Fifteen years ago, I wrote my very first post on composting toilets and the first comment was: "Composting toilets are NEVER going to make it into the main stream market. Debating it is silly. No one will want this inside their house. I know this, because I still have a few teeth in my head and a few friends in town."

I thought of this when I read Natalie Boyd Williams's post, titled "Toilet taboo: we need to stop being squeamish about recycling human waste." She is a Ph.D. candidate in Biological and Environmental Sciences at the University of Stirling, a chemical engineer turned social scientist, and knows her poop. Williams notes, as does my commenter, that we have a cultural problem—not a technological one.

Natalie Boyd Williams / University of Stirling

Williams is working primarily in Nepal and India, working to overcome local cultural taboos about using human waste products. We have noted before that there is real value in feces and urine as fertilizer and a source of phosphorus. But in Nepal they are connecting the toilets to anaerobic digesters that turn poop into biogas they can cook with, replacing firewood, kerosene, or dung that is often difficult to gather or expensive to buy. As she writes in the study: "Toilet-linked anaerobic digesters (TLADs) can provide users with a clean gaseous fuel and a fertiliser product as well as offer waste management services."

They squeeze a lot of value out of the feces, feeding it and animal waste into the digester, and getting biogas and a nutrient-rich slurry that can be used as fertilizer after being cooked in the digester. Williams finds that "respondents liked the improved health, cleanliness and reduced wood collection offered by the biogas compared to wood fuel and the reduced cost compared to LPG."

Back in the original article, Williams extrapolates to the more developed world.

Indeed. We have a carbon crisis that comes from burning fossil fuels, including huge amounts of natural gas going into making ammonia for fertilizer. Yet we flush away a valuable resource that could replace a significant amount of the stuff we burn or dig up.

And as Williams notes, the problem is cultural. We saw this at the Bullitt Center in Seattle, which recently ripped out its composting toilets. There is no question they had technical problems, but many of the issues were about "user experience" and cultural issues. In North America, we are used to sitting on a pond of water and having a flush valve power-wash the bowl. But we have to get over this.

Treehugger's Sami Grover has shown a home biogas system that turns human and household waste into fuel, "replacing natural gas that might otherwise be fracked and transported from hundreds or even thousands of miles away" and "as an added bonus, you also get free fertilizer for your garden." What if everyone had a version of this, perhaps a bit smaller and higher-tech?

There are ways to make the user experience better with vacuum-flush toilets like the one shown above, which looks and feels like a normal toilet. Imagine if the pump pushed the waste to a bioreactor instead of the gray composting unit. The gas collected could be fed back into the gas lines, metered, and the poop-supplier would receive a fee, giving a whole new meaning to feed-in tariff.

It would be easier in apartment buildings and has been tried in developments like Vauban in Germany: The vision "was for a ‘wastewater free’ house, in which organic and human waste would become a source of energy and recovered nutrients rather than merely a costly pollution problem. Vacuum toilets, which reduce the water usage by nine-tenths, were installed to transport human waste to an anaerobic biogas digester, which produces liquid fertilizer (high in recovered phosphorus) as well as biogas to be used for cooking." The biogas reactor never worked, but "subsequent research has shown that it is a workable system."

All those people who say they want to keep cooking with gas could continue to do so, as long as they made their own. Companies would come and collect the solids, nicely cooked, to be used as fertilizer or compressed into solid fuel that emits truly biogenic carbon. We wouldn't be spending millions of dollars and pumping millions of gallons of water just to flush away a valuable resource. Instead, we might be earning money from it.

That might well be the key to getting people on board. Williams has demonstrated that when the benefits are immediate and personal, even people used to significant cultural taboos get over it and get on board. Or, as comedian Bob Hope used to say, now you're cooking with gas.

Boyd Williams, Natalie, et al. "Taboos, Toilets and Biogas: Socio-Technical Pathways to Acceptance of a Sustainable Household Technology." Energy Research & Social Science, vol. 86, 2022, p. 102448., doi:10.1016/j.erss.2021.102448

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