EXPANSION OF CO-DIGESTION AT LETHBRIDGE ALBERTA

The City of Lethbridge, Canada currently co-digests corn squeezing residuals with wastewater solids in their anaerobic digester system. All of the corn squeezing waste is collected and fed to the digesters over a three month period. The addition of the corn squeezing waste increases the amount of biogas produced by 16,000 m3 (5.6 million ft3) per year and generates an additional 32,000 kW*hr of electricity in their cogeneration system.In order to maximize the capacity of the existing anaerobic digesters and cogeneration system, the City of Lethbridge is embarking on a study to expand the co-digestion process with additional waste streams that are being generated around the area. Additional waste streams under consideration are as follows:Cheese whey residualsChicken processingCanola OilAnimal Hide ProcessingPotato WasteThe study being conducted includes feasibility studies and digestibility studies. The on-going feasibility studies will establish the actual amount of organic waste available to Lethbridge by determining the nature and sources of the wastes and assessing the economic and technological practicality of co-digesting these wastes. The final feasibility study will cover the following subjects:Inventory and Characteristics of Organic WastesCollection and Receiving OptionsPre-treatment Options, if requiredResiduals Management IssuesCo-digestion performanceEnergy Analysis: Biogas Production and Electricity GenerationEconomic Evaluation (including grant application)Initial waste characterizations for several wastes have been completed. The University of Lethbridge is conducting research into how some of these wastes behave when co-digested with municipal wastewater solids. Using, the work conducted so far, The City of Lethbridge and CDM have developed a plan for expanding the co-digestion system for Lethbridge. This plan includes further co-digestion studies, to help predict digester gas production and stability as well as develop design criteria that can be used to predict organic waste loading to maximize cogeneration opportunities without affecting digester stability. Initial analyses will be conducted at laboratory scale with demonstration of the most promising co-digestion mixtures conducted at a full-scale.