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

反渗透和纳米过滤工厂的二级工业废水（例如，炼油厂和纸浆和造纸米尔斯的废水）和膜浓缩物（包括被膜阻挡的污染物，清洁溶液和废水）中的大多数污染物都是溶解形式，有些还含有有毒化合物。目前，大多数膜设备直接将浓缩物排放到地表水或卫生下水道中。需要采用多级预处理工艺进行深度处理，以去除溶解的固体，蒸发或焚烧通常是减少和处置某些废水残留物/污泥体积的唯一选择。与这些高级处理方案相关的高运营和资本成本以及复杂的操作限制了它们的实际应用。冷冻浓缩由于其独特的去除溶解杂质、减少废物体积、不添加任何化学品和预处理、回收纯净水的能力，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，渐进冷冻浓缩（PFC）需要简化从给水中分离冰晶的操作系统，从而可以大幅降低工艺成本。然而，目前还没有系统的研究，在PFC的浓缩效率的机制和PFC工艺用于污水处理的工程设计的信息很少。实验室实验将通过本研究计划进行：（1）考察了所选废水和膜浓缩液的冷冻特性及其对PFC的影响，（2）测定了PFC的除杂效率、毒性降低和体积减少能力，（3）考察了机械搅拌、功率超声对除杂和废物体积减少的影响，（4）考察PFC对微生物的去除效果;（5）研究冰中杂质的分布。本研究的结果有望提供新的见解杂质分离的PFC和更好的设计PFC系统的废水处理的机制。

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.