Posts Tagged ‘water’

Fresh water scarcity will be a thing of the past

April 4, 2017

There is no shortage of water on earth. There is not even a shortage of fresh water resources. However there is a fundamental mismatch between the availability of fresh water and the centres of population. If sea water (or brackish water) can be converted into fresh water at an acceptable energy and economic cost, the problem vanishes.

Excluding the vast amounts of water bound up within rocks in the earth’s core, the fresh water on earth is less than 1% of all the “free” water. (Note also that when humans consume water, the water is not destroyed. Most of it is discharged somewhat contaminated and a small amount is bound up as hydrocarbons. Water “manufactured” by combustion – whether induced by humans or by natural combustion processes – creates water vapour from bound-up hydrogen but the quantities are not very significant).

The UN estimates that by 2025 up to 15% of the world’s population may be subject to fresh water scarcity. Techniques for conversion of sea water into drinking water have been known for at least 3,000  years (and perhaps even 5,000 years). But desalination as an industrial process for providing fresh water to large populations only started in any significant way in the 1960s and started showing high growth rates from the 1990s on.  There are two basic paths to obtaining fresh water from sea water. Through evaporation followed by condensation (multi-stage flash – MSF) or by filtration (reverse osmosis -RO). Whether as heat for evaporation or pumping energy through semi-permeable membranes, the energy requirements (and cost) have been relatively high. Costs have reduced sharply over the last 30 years and currently the lowest cost of production is at less than $0.5/m3. Note, however, that costs of distribution are in addition to the production cost. The world’s population using desalinated water today is fast approaching 1% (perhaps about 500 million people today). But the growth rate here is currently above 5%/year.

For water scarcity to disappear as a potential problem, the cost to access the water (prior to distribution) needs to be less than about 50% of the cost of distribution. For that situation to arise, current desalination costs have to reduce by a factor of about 20 (production cost < $0.02/m3). It seems unlikely that such a cost reduction can be achieved along the evaporation/condensation path. The filtration path remains the best bet but would require

  1. a sharp reduction of the pressure drop across the filtration membrane, and
  2. a reduction in the cost of the membrane, and
  3. developments in the economic handling or treating of large amounts of the salts and minerals filtered out

The rate of development suggests that it is quite probable that such an advance in filtration technology can be achieved over the next 10 – 20 years. The advent of graphene and the use of graphene oxides to create nano-filters is one path which shows great promise.

 Tunable sieving of ions using graphene oxide membranes, Jijo Abraham et al, Nature Nanotechnology (2017), doi:10.1038/nnano.2017.21

BBC: A UK-based team of researchers has created a graphene-based sieve capable of removing salt from seawater. The sought-after development could aid the millions of people without ready access to clean drinking water. The promising graphene oxide sieve could be highly efficient at filtering salts, and will now be tested against existing desalination membranes.

It has previously been difficult to manufacture graphene-based barriers on an industrial scale. Reporting their results in the journal Nature Nanotechnology, scientists from the University of Manchester, led by Dr Rahul Nair, shows how they solved some of the challenges by using a chemical derivative called graphene oxide.

Isolated and characterised by a University of Manchester-led team in 2004, graphene comprises a single layer of carbon atoms arranged in a hexagonal lattice. Its unusual properties, such as extraordinary tensile strength and electrical conductivity, have earmarked it as one of the most promising materials for future applications. But it has been difficult to produce large quantities of single-layer graphene using existing methods, such as chemical vapour deposition (CVD). Current production routes are also quite costly.

On the other hand, said Dr Nair, “graphene oxide can be produced by simple oxidation in the lab”. He told BBC News: “As an ink or solution, we can compose it on a substrate or porous material. Then we can use it as a membrane. “In terms of scalability and the cost of the material, graphene oxide has a potential advantage over single-layered graphene.”

By 2100 global population will be declining almost everywhere. The water scarcity problem will be solved long before the population pressure reduces the demand for fresh water.


 

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More evidence of water in the earth’s interior

March 13, 2014

There could be much more water trapped with minerals deep in the earth’s interior than all the surface water in the oceans.

