Water. desalination + reuse

RESEARCH | 32 | Desalination & Water Reuse | February-March 2014 Completion of the second phase of the joint evaluation of membrane distillation technology by Qatar's ConocoPhillips Global Water Sustainability Center, Qatar Electricity & Water Co (QEWC) and Qatar University was celebrated on 27 November 2013. The research project (see D&WR feature August/September 2013) aims to prove that quality freshwater can be produced from brines discharged from thermal desalination plants using low-grade waste heat from industry and/or renewable sources. The Membrane Distillation Field Demonstration project started in October 2011 and was hosted in the Chemical Engineering Department. The technology uses less energy, has a lower environmental impact and is less costly than conventional methods for desalinating high salinity brines. In collaboration with QEWC, Phase 2 saw the units operating at the Ras Abu Fontas power and desalination plant to evaluate the process under industrial conditions. A waste-heat audit was conducted to identify opportunities whereby the energy needed by MD could be obtained from sources within two Qatari desalination facilities. Phase 2 of Qatar's MD research concluded About 15% of all domestic wells in Texas, USA, are at risk due to high salinity, according to a recent Texas A&M AgriLife Research study. The study Temporal Evolution of Depth-stratified Groundwater Salinity in Municipal Wells in the Major Aquifers in Texas was completed using the Texas Water Development Board's groundwater quality database for the period 1960-2010. Dr Srinivasulu Ale, AgriLife Research geospatial hydrology assistant professor, and Dr Sriroop Chaudhuri, his post- doctoral research associate, have had their study paper accepted for publication in Science of the Total Environment journal. Groundwater withdrawal accounts for about 36% of Texas' municipal water supplies, according to Ale. However, many water quality issues have been reported from around the state, raising serious concerns over groundwater use due to a rise in concentration of sulfates, chlorides, fl uorides, nitrates and total dissolved solids (TDS). TDS is a collective manifestation of all dissolved chemicals and is considered a measure of salinity and an overall indicator of water quality, relating to taste and palatability, he said. Previous hydrogeologic investigations of aquifers in Texas have also examined groundwater salinity, Ale said, but lacked depth-stratifi ed long-term evaluation of groundwater salinization with specifi c reference to potable use. The objective of this study was to offer a qualitative overview of the spatial, both horizontal and vertical, and temporal extent of groundwater salinization in light of regional differences in hydrochemical processes, or changes to the ambient water composition. "We identifi ed hot spots of groundwater salinization at shallow depths across vast regions of West Texas in the southern Ogallala, northwestern Edwards-Trinity and Pecos Valley aquifers; intermediate and deep depths in the southern Gulf Coast aquifer; and deep depths in North Central Texas in the Trinity region," Ale said. For both time periods, the highest average groundwater TDS concentrations in shallow wells were found in the Ogallala and Pecos Valley aquifers, and those in the deep wells were in the Trinity aquifer, he said. In the Ogallala, Pecos Valley, Seymour and Gulf Coast aquifers, about 60% of the observations from shallow wells exceeded the secondary maximum contaminant level for TDS in both time periods, which indicates persistent concern over potable water quality, Chaudhuri said. In the Trinity aquifer, 72% of deep water quality observations exceeded the secondary maximum contaminant level in the 1990s-2000s, compared to 64% observations in the 1960s-1970s, he said. Study fi nds salinity risk to Texas groundwater A study has just been published in Australia on development of a holistic framework for rigorous assessment of the economics of non-potable recycled water schemes, including residential, industrial, municipal and agricultural schemes. Supported by funding from the Australian Water Recycling Centre of Excellence, the study Economic viability of recycled water schemes was carried out by Marsden Jacob Associates. The report found that many water reuse schemes use a variety of limited assessment methods for their costing and planning decisions. Economic and commercial benefi ts are often inappropriately estimated and poorly delineated between parties, rendering the economic case for investment in recycled water projects diffi cult to establish in advance and to determine in hindsight. To remedy these defi ciencies, the report describes a general methodology for assessing both use and non-use values, and identifi es the most prominent costs and benefi ts that apply across all non-potable recycled water schemes. In addition to the general costs and benefi ts, the framework allows for the inclusion of other costs and benefi ts specifi c to each project. Looking at barriers to implementation of projects, the project says that the team's primary feedback was that the greatest impediments were cost-effectiveness and commercial risk. The report makes recommendations to smooth the process and to reduce the risk. Australian study looks at reuse scheme economics

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