Forward Osmosis: What it is and how its used

Forward osmosis is a process using a special water-permeable membrane, which separates water from substances or contaminates contained within it. It works using osmotic pressure, which is created by placing solutions of two different concentrations side by side. The first of these is termed the draw solution, which tends to pull in the feed solution due to its higher concentration. The membrane rests in the middle, and as the feed solution flows through it, it strains the unwanted particulates out of the water. These contaminates or undesirable substances are classified as solutes, because they are dissolved in the water itself.

What is the difference between forward osmosis, and the more well-known process of reverse osmosis? In reverse osmosis, rather than relying upon solutions of different concentrations to drive the cycle, it is powered from an outside force instead. This is necessary, because reverse osmosis forces the higher concentration solution to flow back into the less concentrated one – against the osmotic gradient.

Forward osmosis is far simpler, typically being a one step process, relying upon the solutes alone to carry out the job. These solutes trade places as the filtration occurs, which can produce drinkable water in many cases. Take water from a stream, lake or river with harmful contaminates contained within it as an example. Benign solutes will be in the draw solution, which are safe to ingest. These will take the place of the unwanted particles in the river water, making it potable and safe to drink.

The ease of the mechanism has made forward osmosis a popular choice for portable water filtration, as only gentle stirring or suction is needed. Products intended for backpackers are especially numerous, and these use solutes such as fructose or glucose which can be readily ingested. Thus, the pathogens in the outdoor water sources the hikers select, will be replaced with beneficial sugars instead. Often, a water bottle with a special straw is the form that is offered, as the suction speeds the forward osmosis process. Other units rely upon osmotic pressure alone, though these take a bit longer to perform the operation.

Another product which uses forward osmosis as its base, are special hydration bags for survival situations. These are issued to combat forces in desert regions, as they allow them to filter their own urine and create drinkable water. Even seawater could be successfully filtered using this approach in theory, and it has gained some interest for use in life boat emergency kits.

However, when it comes to desalination, a second step is usually added for better results. Most often, forward osmosis is allowed to take place with the seawater, and then the resulting solution is subjected to a secondary filtration method. There are many options available today, such as using another specialized membrane or heat to finish the job.

What are the benefits of this approach? Much of the salt is removed by the forward osmosis, allowing the equipment used in the rest of the process to run far smoother overall. Salt water has a reputation for causing mechanical issues, and desalination plants using reverse osmosis as their first step often run into problems.

The only downside to forward osmosis is that the draw solutes end up in the filtered water, and a second step is necessary to remove them. However, this isn’t required when solutes which are safe to ingest are used. As amply demonstrated by the above discussion, this is a small limitation, as forward osmosis has many practical applications due to its simplicity. It has several advantages over reverse osmosis too, making it an excellent choice for removing harmful contaminants in a variety of different situations.

Electrochemical water treatment is a rare but highly effective way to produce clean and germ-free water. However, electrochemical products are currently scarce in the market because of the relative unfamiliarity to the technology as well as the enormous competition of other water treatment methods.

Basically, this type of disinfection is done by passing a current of electricity between electrodes (cathode and anode), resulting to changes in pH levels that in turn encourage pollutant desorption. The technique does not require addition of chemical compounds, but it is nevertheless the action of various chemical substances in the water that does the decontamination. Electrodes made from platinum group metals and their oxides are most suited for this type of process.

There are many reasons why electrochemical water disinfection has only been developed recently. Sufficiently stable electrodes have only been enhanced in the last forty years. Also, the practical interrelationships between chloride concentrations, electrolysis and water quality have been investigated methodically just in the previous decades. Lastly, only a few electrochemists had been engrossed in the topic which resulted to errors in device-making and irrational hypotheses to the mechanism of the process.

How Electrochemical Disinfection Works

The mechanism behind electrochemical disinfection is fairly simple. It is agreed that the cleansing of the water springs from desorption induced regeneration that affects the surface of porous carbons. Simply put, the electrical current allows chemicals to effectively react to microorganisms and kill them in the process.

The cathode, which is the reducing electrode, generates hydroxide ions that increase the alkalinity of the water around it. Through this, desorption of pollutants is promoted and they migrate to the anode for oxidation – hence their destruction.

Pros and Cons of Electrochemical Treatment

The advantages of this type of treatment are obvious. There is no need for the transport, storage and utilization of disinfectants which are otherwise needed for chemical methods of water treatment. The disinfection also has an inherent reservoir effect thereby marking cost-effectiveness and the need for less maintenance. Finally, there is no real need to induce power from an electrical supply grid as the principles of photovoltaic or solar energy can be used.

This is crucial to disinfect water in developing countries.

On the other hand, the major disadvantage comes with the mass transfer limitations between the electrodes. Residual pollutants could not be avoided and thus the cathode has to be cleaned after several cycles. If not, pore blockages and damage to adsorption sites decrease the regeneration efficiency. There is current research though that aims to develop adsorbents that are able to regenerate 100% of their capacity through electrochemical regeneration.

