Designing Systems for Water Security

Introduction Abundance and quality water supply is essential for all living species. Sustainable agriculture and industrial production need steady supply of freshwater. In many parts of the today’s world, desalination plays a vital role for sustaining human habitation besides the existing conventional water treatment technologies. Membrane based RO process has become a popular method to supply the fresh water from seawater and brackish water in different regions. RO (Figure 1) is a pressure driven process which under pressure reverses the flow direction of the solvent (in the opposite direction of osmosis process). Substantial efforts have been made by researchers on freshwater production (Sassi, 2012) and wastewater treatment (Stoller et al., 2016) using the RO. Rapid growth of membrane desalination processes enhanced the removal of ionic contaminants (Sassi and Mujtaba, 2013), pharmaceutical active compounds (Gur-Reznik et al., 2011) and other types of effluents from chemical, petrochemical, electrochemical, food, paper and tanning industries. Demineralised water can be supplied to several industries by treating the saline water using the RO process. However, there are limited studies on the production of demineralised water. Demineralised water is completely free (or almost) of dissolved minerals (Kremser et al. 2006) which has total dissolved solids (TDS) as low as 1 mg/l. Kremser et al. (2006) described operating experience on demineralized water plant. In this work, RO based desalination process is considered using three stages described by (Sassi, 2012) as shown in Figure 1. The plant nominal operating and design parameters (of commercial Film Tec spiral wound RO membrane elements) are taken from Abbas (2005). Firstly, the model prediction is validated against those reported by Sassi and Mujtaba (2010). Secondly, an optimization problem incorporating a process model is formulated to optimize the design and operating parameters in order to minimize specific energy consumption and the results are compared with Sassi (2012). Since those models (Sassi, 2012) are validated for freshwater production, the model parameters such as (water and salt permeability coefficients) needs to be updated for demineralised water. A structure of the RO network is developed based on RO network (two-stage seawater pass and two-stage brackish water pass). Different parameters are updated for the model from the literature.

Introduction: This publication is a revised edition of our Design Criteria for Community Public Water Systems. They have been prepared as a guide to water systems, design engineers, and our own staff. There has been no attempt to address every situation. We also know that there will be occasions when these criteria will not apply. Exceptions will be handled on an individual basis. The Tennessee Safe Drinking Water Act of 1983 requires The Department of Environment & Conservation to: "Exercise general supervision over the construction of public water systems throughout the state. Such general supervision shall include all the features of construction of public water systems which do or may affect the sanitary quality or the quantity of the water supply. No new construction shall be done nor shall any change be made in any public water system until the plans for such new construction or change have been submitted and approved by the department." (Extract of part of Section 68-221-706, Tennessee Code) Where the terms shall and must are used, it is intended to be a mandatory requirement. Other terms such as should, recommend, preferred, and the like, are intended to show desirable equipment, procedures, or methods. We encourage development of new methods and equipment. However, any new developments must be demonstrated to be satisfactory before we can approve their use. Operating data from other installations, or demonstration of the equipment by a manufacturer's representative, or both, may be needed for our review. These criteria are a compilation of information from a number of sources. The principle source, however, is Recommended Standards for Water Works, 1982 Edition. This publication is a report of "The Committee of the Great Lakes Upper Mississippi River Board of State Sanitary Engineers" and is commonly known as Ten-State Standards.