Proceedings

Abstract The concurrent megatrends of diversion of organics from landfills and resource recovery at wastewater treatment plants position food waste disposers as important potential tools for municipal authorities. The additional organic loading to treatment plants has historically been viewed as burdensome, but given the actual characteristics of food waste, especially the high carbon to nitrogen and phosphorus ratio, based on BioWin modeling of three types of wastewater treatment processes, there are overlooked benefits from more extensive use of disposers, including a net energy gain from combined heat and power systems utilizing biogas, and improved nutrient removal for plants striving for lower effluent limits.

Keywords Anaerobic digestion, activated sludge, Bardenpho, biogas, co-digestion, food waste disposer, Modified Ludzack-Ettinger, nitrification.

Introduction In urban areas, food waste may be managed through onsite composting, landfilling, codigestion, or wastewater treatment via disposers. A graphical comparison of strategies for food waste management is presented in Figure 1. 7th European Waste Water Management Conference www.ewwmconference.com Organised by Aqua Enviro Technology Transfer Figure 1: Alternative management strategies for food waste in urban systems. Food Waste Properties Relevant To Wastewater Treatment Generation of Food Waste The estimated generation rate of residential food waste is 0.3 kg/cap·d (wet basis) (Diggelman and Ham, 1998; Tchobanoglous et al., 1993). The amount of food waste total solids (TS) resulting from kitchen sinks and dishwashers is about 0.07 kg/cap·d (wet basis) while the amount processed through FWDs, where they are used in conjunction with other food waste management options (i.e., not mandated or used exclusively), is about 0.1 kg/cap·d (wet basis). The food waste discharge to wastewater at an assumed moisture content of 70 percent, with and without a FWD, can be computed as follows: Food waste TS in wastewater without FWD (i.e., kitchen sink, dishwasher) = (0.07 kg/cap·d)(0.3) = 21 g/cap·d (dry basis) Food waste TS in wastewater with FWD (i.e., kitchen sink, dish washer, FWD) = (0.17 kg/cap·d)(0.3) = 51 g/cap·d (dry basis) The addition of a FWD will therefore increase the discharge of food waste TS by about 30 g/cap·d (dry basis). The fraction of food waste TS is present as suspended solids (TSS), without and with a FWD, is estimated to be 21 and 35 percent, respectively (Diggelman and Ham, 1998). 7th European Waste Water Management Conference www.ewwmconference.com Organised by Aqua Enviro Technology Transfer Food waste TSS in wastewater without FWD (i.e., kitchen sink, dishwasher) = (21 g/cap·d)(0.21) = 4.5 g/cap·d (dry basis) Food waste TSS in wastewater with FWD (i.e., kitchen sink, dish washer, FWD) = (51 g/cap·d)(0.35) = 18 g/cap·d (dry basis) When diluted with residential greywater at a rate of about 350 L/cap·d, the increase in wastewater TSS is estimated as follows: Incremental change in TSS with 100 percent FWD use = (18 – 4.5 g/cap·d) / (350 L/cap·d) = 39 mg/L It is expected that the increased TSS loading resulting from use of FWD will be partially removed in the primary clarifier and, where available, processed subsequently in an anaerobic digester or waste to energy facility. In some cases, the soluble and colloidal fraction of food waste that passes through primary treatment has been found to have a positive impact on the removal of nitrogen and phosphorus from wastewater (Battistoni et al., 2007, Evans et al., 2010). Therefore, it has been hypothesized that food waste can be a beneficial carbon source in municipal wastewater treatment systems.