water treatment

Here’s a cool infographic on water challenges in the 21st century, courtesy of the Waterblog by Suez Environment and the World Water Forum. Fair warning: There are some alarming projections here about clean water shortages. That sort of thing might make you a little sad on this lovely Monday, so here’s a link to some adorable animal videos that you can clear your mind with afterward.

Among the many interesting statistics (It takes 11,000 liters of water to make 1 pair of jeans!) is the note that 2% of fresh water is expected to be produced by desalination by 2015. It seems like every other day we’re hearing about a big new desalination facility opening up somewhere in the world, or an advancement that improves the desalination process.

One such advancement whose popularity is growing is forward osmosis (FO) for desalination. In short, forward osmosis utilizes natural osmotic pressure to aid in water treatment, therefore requiring less energy and hydraulic pressure. Forward osmosis can also be used as pretreatment for a reverse osmosis system to create a continuous flow process with even greater efficiency. For more research on FO, Yale University’s Elimelech Lab is an excellent resource for forward osmosis desalination. You can also take a look at our new collection of forward osmosis cells and pumps for this application.

Visit Waterblog here

A recently completed test in Poland found that enhancing ultrafiltration (UF) flat sheet membranes with an anionic polymer increased the membrane’s ability to purify samples of galvanized wastewater. For this experiment, the researchers tested multiple concentrations of wastewater infused with zinc, nickel, and copper ions against EW and MW designation flat sheet membranes that were infused with a polyelectrolyte, in this case polysodium 4-styrenesulfonate (PSSS) with cation-exchange properties. The result was a more-efficient metal binding agent, enabling 97-99% retention of the target metals.

The EW membrane is made with Polysulfone while the MW is a modified Polyacrylonitrile known as Ultrafilic. Both designations ably treated the galvanized wastewater, but the MW membrane did have 2-3 times higher permeate flux values due to the membrane’s higher permeability.

In addition to membrane separation, common treatment options for galvanized wastewater include chemical processing and the ion exchange method. Unlike these other methods however, an effective membrane separation methodology has the potential to remove higher concentrations of effluent in a continuous process so these findings could impact how galvanic wastewater is processed in the future.

You can read the published paper here.

The Environmental Protection Agency announced last week that they are planning to develop standards for wastewater discharges produced by natural gas extraction from underground coalbed and shale formations (a process commonly referred to as “Fracking”). This method of extraction involves fracturing rock formations by injecting them with a pressurized fluid consisting mostly of water, a little bit of sand, and some chemical additives as well. The debate over the possible environmental consequences of fracking is a hot button issue right now, and since its popularity has grown to the point where it now accounts for about 15% of all natural gas production in the US, it is understandable that the EPA wants to look into setting some uniform regulations.

Any potential EPA standards in this area can be broken down into two areas: shale gas standards and coalbed methane standards. In shale gas extraction, wastewater is prohibited from being discharged into waterways. Instead, it is either recycled back into use or sent to a treatment plant. Unfortunately, many of these treatment plants are not properly equipped to handle shale gas wastewater so the EPA will look into standards that could be implemented on wastewater before it reaches the treatment plant.

Creating a coalbed methane standard for wastewater treatment is a little bit trickier, since there aren’t any national standards for it yet. Currently it is up to individual states to regulate where the wastewater is discharged and what pre-treatment standards to follow. The EPA is hoping to address the matter by creating a uniform standard for the whole nation.

Based on the current EPA schedule, a proposed rule should come in 2013 for coalbed methane and 2014 for shale gas. This is to allow the EPA time to consult with stakeholders and allow for public comment.

You can read the full announcement from the EPA here.

Today’s Laboratory Equipment newsletter features an interesting article on how Purdue researchers have created a water-disinfection system that uses ultraviolet radiation from the sun to remove pathogens. With 800 million people unable to access clean drinking water, the potential for water-cleaning system that can be powered by natural resources is tremendous. According to Water.org and the United Nations Human Development Report, every 20 seconds a child dies from a water-related disease.

This water treatment device uses a parabolic reflector to capture sunlight and focus it onto a UV-transparent pipe through which the water flows. In a brilliant development, the reflector is made out of a type of wood, paulownia, which is inexpensive and easy to find in regions around the equator where these systems are most needed. Since these people do not have significant funds or materials, for any solution to be effective it would have to be inexpensive and practical to construct.

In tests the UV treatment system has shown that it can incapacitate E. coli bacteria, but it has yet to show that it can neutralize other pathogens like those that cause cholera, typhoid and diarrhea. The engineers are looking into different reflective materials, such as metalized plastic, that could improve the effectiveness of the UV treatment method. The Purdue team has also been experimenting with a sand and gravel filtration system, which could possibly be used in conjunction with the sunlight treatment as a means of providing cheap drinking water. We’ve discussed sand filtration before, and the basic operation of this kind of filter is similar to filtration by other materials. Water flows slowly through layers of sand and gravel, allowing a bacterial film to build up on the surface of the filter which removes contaminants.

