Power ultrasonic freezing for membrane concentrate treatment

近年来，由于饮用水需求的增加和无污染水源的减少，膜技术的应用急剧增加。膜过滤，特别是反渗透(RO)和纳滤(NF)是处理非传统水源水的主要技术，如海水、微咸水和再生水的饮用水和非饮用水用途。然而，膜过滤操作会产生大量废水/液体废物，包括废盐水、反冲洗水和膜清洗液。例如，一些反渗透/纳滤膜海水淡化厂的产品水回收率只有30-40%。随着膜设备的不断安装，精矿的处理正成为影响许多膜项目生存能力的主要因素。目前，膜过滤操作产生的大部分浓缩物未经任何处理就排放到地表水或卫生下水道中(除用于清洁废物的某种类型的pH调节外)。在膜过滤过程中，给水中含有的盐类、金属和有机污染物与化学物质和前处理反应副产物一起被浓缩。将海水淡化厂的膜浓缩液排放到海水中被认为是一个安全的选择，但最近的研究表明，海水对浓缩液的稀释可能比预期的要低。继续排放大量未经处理的膜浓缩物可能会对水环境造成严重的不利影响。膜浓缩物的处理变得越来越必要，一些操作可能很快就需要最小化体积，甚至是零液体排放。然而，到目前为止，开发实用的膜浓缩物环境友好管理处理技术的努力还很少。本研究方案为膜处理和减容提供了一种创新的方法。冷冻浓缩是一个物理过程，涉及水的分离结晶和随后的冰的去除。当冷冻浓缩用于净化水或液体废物时，杂质从冰晶中分离出来，并集中在未冷冻的液体中。冷冻浓缩处理具有不加药剂、处理效率高、减废能力强、处理设施腐蚀性小、可从原废液中回收纯净水等优点。功率超声冷冻是一种很有前途的技术，可以显著提高冷冻过程的效率。拟议研究的主要目标是开发一种功率超声冷冻浓缩(PUFC)工艺/装置，可用于新的或现有的OR/NF海水淡化或水/废水处理厂的膜浓缩处理。这项研究的意义在于，它不仅可以为膜浓缩物的处理提供一种有效的技术，而且可以通过从膜浓缩物形成的冰中产生纯水来提高反渗透/纳滤膜过滤厂的产品水回收率。这项研究还将加深我们对超声波对冻结材料的化学、物理和/或生物特性、冰的成核以及水-冰(固)界面中杂质掺入/排斥的影响的认识。基于膜的海水淡化工业、内陆水和废水处理厂，以及所有与冷冻相关的工业过程，如制冷、制药、化工和食品加工，都将从这项研究中受益匪浅。

Application of membrane technologies has increased dramatically in recent years due to increasing demand for drinking water and decreasing unpolluted source water. Membrane filtration, especially, reverse osmosis (RO) and nanofiltration (NF) are the leading technologies for treatment of nontraditional source water such as seawater, brackish groundwater and reclaimed wastewater for potable and nonpotable uses. However, membrane filtration operations generate large volumes of wastewater/liquid waste, including reject-brine, backwash water and membrane cleaning solutions. The product water recovery, for instance, is only 30-40% for some RO/NF membrane based desalination plants. With continued installation of membrane plants, disposal of the concentrate is becoming a major factor affecting the viability of many membrane projects. Currently, most concentrate generated from the membrane filtration operations is discharged into surface water or sanitary sewers without any treatment (except some type of pH adjustment for cleaning wastes). Salts, metals and organic contaminants contained in the feed water become concentrated during membrane filtration processes, along with chemicals and reaction byproducts from pretreatment. Discharging the membrane concentrate of desalination plants into seawater has been considered a safe option but recent studies have shown that the dilution of the concentrate by seawater may be lower than expected. Continue to discharge large volumes of untreated membrane concentrate may result in serious adverse impacts on the aquatic environment. Treatment of membrane concentrate is becoming necessary and volume minimization, even zero-liquid discharge may be soon required for some operations. However, little effort has been made so far to develop practical treatment technologies for environmentally friendly management of membrane concentrate. This research proposal presents an innovative method for membrane treatment and volume reduction. Freeze concentration is a physical process that involves the fractional crystallization of water and subsequent removal of ice. When freeze concentration is used to purify water or liquid waste, impurities are separated from ice crystals and concentrated in the unfrozen liquid. The advantages of freeze concentration treatment include no addition of chemicals, high treatment efficiency, high capacity of waste volume reduction, low corrosion of the treatment facility, and recovery of a pure water stream from the original liquid waste. Power ultrasonic freezing is a promising technology that may significantly improve efficiency of freezing processes. The primary objective of the proposed study is to develop a power ultrasonic freeze concentration (PUFC) process/unit that can be used in new or the existing OR/NF desalination or water/wastewater treatment plants for membrane concentrate treatment. The significance of the proposed research lies in its potential not only to provide an effective technology for membrane concentrate treatment but also to improve the product water recovery rate for the RO/NF membrane filtration plants by generating a pure water stream from the ice formed from membrane concentrate. This research will also advance our knowledge of the effect of ultrasound waves on chemical, physical and/or biological characteristics of freezing materials, ice nucleation and impurity incorporation/rejection in water-ice (solid) interface. The membrane based seawater desalination industry, in-land water and wastewater treatment plants, as well as all freezing related industrial processes such as refrigeration, pharmaceutical, chemical and food processing will greatly benefit from this research.