Ajman University participates in the Third International Conference on Water, Energy and Environment in the American University of Sharjah
AUST has participated in the 3rd International Conference on Water, Energy and Environment, organized by the American University of Sharjah in cooperation with the United Arab Emirates University, during the period 24-26 March 2015, with a scientific paper titled “Environmental Impacts of Water Desalination in the United Arab Emirates: Challenges and Alleviation Measures”.
This scientific paper was prepared by Prof. Zeinelabidin Rizk, Dean of the Institute of Environment, Water and Energy. On Wednesday, 25 March 2015, He co-chaired the afternoon session on “Treated Wastewater” and presented his research paper in the “Desalination and Membranes” session the same day.
Prof. Rizk’s research paper addressed the evolution of water desalination in the UAE, environmental challenges facing water desalination and suggested solutions for alleviating negative environmental impacts of the water desalination industry.
Prof. Zeinelabidin pointed out that the UAE adopted water desalination since early 1970’s in order to bridge the gap between the limited natural water resources and the growing demand for water for different purposes. He indicated that the per capita share of natural water in the UAE is 180 cubic meter (m3) per year, while the United Nations consider the countries where the per capita share of natural water is less than 1,000 m3 per year a water-poor country. He added that this explains why the UAE is the second country in the World in water desalination, producing 14% of the World’s production. In the meantime, the per capita water consumption in the UAE is among the highest in the world (596 liter per day (L/day).
The available water in the UAE in 2008 was 4,549 MCM to which the contributions of different sources were 51.1% (2,326 MCM) groundwater, 36.6% (1,664 MCM) desalinated water and 12.3% (559 MCM) reclaimed water. During 2008, agriculture consumed 93% of groundwater resources, while domestic and industrial sectors consumed 92% of desalinated water. The total groundwater use in the UAE in 2008 was 2,326 MCM and most was used for irrigation. Agriculture used 1,472 MCM (63%) and forestry consumed 694 MCM (30%). Only 112 MCM (5%) of fresh groundwater was utilized for domestic and industrial purposes, and the remaining 48 MCM (2%) was applied for landscaping. The predicted available water resources in the years 2020 and 2025 are 4,717 and 7,134 million cubic meters (MCM), respectively. The predicted water uses area 10,197 and 14,380 MCM during 2020 and 2025, respectively. The water deficit is expected to increase from 5,480 MCM in 2020 to 7,246 MCM in 2025.
Prof. Rizk described the evolution of water desalination industry in the UAE, and indicated that the production of desalination plants increased from 7 MCM in 1973 to 1,825 MCM in 2012. The UAE has 83 desalination plants, mostly located in coastal areas, with a few plants in desert areas. The coastal plants desalinate sea water while desert plants desalt brackish to saline groundwater. The MSF is the dominant desalination method representing 52% in Sharjah, 88% in Abu Dhabi and 99.8% in Dubai. The MED method represents 10% in Abu Dhabi and 30% in Sharjah. The RO desalination is 0.2% in Dubai, 2% in Abu Dhabi and 18% in Sharjah. Abu Dhabi has three experimental solar desalination plants with total production capacity of 648 cubic meters per day (m3/d). Generally, the thermal desalination plants, in operation and under planning, account for 81% of desalination capacity and RO plants account for 19%.
In addition to the problems affecting desalination plants such as scale formation, precipitation, membrane fouling and corrosion, water desalination has been criticized on environmental grounds. The brine discharge from desalination plants to the marine environment causes negative physical, chemical and biological impacts.
The physical impacts arise from the temperature difference between intake water and reject brine. Reject brines are typically 10-15C higher than the ambient seawater temperature, which causes negative impacts on marine ecosystems. Increased temperatures reduce the oxygen solubility in water, and significant decrease in oxygen levels can be toxic for marine species. Temperature change represents a minor problem in hot regions where large annual temperature variations are a natural phenomenon, but significant long-term alterations in seawater temperature can be harmful and result in the death of organisms.
The chemical impacts result from chemicals remaining in the brine after being added during pre-treatment, chlorination and as antiscalants. Desalination plants in the Arabian Gulf region pump out tons of metals, chemicals and chlorine (Cl) into the ocean. Brine discharges contain high levels of Fe, Cr, Ni and Mo. Cl is the most commonly used anti-fouling additive. It reacts with organic compounds in seawater forming a large number of chlorinated and halogenated organic by-products. Eutrophication problems have been observed near the outlets of desalination plants where polyphosphates were used. Antiscalants influence natural processes of Ca2+ and Mg2+ and other divalent metals in the marine environment. Cu compounds settle down and accumulate in the sediments, absorbed by benthic organisms and transfer into the food chain. Cu can be toxic and reduce growth and reproduction at higher concentrations. The discharge of backwash water containing coagulants and suspended material to the seawater without treatment causes intense coloration, increase turbidity and reduce light penetration and bury benthic organisms in the discharge site. The alkaline solutions (pH 11-12) and acidic (pH 2-3) cleaning solutions and their additives are harmful to aquatic life if discharged to surface water without treatment.
