The idea of recycling material, mainly liquids, into a form of fuel is not a novel idea by any means. In fact, vegetable oils, used cooking oils, and sometimes even animal fat can be converted into biodiesel. But what if we could take one step further and use what’s left over from sewage treatment by simply introducing one more step to break down the sludge further and convert it into biogas?
Researchers at Washington State University in the Waste Management research group found that introducing one step during the pretreatment of leftover sewage sludge can efficiently convert over 85% of it into biogas through a process called anaerobic digestion (or AD). Biosolids, the sludge left over from wastewater treatment facilities, require special disposal. With the improvements made for sewage sludge digestion, the amount of organic material available in the sewage sludge can be treated and used to produce bioenergy.
The Energy Policy Act of 1992 addresses all aspects of energy supply, including alternative fuels. This includes biofuels, and requires states to provide alternatives. After being amended several times to now include infrastructure development and alternative fuel use. The department of energy has the power to authorize alternatives that meet certain requirements.
The current process for breaking down the leftover sludge after treatment has proven inefficient, with large amounts of electricity used to process municipal waste. Often, these facilities are the largest users of electricity in smaller communities.
For this research, the waste is treated through the process of anaerobic digestion. The sludge is subjected to oxidizing agents under high temperatures and pressures in a thermochemical process of both wet oxidation and steam explosion. In the end, complex structures break down, resulting in better digestibility of the organic matter. This process is significantly more efficient because it requires no chemicals for recovery and lowers byproduct inhibitions. This treatment yields a higher level of methane during anaerobic digestion.
The method is new, but the idea has been around for a while. Scientists have, on multiple occasions, tried to turn human waste and sewage into responsibly produced biofuel for decades. One such study from the US National Renewable Energy Laboratory converted volatile fatty acids into paraffin, a preferred combustible component for sustainable aviation fuels.
Another study at an outdoor laboratory in South Korea was created to blend creative function and research to better understand potential biogas possibilities. The researchers’ primary focus was a waterless toilet system, encouraging a more natural biological breakdown of waste into a compostable material, which is then converted into biodiesel through a microbial energy production system.
Across these research projects and scientific breakthroughs, the aim is a reduction in the negative footprint of urbanization on ecosystems. It could prove especially beneficial for smaller communities.
Sources: Eurekalert, AFDC, Sciencedirect, Popular Mechanics, ScienceDaily