New research conducted by leading wastewater authority George Tchobanoglous, co-author of Wastewater Engineering, Treatment and Reuse, has yielded surprising information about the impacts of food waste disposers on nutrient removal, as well as energy demand.(1) By modeling the use of disposers on three types of wastewater plants, Tchobanoglous and fellow researcher Harold Leverenz from UC Davis determined that even if 50% of households in a community use disposers there would only be a slight increase in nitrogen and phosphorus in the influent, Figure 1.
Figure 1 – Impact of Food Waste Disposers on Nutrients in Raw Wastewater
More importantly, there is no increase in nutrients in the effluent of a conventional treatment plant that nitrifies. Also, because food waste contains a much higher carbon-to-nitrogen ratio than human waste and with wastewater treatment plants carbon deficient, as Figure 2 demonstrates, for treatment plants utilizing techniques to remove nutrients, the effluent quality actually improves with regard to nitrogen and phosphorus.
Figure 2 – Food Waste Disposer Impacts on Wastewater Effluent
Based on the study by Tchobanoglous and Leverenz, the perception that food waste disposers will degrade water quality due to increased nutrient loadings is unsubstantiated. In addition, all three scenarios result in a net energy gain when utilizing anaerobic digestion and combined heat and power.
(1) Leverenz, Harold and George Tchobanoglous. 2013. “Energy Balance and Nutrient Removal Impacts of Food Waste Disposers on Wastewater Treatment.” Report for InSinkErator.