Production Technology: Converting waste into savings
“What’s really driving a lot of our clients, with respect to solid waste, is more landfill closure and the lack of landfill space,” adds Greg Chung, environmental engineer for Kennedy/Jenks Consultants. Kennedy/Jenks works with clients, either corporations or municipalities, to build wastewater treatment facilities.
Doug Parker, associate professor at the University of Maryland, notes that there have been many concerns about the water quality in the Chesapeake Bay. Other state and local governments are clamping down more and more on how companies are allowed to dispose of their waste. Chung also points out that landfills can close, making it more imperative that companies look for alternatives to waste disposal.
The waste treatment facilities take an organic waste stream and convert it into a usable gas. Chung likens a waste digester to a stomach, in that they are both anaerobic processes.
“The bacteria in [the digester] uses that organic waste as a food source, and the byproduct of consuming that food is the usable digester gas,” he explains. The digester gas, generally methane, is something that can be cleaned and burned, converting it into electricity or energy to help power or heat a facility.
A company can construct a facility for its own use, assuming economic factors make the return on investment worthwhile. Companies would need to take into account the cost they are paying for electricity, as well as the hauling cost and tipping fees that are associated with how they presently dispose of their organic waste.
Chung says that the average life of a system is approximately 20 years. If a company is paying a large amount to have its waste hauled away and has considerable electricity usage, it may be an obvious choice. A company that can pay off the expense within five years can enjoy 15 years of energy savings before the system needs replacing. There are several questions a company must consider to construct a plant that is a good fit for the operation.
“It’s driven by economy of scale, so the first question is how much waste do they have,” Chung says. Similar to a stomach, an anaerobic digester functions best when it is neither overfed nor underfed, but rather given a steady waste stream. For that reason, Chung says, a company with a seasonal business is not as good a candidate for a waste treatment facility as one with a constant operation.
The type of digester needs to be considered as well, as it’s the biggest capital investment in constructing a system. Municipal plants tend to use large concrete reactor tanks, but those are relatively rare among commercial businesses. Steel reactor tanks or lagoons are the better options for processors.
Chung says that dairies, which are typically in rural areas with a large amount of available land, tend to use lagoons. Lagoons are easier to construct than other types, and they don’t need to be cleaned as often as a tank system. However, he cautions that lagoons do have footprint and longevity concerns.
“Having tanks that you can get into, hose down and pump out is much more convenient than having to strip a liner off a lagoon and try to get in and dredge it,” he says. A steel tank is smaller than a concrete one, and it is less of a capital investment.
Another consideration is operating the plant once it has been built. The co-generation systems that burn the methane gas to produce electricity and energy are engines, such as reciprocating engines or micro-turbines. The operations can be complex and far from a company’s area of expertise, and some facilities have hired contractors to oversee that aspect of the business rather than handle it internally.
If a company does not want to build its own digester system, it still may have options to reduce its waste through existing municipal treatment plants.
“The nice thing about sending the organic waste stream to municipal plants is that many times municipal wastewater treatment plants will have excess digester capacity,” Chung notes. The municipality may charge a tipping fee, but it generally will be able to accept the waste. Chung also points out that in many cases these plants are located close to industry, so companies won’t have to haul their waste to a regional rendering facility.
Tangible, intangible benefits
Chung says that his company’s clients have seen several positive results in using a waste treatment facility.
“They’ve realized the predicted energy productionfrom gas that you would expect from receiving an organic waste stream,” he says. That energy can be used by the company, Parker points out, or it can be sold back to the electric grid.
Some of the municipal clients that have a steady waste stream have even noticed a reduction in the amount of wastewater solids. Chung theorizes that the biological activity in the digesters becomes more efficient when it has a steady and consistent waste stream.
Along with energy savings, companies and communities that have gotten on board with waste treatment have seen a public-relations boost as well. Not that the process has been completely flawless â€” Chung acknowledges that there have been some problems as far as the reliability of the co-generation systems, specifically in how clean the digester gas can be kept before going to the engine.
“There are hiccups here and there,” he says.
Using a municipal plant isn’t without its costs as well. Parker says that those plants are reaching the point that they will need upgrades.
“They will need ways to raise the money,” he says. Along with charging tipping fees to their waste suppliers, the Environmental Protection Agency and some states have funds available to help pay for the costs.
On the horizon
Waste treatment technology is still developing, and future innovations can help companies reduce their waste amounts and energy costs even further. Chung points to better construction and better ways of pre-treating the waste before going into the digester to improve the output. He also notes that the production of bio-hydrogen to replace methane is currently in research.
“It’s been theorized and done in pilot scale that hydrogen has a higher BTU value per volume than methane does,” he says. “The nice thing about it is that it allows us to extract more energy from the same waste streams. It’s a more efficient process.”