Comparison of nutrient solubilisation and dewatering by freeze/thaw processing of sludge from Biological Nutrient Removal (BNR) and Non-BNR wastewater treatment plants.

Abstract

Natural freeze/thaw processing is a simple, practical and low-cost solid-liquid separation method, which can effectively dewater wastewater sludge in Northern Canadian communities located in cold climate conditions. This method is especially effective when used in small treatment plants in remote and cold regions as typical dewatering methods require complex and expensive equipment, skilled operators and special maintenance. The objective of this research was to evaluate freeze/thaw processing as a method for dewatering, nutrient solubilisation and organics separation of wastewater sludge originating from two different wastewater treatment facilities: a Biological Nutrient Removal (BNR) plant and non-BNR plant. The results of experiments showed the effectiveness of this method for sludge dewatering and solubilisation of organics and nutrients. The sludge solid content increased approximately 10-fold after freeze/thaw processing. The treatment solubilised 15.2%, 33.5% and 21.5% of the initial total nitrogen, total phosphorus and total chemical oxygen demand, respectively for the non-BNR sludge. These values were 6.3%, 80.0% and 16.5%, respectively for the BNR sludge. The released phosphorus and nitrogen in the water can be recovered and used as fertilizer for agricultural purposes, supporting northern food production.