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

来自反渗透和纳滤厂的二级工业废水(例如炼油厂和纸浆造纸厂的废水)和膜浓缩物(包括被膜阻挡的污染物、清洗液和反冲洗水)中的大多数污染物都是溶解的，有些还含有有毒化合物。目前，大多数膜厂直接将浓缩物排放到地表水或卫生下水道。为了去除溶解的固体物质，需要采用多级预处理工艺进行深度处理，而蒸发或焚烧往往是一些废水残渣/污泥体积减少和处置的唯一选择。与这些先进治疗方案相关的高昂的运营和资本成本以及复杂的操作限制了它们的实际应用。冷冻浓缩因其独特的去除溶解杂质、减少废物体积、无需添加任何化学物质和进行前处理、回收纯净水等优点，在这些领域具有很大的应用潜力。与传统的悬浮结晶法不同，渐进式冷冻浓缩(PFC)需要简化的操作系统将冰晶从给水中分离出来，从而大大降低了工艺成本。然而，目前还没有对PFC的浓缩效率机理进行系统的研究，也没有关于PFC污水处理工艺的工程设计资料。通过本研究项目，将进行以下实验室实验：(1)考察选定的废水和膜浓缩物的冻结特性及其对PFC的影响；(2)确定PFC的除杂效率、毒性降低和减容能力；(3)考察机械搅拌、功率超声波对杂质去除和减少废物体积的效果；(4)考察PFC去除微生物的益处；以及(5)研究冰中杂质的分布。本研究的结果可望对PFC分离杂质的机理和污水处理PFC系统的优化设计提供新的见解。

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.