The investment in bioengineering technology appears to be paying off as projects emerge from the research-and-development phase into practical applications that have important implications for the MSW industry.

By Charles D. Bader

When asked for his assessment of today's new technology developments that might significantly influence MSW operations, SWANA Executive Director and CEO John Skinner replied without hesitation, "Bioengineering."

It's hard to disagree with him. As this article was researched, the truth of that assessment became evident. In other areas of the industry, it seems last year's promising technologies either have fallen by the wayside or have emerged as mature production products or processes that already are having an impact on the industry.

For example, the composting of food and other organic waste that Norcal Waste Systems was pioneering for the City of San Francisco, CA, now is a full-scale component of that city's waste disposal program. In addition to collecting foodwaste from restaurants, the city is collecting source-separated food and greenwaste from residents. As a result of this increase in feedstock to be composted, Norcal's composting operation is up to 250 tpd on its 15-ac. site, according to Site Manager Chris Choate.

Similarly, the application of the Navstar global positioning system to landfills for compaction pass monitoring and grade/slope precision of landfill cover seemed to be cutting-edge technology when Caterpillar and Trimble Navigation jointly developed Caterpillar's Computer-Aided Earthmoving System (CAES). Already, however, CAES has been replaced in the Caterpillar line by CAESultra, which the company claims is "faster, easier to use, and more robust than its predecessor"–and better meets user requirements.

Processing of single-stream recyclables? The hotly debated issue of whether or not this was a practical technology seems to have been settled by Waste Management's significant investment in about 20 of these costly systems. What's more, Van Dyk Baler, which supplied the majority of these single-stream (Bollegraph) processing systems to Waste Management, has had very strong growth in this market. According to Wilfred Poiesz of Van Dyk Baler, the company has been experiencing 30% annual growth over and above the 15 single-stream systems it has sold to Waste Management Inc. "Single-stream processing is out of the design phase and is in every sense a production business now," he notes. "With this volume and our ERP [Enterprise Resource Planning] production program, costs are coming down so that today's systems are more cost-effective than ever."

All of which leaves bioengineering in all of its different facets as the most promising 2002 technology for the MSW industry. Why the concentration on bioengineering? It has resulted from the confluence of three national priorities:

1. Renewable Energy. With the escalating unrest in the Middle East, even this country's petroleum-oriented administration is seeing the importance of renewable energy sources. Biogas in general and landfill gas (LFG) in particular represent ready and comparatively inexpensive sources of energy. Each year, more than 4 trillion ft.³ of energy-containing LFG are flared worldwide, most because no economic use has been developed for it.
2. Air Pollution. Whether or not the administration decides to reverse its reneging of the Kyoto Accord, many states, as well as private citizens, are deeply concerned about the greenhouse effects of air pollution and fugitive gas emissions. And landfills represent a large source of fugitive emissions that are escaping into the atmosphere.
3. Waste Disposal. Despite inroads from recycling and reuse programs, landfilling remains the principal waste disposal approach in this country as population and MSW generation rates continue to grow. Bioengineered waste disposal has the potential to significantly reduce landfill use and/or extend landfill life.

There is a variety of promising bioengineered projects in the MSW industry. Among them are controlled bioreactor landfills, LFG conversion equipment, in-vessel anaerobic digestion, pyrolysis, and biorefining. The balance of this article describes a representative sample of such projects.

Bioreactor Landfills

Bioreactor landfills, as contrasted to "dry tomb" landfills, are by no means new. As pointed out by Debra Reinhart and Timothy Townsend, who literally wrote the book on the subject (Landfill Bioreactor Design and Operation, CRC Press, 1997):

One of the potentially significant benefits of an anaerobic bioreactor is the fact that it can generate large quantities of LFG with a methane content that can produce useful and marketable energy. However, not everyone concedes that this is advantageous. John Schert, executive director of the Florida Center for Solid and Hazardous Waste Management, summarizes the pros and cons:

"An aerobic bioreactor simply involves blowing air, and hence oxygen, into the landfill, and this accelerates the decomposition and stabilization of the waste. This also reduces the emission of methane that contributes to the greenhouse effect. You might prefer aerobic to anaerobic bioreaction if you were in a hurry to achieve settlement so that you could add more MSW to the landfill and you could cut your leachate management costs. However, you'd pay a big energy penalty both to operate the needed blowers and by precluding any revenues from collected gas. All in all, I'd say people who opt for aerobic bioreaction would have to have a unique and compelling reason to do so."

