Methane: The Little-Used Fuel Product of Sewage Treatment Plants

Our ancestors burned animal dung for heat to keep warm and to cook food. Native American Indians used buffalo droppings for this purpose, and the indigenous peoples on the continents of Africa, Europe, the Middle East, and Asia do the same for poop scooped up from the animals with which they share the land. In the absence of more traditional firewood, modern-day weekend warriors sometimes rough it up with a cow paddy or two.

While it may be more common knowledge that people burn animal dingles for cooking and heat, it's a lesser-known (and sometimes unthinkable) fact that human poo may do just as well, or even better.

Gaseous Methane Fuel from Human Poop

While raw human sewage has been recycled for millennia by traditional peoples as fertilizer for crops, so-called "modern" sewage and water treatment plants across the globe take on a "just deal with it" attitude in their design. Wastewater and sewage treatment plants do little more to human sewage than just allow it degrade sufficiently so that it no longer constitutes a biohazard. After processing, human dung is frequently disposed of in landfills, or sold off as pure compost for commercial use.

While being processed in its raw form, a relatively simple process mimicking natural decomposition uses industrial-strength bacterial compounds to "digest" the human sewage. This process yields methane and other combustible gases as by-products.

In smaller plants, these gases are invariably allowed to waft off into the atmosphere. On the chance a plant resides somewhat close to a human population, the concentration of gases may constitute a health hazard, aside from being a source of offensively odiferous gases. In this case a treatment plant will collect and burn these gases, thus producing harmless (and not so smelly) carbon dioxide and water.

Poop Power

The problem with just burning the gas produced by human feces and other organic compounds is that it doesn't take advantage of the combustion process.

Depending on the level of sophistication in the sewage plant's design, the facility can use the heat produced from burning the methane it produces. This methane can be used in one or more of several ways.

Electricity from Poop

Methane can power a small turbine jet engine attached to a generator that produces electricity. The treatment plant can use this electricity to help power motors and other machinery (such as centrifuges), and thus markedly reduce its power draw from the electrical utility grid and likewise reduce operational costs.

Methane Heat for Accelerated Sewage "Digestion"

Another application for the methane released by raw sewage is to speed along its own sewage digestion process.

During the cold of wintertime the overall operating temperature of sewage and wastewater treatment plants goes down. Because the bacteria and other organisms used to digest raw sewage rely on heat to drive their chemical activities, productivity in a sewage plant likewise goes in cool weather. This results in longer water processing time, and overall less efficient sewage digestion.

To counter this loss in productivity, the heat derived from the combustion of methane gas can itself be used to help heat up the plant's digestion fluids. This extra heat can help raise sewage temperatures - even if by a degree or two - and thus greatly help the digestion process along.

Another plus to this method is that it's "self-encouraging". By using heat from the methane produced at colder temperatures, the heated digestion fluid in turn heats itself, which in turn causes more gas to be produced, which in turn produces more fuel to make heat, which in turn further raises the temperature of the sewage, which...

Methane Heat: Not In Use

Because the costs associated with developing efficient forms of these technologies are prohibitively high, few to no wastewater and sewage treatment plants use the heat energy that methane can provide.

Many of these plants merely burn the methane and allow its precious energy to rise - forever lost - into the sky.