Impurity separation efficiency of multi-component wastewater in a pilot-scale freeze crystallizer

Abstract

New directions in wastewater treatment consider not only the adequate purification efficiencies but also water and material recovery for recycling and reuse. Freeze crystallization offers the potential for the simultaneous separation of water (ice) and material (i.e., salts and nutrients) from wastewater using a single wastewater purification process. However, the impurity-separation performance of freeze crystallization applied to multi-component wastewaters is still unclear, particularly for industrial or municipal scales. In this study, a prototype was developed to demonstrate the application of freeze crystallization to wastewater purification on the industrial scale. This freeze crystallizer, a 120 L jacketed vessel equipped with stirring and ice scraping mechanisms, produced relatively large (500 µm) ice crystals, primarily in water suspension. To evaluate the purification efficiencies of the prototype system, a comprehensive number of water-quality indicators were measured following the purification of highly concentrated landfill leachates. The prototype system achieved a >95% average impurity removal efficiency for both organic and inorganic matter, including heavy metals. This excellent separation ability, given the variety of impurities present in the leachates, shows the non-selective nature of freeze separation for wastewater treatment. These outcomes represent an important step forward in scaling up and developing the full scale freeze purification process for wastewaters.