Schert concedes, however, that no one is sure of the magnitude of these pros and cons. Hence, his Florida Landfill Bioreactor Demonstration Project, a large (26-ac.) enterprise, will contain aerobic as well as anaerobic areas. The project team will evaluate the use of both aerobic and anaerobic landfill technologies and compare the quantitative advantages and disadvantages of the two directly.

Across the country in California, Yolo County is completing a full-scale, 12-ac. bioreactor landfill module that, among other things, will compare aerobic and anaerobic performance. One 9.5-ac. cell will be operated anaerobically, while the other 2.5-ac. cell will be operated aerobically. The county will construct the second phase of this bioreactor landfill in two years and, depending on the results of the first phase, might operate Phase 2 either aerobically or anaerobically.

That's simply a side element of Yolo County's overall goals for its bioreactor landfill, though. "We have been operating a 9,000-ton test cell for several years, and the new 9.5-acre anaerobic cell will be a larger-scale replica with which to validate the test cell results," states Ramin Yazdani, assistant director of the Yolo Division of Integrated Waste Management and the driving force behind the county's multiyear development program. "Figures 1 and 2 graph the results of its operation. Based on these data, which we have collected over [a period of] more than three years, the time it takes a bioreactor landfill to stabilize [five to 10 years] might be 30 years less than current landfill expectations.

"In addition, the rate of enhanced methane recovery of a full-scale bioreactor landfill may be an order of magnitude greater than that of current dry-tomb landfill methane recovery. We will have landfilled about 200,000 tons of waste by the end of this October. We expect this to produce a total volume of landfill gas of about 600 million cubic feet, averaging 120 million cubic feet per year–assuming we complete the gas capture in five years as we expect. This translates to about 280 cfm [cubic feet per minute] of gas. With the average methane content of 53% measured in the pilot project, this byproduct of anaerobic landfill waste composting can be a substantial source of badly needed renewable energy that can be recovered for electricity or other uses.

"Other expected benefits of a bioreactor landfill that we will be verifying and quantifying with our 12-acre landfill include increased landfill waste settlement and therefore an increase in capacity and landfill life, improved opportunities for treatment of leachate liquid that may drain from fractions of the waste, possible reduction of landfill postclosure management time and activities, landfill mining, and abatement of greenhouse gases through highly efficient methane capture over a much shorter period of time than is typical of waste management through conventional landfilling."

Clearly bioreactor landfills are emerging from the research and development (R&D) phase to the practical engineering and production phases with a solid body of data from sophisticated instrumentation upon which to rely.

LFG Conversion Equipment

One of the keys to the success of bioengineering projects is the ability to effectively use the output potential of the biogases. This is particularly true in the case of LFG, which has to be collected and treated to be used for energy purposes as opposed to being flared or released to the atmosphere and thereby contributing to the greenhouse effect.

Yazdani cites a Department of Energy (DOE) study that indicates that wide application of controlled landfilling could reduce US greenhouse gas emissions by 50 million—100 million tons of CO₂ equivalent when both emission prevention and fossil CO₂ offsets are taken into account. Another DOE analysis concluded that, over a range of representative landfill conditions, greenhouse gas abatement could be attained at a cost of $1-$5/ton of CO₂ equivalent, a cost that is tenfold lower than other options.

However, this analysis primarily considers large landfills where the amount of LFG potential justifies the cost of large pretreatment systems and turbines that economically can convert the LFG into usable and marketable energy. These gas-collecting landfills (325 by EPA's Landfill Methane Outreach Program's recent count) represent just a fraction of the total number of landfills producing uncollected LFG. At the March 2002 meeting of SWANA in Monterey, CA, EPA presented its estimate that only about a quarter of the total LFG being generated is captured, converted, and used.

"Thousands of small landfills and closed landfills need collection systems too," points out George Wiltsee of Capstone Turbine Corporation of Chatsworth, CA. "But the operators of these small landfills can't cost-justify large pretreatment systems and turbines, so they are unlikely to invest in a gas capture and conversion system unless some regulatory body mandates it. Today there is a very good reason to do so. One of our recent microturbine tests demonstrated NO_x levels of only 1.3 ppm [as opposed to approximately 50 ppm for a typical reciprocating engine]. That level is 10 to 20 times less than landfill gas flare levels."

Capstone's line of microturbines certainly helps the cost-justification economics of gas recovery and usage by operators of small landfills too. Both its 35- and 60-kW models now on the market and its 200-kW version soon to be released are sized–and priced–for the requirements of small landfills. (Multiple microturbines can be combined to behave as a single generating source.) All three models can be used to provide both onsite power needs and power to electric grids. And they can be equipped with options that allow the user to recover waste heat for such purposes as heating greenhouses, office space, or water.