While industrial water treatment is obviously much faster and more effective on a larger scale, this filter made of natural materials could create enough drinking water for a family to live on. Aqua Clara International, a non-profit firm in Michigan, has been working with Purdue and Moi University in Kenya and so for they have installed almost 2,000 of these sand filtration systems in Kenya!

Read the announcement from the Purdue Newsroom

Western Biodiesel Inc. was fined $160,000 (Canadian dollars) yesterday by the Provincial Court of Alberta for releasing wastewater that contained methanol into the environment and for providing false or misleading statements to investigators. The fine is the outcome of an incident in October 2008 in which Western Biodiesel dumped around 16,000 liters of methanol-laced water onto its property.

Problems arose for Western Biodiesel the day after this release occurred when an unsuspecting welder accidentally ignited the wastewater with his torch, causing a fire that luckily yielded no injuries. In what had to be an incredibly gutsy and foolish move, the (now former) plant manager denied the release occurred when investigators showed up. He was later sentenced to four months house arrest.

So besides dumping it in a river and hoping nobody lights a match, what are the actual proper methods of methanol disposal? Methods for extracting methanol from biodiesel include: Vacuum stripping, flash evaporation, distillation, and water washing. Methanol and especially glycerol are high-value byproducts of biodiesel production, so facilities try to reclaim as much as possible for resale. Membrane separation is also used as an effective biodiesel purification method, particularly for removing glycerol particles.

Methanol is routinely used in biodiesel production during the transesterification reaction to turn plant or animal fats into fatty acids and glycerol. (Fun fact: Methanol is also a byproduct in liquor distillation and can cause blindness if ingested in large enough quantities!). European Standard 14214 specifies that biodiesel should contain no more than 0.2% methanol.

For more information you can check out the official statement from the Government of Alberta and this publication on biodiesel production from the University of Idaho.

The Silt Density Index is most frequently used to determine fouling potential prior to RO filtration. You can think of SDI as a bouncer, keeping the riff-raff out of the RO feed water. The higher the number, the greater the likelihood of fouling. The maximum SDI number allowed depends on the type of RO membrane being used; most manufacturers recommend a maximum SDI of 4 or 5.

SDI is found by calculating the rate at which a membrane filter is plugged. ASTM standard D4189-07 defines that the nominal filter for this application is a white hydrophilic MCE membrane filter, with 0.45 μm pore size and a 47 mm diameter. The reason this particular membrane is used is that it is more susceptible to plugging from colloidal material than from hard particles such as sand, therefore giving a better indication of the factors that might plug an RO membrane down the line.

Other measures that can be derived from the SDI include the plugging factor and the Modified Fouling Index (MFI). The plugging factor expresses the level of suspended solids as a percentage of the measured SDI value to the maximum SDI value, so a 100% plugging factor would indicate that your membrane is completely plugged. The MFI incorporates cake filtration theory into its calculation of fouling potential. Since this formula is more complex than SDI, it is not as frequently used in the field.

SDI can be determined manually or automatically with a measurement kit. Got any tips or experiences measuring SDI? Let us know in the comments!

This study from the ACS journal Applied Materials & Interfaces has been making headlines recently for introducing a new way to purify drinking water. Scientists from Rice University have created a new filter material, dubbed “super sand,” by coating regular sand with the nanomaterial graphite oxide. Their tests have shown that this super sand has the potential to be a cheap form of water filtration for developing areas.

The use of sand as a water filter isn’t anything new – it’s actually been done for around 6,000 years. However, by combining this old world technique with cutting edge nanotechnology scientists have made sand filtration at least 5 times more efficient. Their report indicates that the modified sand adsorbed 6 times the amount of liquid mercury and 5 times as much heavy metal and organic dye than regular sand.

In addition to the improved filtration capacity, there are other benefits of super sand that increase its prospects for real-world integration. The materials needed to make super sand, graphite and regular sand, are inexpensive and readily available. Another crucial advantage is that super sand can be created around room temperatures. These factors lead experts to believe that super sand could become a cost-efficient and viable method of water filtration in the future.

After our last post discussing how experiments with carbon nanotubes (CNT’s) might greatly improve the effectiveness of reverse osmosis desalination now comes a new report from the Institute of Physics that shows researchers are getting closer to making this a reality. Already over a billion people do not have regular access to clean water and the problem will likely get worse as the demand for drinkable water is expected to grow dramatically in the near future. With natural sources increasingly scarce, this urgent need means there is an intense global interest in any potentially viable forms of water purification.

Right now the main issues preventing RO desalination on a large-scale basis are that the membranes used to perform seawater to freshwater separation do not remove salt ions with enough efficiency and they also require great amounts of energy (and therefore expense) in order to purify the water. Jason Reese, a Professor of Thermodynamics and Fluid Mechanics at the University of Strathclyde and also the author of this report, states, “The holy grail of reverse-osmosis desalination is combining high water-transport rates with efficient salt-ion rejection.” Incredibly, these little carbon nanotubes may be able to satisfy both of these requirements for widespread adoption.