D. G. Pearson, F. E. Brenker, F. Nestola, J. McNeill, L. Nasdala, M. T. Hutchison, S. Matveev, K. Mather, G. Silversmit, S. Schmitz, B. Vekemans, L. Vincze.Hydrous mantle transition zone indicated by ringwoodite included within diamondNature, 2014; 507 (7491): 221 DOI: 10.1038/nature13080

Deep Earth

Ringwoodite is thought to form between 410km and 660km beneath the Earth’s surface graphic BBC

BBC: Diamonds, brought to the Earth’s surface in violent eruptions of deep volcanic rocks called kimberlites, provide a tantalising window into the deep Earth.A research team led by Professor Graham Pearson of the University of Alberta, Canada, studied a diamond from a 100 million-year-old kimberlite found in Juina, Brazil, as part of a wider project. They noticed that it contained a mineral, ringwoodite, that is only thought to form between 410km and 660km beneath the Earth’s surface, showing just how deep some diamonds originate. 

While ringwoodite has previously been found in meteorites, this is the first time a terrestrial ringwoodite has been seen. But more extraordinarily, the researchers found that the mineral contains about 1% water. While this sounds like very little, because ringwoodite makes up almost all of this immense portion of the deep Earth, it adds up to a huge amount of deep water.

Dr Sally Gibson from the University of Cambridge, who was not involved in the work, commented: “Finding water in such large concentrations is a hugely significant development in our understanding of the ultimate origin of water now present at Earth’s surface.”

University of Alberta Press Release:

BlueRingwoodite.jpg

Crystal (~150 micrometers across) of Fo90 composition blue ringwoodite synthesized at 20 GPa and 1200 °C. Wikipedia

…. discovered the first-ever sample of a mineral called ringwoodite. Analysis of the mineral shows it contains a significant amount of water—1.5 per cent of its weight—a finding that confirms scientific theories about vast volumes of water trapped 410 to 660 kilometres beneath the Earth, between the upper and lower mantle.

“This sample really provides extremely strong confirmation that there are local wet spots deep in the Earth in this area,” said Pearson, a professor in the Faculty of Science, whose findings were published March 13 in Nature. “That particular zone in the Earth, the transition zone, might have as much water as all the world’s oceans put together.”

…. Ringwoodite is a form of the mineral peridot, believed to exist in large quantities under high pressures in the transition zone. Ringwoodite has been found in meteorites but, until now, no terrestrial sample has ever been unearthed because scientists haven’t been able to conduct fieldwork at extreme depths.

Pearson’s sample was found in 2008 in the Juina area of Mato Grosso, Brazil, where artisan miners unearthed the host diamond from shallow river gravels. The diamond had been brought to the Earth’s surface by a volcanic rock known as kimberlite—the most deeply derived of all volcanic rocks.

……. Scientists have been deeply divided about the composition of the transition zone and whether it is full of water or desert-dry. Knowing water exists beneath the crust has implications for the study of volcanism and plate tectonics, affecting how rock melts, cools and shifts below the crust.

“One of the reasons the Earth is such a dynamic planet is because of the presence of some water in its interior,” Pearson said. “Water changes everything about the way a planet works.”

Water in the Earth’s interior

March 14, 2013

Phase diagram for water substance. image – craigssenseofwonder.wordpress.com

Water at supercritical conditions is a strange beast and has some remarkable chemistry. It is a fluid with properties that are a blend of gas and liquid properties. Steam at supercritical conditions (around 220 – 250 bar and about 600 °C)  is in common use in large power plants since it can be expanded in steam turbines for power generation. It has gas-like properties such that – as an Oxygen carrier – it could even support combustion/oxidation processes. It has liquid like properties and can be used as a solvent.

It would seem that if water is contained in the interior of the earth’s crust it could be at pressures above 22 MPa (220 bar) and temperatures above 374°C, beyond the critical point, and its properties as a very aggressive solvent  could be controlling the behavior of magma. So perhaps plate tectonics is all down to water?

I am a little skeptical since I observe – in passing – that the behaviour of supercritical steam does not seem to dissolve away steam turbine blades or casings when used in power generation!

