如何利用新技术的推动下循环用水增长

June 26, 2014

这个故事最初出现在Yale360and is reprinted with permission.

A ferry plows along San Francisco Bay, trailing a tail of churned up salt, sand and sludge and further fouling the already murky liquid that John Webley intends to turn into drinking water. But Webley, CEO of a Bay Area start-up working on a new, energy-skimping desalination system, isn’t perturbed.

“Look at the color of this intake,” he says, pointing to a tube feeding brown fluid into a device the size of a home furnace. There, through a process called forward osmosis, a novel solution the company developed pulls water molecules across a membrane, leaving salt and impurities behind. When low temperature heat is applied, the bioengineered solution separates out like oil, allowing clean water to be siphoned off.

这种方法使用不到四分之一的电工实习icity needed for standard desalination, making it easier for the technology to run on renewable power, said Webley. His company,特雷维系统, recently won an international low-energy desalination competition and is building a pilot solar plant to desalinate seawater in the United Arab Emirates.

With world water demands rising and extreme droughts like the one now gripping California expected to grow more frequent and widespread as the climate warms, drawing fresh water from oceans and other salty sources will be increasingly important.

“Eventually, we’ll have to develop new sources of water,” said David Sedlak, a University of California-Berkeley professor of civil and environmental engineering and author of“水4.0：过去，现在和未来世界上最重要资源。”海水淡化，与废水回收和捕获和储存雨水一起，将“三大支柱”，他说，以取代“那将会变得不那么可靠，在未来的较少的可用水源。”

However, desalination is expensive, energy-intensive and can damage marine ecosystems. Moreover, while seawater accounts for 60 percent of desalinated water today, Sedlak and others say it’s much more practical and sustainable to desalinate less-salty brackish water and use the technology to recycle wastewater. So companies around the world are working on new technologies that cut desalination costs, reduce environmental impacts and broaden its applications.

除了从海水除盐技术，如许愿也可以在经济上净化含盐地下水，废液工业废水和其他形式。这包括下水道淡化水回灌到地下含水层，它不久将开始做了很大的在南加州城市水区。

“那有什么特别有趣的 - 我们可以真正运行的，真正的脏水，”韦伯利说。“如果你真的应该与这件事开始，让我再次挤压的一切，我们可以重新使用了，然后开始谈论其他的选择。”

17000多个海水淡化厂在150个国家开展业务的全球，这可能会接近2020年增加一倍的容量，根据United Nations World Water Development Report 2014。海水淡化产生水，每天21个十亿加仑根据International Desalination Association，提供在干旱地区，如中东和澳大利亚的关键水源。主要的新的海水淡化设施，在工程China,Chile和其他地方。

然而，目前的标准技术，反渗透 - 在这种高压通过半透膜泵力水排除盐和杂质 - 使用大量的能量和对环境的影响丰厚。这些效应包括对水生生态系统，如在鱼卵与其摄取水吸入损害;使用刺激性的化学品清洁膜和释放大量高咸卤液放回水中。成本各不相同，但最低价格从反渗透装置脱盐海水大约是$ 750英亩 - 英尺（325851加仑） - 的两倍以上地下水的平均成本。

Engineers and entrepreneurs across the globe are now trying to devise greener desalination. Some are inventing new alternatives to traditional reverse osmosis. Among them: Israel, whose own dependence on desalinated water has made it a world leader in the process, has come out with several state-of-the-art technologies, including a novel “semi-batch” reverse osmosis process developed by Desalitech that shrinks energy and brine, and a chemical-free “plant in a box,” produced byIDE技术; and Memsys, of Singapore and Germany, is working on hybrid-thermal membrane technology that is energy-efficient enough to run on solar power.

In the U.S., water-strapped California leads in both innovations and needs. The largest seawater desalination plant in the Western Hemisphere, a $1 billion state-of-the-art reverse osmosis facility being built near San Diego, is set to begin producing 54 million gallons a day — supplying water to 300,000 residents — in early 2016. At least 15 other desalination plants on the West Coast are in some stage of planning, and some small ones are already operating.

But residents’ concerns about the expense and environmental impacts like chemical use and brine disposal problems have slowed down and even halted some recent projects.

