Reverse osmosis environmental remediation. Development and demonstration pilot project

Abstract

More stringent environmental legislation and new or updated water management strategies have been adopted at both federal and local levels to address the growing problem of increasing demand on limited fresh water resources. Competition for access to available fresh water resources is increasing the pressure for sustainable water management practices that emphasize water reuse and recycle, with reduced fresh water withdrawals. In some jurisdictions targets for fresh water withdrawals have been set to zero, demanding innovative new technologies and applications of existing technologies to supplement natural fresh water sources. The serious need for new sources of potable water for human consumption has been widely recognized for some time, leading to a rapidly growing use of reverse osmosis (RO) for seawater desalination as well as significant advances in membrane technology itself. However, it is only in recent years that the implications of limited fresh water availability have begun to be seriously examined in other sectors. The usage of fresh water in the industrial sector has been immense, often leading to large volumes of contaminated waste water to be disposed of. In many instances the predominant contaminant is salt. Past practices in many industries have also left large volumes of salt contaminated surface and sub-surface soils at existing and/or abandoned industrial sites. Rain water or natural ground water flowing through these soils leaches out the salt, threatening fresh water resources. The growing recognition of the potential toxicity of the soil at these sites has led to increased requirements for environmental remediation prior to removing land from industrial usage. This, in turn, has led to increased volumes of salt contaminated waste water that must be disposed of, with a corresponding increase in the difficulty and cost of disposal. More economical, environmentally sound alternatives to current disposal methods must be found. Preliminary design calculations have been performed to establish a suitable configuration for a reverse osmosis environmental remediation system that can address this situation. The key design objectives for the system were to significantly reduce the volume of salt-contaminated leachate from environmental remediation operations that must be disposed of as contaminated waste water, to produce relatively large volumes of clean water at an environmentally acceptable level to allow its reuse or safe return to the environment, and to significantly reduce or eliminate the threat to adjacent fresh water sources. The preliminary analyses carried out to date indicate that these objectives are achievable and that an RO environmental remediation system can provide an economical solution to this problem. RO system design and operation is site specific, depending among other things on feedwater conditions such as salinity, total dissolved solids (TDS), feedwater temperature, silt density index (SDI), etc. In order to progress from theoretical studies to implementation, a pilot project aimed at identifying and establishing system design specifications and requirements at a specific site was undertaken. An existing seawater desalination demonstration rig was modified to operate in a mode suitable for pilot scale developmental testing in an environmental remediation application. The mobile pilot test unit was taken to a remote industrial site currently undergoing environmental remediation. On-site testing was aimed at developing an understanding of the specific limitations and constraints of RO systems operating in such an environment and investigating how those might be most effectively overcome. The pilot plant testing allowed experimental investigation of potential operating modes and system design and operating parameters in order to obtain the necessary data for an informed evaluation of performance vs. cost in setting system design characteristics. The results of the testing are being used to guide the design of an operational system that can be used successfully over the next several years of site remediation.