Food Waste Impact Study: Sewer Process Modelling for Future Options Assessment

The City of Los Angeles Bureau of Sanitation (LASAN) has conducted a study to assess the impacts associated with conveying food waste using an existing wastewater collection system. A proposed Organics Processing Facility (OPF) is located 29 kilometer (17 miles) upstream of the Hyperion Wastewater Reclamation Plant (HWRP). The OPF will separate food waste and other digestible organics from non-processable and non-digestible materials to create an organic food waste slurry. The combined waste stream (existing municipal wastewater and food waste slurry) will be treated at HWRP with a portion of the waste converted into renewable energy via anaerobic digestion. This study examines (1) the food waste characteristics and (2) predicts impacts to the conveyance system and the influent wastewater quality to HWRP.To determine the impacts, the volumes and constituents, including the physical, chemical, and biochemical characteristics of the food waste slurry relevant to process analysis, are defined. Physical-chemical characteristics of the food waste slurry, as well as its biochemical characteristics are detailed based on available technical literature. Sewer process modeling using the Interceptor-powered-by-WATS model is undertaken to predict the impact of the food waste on the HWRP influent water quality and the wastewater conveyance, including sewer ventilation odor treatment systems. The sewer model covers microbial and chemical transformation processes in the conveyance system network related to relevant process parameters such as organic matter, pH and sulfurous compounds under aerobic, anoxic, and anaerobic conditions.The impacts to the HWRP influent key constituent characteristics are estimated. This includes an approximation of changes to the properties of the food waste slurry within the conveyance system prior to reaching the HWRP. The impact of the additional food waste to the wastewater conveyance system on the existing sewer ventilation odor treatment systems are also estimated. Limitations relative to prediction of waste characteristics and the potential impacts of the additional food waste are noted, with some recommendations provided for further verification and/or analyses.