Understanding fundamental process mechanics of volatile fatty acid production and metabolism in fermentation of primary sludge

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The eutrophication of natural water systems represents a major surface water quality problem and can result from an excess supply of nutrients such as phosphorus and nitrogen which support the proliferation of algae and aquatic plants. Municipalities across Canada are struggling with finding the most cost effective legislated limits for nutrients in municipal wastewater treatment effluents to manage loadings to receiving waters. The provincial government in Alberta is now enforcing Total Daily Maximum loadings (TMDL) limits for the City of Calgary. The concentration limits are no longer suitable and additional TMDL limits have been implemented. This effectively limits the Wastewater treatment plants operated by the City of Calgary to 240 kg/d of Total Phosphorus (TP) discharged into the Bow river. In order for the City to expand based on historical and projected population growth rates, the concentrations of TP has to decrease in their effluents. Although Biologically Enhanced Phosphorus Removal (BEPR) processes have proven to be an effective treatment alternative, their inherent biological nature causes variability in process efficiency and subsequent effluent quality. The demands of stringent effluent quality criteria highlight the need for better process control and optimization to achieve a more consistent and effective level of treatment. The importance of incorporating primary sludge fermenters in the design of BEPH facilities has clearly been demonstrated, particularly in areas with temperate climates with organically weak wastewaters in which stringent effluent phosphorus standards, of below 1 mg/L, must be met. This unit process ferments the complex organic material found in primary sludge to simple carbonaceous compounds, the most important of which are Volatile Fatty Acids (VFA). Optimization of primary sludge fermenter VFA production is a relatively new concept in wastewater treatment. The main objective of this research program is to optimize the production of VFA from the Bonnybrook full scale fermenter systems. The long term objective of this research program is to first elucidate the biochemical pathways employed by microorganisms in fermenting primary sludge and to use this mechanistic information to overcome the limitations imposed by their metabolic systems to inhibit the production of VFA. The development of these new strategies will be used to improve and test the efficacy in a full scale system. This research would not only improve and enhance both the functional nature of the phosphorus removal process but also the reliability to ensure there are no violations of the conditions set out in the City of Calgary’s approval to operate wastewater treatment works.