“Desalination is a really a hot button issue in California — a lot of people oppose it,” said Aaron Mandell, co-founder and chairman ofWater FX。

Mandell hopes to quell those concerns with his company’s new process using large parabolic mirrors to collect and concentrate the sun’s energy. Inside this solar still, pure water evaporates, while solids remain behind. The system is being tested by a water district in California’s agricultural Central Valley, cleaning irrigation runoff tainted with salts leached from the soil. The demonstration is producing about 14,000 gallons of fresh water a day — a welcome boon to local farmers who received no water from federal allotments this year. The company plans to expand and boost production to 2 million gallons a day early next year.

Mandell points out that his salt byproduct is dry and can be mined for useful chemicals, rather than winding up with hazardous brine that’s costly to discard. What’s more, water districts and farms otherwise have to fallow land and lose income to dispose of the brackish effluent now being recycled into new water for crops.

“我们看到了机会costing quite a lot of money as a waste product and turn it into something of value,” he said. “In essence, we are tackling both sides of the water problem ... disposal and re-use.

“我们的一个最大的挑战是，我们正在处理大量的农业企业仍然排序祈雨的。很多农民都真正依靠这些季节性的水循环。所以，让人们不同的角度思考气候变化，而不仅仅是季节性干旱绝对是一个挑战。”

Researchers at Lawrence Livermore National Laboratory and Stanford University are working on a new desalinating method using porous carbon aerogel electrodes. The system, which they callflow-through electrode capacitive desalination, or FTE-CD, removes salt electrically. Although still in the early stages, its developers say the technique requires little equipment or energy, and the system could be scaled to fit any need: from portable personal devices to city water treatment.

“在像加利福尼亚州，那里是含盐地下水在大量的地方，FTE-CD可以在比海水脱盐的潜在低得多的成本提供饮用水可以实现的，”共同开发迈克尔Stadermann，在劳伦斯·利弗莫尔物理化学家说。“对于淡化苦咸水，我们预测，这个方法可能高达五倍的能量比反渗透高效。”

One of the hottest new technologies on the bench in laboratories in the U.K., Saudi Arabia and South Korea and elsewhere is one-atom thick, perforated graphene membranes that can cut reverse osmosis desalination to a fraction of its current cost. Developed at the Massachusetts Institute of Technology, the membrane’s pores can be tuned to optimize permeability. The hang-up for now is how to mass-produce the material.

对于城市用水需求，即使是那些对替代方法的工作说反渗透（RO）可能仍将是可预见的未来的首选。

“You can talk about some of the other technologies, and I work on some of them,” said Menachem Elimelech, professor of environmental and chemical engineering at Yale University and director of Yale’s Environmental Engineering Program, “but if you need to produce water for the drinking water supply, I still think RO is the gold standard.”

Reverse osmosis has become much more energy-efficient in recent years, and is now near its maximum, Elimelech said. Still, he and others are trying to make further gains by improving membranes. One of the biggest problems is fouling — biofilms that grow on membranes over time, making pumps work harder to force water through. Elimelech is working with nanotechnology to make bacteria-resistant membranes.

回收能量的新方法也划破膜抽水所需的电力。生产厂家能量回收公司。估计被安装在新的圣地亚哥地区反渗透装置的活塞式压力器将节省115千瓦小时的电力，每年 - 相当于保持超过45000吨导致气候变暖的二氧化碳从空气中。

Even so, desalinated water produced by the new plant will cost the San Diego County water district around $2,000 an acre-foot — twice as much as it currently pays for freshwater shipped in from the Colorado River and San Joaquin River Delta. Those sources, however, are over-tapped and growing increasingly unreliable, leaving residents of a county with scarce water resources to feel they have few other options.

世界上很多有一天可能会觉得同样的紧要关头，将干旱防爆供水无价在炎热的未来。但现在，许多专家说，而新兴技术正在淡化以往任何时候都更可行，经济和环境成本仍然过高。

“There are technologies available to minimize and in some cases eliminate some of the environmental impacts,” said Heather Cooley, director of the water program at the太平洋研究所在奥克兰，加利福尼亚州的非营利性研究机构埋葬取水口，例如，保持海洋生物出来，扩散器可淡盐水更安全的水平。至于“其他环境影响：能源使用和所产生的温室气体排放，”库里说，技术进步降低了两个，但问题仍然存在，“其他可用的选择吗？”