February 25, 2008 | General

Supercharging Solid Waste Energy Production

BioCycle February 2008, Vol. 49, No. 2, p. 39
Biomass Energy Outlook
Mark Jenner

THERE is a lot of excitement in landfill gas power projects. The U.S. EPA’s Landfill Methane Outreach Program website reports that nationally there are 435 landfill gas projects with a generating capacity of 1,350 MW. That is an impressive amount of energy with more on the way. The projects not producing electricity are flaring the gas, or piping it to a nearby industry. Landfill gas power projects are enjoying an expansion that is a bit like a mini ethanol plant boom.
Capturing the methane from solid waste and turning it into electricity is a triple benefit, remediating waste, creating power and providing additional revenue. But in this new bioenergy age, even more efficient projects are emerging. These new energy conversion projects not only capture emissions, but intensively manage the carbon for use as solid and liquid fuels.
There are a number of things working in favor of producing more energy from solid waste. First, half to two-thirds of the material going into landfills is derived from biomass. If separated, this material could be utilized as a liquid, solid or gaseous biofuel and made into bioproducts (e.g., compost). As demand grows, the markets will provide the means to keep energy-latent solid waste feedstocks from getting mixed up with the inert materials.
The wastewater treatment model is an interesting one to consider for solid waste. Nearly all of the wastewater entering a wastewater treatment facility on the front end leaves the facility once it is treated. With current landfill technologies, millions of tons of energy enter, but only the emissions and leachate leave. Today’s landfill gas energy expansion is based on the marginal leakage that cannot be contained in the landfill itself. By adopting the wastewater treatment model, output from the treatment process would approach the volume of the influent.
Methanogenic bacteria, which respire methane gas, live in a liquid environment. While large landfills can produce enough methane gas to power megawatts of generating capacity, it is not a large percentage relative to the large amount of biomass energy delivered to the landfill. Landfills are producing energy, but today’s technology is not an efficient power plant. Like corn and beans – which contain energy, but are not efficient energy crops – landfill gas projects provide an excellent first step into this transition into biomass energy production.
A significant advantage that solid waste management systems have over other bioenergy feedstocks is that it provides a captive supply of material ready for processing. Transporting and storing biomass is bulky and expensive. The solid waste “feedstocks” are already being delivered, e.g., to a transfer station or landfill, which gives these biomass fuel feedstocks an economic edge over the virgin energy crop projects.
One of the six commercial cellulosic ethanol projects funded by the U.S. Department of Energy in 2007, BlueFire Ethanol, is using solid waste feedstocks to make liquid fuels. The first BlueFire facility is under development in southern California. BlueFire is working on a modular unit with a 3-million gallon production capacity that can be delivered ready-built to any landfill. BlueFire Ethanol is also considering production of butanol. Butanol, a biofuel like ethanol, has a higher energy content and blends more readily with the existing fossil fuels.
BlueFire Ethanol is not the only landfill-to-liquid fuel player. A group in Franklin County, Ohio is looking at using solid waste to produce jet fuel. In Blackfoot, Idaho, construction began last fall on a solid waste-to-ethanol project. In addition to cellulosic ethanol, the unused fiber will be used in the production of building materials. One other solid waste ethanol plant in the works is the Pencor Masada OxyNol project planned for Middletown, New York. This project has not been without challenges, but it was reported in November that progress has been made to resolve them.
In addition to liquid fuel production, solid waste also has value as a solid fuel. Northwest Missouri State University is a great example. They burn biomass (waste wood and paper) to supplement their energy needs, densifying several thousand tons of paper each year through a pellet mill before loading it in their boilers. Gasification is also a candidate for conversion of solid wastes to energy. BFC Gas & Electric in Cedar Rapids, Iowa converts 150 tons/day of solid materials, providing enough heat to fuel a 7.5 MW steam generator. The city of Tallahassee, Florida is planning to install a plasma arc gasifier that will run off municipal solid waste. Running an electrical current (the plasma arc) through the gasifier of this conversion “supercharges” the technology.
As mentioned above, methanogenic bacteria grow in a liquid environment that is not a fundamental characteristic of a dry tomb landfill. However, technologies are emerging that use anaerobic digestion on high moisture solids to enhance energy production. BioCycle has chronicled the commercialization of the high solids digester being developed by the University of California, Davis and Onsite Power Systems that produces both hydrogen and methane from solid waste.
Juxtaposed against this landscape of energy conversion technologies is composting, which creates high-value products from the residual carbon in biomass. To fully “supercharge” tomorrow’s energy from waste, the highest and best end uses for recoverable carbon must be determined. These new best uses will likely include diversion of residual carbon through recycling, composting, bioenergy or a combination of all of the above.
Mark Jenner, PhD, operates Biomass Rules, LLC and has over 25 years of biomass utilization expertise. Burning Bio News is Jenner’s monthly scorecard of bioenergy project adoption, available at www.biomassrules.com.

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