Water softening systems and the history of water softeners
Water treatment goes all the way back to 3500 BC. In ancient Mesopotamia where boiling water was mainly used as the only water treatment method. Even though water hardness was not an issue for the inhabitants of Mesopotamia. Boiling water as a water treatment method turned out to be an effective way to remove temporary hardness from the water.
It was not until the Aqueducts of Ancient Rome were constructed in 312 BC, that the need to develop methods of dealing with hard water on a large scale became necessary. The Romans certainly knew about various qualities of water. Some of the rivers, streams, and springs that they tapped and diverted to their cities were excellent sources, others not so good. Based on the quality, the Romans created aqueducts that specifically brought in water for consumption and water that was for other purposes, like cleaning and bathing.
The Romans understood that water from specific sources would lead to incrustations and narrowing of the channels due to scale build-up. They however did not understand why this was happening. To solve this problem, the Romans built huge settling pools at the head of the aqueducts. These had sloped floors to facilitate the removal of the particles that accumulated. Unfortunately, this dealt with TSS (total suspended solids) but it did not help with the problem of hard water, because this is due to dissolved minerals in the water – commonly referred to as TDS (total dissolved solids).
Since the problem of water hardness could not be solved. This led to a change in aqueduct design that allowed for the cleaning of the scale off the walls of the conduits by hand. This meant that aqueducts needed to have channels or ducts that were large enough for workers to access the aqueducts. This is why periodic vertical access shafts were included in the design. These access shafts served a dual purpose, they were also used as air vents. The Romans believed that exposure to air improved water quality. This notion turned out to be true and is referred to as Aeration. Aeration is when water and air are in close contact with each other. The reaction helps to remove dissolved gases (such as carbon dioxide) and oxidizes dissolved metals such as iron, hydrogen sulfide, and volatile organic chemicals (VOCs). Oxygen can also increase the palpability of water by removing the flat taste.
The need to remove the hardness (minerals) in the water did not become important again until the Industrial Revolution. The Industrial Revolution that occurred in the 18th and 19th centuries was where economies evolved from mainly agricultural and handicraft economies into mechanized manufacturing and large-scale production economies. During this period, the utilization of water during the manufacturing process became very important. Specifically, for heat transfer and steam power. This led to various methods of water softening (removal of minerals) being used and the need for innovating water softening techniques. Below you will find the different methods used:
Distillation
Distilling water at least dates back to 200 A.D. when Alexander of Aphrodisias first described the distillation of seawater into clean drinking water. Even though most would think that boiling water is the same as distilling. Both processes use heat to boil the water. The difference being that in the distilling process you capture the steam in a separate container, then cool the captured steam so it returns to its liquid form. The resulting water will have the minerals removed.
Lime Softening
Discovered in 1841 by Scottish professor Thomas Clark. Lime Softening is a water treatment process that uses calcium hydroxide, or limewater, to soften water by forcing precipitation of calcium and magnesium ions. In this process, hydrated lime (calcium hydroxide) is added to the water to raise its pH level and precipitate the ions that cause hardness. This process is commonly referred to as the Clark Process.
Ion Exchange
Some believe that ion exchange dates to biblical times based on a statement that Moses makes in Exodus 15: 23-25 “They could not drink of the waters of Marah, for they were bitter . . . And he cried unto Jehovah; and Jehovah showed him a tree, and he cast it into the waters, and the waters were made sweet.” I suppose it depends on how you interpret that, but it is commonly interpreted as the first mention of ion exchange as a method of water treatment. The first person to mention the process of water filtration using ion-exchange was Aristotle. He stated, “seawater loses part of its salt content by percolating through certain sands.” It is unlikely that Aristotle understood the concept of ion exchange, nevertheless, ion exchange was what was happening.
It was not until 1845 when H.S. Thompson managed to remove ammonia from a sample of manure by passing it through ordinary garden soil. In 1850, H.S. Thompson took his findings and collaborated with J.T. Way and the two of them successfully extracted ammonia and released calcium from clay samples using carbonate and ammonium sulfate. This is the very first instance of ion exchange methods being used in scientific processes and was a turning point in the advancement of ion exchange.