The biological impacts in represented by the loss of biota in the intake zone of desalination plants due to impingement and entrainment effects and chlorination process. The high biochemical oxygen demand (BOD) in the reject brine leads to low dissolved oxygen (DO) in seawater adjacent to the brine release area. The salinity of desalination effluents exceeds the natural ocean levels and affects open water organisms and seabed dwellers. High salinity levels around the discharge location of RO plants poses a threat for a variety of marine species. The change in seawater quality and increase of salinity in the vicinity of desalination plants may adversely affect the growth and the health of mangroves, seagrass and corals. The corals are very sensitive to the increase in the seawater temperature, which is already high in the Arabian Gulf. The poor water quality also affects other species such as fish which depends on these biotas. In the environment, both ionized and unionized ammonia occurs. The unionized ammonia (NH3) is very toxic to aquatic species.
For alleviation of the negative environmental impacts of water desalination, Prof. Rizk, suggested recycling of reject brine for production of salts and industrial chemicals, application of solar bond technology, use of renewable energy sources and support of research and development in water desalination area.
Studies in Australia showed that the value of discharged brines is six-times higher than the value gained from the production of potable water. Instead of pollution caused by brine discharge from desalination plants in seawater, brine processing leads to zero brine discharge, increases the value of salt industry and promotes chemical industries around these plants. Characteristics of the rejected brine are dependent on the quality of feed water used, desalination technique, percent recovery and chemical additives used for the process. Instead of pollution associated with disposal of reject brine in marine environment, brine recycling can achieve zero brine discharge, in addition to promotion of salt and chemical industries near desalination plants.
Dubai Electricity and Water Agency (DEWA) has proposed a system for desalination and brine management via a multiple process of desalination coupled with the use of salinity gradient solar ponds. This system eliminates the disposal of reject brine in seawater and reduces the energy derived from fossil fuel through the use of solar ponds. The combined use of RO and MES (Multi-Effect Solar) desalination plants can improve the recovery rate from 40 to 90%. MES desalination plants keep the brine in a closed circle and do not discharge any brine or chemicals into the sea. MES plants may also convert the brine discharge from existing desalination plants into drinking water.
The brine returned to the sea contains valuable salts, including NaCl, Epsom salt (MgSO4.7H2O), KCl, MgCl2, Br and Li salts. Potentially salt may be extracted from the rejected brine. This brine can be converted into higher value products such as caustic soda, NaHCO3, Na2CO3, NH4Cl and MgCl2 sodium cyanide, sodium hypochlorite, polyvinyl chloride, titanium tetrachloride, titanium metal, hydrochloric acid, Epsom salt, potassium, bromine and lithium salts. Brines can also be converted into valuable products for use in: wastewater and sewage treatment, scrubbing sulphur dioxide and sulphur trioxide, making light-weight flame retardant panels and boards, Epsom salt production for horticulture, refractory bricks for industrial furnaces and magnesium metal production. Brines also contain valuable K, Br and Li salts. Br is essential feedstock for many fumigating agents, petroleum products and medicine whereas Li is mostly used in the making of lithium batteries. Brine concentration results in successive precipitation of the least soluble salts, CaCO3 and CaSO4, followed by the production of NaCl and finally Mg and K salts. Salt production from SWRO (seawater reverse osmosis) brine is a lucrative application for the UAE where favorable conditions are represented by: strong solar radiation, very low precipitation, low cost desert land, short and easy transportation to ports and relatively good accessibility to Asian markets, which are large consumers of salt.
Solar pond consists of three main layers. The top layer is cold and has little salt contents, but the bottom layer is hot (70-100°C) and very salty. Separating these two layers is important gradient zone, in which salt content increases with depth. The gradient zone acts as transparent insulator, permitting sunlight to be trapped in the hot bottom layer, from which useful heat is withdrawn, and can be used to run the desalination plant.
Because each km2 of Rub' al Khali receives annual solar energy equals 1.5 million barrel of crude oil, the UAE, since 1984, has constructed three experimental solar desalination plants. These plants desalt seawater and groundwater with a total capacity of 648 m3 per day. The first wind energy desalination plant in the Arabian Gulf and the Middle East was established in 2004 on Sir Bani Yas Island in the UAE. The plant enabled acquiring operational experience and produced energy at competitive prices to solar energy. Pumps operating with wave energy are capable of storing large quantities of sea water to use it for energy generation and water desalination.
Near the end of his presentation, Prof. Zeinelabidin pointed out that that UAE supports national and regional institutes engaged in desalination research with the target of reaching innovative solutions to processes and environmental problems of water desalination. The exchange of knowledge and expertise between the GCC countries is a necessity because the similarity of applied desalination technologies, types of feed water and climatic conditions. The cooperation should include establishment of data banks including desalination data, case studies, expert profiles, publications, workshops, short courses and training activities in water desalination.
During the last six decades, the GCC countries developed practical experience in installation, operation and maintenance of desalination plants. This gives the GCC countries advantages in dealing with desalination problems and promoting excellent practices in the desalination industry.
