Google analytics tag

Showing posts with label Seawater deslination. Show all posts
Showing posts with label Seawater deslination. Show all posts

Wednesday, February 12, 2014

Desalination plants contribute to climate change

There is a growing evidence that shows increasing salinity of seawater effects the “water cycle” resulting in climate change. Apart from the natural cycle, the highly saline brine discharged from man-made “desalination” plants around the world also contributes to the increasing salinity of seawater. There are only few desalination plants suppliers world-wide who build such large scale desalination plants and they use only decades old desalination technologies. They recover 35% of fresh water and discharge 65% highly concentrated, toxic effluent back into the sea. Their main focus of innovation is to reduce the energy consumption because it is an energy intensive process. Such energy comes mainly from fossil fuels. The result is unabated Carbon emission, toxic brine discharge into the ocean, warm saline water discharge into the ocean from “once through cooling towers” from co-located power and desalination plants.Currently about 5000 million cubic meters of fresh water is generated per year from seawater desalination plants around the world; this capacity is expected to increase to 9000 million cubic meter per year by 2030.The brine outfall from desalination plants will amount to a staggering 30 billion cubic meters/yr. Such a huge volume of saline water with salinity ranging 70,000 ppm up to 95,000 ppm will certainly alter the water chemistry of the ocean. Desalination plant suppliers are not interested in “innovation” that can recover fresh water without “polluting” the sea. They rather justify using “environmental impact study” which invariably concludes there is absolutely no impact on environment and any toxic discharge into the sea is “harmless”. This practice is going on for decades without any check. Dwindling fish population world–wide is a direct impact of such discharge. Financial institutions such as world bank, Asian development bank etc are willingly finance such projects without questioning such technologies and their impact on marine environment. Their focus is only “return on investment”–the only criteria that is required for funding and not the “cost and benefit analysis”. A detailed analysis will reveal “handful of rich and powerful” Governments and individuals can influence the world’s climate intentionally or unintentionally. The same “rich and powerful” can shun any innovations “that might threaten their business model” and “ nip such innovations or inventions at their bud” because they simply do not believe in Research and Development or unwilling to direct their “cash flow” into R&D because they do not want any threat for their existing technologies. There are very few financial professionals who can think “outside the box” or predict their financial impact due to innovative technologies of the future. Their financial decisions reflect the sentiments of the financial institutions, namely “the return on investment”. “When you read about human-induced climate change it's often about melting glaciers and sea ice, increasing frequency of heat waves and powerful storms. Occasionally you'll hear about the acidification of the oceans too. What you don't often hear about is the saltiness of the seas. But according to a new piece of research just published inGeophysical Research Letters that is changing too. The saltiness, or salinity, of the oceans is controlled by how much water is entering the oceans from rivers and rain versus how much is evaporating, known as 'The Water Cycle'. The more sunshine and heat there is, the more water can evaporate, leaving the salts behind in higher concentrations in some places. Over time, those changes spread out as water moves, changing the salinity profiles of the oceans. Oceanographers from Scripps Institution of Oceanography and Lawrence Livermore National Laboratory fingerprinted salinity changes from 1955 to 2004 from 60 degrees south latitude to 60 degrees north latitude and down to the depth of 700 meters in the Atlantic, Pacific and Indian oceans. They found salinity changes that matched what they expected from such natural changes as El NiƱo or volcanic eruptions (the latter can lower evaporation by shading and cooling the atmosphere). Next the ocean data was