Municipal wastewater treatment plants (WWTPs) do the unheralded work of taking sanitary waste and treating it so it can be safely managed. Over a hundred years ago, cholera and other diseases of exposure to crude sanitary waste were commonplace in the US. But quietly, because of well-run WWTPs we have few cases any more.

While treating the solid waste portion of sanitary waste, bacteria digest the solids anaerobically to form digester gas, a gas that contains methane and has combustion capabilities. However, digester gas is more dilute, in terms of methane – than natural gas, and, therefore, is not very useful. Many WWTPs have purchased generators that can combust digester gas for supplemental power, but otherwise, there has been little interest in using digester gas for energy, particularly outside the WWTP.

A new process has been developed to convert digester gas to natural gas. This is often called RNG or renewable natural gas to differentiate it from natural gas that comes from the Earth and is mined, a fossil fuel. A large Phoenix WWTP is currently implementing this new process to turn digester gas into RNG and to place it in the city’s natural gas pipeline to use as a transportation fuel for its bus lines, making it the largest in the U.S.

This illustrates an opportunity for governments to take an asset it has (digester gas) and turn it into something useful for a different, large function (providing fuel for a bus fleet), saving much costs. It is also possible that governments could market and sell RNG to private entities, making such municipal functions money-makers. Of course, using RNG to displace fossil natural gas or diesel fuel has environmental benefits, as well, and can be part of an effort to make the municipality more sustainable. The project is expected to initially generate $1.2 million in annual revenue. While the cost of the project is high and the payback may not be strong, this is a useful endeavor for the Phoenix area and give leaders flexibility in terms of how to power their plants and fleets.

CCES can help your firm evaluate your energy sources and provide you with cost savings and greater flexibility of future use. Contact us today at 914-584-6720 or at karell@CCESworld.com.