This month I stayed on Hayden Island in Portland, OR for this year’s BioCycle West Coast Conference. We were somewhat isolated, and I heard a municipal official say something to the tune of, “We’re looking for options other than losing resources down the sewer.” In more ways than one I felt in the “Land of the Lost” – the show I watched as a kid and later made into a comedy with Will Ferrell. It seems, at least to some people, that sending food waste through a disposer and household plumbing to the water resource reclamation plant is somehow considered lost.
The notion that mixing food waste with wastewater results in lost resources comes from the supposition that only food waste is a resource, while wastewater on the other hand is waste. I am reminded that long ago I learned that wastewater is 99% pure water. That’s right only 1% is the nasty stuff. (This, incidentally, is the same claim made by Ivory soap years ago in their advertising.)
There is the claim that to recapture the food waste “resource,” the mixed food waste and sewage must be separated at the treatment plant. Wastewater treatment does just that through physical and biological processes – physical being sedimentation and biological being secondary aeration.
So I submit that sending food waste through sewers to the treatment plant does not mean it’s lost. Far from it. In fact, treatment plants make the most of all the embedded resources in ways composting cannot.
First, food waste is 70-90% water, so water is the end product of wastewater treatment. Second, biosolids can be used as a soil amendment and fertilizer, just like compost. Third, energy can be generated from food waste through anaerobic digestion to process sludge into reusable biosolids.
Although wastewater treatment is the greatest contribution to human health on this planet, there is a stigma about these facilities, even among those who you’d think would know better.