"A 30-kilowatt system packages the turbine, a generator, and electricity conditioning equipment in a single case about the size of a refrigerator," Wiltsee remarks. "As a landfill develops, microturbines can be moved in to increase generating capacity or removed as gas flows decrease. Closed landfills can use microturbines to recover remaining landfill gas flows to power onsite uses such as gas collection and leachate recovery systems. Microturbines are also well suited to remote landfills … since they require no operator intervention and almost no maintenance."

A separate but equally important element is a fuel gas compressor to maintain a minimum fuel pressure of 55 psig. A refrigerator/dryer chills the LFG to drop out condensate and then reheats it to produce dry gas and to drop out half of the siloxanes (a carbon filter removes the other half). The power consumption of the compressor is approximately 3 kW, or about 5% of a 60-kW microturbine's rated output. The capital cost of this combination of pretreatment equipment and a 60-kW microturbine is approximately $1,100/kW.

"While we believe the primary market for microturbines will be small or closed landfills, the units are being used now in large landfills to capture landfill gas that otherwise would be flared," Wiltsee adds. "At the Los Angeles DWP's [Department of Water and Power] Lopez Canyon Landfill, for example, we have 50 microturbines in use. The way the LADWP acquired these units is unusual. Some time ago the utility had to pay a fine to the Southern California AQMD [Air Quality Management District] for exceeding its NO_x emission limits. The SCAQMD used this money to buy the 50 microturbines and turned them over to the LADWP, which is now using them at Lopez Canyon to reduce its NO_x emissions [and to convert the gas for its Greeenpower program]."

At this time, the microturbine is well beyond its R&D phase. Mass-produced now, it is being used at wastewater treatment plants, oil and gas fields, and landfills. Its acceptance has been strong. As Ed Wheless of the Los Angeles County Sanitation District reportedly said, "Three things about microturbines attract my attention: First, they have almost no NO_x emissions. Second, they require virtually no maintenance. And third, they can be installed or relocated with little effort."

Recently Ingersoll-Rand entered the LFG-to-energy arena with its IR PowerWorks microturbine system with a 70-kW output generator featuring a two-shaft design and an advanced engine recuperator and combustor to boost fuel efficiency. The system is designed to use waste heat–100,000-400,000 Btu/hr.–for hot water and other heating applications, employing a variety of cogeneration schemes to maximize the unit's thermal efficiency.

Another LFG conversion project is well underway in San Diego, CA. A year ago, EPA's Brian Guzzone reported in MSW Management that a new technology for converting LFG to a liquefied natural gas fuel was being demonstrated at that city's closed Chollas Landfill. The technology produces a fuel that is more than 97% methane. The fueling unit, which is supplied by Applied LNG Technologies and its subcontractors, will produce 3,000 gpd of liquefied methane. The city will use a fuel consisting of 85% methane and 20% diesel fuel in its waste collection vehicles. At that time, San Diego had converted more than 50 trucks to burn the dual fuels; today, a year later, the city has converted 69 Caterpillar engines in its entire fleet of 165 trucks.

In-Vessel Anaerobic Digestion

Microturbines are sized for small landfills.

A Valorga facility in Freiberg, Germany

In-vessel anaerobic digestion systems are becoming relatively common in Europe where landfills are completely banned or at least greatly discouraged. As a sort of substitute for a bioreactor landfill, these in-vessel systems tend to be quite large, with capacities as large as 100,000 tpy not uncommon. They process run-of-the-day MSW to produce a high-grade compost and significant amounts of biogas. The German firm of Steinmuller Valorga, which has full-scale systems in seven European countries, reports that the biogas generated by any of its facilities designed to compost 500 tpd of MSW will have sufficient energy content to operate the facility and produce about 2.5 MW of excess electricity per hour.

A US firm, Waste Recovery Systems Inc. of Newport Beach, CA, is marketing the Valorga system in North America. According to President Steve Morris, the firm is promoting a program of solid waste management that includes the composting of MSW with sewage sludge using the Valorga process of anaerobic digestion followed by aerobic curing.

The MSW feedstock is mixed with the sludge and water to achieve a ratio of 35% solids to 65% water. At the mixer, steam is added to bring the temperature of the mixture up to the thermophyllic range to ensure that pathogens are killed. The heated mixture then is pumped to the digester. There are no moving parts in the digester, but a baffle system separates incoming from outgoing material. A 24-in. pipe carries the pumped slurry into the digester and over the next 14 days the pressure of incoming material forces the slurry around the circular digester, past the opening in the baffle and out a similar pipe at the other side of the digester. In the course of this two-week odyssey, jets of air keep the material mixed, and the biological decomposition continues. As waste is added each day, a comparable amount of compost exits the digester. When the biogas leaves the digester, it is routed to either (1) a biogas compressor and thence to pressurized biogas storage or (2) a steam line to generate electricity.