Early tests and simulations have shown that CNT membranes could have water permeability that is 20 times greater than today’s materials. Additionally, carbon nanotubes can be chemically tailored to better reject salt ions, thus improving upon the desalination process in multiple key areas.

While it is still early, these features are promising enough that scientists such as Professor Reese feel it is a very real possibility that this application of nanotechnology could be used to curtail our growing water demand.

Read more about this report here.

One of the most promising new frontiers in filtration technology involves infusing different membrane types with nanomaterials in order to improve performance or to pass along certain material attributes. Here we will look into one prominent example from recent years, the incorporation of carbon nanotubes (CNTs) into ultrafiltration membranes used in water treatment. We’ll also look at how our stirred cells have aided in this specialized membrane manufacturing process.

First off, what is there to gain by using CNT’s to manufacture water treatment membranes? While scientists have identified several potential advantages for CNT implementation, since the process is still in the R&D phase they have not necessarily been proven in all cases. One key possible benefit is that membranes made with these materials would be much stronger than traditional membranes, thus reducing instances of membrane breakage and fouling, two problems that contribute significantly to high maintenance costs in water treatment. Another unique advantage is that CNTs have antibacterial properties that may reduce biofilm formation and therefore prevent or limit biofouling. Lastly, the process of manufacturing ultrafiltration membranes with CNTs allows the producer to chemically modify the membrane surface which can further reduce fouling by tailoring the membrane for specific organic solutes.

As with standard membrane manufacturing processes, the stirred cell is an ideal piece of equipment for establishing the permeability of the test membranes. For this particular study on the effectiveness of polysulfone ultrafiltration membranes manufactured with CNTs, the cell (an HP4750 in this case) was set to perform dead-end filtration with ultrapure water at 38 bars of pressure (about 551 psi).

The HP4750 Stirred Cell

In order to determine permeability, the HP4750 was directly connected to the pressure regulator of the compressed air tank. Each membrane was compacted at 38 bars until the flow rate was stable (minimum of 30 minutes). Then the flow rate was measured by weighing the permeate as a function of the pressure applied (between 5 and 35 bars). To confirm the results, this test was performed in triplicate.

Permeability is an important test characteristic for determining the membrane’s susceptibility to fouling and its overall efficiency. In the study cited here, researchers found no statistically significant difference in permeability between CNT and non-CNT amended membranes. These findings supported their conclusion that their process for grafting CNTs onto membranes was ineffective. In the conclusion the authors note that because the CNTs only partially dispersed in the host material that they were prevented from taking on the mechanical properties of the CNTs.

While this particular study did not yield the desired results, new methods of integrating nanomaterials onto membranes are constantly being explored and hopefully it’s only a matter of time until these superior membranes become available.

Visit here to read the full study:
http://cohesion.rice.edu/engineering/pedroalvarez/emplibrary/85.pdf

An increase in salinity levels at the North Reverse Osmosis Water Plant in Kill Devil Hills (yes, that’s the town name) that had been creating stress for some local officials has been explained in a recent study. Researchers from nearby Duke University found that the rising salinity levels at this coastal aquifer are the result of fossil seawater and not seawater intrusion, as had been feared. Since the well’s installation in the late 1980’s salinity has more than doubled from about 1,000 mg/L to about 2,500 mg/L. There was much cause for relief however, when researchers were able to attribute the rise to fossilized seawater and not to seawater leaking in from the coast.

According to the director of the study, Duke Professor Avner Vengosh, knowing the source of the salinity increase is important because fossil seawater raises salinity, “At a relatively slow and steady rate that is more manageable and sustainable than the rapid increase we’d see if there was modern-day seawater intrusion.” As a result of this study the community will be able to rely on this aquifer for decades to come without having to resort to more expensive seawater desalination techniques which require more energy and advanced filtration methods.

Current treatment for groundwater desalination includes the use of reverse osmosis (RO) membranes to separate dissolved salts from potable water. Even with the rising salinity level these membranes remove around 96 to 99 percent of the dissolved salts. RO membranes also remove between 16 and 42 percent of the boron and 54 to 75 percent of the arsenic from the groundwater. Additional treatment following reverse osmosis desalination continues to remove arsenic until it is within safe drinking levels (10 parts per billion, according to the EPA).

Because seawater consistently has more salt than groundwater it requires more energy to treat, and therefore the cost is higher. Per this report on desalination from the Pacific Institute, “Energy is the single largest variable cost for a desalination plant, varying from one-third to more than one-half the cost of produced water.” The report also states, “At these percentages, a 25% increase in energy cost would increase the cost of produced water by 11% (for RO plants).” In looking at these percentages, it’s easy to see why the plant was concerned about seawater intrusion. Thanks to this research, the local citizens can drink easier knowing they have a supply of healthy, affordable water for a long time to come.

Click here to learn more about this case.