In 1905, Dr. Robert Gans developed the first commercial-scale hardness removal system utilizing a natural zeolite type of soil. This invention was based on the principles that Thompson and Way discovered during their research. Unfortunately, Dr. Gans used a natural zeolite soil that was not cost-effective enough to use on a large-scale manufacturing process. Dr. Gans' invention never took hold but it was the catalyst for the search of alternative resins.
The first ion-exchange resins were described by Adams and Holmes, a water-treatment expert and polymer chemist respectively, of the British Chemical Research Laboratory (1935). These ion-exchange resins were condensation products of phenol [CAS: 108-95-2] and formaldehyde [CAS: 50-00-0]. The granular-type cation-exchange resin contained sulfonic groups, and the anion exchanger contained aromatic amine groups. They are termed strong-acid and weak-base ion exchangers. Several condensation-type ion-exchange resins were manufactured during 1935-1945 based on Adams and Holmes' research.
The first commercial deionization system was installed in 1939. The next important step in ion-exchange resin technology was the synthesis of sulfonated styrene-divinylbenzene (DVB) cation exchangers. Commercial quantities of strong-base styrene-DVB anion exchangers appeared in 1948. The first anion exchangers, the weak base type, removed only strong mineral acids from water, such as HCI (hydrochloric acid). The strong-base materials remove all acids, thus paving the way to produce water of equal or better quality than distilled water and at a much lower cost. Ion exchange is still the most widely used method of dealing with water hardness. Ion exchange is the water softener systems you will typically see in homes throughout the world. These water softeners utilize ion exchange by exchanging sodium for calcium and or magnesium. Unfortunately, this method is not good for the environment and causes issues at the wastewater treatment plants. So much so, some states are banning their use.
Salt being added to a water softener
Reverse Osmosis (RO)
Reverse osmosis is the process of forcing a solvent (water) from a region of high solute concentration through a semipermeable membrane to a region of low-solute concentration by applying a pressure greater than the osmotic pressure. (Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane.) It is also defined as the measure of the tendency of a solution to take in a pure solvent by osmosis. The largest and arguably most important application of reverse osmosis is the separation of pure water from seawater and other brackish waters: The seawater, or brackish water, is pressurized against one surface of the membrane, causing the transport of salt-depleted water across the membrane and creating pure water on the low-pressure side.
Reverse Osmosis was first discovered in 1748 by Jean-Antoine Nollet, using a pig’s bladder as a membrane. He proved that a solvent could pass selectively through a semi-permeable membrane through the process of natural osmotic pressure and the solvent will continually enter through the cell membrane until a dynamic equilibrium is reached on both sides of the bladder.
In 1949, the University of California Los Angeles (UCLA) discovered that reverse osmosis would work for desalinating seawater. The University of Florida furthered this work in the 1950s, by developing a process to turn seawater into freshwater. Unfortunately, due to the expense of the process they developed, it was impractical to use.
The biggest breakthrough in RO membrane technology was when John Cadotte discovered the FT-30 membrane in 1969. John made this discovery while researching at the Midwest Research Institute, a not-for-profit organization performing research on RO membranes under a government contract. The FT30 membrane consists of three layers: an ultra-thin polyamide barrier layer, a microporous polysulfide interlayer, and a high-strength polyester support web. The FT30 membrane has been continuously updated and refined to provide higher rejection, improved membrane flux, and low fouling performance. Today's FT30 membrane is uniquely uniform in performance and quality, without the taped or glued defects that can cause other membranes to fail. The DOW chemical company purchased the rights to the FT-30 membrane technology and remains one of the best available reverse Osmosis membranes on the market.
Washing Soda Method (Na₂CO₃)
Sodium carbonate (also known as washing soda or soda ash), Na₂CO₃, is a sodium salt of carbonic acid and is a strong, non-volatile base. Na₂CO₃ commonly occurs as a crystalline heptahydrate that readily forms into a white powder, the monohydrate. It has a cooling alkaline taste and is extracted from the ashes of many plants. It is also produced artificially in large quantities from common salt. Sodium carbonate is mainly used in the manufacture of glass (55%), pulp and paper (5%), soap, and many other chemicals (25%) such as sodium silicates and sodium phosphates.