When the slurry exits the digester, it passes through a press that squeezes out water to get the ratio to the correct level. The still-warm water is recycled to the mixing stage where it provides resident heat and some microorganisms to the new mixture. The wet compost goes into an aerated tunnel, where it is cured for two to three weeks. This is an enclosed tunnel so no odors can escape during this phase either.

The University of California, Davis has developed and patented a smaller-scale anaerobic digestion system it calls Anaerobic Phased Solids Digester (APS-Digester) and has now licensed this technology exclusively to Onsite Power Systems, a Camarillo, CA, company specializing in renewable energy generation. Much smaller than the European systems, this high-rate scalable system was researched and developed by researchers in the laboratory of Ruihong Zhang, Ph.D., of UC Davis's Biological and Agricultural Engineering Department. According to Zhang, "The APS-Digester system combines the favorable features of both batch and continuous operations into one biological system. Solids to be digested are handled in batches, while the biogas production is continuous. This allows the solids to be loaded and unloaded without disrupting the anaerobic environment for the bacteria."

"Separating the operations enables us to optimize the environmental conditions for the two types of bacteria," adds Dave Konwinski, president of Onsite Power Systems. "Thus, the overall system is more robust and more efficient than single-phase systems. Our system operates at either 95^o or 135^o Fahrenheit, resulting in much more rapid digestion than would occur at ambient temperatures."

The system originally was designed to handle agricultural waste, and its first commercial application will be at a new 1,900-head horse-training farm in Florida. However, Konwinski claims, the system is flexible and can handle any organic feedstock so long as it is digestible and can be stable. Onsite Power System is creating a "recipe book" of organic feedstocks in the form of computer simulations that will predict what will result from various blends of organics.

While Onsight Power Systems continues to focus its efforts on agricultural materials, Konwinski points out, "One of the major advantages is that the system can be scaled in size to meet any user's supply of feedstock. Thus, project capital costs can be as low as $750,000. A city might well prefer multiple small facilities each located close to the source of a different feedstock, perhaps one at the docks to process fish waste, another at a transfer station to process greenwaste, and so on. Such decentralization would reduce truck traffic, and the smaller facility size would simplify siting."

Zhang projects that the investment for an APS-Digester facility will be paid back in three to seven years. She bases this solely on projected financial returns, primarily from (1) the value of heat and electricity generated, (2) the cost savings of otherwise disposing of the waste feedstock, and (3) the value of the high-quality soil amendment the system produces. It does not reflect income or savings from the incentive program for renewable energy sources that appears to be in the offing.

Pyrolysis

The SWERF system produces syngas to be converted into electric power or used as stream or as a chemical feedstock.

Whereas the anaerobic digestion systems are counting on producing at least some composted soil amendments as a revenue source, there is only one significant product produced by Brightstar Environmental's solid waste energy and recycling facility (SWERF) system: biogas–or syngas, as the company calls it. That's not strictly true, since SWERF does pull out recyclable materials. However, since curbside collection already has pulled out most of the high-value recyclables in most communities, SWERF recycling is done principally to get rid of nonorganic nuisances.

Although its only fully operational plant to date is in Wollongong, Australia, this Australian firm is strongly marketing its system in the United Kingdom and the US (from its offices in Houston). And Brightstar's marketing effort places unusual emphasis on environmental benefits, particularly reduction of greenhouse gas emissions. Consider its Web site (www.brightstarenvironmental.com) dealing with the subject:

"As an environmental services business, Brightstar Environmental considers environmental factors to be a central component of its business strategy.

"SWERF plants utilise waste that would otherwise cause disposal and emission problems and produce electricity reducing society's reliance on fossil fuels.

"A SWERF captures 100% of the total syngas produced from the conversion of the organic waste thus eliminating greenhouse gas emissions associated with the deposition of waste in landfills and the resulting production of landfill gas over a 15 to 25 year period.

"The diversion of organic material from landfill disposal to an energy recycling facility will have significant greenhouse gas benefits through avoidance of landfill gas production and avoidance of fossil fuel consumption to generate electricity.

"Landfill gas contains approximately 50% methane, which has a global warming potential 21 times greater than carbon dioxide. Therefore, a SWERF will provide significant reductions in greenhouse gas compared to landfilling.

"The technology also alleviates many of the long-term issues associated with the operation of landfills and the restoration of post closure sites, for example the elimination of leachate production, landfill gas migration, odour, vermin, wind blown rubbish and bird control.

