Where To Find Money In Biogas
On the surface, wastewater treatment operations don’t appear to be handling precious material. But these facilities are actually processing a great deal of value every day.
Sludge, a byproduct of wastewater treatment, turns out to be an entity worth cherishing.
“Depending on treated sludge quality, the final product can be land applied, landfilled, incinerated, or composed,” according to Biomass Magazine.
While there is an opportunity to sell sludge as fertilizer for agricultural use, or at least give it away in exchange for the expense of transporting it, perhaps the most lucrative opportunity at wastewater treatment plants is found in biogas.
“In secondary treatment, wastewater is aerated in a basin to promote microbial growth,” explained Biomass Magazine. “These microbes form flocs and settle out as activated or secondary sludge… Sludge thickening is done by all [wastewater treatment plants] to increase solids content and sludge.”
Larger wastewater treatment operations anaerobically digest thickened sludge, using bacteria to break it down and reduce volume, volatile solids, and pathogens. That sludge digestion process is what creates biogas, which can be harnessed for other uses.
“Sludge digestion produces biogas, the amount of which depends on sludge quantity and composition (ratio of primary to secondary), digester residence time, bacteria metabolic rate, and several other parameters that influence how it is managed,” reported Biomass Magazine. “If a substantial quantity of biogas can be produced, it can be used as a cogeneration fuel source. Power can be used for internal purposes and sold to the electricity grid.” Biogas production is particularly attractive for treatment plants serving large populations, as opposed to smaller populated areas, as the cost involved to harness that fuel would not be cost effective.
That fuel can be used to maintain a plant’s digester temperature. It can also be upgraded to renewable natural gas, a process that increases its methane concentration by removing fouling components. Upgraded biogas can be transported as compressed natural gas, or injected into the gas grid at a profit. Renewable natural gas is worth about $15 to $20 per one million BTU.
If operations are capable of harnessing the biogas that is a natural byproduct of their work, they can offset some of their operating costs. It may even be possible to turn a profit. But the first step will be looking at sludge as an opportunity, not a burden.
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