The creation of sodium carbonate is achieved through one of the two known processes. The Leblanc process and The Solvay process.
Leblanc Process
In 1791, the French chemist Nicolas Leblanc patented a process for producing sodium carbonate from salt, sulfuric acid, limestone, and coal. First, sea salt (sodium chloride) was boiled in sulfuric acid to yield sodium sulfate and hydrogen chloride gas, according to the chemical equation:
2 NaCl + H₂SO₄ → Na₂SO₄ + 2 HCl
Next, the sodium sulfate is mixed with crushed limestone (calcium carbonate) and coal, and the mixture is burned, producing sodium carbonate along with carbon dioxide and calcium sulfide.
Na₂SO₄ + CaCO₃ + 2 C → Na₂CO₃ + 2 CO₂ + CaS
The sodium carbonate is extracted from the ashes with water and then collected by allowing the water to evaporate. The hydrochloric acid produced by the Leblanc process is a major source of air pollution, and the calcium sulfide byproduct also presented serious waste disposal issues. However, it remained the major production method for sodium carbonate until the late 1880s. For the most part, this process is no longer used.
Solvay Process
In 1861, the Belgian industrial chemist Ernest Solvay developed a method to convert sodium chloride to sodium carbonate using ammonia. The Solvay process centered around a large hollow tower. At the bottom, calcium carbonate (limestone) was heated to release carbon dioxide:
CaCO₃ → CaO + CO₂
At the top, a concentrated solution of sodium chloride and ammonia entered the tower. As the carbon dioxide bubbled up through it, sodium bicarbonate precipitated:
NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl
The sodium bicarbonate was then converted to sodium carbonate by heating it, releasing water and carbon dioxide:
2 NaHCO₃ → Na₂CO₃ + H₂O + CO₂
Meanwhile, the ammonia was regenerated from the ammonium chloride byproduct by treating it with the lime (calcium hydroxide) left over from carbon dioxide generation:
CaO + H₂O → Ca(OH)₂
Ca(OH)₂+ 2 NH₄Cl → CaCl₂ + 2 NH₃ + 2 H₂O
Because the Solvay process recycled its ammonia, it consumed only brine and limestone and had calcium chloride as its only waste product. This made it substantially more economical than the Leblanc process, and it soon came to dominate world sodium carbonate production. By 1900, 90% of sodium carbonate was produced by the Solvay process, and the last Leblanc process plant closed in the early 1920s.
Sodium carbonate is soluble in water but can occur naturally in arid regions, especially in the mineral deposits formed when seasonal lakes evaporate commonly referred to as evaporites. Deposits of the mineral natron, a combination of sodium carbonate and sodium bicarbonate, have been mined from dry lake bottoms in Egypt and other parts of the middle east since ancient times when natron was used in the preparation of mummies and the early manufacturing of glass. Sodium carbonate has three known forms of hydrates: sodium carbonate decahydrate, sodium carbonate heptahydrate, and sodium carbonate monohydrate.
Sodium carbonate is still produced by the Solvay process in much of the world today. However, large natural deposits found in 1938 near the Green River in Wyoming, have made its industrial production in North America uneconomical since it can simply be mined.
Domestically washing soda is used as a water softener in washing machines. In this application, the sodium bicarbonate competes with the ions magnesium and calcium in hard water and prevents them from bonding with the detergent being used. Without using washing soda, additional detergent is needed to soak up the magnesium and calcium ions.
Water Conditioning Devices
Technically water conditioners do not soften water. Instead, they are an alternative approach to solve the problems that hard water can cause. The main technologies in this area deserve to be mentioned when explaining water softening because the goal of using a water conditioner and water softener is the same. Water Conditioners use various methods to create a catalytic reaction that changes the way minerals and biological contaminants behave in a liquid solution. The end goal is to keep this matter from building up on surfaces and causing serious issues like biofouling and scale buildup.