"When compared to landfilling and electricity produced from conventional coal fired power stations, the processing of waste through a SWERF eliminates the emission of approximately 2.7 tonnes of CO₂ equivalent for every tonne of waste processed."

The system operation is quite unusual. According to Brightstar's Ron Menville, MSW, commingled with recyclables, is placed into a large (40-ft.-long x 15-ft.-diameter) pressure vessel called an autoclave. Hot water and steam then are injected into the autoclave, which proceeds to roll on a large roller. The combination of the mechanical agitation, high heat (140^oC), and steam not only sterilizes the mix, but it splits open plastic bags, breaks bottles, crushes cans, melts plastic bottles into a clump, and pulps the organic matter into a homogeneous slurry.

"The ‘cooked' waste pulp is then separated into component streams through a series of screens, trommels, and magnets, similar to those found in existing materials recycling facilities," Menville describes. "The organic stream is gasified in a two-stage process; initially using an externally fired flash pyrolysis process which produces a high-energy-content synthesis gas [syngas], liquid hydrocarbons, plus a solid residue containing inorganic and organic compounds and elemental carbon. The energy-rich liquid hydrocarbons and solid residues are further processed using steam reformation to complete the conversion of the carbon and organic compounds into additional syngas. Since there is no oxygen inside the vessels, the process does not involve any form of solid waste combustion or incineration.

"The syngas is subsequently cleaned using traditional technology that chills it to near freezing temperatures to condense out particulates [the solid residues], soluble compounds, and high-boiling-point residual hydrocarbons. The clean and dry syngas is then delivered to the reformers and gas-fired generation plant. The pure syngas can be converted into electric power, used as steam, or used as a chemical feedstock."

Biorefinery

The Masada Resource Group of Birmingham, AL, has developed a process it calls CES OxyNol for the useful reclamation of MSW. The CES OxyNol process converts the MSW biomass cellulose and biosolids to ethanol, a "green fuel" usually derived from corn. In the process, the glass, plastic, and metals recyclables are removed and the cellulose is converted into simple sugars, primarily glucose. The sugar then is fermented to produce ethanol, and the ethanol is distilled to market-grade purity.

According to Masada's Daryl Harms, "The CES OxyNol process integrates a MRF [materials recovery facility] with an ethanol production plant in a continuous process. All nonhazardous municipal solid waste is processed in the MRF: metal, glass, and plastics are separated for recycling. The remaining waste is dried and shredded, thereby eliminating odor. Once dried and shredded, the waste becomes cellulose, a ‘biomass feedstock' for the integrated ethanol production plant.

"An acid hydrolysis process using concentrated sulfuric acid converts the cellulose into glucose. Then conventional brewery techniques are used to ferment the glucose to produce ethanol and then to distill the ethanol to market-grade fuel purity."

Masada plants are relatively small (9.5 million— to 13 million—gal. capacity), so they require significantly less space than a landfill; that, combined with their high environmental integrity, more easily meets the requirements of local regulatory interests. The facility can be located near areas with high concentrations of MSW, including existing or old landfill sites.

Masada is under contract to design, build, and operate a recycling and ethanol production facility (99.5 million gal./yr. capacity) in the city of Middletown, NY. The facility will utilize Masada's patented process to recycle or convert to beneficial use more than 90% of the waste that enters the plant. The Masada facility will provide a local, economically viable, and environmentally responsible method of treating MSW and wastewater biosolids for a consortium of 24 municipalities in New York's Orange County that are linked together by the common needs of economical and environmentally sound waste disposal.

"These communities had seen tipping fees rise from $2.50 to $65 a ton in just 15 years," Harms explains. "Then a proposal for a major landfill expansion to mitigate these fees was thwarted, and the county lost its court case for opening a new landfill. Therefore, our biorefinery technology made good economic sense to these communities who proceeded to commit their waste for 20 years to the Masada plant that is permitted to handle 230,000 tpy of MSW. The plant is designed to beneficially reuse 90% of that wastestream. Communities that contribute waste to the facility will realize immediate savings from stabilized tipping fees, from reduced collection costs possible with commingling and from avoided potential environmental litigation associated with landfilling and incineration."

And of course there is that 9.5 million gal. of ethanol that is likely to be of great value as part of this country's renewable energy program to help meet our energy needs. All in all, it would appear to be a good business decision as well as a sound environmental move for both Masada and the 24 communities.

"The term ‘environmental business' isn't the oxymoron it once was," Harms asserts. And in view of the confluence of national priorities to stimulate developments like these bioengineering systems, it's as hard to disagree with him as it was to disagree with John Skinner.

Charles D. Bader is with Dateline II Communications in Los Angeles, CA.