A new paper on the 

Microscopic structure of water at elevated pressures and temperatures  by C. J. Sahle, C. Sternemann, C. Schmidt, S. Lehtola, S. Jahn, L. Simonelli, S. Huotari, M. Hakala, T. Pylkkanen, A. Nyrow, K. Mende, M. Tolan, K. Hamalainen and M. Wilke.

 Proceedings of the National Academy of Sciences, 2013; DOI: 10.1073/pnas.1220301110

From the press release from the Helmholtz Centre, Potsdam

13.03.2013 | Potsdam: Earth is the only known planet that holds water in massive quantities and in all three phase states. But the earthly, omnipresent compound water has very unusual properties that become particularly evident when subjected to high pressure and high temperatures. In the latest issue of the Proceedings of the National Academy of Science (PNAS), a German-Finnish-French team published what happens when water is subjected to pressure and temperature conditions such as those found in the deep Earth. At pressures above 22 MPa and temperatures above 374°C, beyond the critical point, water turns into a very aggressive solvent, a fact that is crucial for the physical chemistry of Earth’s mantle and crust.

“Without water in Earth’s interior there would be no material cycles and no tectonics. But how the water affects processes in the upper mantle and crust is still subject of intense research”, said Dr. Max Wilke from the GFZ German Research Centre for Geosciences, who carried out the experiments along with his colleague Dr. Christian Schmidt and a team from the TU Dortmund. To this end, the research team brought the water to the laboratory. First, the microscopic structure of water as a function of pressure and temperature was studied by means of X-ray Raman scattering. For that purpose, diamond anvil cells of the GFZ were used at the European Synchrotron Radiation Facility ESRF in Grenoble. Inside the cell, a very small sample of water samples was enclosed, heated and brought to high temperatures and pressures. The data analysis was based on molecular dynamics simulations by the GFZ scientist Dr. Sandro Jahn.

“The study shows that the structure of water continuously develops from an ordered, polymerized structure to a disordered, marginally polymerized structure at supercritical conditions,” explains Max Wilke. “The knowledge of these structural properties of water in the deep earth is an important basis for the understanding of chemical distribution processes during metamorphic and magmatic processes.” This study provides an improved estimate of the behavior of water under extreme conditions during geochemical and geological processes. It is believed that the unique properties of supercritical water also control the behavior of magma.

At least 275 water molecules needed to form an ice crystal

September 24, 2012

 

In idle moments I contemplate on strange things such as the origins of water on earth (which is largely unknown) and the life-span of water molecules (in the order of milliseconds) and the manner  in which water molecules are added to or lost from the apparently constant amount of water on earth. None of these questions are illuminated further but this interesting paper by researchers in Germany and the Czech Republic describes a technique for studying clusters of water molecules and provides some answers on the formation of ice crystals.

A Fully Size-Resolved Perspective on the Crystallization of Water Clusters by Christoph C. Pradzynski, Richard M. Forck, Thomas Zeuch, Petr Slavíček, Udo Buck . Science 21 September 2012:
Vol. 337 no. 6101 pp. 1529-1532 DOI: 10.1126/science.1225468

ABSTRACT

The number of water molecules needed to form the smallest ice crystals has proven challenging to pinpoint experimentally. This information would help to better understand the hydrogen-bonding interactions that account for the macroscopic properties of water. Here, we report infrared (IR) spectra of precisely size-selected (H2O)n clusters, with n ranging from 85 to 475; sodium doping and associated IR excitation–modulated photoionization spectroscopy allowed the study of this previously intractable size domain. Spectral features indicating the onset of crystallization are first observed for n = 275 ± 25; for n = 475 ± 25, the well-known band of crystalline ice around 3200 cm−1 dominates the OH-stretching region. The applied method has the potential to push size-resolved IR spectroscopy of neutral clusters more broadly to the 100- to 1000-molecule range, in which many solvents start to manifest condensed phase properties.

Illustrations of the molecular structure of three water clusters

Illustrations of the molecular structure of three water clusters : from http://physicsworld.com/cws/article/news/2012/sep/21/how-many-water-molecules-does-it-take-to-make-ice

 

A new market segment!

February 20, 2011

No comment needed!

from the Guardian

Camel drinking, Jordan, Petra.

A new market segment - Camels in Jordan: image The Guardian

 

 


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