(655a) Application of Semi-Batch Reverse Osmosis (RO) Operation for Water Purification in Small Communities

Various remote communities around the world are confronted with impaired local water supplies due to both increased salinity and rise in nitrate level. In such communities establishing and maintaining reliable distributed water treatment systems for the production of safe drinking water is a major challenge. Water treatment systems for deployment in remote communities must possess the following attributes: a) provide a physical barrier for reliable contaminant removal, b) high operational flexibility to handle geographical and temporal variability of feed water quality and other operational requirements (e.g., water recovery), c) amenable to process automation, d) compact foot-print capable for fixed or mobile deployment, and e) standardized system configuration (for ease of maintenance and operator training). In this regard, membrane-based (nanofiltration (NF) and low-pressure reverse osmosis (RO)) water treatment is most suitable for meeting the above needs. Accordingly, in the present work, a novel desalination pilot system was developed that can operate in either semi-batch or continuous steady-state mode. This system enabled the generation of fundamental data needed to compare the performance of semi-batch and continuous RO operation with respect to energy consumption as well as attainable recovery. Experimental data were then compared with predictions of RO model for continuous and semi-batch RO. Analysis of the semi-batch process was accomplished considering the influence of axial salt dispersion during the concentrate flushing period. The present study suggests that dispersion within the RO system affects the efficiency of flushing (i.e., removal of excess salt buildup in the RO system during the filtration period), which in turn has a profound impact on the specific energy consumption. It is also shown that, for a given product water recovery, there exists an optimal system flushing rate at which energy optimal performance is attained. Moreover field studies have demonstrated effective field development of the concept of compact semi-batch RO for both salinity reduction and nitrate removal to provide safe drinking water for remote communities.