The Bottom Line

The use of electrolysis to chemically treat water has more advantages compared to other conventional techniques. This has been proven with its use in disinfecting drinking water, swimming pools, dental water supplies and industrial cooling water. Although this technology is not in full use today, the cost and performance advantages will eventually pan out to the wider use of electrochemical techniques in the future.

Distilled Water: Uses and Misuses

When you think of distillation, it’s likely your mind wanders to the creation of your favorite single malt whiskey. Fair enough, really. However, when you look beyond the bottle, distillation can also be used as a method of water purification.

Distillation is a fairly simple process. Essentially, unpurified water is boiled to the point of vaporization. Most salts and minerals have a higher boiling point than water, and so while the water vaporizes, most contaminants are separated from the water and remain in the vessel. Once the water has vaporized it is channeled into a condenser where it is cooled down to return to its liquid form and it collected in a clean container. This process is often repeated several times to purify the distilled water as much as possible.

Distilled water is most commonly generated for industrial use. Due to the de-mineralization of distilled water, it is perfect for chemical and biological laboratories, photo and printing stores, lead acid batteries in cars and trucks and for automotive cooling systems. Distilled water definitely has its place in the industrial world, as minerals can be corrosive to machinery and can have undesirable reactions with some chemicals. However, distilled water is not ideal for everyday human consumption.

So why do people opt for distilled water? Well, distillation is a fairly reliable method of removing dangerous bacteria, viruses and heavy metals. In developing countries these contaminants pose a real risk, and so distillation is a valuable process to save people from potentially life-threatening contaminants.

However, in Western countries drinking distilled water usually does more harm than good. In the Western world, most of the extremely dangerous contaminants are filtered out by municipal water treatment facilities, so other forms of water purification are most ecological, efficient and healthy than distillation.

Distillation doesn’t remove synthetic chemicals because their boiling point is lower than water. So pesticides, herbicides, and chlorine solutions remain in the water, which isn’t usually dangerous, but isn’t ideal either.

Another downside is that distillation relies on an energy source kept at a constant temperature. To power the energy source, approximately 5 gallons of tap water are needed to create just one gallon of distilled water. Of course, it is possible to use solar energy as a heat source, but with technology available at present it takes up to five hours and only works for small quantities of water.

The worst part of all is that distillation removes trace elements that are naturally present in water. Removing elements from water through distillation makes hydrogen a greater percentage of the distilled water’s composition, thereby making the water acidic.

Although drinking acidic, demineralized water is better than ingesting harmful contaminants, long term consumption of distilled water can lead to mineral deficiencies

How effective are ceramic filters at generating potable water?

ow effective are ceramic filters at generating potable water?

Although the technology they use is extremely simple, ceramic filters are increasingly popular water filtration devices. Ceramic filters trap bacteria in tiny pores like a sieve, allowing potable water to filter through.

So, how effective are ceramic filters? Ceramic filters are effective at catching cryptosporidium and giardia, the two primary causes of diarrhea from drinking dirty water. However, volatile organic compounds and chlorine will remain in the potable water as the microns are small enough to pass through.

There are several issues with ceramic filters. One common concern about ceramic filters is that one cannot know exactly how effective any particular ceramic filter is. The effectiveness of ceramic filters is dependent on their pore size. The pore size of a ceramic filter is dependent on two main variables: the ceramic material used and the temperature at which the kiln is set when the ceramic filter is vitrified. Although the composition varies from filter to filter, most ceramic filters are made of diatomaceous earth, a fine silica powder found in certain types of algae.

Ceramic filters must be vitrified in order to work effectively. When struck, a properly vitrified ceramic filter should ring like a bell. When vitrified, ceramic filters should not retain black specks, as this means the carbon hasn’t broken down during the firing process.

Effective ceramic filters are relatively slow to work. Most have a slow flow rate, passing water through the ceramic element at a rate of two liters an hour. For this reason, ceramic filtration is one of the least time-efficient methods of water filtration. However, in developing countries, ceramic filters are adequate as they are low-maintenance and don’t require batteries or electricity to run. For this reason, ceramic filters have been used to increase the standard of living in many areas throughout Asia and Africa.

Ceramic water filters are more effective if used in conjunction with other forms of water filtration. In areas where ceramic filters aren’t entirely effective, they can still be helpful as a pre-treatment before reverse osmosis water treatment systems.

The main disadvantages with ceramic water filters are the limited volume of potable water one can produce from a single filter and filtration in areas with dangerous chemicals such as arsenic in the water. Ceramic filters are slow to produce a small amount of potable water, so they aren’t the best option for large NGOs trying to provide potable water for whole communities. Any organization planning to use ceramic filters as the primary source of water filtration would need to thoroughly research the water quality and do extensive testing to ensure that ceramic filters provide sufficiently potable water.

As with many filtration devices, it is essential to avoid touching the vessel catching the purified water from the ceramic filter. Often, your hands come into contact with contaminated water while you are filling the filter, so it’s important not to contaminate the water you have just gone to all the effort of purifying. However, if in doubt, simply pour the water through the ceramic filter a second time.