Water Desalination & RO

Introduction Environmental changes, global warming, and inappropriate planning are two sides of the worldwide water shortage coin. Figure 1 shows the status of different countries based on water-stressed scenario. Based on United Nations report, more than 2 billion people will experience water scarcity by 2050. All the previous projections show the vitality of drinking water production and desalination technologies. Currently, there exist two main commercial water-treatment process classes including thermal-based processes (including multistage flash distillation (MSF), vapor compression (VC), and multieffect distillation (MED)) and membrane filtration processes (including reverse osmosis (RO), nanofiltration (NF), and related energy recovery devices (ERD)). Thermal processes were more common previously. However, membrane technologies are outweighing the older processes. Main reasons for RO desalination process growth have mentioned to be rapid technical advances along with its simplicity and elegance. Despite all advances in the field, fouling in its different types (colloidal matters, organic fouling of natural and synthetic chemicals, inorganic fouling (scaling), and biological fouling (biofouling)) is the remaining issue of industrial membrane processes. Various types of fouling will result in feed pressure increment and higher operational costs, more frequent requirement of chemical cleaning of the modules and shortened lifetime of the membranes. Fouling types happen simultaneously and could affect each other. This is while biofouling is identified as the critical issue as it is imposed to the membrane surface by living and dynamic microbiological cells and viruses. As the biological attachment, division of the cells and colonization on the surface occurs, the microbiological species and the exopolymeric substance produced by them, create resistance to antimicrobial treatments and the resulted biofouling starts to impose bio-corrosion and lowering the performance of the system. Exposure of the membrane systems to feed’s biological contamination highly depends on the environmental factors of the feed itself (nutrient content, available biological species, temperature, light, turbidity, and currents (tides and waves)).

Executive summary   Water demand is increasing worldwide as a result of growing populations and rising standards of living. Further, increasing climate variability is disrupting historical patterns of precipitation and water storage. While conservation and reuse efforts have helped to moderate the demand for new freshwater resources in some locations, desalination technology is increasingly being used to meet demand worldwide. Currently installed capacity is almost 90 million m3/day (90 billion liters per day) of desalinated water, a value that has been growing rapidly, with growth projected at 12% over the next five years. Energy consumption is the major cost of desalination, accounting for more than 1/3 of the cost of water in modern plants, and energy use also represents the major environmental impact of desalination. Thus, de-salination using low-cost energy sources that have low greenhouse gas emissions is highly desirable. During 17-18 October 2016, MIT brought together an international panel of experts from academia, industry, and government for a workshop on driving down the carbon footprint of desalination systems. Organized at the request of the Global Clean Water Desalination Alliance and sponsored by MIT Abdul Latif Jameel World Water and Food Security Laboratory1 , the workshop produced this report. Participants in the workshop contributed prewritten material on research and development needs that they regarded as critical to the reduction of the global warming potential (GWP) of desalination. These inputs form the bulk of this report. The workshop itself was devoted to a vigorous and wide-ranging discussion of the opportunities and priorities for powering desalination systems with low-carbon energy in the context of current and emerging trends in desalination and energy production. The report summarizes the experts’ assessment of available technologies and their recommendations for research, development, and demonstration (RD&D) of low carbon desalination. A major conclusion of this workshop is that currently available energy and desalination technologies can be effectively combined to reduce desalination’s GWP in the near term. This report was produced on a compressed timetable, with the aim of having results to share at COP22 in Marrakech, Morocco on 16 November 2016. A more in depth study is planned as a follow on to this initial effort.