Heavy Metal Town

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Wacken Open Air, Wacken, Germany

Heavy metal from my era has inundated TV commercials over the past few years. Classic rock and roll by Led Zeppelin, ACDC, and Judas Priest is the background music for selling cars and cologne, but heavy metal is not so popular when it comes to organics management.

I recently joined in a Facebook conversation in the Solar Cities group regarding food waste recovery using anaerobic digestion at the Reedy Creek Wastewater Treatment Plant in Orlando. It specifically focused on the concept of codigestion. Concern arose over mixing food waste with sewage sludge – it was thought that the value of food scraps was lost due to contamination by or with heavy metals.

Heavy metals are found in the soil, and are also present in food. Arsenic is found in apples and Mercury is found in fish. (In fact, some of us even take vitamins with heavy metal ingredients.)  But did you know compost has heavy metals too? It should be no surprise that both biosolids and compost are regulated to control the levels of heavy metals. Composting is not the only way to return carbon and nutrients to the soil – land application of residuals from wastewater treatment digesters (biosolids) is also a viable means of recycling carbon and nutrients.

Reluctance to see food waste codigestion as resource recovery is throwing the baby out with the bathwater or, put another way — “throwing out the baby to save the bathwater.” Environmentally conscientious people should embrace the concept of recycling both food scraps and biosolids together because both are resources and neither should be discarded.