Mean Sewers
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Just what makes a sewer nice?
Does it offer to buy you coffee? Say please and thank you?
At the recent New York Water Environment Association’s 86th Annual Conference named, “Utilities of the 21st Century: Going from Net Zero to Net Positive” ‒ the hot topic was maximizing energy production utilizing additional feedstocks for anaerobic digestion, especially from commercial and industrial sources. A panel discussion by five wastewater people spent a lot of time on the addition of food waste to digesters from source-separated organics processed at the treatment plants. That’s a lot of work. Nobody on the panel mentioned food waste disposers. One of disposers’ chief benefits is that the waste generator does all of that work for you.
When prompted by a question from the audience about using “in-sink grinders” a panelist stated “…They only make sense for other cities with nice sewers.”
I guess that would make his city’s sewers mean. Of course not– the panelist was referring to his home city’s combined sewers. With that type of system, there is the potential of a wet weather combined sewer overflow, when food waste may end up in local waterways. The greater environmental health hazard from combined sewer overflows are the pathogens in raw sewage, not microscopic ground food waste. (I have noted numerous times in this blog that despite some misconceptions, “chunks” of food are not disbursed to sewers by disposers.)
Furthermore, according to Metcalf & Eddy’s 5th Edition of Wastewater Engineering, ground food waste makes up only about 20% of the suspended solids and biochemical oxygen demand in sewage.
Communities with combined sewers should be eliminating them, and are required by the EPA to do so as part of their Long Term Control Plans. Hopefully some day we will see the demise of the mean sewer. In the meantime, food waste is, and will continue to be, a small fraction of the total composition of wastewater.