compared to 11,000 years of ocean data generated by simulations from 20 of the latest global climate models. When they did that they found that the changes seen in the oceans matched those that would be expected from human forcing of the climate. When they combined temperature changes with the salinity, the human imprint is even clearer, they reported. "These results add to the evidence that human forcing of the climate is already taking place, and already changing the climate in ways that will have a profound impact on people throughout the world in coming decades," the oceanographers conclude.” (Ref: Larry O'Hanlon, Discovery News) SALINITY Although everyone knows that seawater is salty, few know that even small variations in ocean surface salinity (i.e., concentration of dissolved salts) can have dramatic effects on the water cycle and ocean circulation. Throughout Earth's history, certain processes have served to make the ocean salty. The weathering of rocks delivers minerals, including salt, into the ocean. Evaporation of ocean water and formation of sea ice both increase the salinity of the ocean. However these "salinity raising" factors are continually counterbalanced by processes that decrease salinity such as the continuous input of fresh water from rivers, precipitation of rain and snow, and melting of ice. SALINITY & THE WATER CYCLE Understanding why the sea is salty begins with knowing how water cycles among the ocean's physical states: liquid, vapor, and ice. As a liquid, water dissolves rocks and sediments and reacts with emissions from volcanoes and hydrothermal vents. This creates a complex solution of mineral salts in our ocean basins. Conversely, in other states such as vapor and ice, water and salt are incompatible: water vapor and ice are essentially salt free. Since 86% of global evaporation and 78% of global precipitation occur over the ocean, ocean surface salinity is the key variable for understanding how fresh water input and output affects ocean dynamics. By tracking ocean surface salinity we can directly monitor variations in the water cycle: land runoff, sea ice freezing and melting, and evaporation and precipitation over the oceans. SALINITY, OCEAN CIRCULATION & CLIMATE Surface winds drive currents in the upper ocean. Deep below the surface, however, ocean circulation is primarily driven by changes in seawater density, which is determined by salinity and temperature. In some regions such as the North Atlantic near Greenland, cooled high-salinity surface waters can become dense enough to sink to great depths. The 'Global Conveyor Belt' visualization (below) shows a simplified model of how this type of circulation would work as an interconnected system. The ocean stores more heat in the uppermost three (3) meters than the entire atmosphere. Thus density-controlled circulation is key to transporting heat in the ocean and maintaining Earth's climate. Excess heat associated with the increase in global temperature during the last century is being absorbed and moved by the ocean. In addition, studies suggest that seawater is becoming fresher in high latitudes and tropical areas dominated by rain, while in sub-tropical high evaporation regions, waters are getting saltier. Such changes in the water cycle could significantly impact not only ocean circulation but also the climate in which we live." (Ref: NASA earth science) The four main forces that control the earth’s climate are “Sea, Sun, Moon and earth’s rotation and interference by human beings will alter the equilibrium of the system. In order to maintain its equilibrium, Nature is forced to change the climate unpredictably with devastating effects. We cannot underestimate the pollution caused by human beings because they are capable of altering the Nature’s equilibrium over a period of time no matter how “miniscule” (parts per millions or billions) the pollution may be. Any future investment on large scale infrastructures should take into account the “human induced climate change” in their model and projections, failing which “climate change” will prove them wrong and the consequences will be dire. Reference : Environmental Impacts of Seawater Desalination: Arabian Gulf Case Study Mohamed A. Dawoud1 and Mohamed M. Al Mulla 1 Water Resources Department, Environment Agency, Abu Dhabi, United Arab Emirates 2.Ministry of Environment and Water, Dubai, United Arab Emirates

