Scientist Justin Biling, a researcher on biofuels at Pacific Northwest National Laboratory in Richland, USA held an AMA (Ask Me Anything) on Reddit last Thursday in which he discussed a new, previously unthought of the way to produce biofuel. He and his team are researching new sources for biofuels and sewage waste seems to look promising, according to the American scientists.
The idea is to ‘help diversify our energy portfolio while diverting a significant societal waste stream to a useful purpose’, as Justin Biling puts it.
The process of production is based on a technology called hydrothermal liquefaction which mimics the Earth’s natural, geological conditions for making crude oil in order to transform sewage waste into fuel. Using high pressure and temperature, bio-crude can be produced in a matter of minutes compared to the millions of years it took for the planet to produce the oil we consume today. The crude product can then be refined using the same conventional techniques applied to petroleum.
So far so good, but why is human waste fuel better?
In the AMA people were concerned about the efficiency of this new type of fuel? How clean is it? And what challenges could prevent it from becoming widely adopted?
In order for an energy source to be considered an efficient, it must have an EROI (Energy Return on Investment) ratio of at least 3:1 and research showed an EROI of between 3 and 4 for the sludge conversion process compared to anaerobic production of biodiesels on which return is slightly above 1.
The main reason AD (anaerobic digestion) is not as efficient is the poor conversion rate. For example, from 100 units of carbon, you can get at best 35 units of fuel out, which then has to be further cleaned. On the other hand, HTL technology is ‘much faster throughput, less capital intensity, higher value fuel product’ and they hope ‘that in some cases HTL could replace aging, problematic AD or become part of expansions/revamps’ according to Justin Biling. Overall, the HTL process is not a perfect one, but it could make improvements to existing processes.
When speaking about the cleanliness of the oil produced by sewage, the first thing we need to clarify is what makes a fuel eco-friendly. What matters is the source material and the energy input during the making of the fuel. Biomass is carbon neutral, but on the other hand, the energy may not come from solar, wind or other renewable sources, so that wouldn’t make the end product carbon neutral.
The solution developed by Biling’s team is still at a very early stage and in order to take off it will have to be scaled up. The problem with that, as scientists put it, is that ‘scaling up all unit operations is not trivial,’ ‘pumping wet solids to high pressure is not trivial,’ ‘continuous ash removal is not trivial.’ ‘Commercially, establishing real off-take contracts is the valley of death for biofuels. One must produce a certain amount to attract refiners’ attention, but at the same time, one has to produce something useful/compatible, which one may not know absolutely until you produce enough of it to find out! Process scaling is what we do, so we’re active on all these fronts.’
The urgent need to switch to energies that do not damage the planet further has led us to uncover the potential of energy sources that we had not taken into consideration before. We are discovering that through scientific breakthroughs and innovative thinking we can be self-sustained.