Biogas from Waste
One of the most consistently growing industries over the last few decades is that of waste management. In terms of workforce, earnings and markets, companies engaged in this business show no signs of pulling back. For sure, the industry expands because waste proliferates. Dealing with it seems a never-ending challenge. Hopeful signs, however, relate to the potential of waste as a resource. Biogas from waste can be captured and converted to electrical power. The net effect is two-fold: less waste for landfills and more energy for economic growth, quality of life and even national security. Technology has enabled this development.
What Qualifies as “Waste”?
Yes, time, money and potential can all get wasted. Yet the waste that costs so much to manage is known as solid waste. According to the U.S. Environmental Protection Agency, solid waste is best defined by the 1976 Resource Conservation and Recovery Act (RCRA). Under RCRA, solid waste is “any garbage or refuse, sludge from a wastewater treatment plant, water supply treatment plant, or air pollution control facility and other discarded material, resulting from industrial, commercial, mining, and agricultural operations, and from community activities. Nearly everything we do leaves behind some kind of waste.” EPA clarifies that solid waste may contain liquid and gaseous elements as well.
Waste Management in the United States
U.S. municipalities generated 88.1-million tons of solid waste in 1960. By the year 2017, that generation reached 267.8-million tons. The population expansion and development of new industries — among other culprits — can claim credit for this. By the same token, sound conservation measures may be the reason this figure is not higher. To this point, the number of landfills in the country dropped from 6,326 in 1990 to 1,269 in 2017. A prime factor here is recycling: 6.4 percent of solid waste was recovered for recycling in 1960; by 2017, 35.2 percent was recovered. Clearly, progress is evident over the decades. Still, managing waste continues to be a major challenge.
What Fills the Landfills?
As mentioned above, solid waste is not strictly solid: liquids and gasses mix with solid materials. This is especially true for landfills. Anaerobic bacteria, i.e. bacteria that lives without the presence of oxygen, emit biogas. This landfill gas, as it is called, possesses a high concentration of methane. Collected properly, this biogas production from waste can generate electricity for homes, vehicles and machinery. Using a methane gas recovery system, U.S. cities extracted 270 billion cubic feet of landfill gas in 2018 from 352 different landfills. When burned, this biogas from waste generated 11-billion kilowatt-hours of electricity, constituting 0.3 percent of electricity nationally. This from trash to gas biomass energy also reduces the total landfill density.
So much garbage and refuse is organic in nature: banana and potato peels; egg shells and carrot stems; meat drippings and trimmed fat, to name just a few common waste products. The solar energy inherent in these materials is what yields the biogas of which methane (CH4) and carbon dioxide (CO2) are the primary constituents. Biogas production from organic waste can happen in the landfill, which serves as an anaerobic organic waste digester, keeping out oxygen and letting the bacteria do their work. Because methane is a flammable pollutant, precise technologies are required for its collection.
Yet biogas generation from food waste can happen in smaller settings. Modestly scaled anaerobic digesters can serve households as well. This sort of compost and food waste biogas plant can significantly cut electric bills.
Old MacDonald Has More than a Farm
The waste from agricultural operations is a perfect example of organic matter. From rotting silage to livestock manure, farms produce no shortage of substrate (raw material) for biogas production from agricultural waste. On-farm anaerobic digesters can receive the manure of cattle, swine or poultry and produce enough methane — and therefore electricity — to power the farm and have a surplus to sell to a public utility. Not only are substantial energy savings realized. but greenhouse gas emissions are slashed and odors are abated, as well.
Not only does anaerobic digenstion create energy resources, the ash left after the biogas from agricultural waste is collected serves as a potent fertilizer for crops. Effluent from dairy cattle, for instance, demonstrates a higher nitrogen content than untreated manure does. Crops high in solar energy, like maize, make silage that is also an effective substrate for biogas from vegetable waste.
A “Sewer” Path to Power
Water treatment facilities are now getting into the electricity business. The organic substances found in sewage sludge are converted anaerobically to hydrogen, alcohol, CO2 and fatty acids. In the second stage, sewage biogas,consisting mainly of CH4 and CO2, is extracted. The biogas from sewage at one such facility in Austria generates 1.4 gigawatt-hours of electricity every year. Meanwhile, in Saitama Prefecture, Japan, another digester operation powers 5,000 homes as well as automobiles, all the result of biogas production from sewage sludge.
Other Substrates for Biogas
Household digester systems are successful at producing biogas from grass clippings and other dead flora. In addition, biogas from algae is promising, though research continues. Other areas of ongoing study include seaweed biogas. Though the amount of yielded methane from human feces is considered modest compared to that of livestock manure, there is a human waste biogas plant in India — doubtless not the only place — that better sanitizes its water systems through its ude of digesters.
Biogas from waste holds promise for a world where electric power is in high demand and biomass is highly available. As anaerobic digester technology improves, the substrates from which the biogas is collected will expand in number. This is good news for public works, public health, economic growth and environmental sustainability.