 22.5 pounds of burned coal to fully charge an extended range Tesla Model 3. Add it up and that’s easily 1000 pounds of burning coal per year of driving. Imagine how much burning coal those five electric Asheville buses will use!

        Calculations:
        The extended range Tesla Model 3 has an 80kWh battery (source: thedrive.com and epa.gov).
        In the US there is an approximate 8-15% transmission power loss from the power plant to your home (source: insideenergy.org, schneider-electric.com, and others). In India, China, and other developing nations that number is as high as 30%. Let’s split the difference and take an 11% average loss in the US.
        Therefore, it takes 91kWh of power at the power plant to fully charge an extended range Tesla Model 3 at your house.
        Converting 91kWh (kiloWatt-hours) to TCE (Tons of Coal Equivalent) and then converting tons to pounds (kylesconverter.com and others) … It takes 22.5 pounds of burned coal to fully charge an extended range Tesla Model 3.

        #greenwashing

  2. Robin

    It should be telling that an MSD cost-benefit analysis steered them away from methane capture incineration, and back to conventional drying and treatment. The largest waste treatment facility in Western North Carolina can’t make a financial case for it; yet the letter writer read an article and is convinced that’s how to save the planet.

    Speaking of making a case, here’s a question for Ms. Holt: How much did Oakland pay for their waste treatment plant to net them a $3 million/year return? I can’t find an exact number, but what citations I found show that it cost over $375 million. If that’s true, it will only take 125 years to find a return on their investment, which is 50 years beyond where that plant fails and they’ll need another $375 million. Read a little deeper into the Bay area, and you’ll find that they are under an EPA mandate to address their waste issues, to the tune of $5 million/year for 22 years. That’s another $110 million off the ROI, which makes the payback 161 years. In that 161 years, they will have rebuilt or remodeled their plant at least 3 times (probably another billion dollars); taking the actual ROI to 375 years. 375 years does not sound like a wise investment to me. It’s all wine and chocolates until you start doing math.

    Also, in response to Cecil’s comment: Electric buses and trucks are significantly cleaner while they’re operating. Ron’s answer to Cecil is spot on. The environmental downside on electric fleets are those enormous batteries that cost $10-40 thousand. They cost another arm and leg to dispose of when you do have to change them, and the upstream environmental harm is devastating. (Look up strip mining scars: http://appvoices.org/end-mountaintop-removal/before-after-images/ And, those are in America, where the practice is somewhat regulated.)

    Another correction to Cecil, Electric is not “renewable”. If you plug your Tesla or green bus into the local electric grid, you are running on fossil fuels. Even the greenies will tell you that fossil fuels are not a renewable energy source.

    • Lulz

      Well actually they are. Apparently there are some oil wells that keep refilling and no one has any explanation for it,

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