Progressive freeze concentration for wastewater treatment: dissolved solids removal and waste volume reduction

点击翻译按钮获取中文摘要

Most contaminants in secondary industrial effluents (for example, effluents from petroleum refineries and pulp and paper mills) and membrane concentrate (which includes the contaminants blocked by the membranes, cleaning solutions and backwash water) from reverse osmosis and nanofiltration plants are in the dissolved form, some also contain toxic compounds. Currently, most membrane plants directly discharge the concentrate into surface water or sanitary sewers. Advanced treatment with multiple stage pretreatment processes is required to remove dissolved solids and evaporation or incineration is often the only choice for some wastewater residue/sludge volume reduction and disposal. High operating and capital cost and complex operations associated with these advanced treatment options limit their practical applications. Freeze concentration, due to its unique ability to remove dissolved impurities, reduce waste volume without addition of any chemicals and pretreatment, also recover a pure water stream, has great application potentials in these areas. Unlike the conventional suspension crystallization method, progressive freeze concentration (PFC) requires simplified operating system for separation of ice crystals from the feed water, thus can substantially reduce the process cost. However, no systematic investigation has yet been carried out on the mechanism of concentration efficiency in PFC and little information is available for engineering design of PFC processes for wastewater treatment. Laboratory experiments will be undertaken through this research program to: (1) investigate the freezing characteristics of selected wastewaters and membrane concentrate and their influence on PFC, (2) determine the impurity removal efficiency, toxicity reduction, and the capacity of volume reduction by PFC, (3) examine the effect of mechanical agitation, power ultrasound on impurity removal and waste volume reduction, (4) investigate the benefits of PFC on removal of microorganisms, and (5) study impurity distribution in ice. The results of this study are expected to provide new insight into the mechanisms of impurity separation by PFC and better design of the PFC systems for wastewater treatment.