The exact way a water conditioner achieves this depends on what type of conditioner it is and what the system is capable of. The goal may be to reduce the formation of limescale, to slow the rate of scaling, or to change the makeup of the scale so that it precipitates and does not adhere to surfaces at all.
No matter how a water conditioner manipulates the behavior of minerals, they all have some key things in common. Conditioners, as opposed to traditional water softeners, they do not remove mineral ions, but they do prevent those ions from building up around the insides of pipes, on the heating element, nozzles, and plumbing fixtures. This solves one of the major problems hard water presents without adding salt. Therefore you'll sometimes hear water conditioners referred to as "no-salt softeners”. This water treatment option is preferable for many people since water conditioners tend to be much lower maintenance and lower cost than traditional water softeners and do not add sodium to the water. Most importantly, water conditioning allows you to keep a healthy source of ionic calcium and magnesium.
Another advantage of the water conditioning process is that it can address biological contaminants, as well. Water conditioners can break up biofilm so that it doesn't adhere to surfaces. Some conditioners, such as HydroFLOW, can even deactivate these biological contaminants.
Below are the main technologies used in the process of water conditioning:
Template Assisted Crystallization (TAC) – Shortened to TAC, this method uses resin beads as a catalytic nucleation site where hardness mineral ions become a stable crystalline form that will not cling to surfaces. These crystals are microscopic and flow with the water naturally and eventually down the drain. Unlike with a softener that uses ion-exchange, this tank of resin beads does not require ongoing regeneration.
Nucleation Assisted Crystallization (NAC) – This is when water goes under nucleation in a pressure vessel, the Calcium Bicarbonate Ca(HCO) is transformed into calcium carbonate CaCO₃ crystals and these crystals formed through decomposition. This kind of crystallization process forms very stable and harmless crystals.
The following equation describes the reaction that occurs inside the pressure vessel when flow over grains of nucleation.
Ca(HCO) → CaCO+ CO + HO
In the pressure vessel, the equilibrium of carbonate species in water is shifted, assisted by the driving force of stable crystal formation. As long as CO₂ is removed, the soluble Ca(HCO) converts into insoluble calcium carbonate (CaCO₃) crystals. The calcium carbonate crystals grow steadily. They are very stable and cannot dissolve (incapable of forming scale) in the water. Glass grains crystallization sites provide increased nucleation sites for the formation of submicron-sized CaCO₃ crystals. Hence this process is called Nucleation Assisted Crystallization.
Electrical Induction: An electrical current can also be used to precipitate water hardness. This precipitate typically forms on an electrode that requires periodic cleaning. The precipitate can create a layer of sludge on some surfaces. However, this sludge can be easily removed by fast-flowing water. The patented and unique HydroFLOW water conditioner is the most innovative way of using an electrical induction to condition water.
Chelation – The term chelation (derived from the Greek word chelos or claw) refers to the mineral or metal-binding properties of certain compounds that can hold a central cation in a claw-like grip. Discovered by French-Swiss chemist, Alfred Werner, who in 1893 developed the theory of coordination compounds, today referred to as chelates. This was a major change in how we classify inorganic chemical compounds. In 1913, Werner received the Nobel prize for his discovery.
Chelation is often referred to as Chelation water softening. Technically this process does not soften the water. Chelation is a conditioning technology that uses a chelating agent (such as citric acid or EDTA) to tie up hardness ions, making them unable to form scale on fixtures and appliances. This technology may prevent scale build-up by up to 99% and may also remove the existing scale. Chelation has not been well proven, especially for higher hardness levels (> 8-10 gpg), or if iron, dissolved oxygen, or dissolved silica are present.
Magnetism: Some conditioners use magnets to create a magnetic field in your water that affects the way the hardness ions behave. Normally, these ions are prone to forming clusters that stick to surfaces, but the magnetism is intended to make them less likely to do this by changing the shape of the clusters. Scientific studies have not confirmed the effectiveness of magnetic water treatment.
*As innovations in water softening emerge, we will continue to add them to this article. Hard water is a problem for 85% of the United States. Helping you understand the options and the effect that each has in dealing with hard water is our goal.