Thursday, December 6, 2012

Innovative desalination technology

Seawater desalination is a technology that provides drinking water for millions of people around the world. With increasing industrialization and water usage and lack of recycling or reuse, the demand for fresh water is increasing at the fastest rate. Industries such as power plants use bulk of water for cooling purpose and chemical industries use water for their processing. Agriculture is also a major user of water and countries like India exploit ground water for this purpose. To supplement fresh water, Governments and industries in many parts of the world are now turning to desalinated seawater as a potential source of fresh water. However, desalination of seawater to generate fresh water is an expensive option, due to its large energy usage. However, due to frequent failure of monsoon rains and uncertainties and changing weather pattern due to global warming, seawater desalinations is becoming a potential source of fresh water, despite its cost and environmental issues. Seawater desalination technology has not undergone any major changes during the past three decades. Reverse osmosis is currently the most sought after technology for desalination due to increasing efficiencies of the membranes and energy saving devices. In spite of all these improvements the biggest problem with desalination technologies is still the rate of recovery of fresh water. The best recovery in SWRO plants is about 50% of the input water. Higher recoveries create additional problems such as scaling, higher energy requirements and O&M issues and many suppliers would like to restrict the recoveries to 35%, especially when they have to guarantee the life of membranes and the plant. Seawater is nothing but fresh water with large quantities of dissolved salts. The concentration of total dissolved salts in seawater is about 35,000mgs/lit. Chemical industries such as Caustic soda and Soda ash plants use salt as the basic raw material. Salt is the backbone of chemical industries and number of downstream chemicals are manufactured from salt. Seawater is the major source of salt and most of these chemical industries make their own salt using solar evaporation of seawater using traditional methods with salt pans. Large area of land is required for this purpose and solar evaporation is a slow process and it takes months together to convert seawater into salt. It is also labor intensive under harsh conditions. The author of this article has developed an innovative technology to generate fresh water as well as salt brine suitable for Caustic soda and Soda ash production. By using this novel process, one is able to recover almost 70% fresh water against only 40% fresh water recovered using conventional SWRO process, and also recover about 7- 9% saturated brine simultaneously. Chemical industries currently producing salt using solar evaporation are unable to meet their demand or expand their production due to lack of salt. The price of salt is steadily increasing due to supply demand gap and also due to uncertainties in weather pattern due to global warming. This result in increased cost of production and many small and medium producers of these chemicals are unable to compete with large industries. Moreover, countries like Australia who have vast arid land can produce large quantities of salt with mechanized process competitively; Australia is currently exporting salt to countries like Japan, while countries like India and China are unable to compete in the international market with their age old salt pans using manual labor. In solar evaporation the water is simply evaporated. Currently these chemical industries use the solar salt which contains a number of impurities, and it requires an elaborate purification process. Moreover the salt can be used as a raw material only in the form of saturated brine without any impurities. Any impurity is detrimental to the Electrolytic process where the salt brine is converted into Caustic soda and Soda ash. Chemical industries use deionized water to dissolve solar salt to make saturated brine and then purify them using number of chemicals before it can be used as a raw material for the production of Caustic soda or Soda ash. The cost of such purified brine is many times costlier than the raw salt. This in turn increase the cost of chemicals produced. In this new process, seawater is pumped into the system where it is separated into 70% fresh water meeting WHO specifications for drinking purpose, and 7-10% saturated pure brine suitable for production of caustic soda and Soda ash. These chemical industries also use large quantities of process water for various purposes and they can use the above 70% water in their process. Only 15-20% of unutilized seawater is discharged back into the sea in this process, compared to 65% toxic discharge from convention desalination plants. This new technology is efficient and environmentally friendly and generates value added brine as a by-product. It is a win situation for the industries and the environment. The technology has been recently patented and is available for licensing on a non-exclusive or exclusive basis. The advantage of this technology is any Caustic soda or Soda ash plant located near the seashore can produce their salt brine directly from seawater without stock piling solar salt for months together or transporting over a long distance or importing from overseas. Government and industries can join together to set up such plants where Governments can buy water for distribution and industries can use salt brine as raw material for their chemical production. Setting up a desalination plants only for supplying drinking water to the public is not a smart way to reduce the cost of drinking water. For example, the Victorian Government in Australia has set up a large desalination plant to supply drinking water. This plant was set up by a foreign company on BOOT (build, own and operate basis) and water is sold to the Government on ‘take or pay’ basis. Currently the water storage level at catchment area is nearly 80% of its capacity and the Government is unlikely to use desalinated water for some years to come. However, the Government is legally bound by a contract to buy water or pay the contracted value, even if Government does not require water. Such contracts can be avoided in the future by Governments by joining with industries who require salt brine 24x7 throughout the year, thus mitigating the risk involved by expensive legal contracts.