FAQS

When water is referred to as ‘hard’ this simply means, that it contains more minerals than ordinary water. These are especially the minerals calcium and magnesium. The degree of hardness of the water increases, when more calcium and magnesium dissolves.

Magnesium and calcium are positively charged ions. Because of their presence, other positively charged ions will dissolve less easily in hard water than in water that does not contain calcium and magnesium.

This is the cause of the fact that soap doesn’t really dissolve in hard water.

In many industrial applications, such as the drinking water preparation, in breweries and in sodas, but also for cooling- and boiler feed water the hardness of the water is very important.

Water purification generally means freeing water from any kind of impurity it contains, such as contaminants or micro organisms. Water purification is not a very one-sided process; the purification process contains many steps. The steps that need to be progressed depend on the kind of impurities that are found in the water. This can differ very much for different types of water.

In which ways is polluted water treated?

Settling

Before the purification process begins some contaminants, such as oil, can be settled in a settling tank. They can then be removed easily, after they have reached the bottom of the tank.

Removal of dangerous microorganisms

Often polluted water has to be freed from microorganisms. The water is than disinfected, usually by means of chlorination.

Removal of dissolved solids

Microorganisms are not only a threat to water; they can also be an advantage when it comes to water purification processes. They can convert harmful contaminants to harmless substances. This biological purification process usually takes a long time and it is only used for water that is polluted with contaminants that the microorganisms, usually bacteria, can convert.

Physical/ chemical techniques

When treatment by microorganisms is not an option we often use different treatment techniques, called physical/ chemical treatment techniques. Chemical treatment often deals with the addition of certain chemicals, in order to make sure that the contaminants change structure and can then be removed more easily. Fertilizers such as nitrates are removed this way. Removal of contaminants can also be done through more difficult specific chemical processes. It takes a lot of education to fully understand these purification steps. Physical treatment usually deals with purification steps such as filtration.

When water contains a significant amount of calcium and magnesium, it is called hard water. Hard water is known to clog pipes and to complicate soap and detergent dissolving in water. Water softening is a technique that serves the removal of the ions that cause the water to be hard, in most cases calcium and magnesium ions. Iron ions may also be removed during softening. The best way to soften water is to use a water softener unit and connect it directly to the water supply.

A water softener is a unit that is used to soften water, by removing the minerals that cause the water to be hard.

Water softening is an important process, because the hardness of water in households and companies is reduced during this process. When water is hard, it can clog pipes and soap will dissolve in it less easily. Water softening can prevent these negative effects.

Hard water causes a higher risk of lime scale deposits in household water systems. Due to this lime scale build-up, pipes are blocked and the efficiency of hot boilers and tanks is reduced. This increases the cost of domestic water heating by about fifteen to twenty percent.

Another negative effect of lime scale is that it has damaging effects on household machinery, such as laundry machines. Water softening means expanding the life span of household machine, such as laundry machines, and thelife span of pipelines. It also contributes to the improved working, and longer lifespan of solar heating systems, air conditioning units and many other water-based applications.

Water softeners are specific ion exchangers that are designed to remove ions, which are positively charged. Softeners mainly remove calcium (Ca2+) and magnesium (Mg2+) ions. Calcium and magnesium are often referred to as ‘hardness minerals’.

Softeners are sometimes even applied to remove iron. The softening devices are able to remove up to five milligrams per litre (5 mg/L) of dissolved iron.

Softeners can operate automatic, semi-automatic, or manual. Each type is rated on the amount of hardness it can remove before regeneration is necessary.

A water softener collects hardness minerals within its conditioning tank and from time to time flushes them away to drain.

Ion exchangers are often used for water softening. When an ion exchanger is applied for water softening, it will replace the calcium and magnesium ions in the water with other ions, for instance sodium or potassium. The exchanger ions are added to the ion exchanger reservoir as sodium and potassium salts (NaCl and KCl).

A good water softener will last many years. Softeners that were supplied in the 1980’s may still work, and many need little maintenance, besides filling them with salt occasionally.

For water softening, three types of salt are generally sold:

– Rock salt

– Solar salt

– Evaporated salt

• Rock salt as a mineral occurs naturally in the ground. It is obtained from underground salt deposits by traditional mining methods. It contains between ninety-eight and ninety-nine percent sodium chloride. It has a water insolubility level of about 0.5-1.5%, being mainly calcium sulphate. Its most important component is calcium sulphate.
• Solar salt as a natural product is obtained mainly through evaporation of seawater. It contains 85% sodium chloride. It has a water insolubility level of less than 0.03%. It is usually sold in crystal form. Sometimes it is also sold in pellets.
• Evaporated salt is obtained through mining underground salt deposits of dissolving salt. The moisture is then evaporated, using energy from natural gas or coal. Evaporated salt contains between 99.6 and 99.99% sodium chloride.

Rock salt contains a lot of matter that is not water-soluble. As a result, the softening reservoirs have to be cleaned much more regularly, when rock salt is used. Rock salt is cheaper than evaporated salt and solar salt, but reservoir cleaning may take up a lot of your time and energy.

Solar salt contains a bit more water-insoluble matter than evaporated salt. When one makes a decision about which salt to use, consideration should be given to how much salt is used, how often the softener needs cleanout, and the softener design. If salt usage is low, the products could be used alternately.

If salt usage is high, insoluble salts will build up faster when using solar salt. Additionally, the reservoir will need more frequent cleaning. In that case evaporated salt is recommended.

It is generally not harmful to mix salts in a water softener, but there are types of softeners that are designed for specific water softening products. When using alternative products, these softeners will not function well.

Mixing evaporated salt with rock salt is not recommended, as this could clog the softening reservoir. It is recommended that you allow your unit to go empty of one type of salt before adding another to avoid the occurrence of any problems.

Salt is usually added to the reservoir during regeneration of the softener. The more often a softener is regenerated, the more often salt needs to be added.

Usually water softeners are checked once a month. To guarantee a satisfactory production of soft water, the salt level should be kept at least half-full at all times.

Before salt starts working in a water softener it needs a little residence time within the reservoir, since the salt is dissolving slowly. When one immediately starts regeneration after adding salt to the reservoir, the water softener may not work according to standards.

When the water softening does not take place it could also indicate softener malfunction, or a problem with the salt that is applied.

When the water does not become soft enough, one should first consider problems with the salt that is used, or mechanical malfunctions of softener components. When these elements are not the cause of the unsatisfactory water softening, it may be time to replace the softener resin, or perhaps even the entire softener.

Through experience we know that most softener resins and ion exchanger resins last about twenty to twenty-five years.

Usually it is not necessary to clean out a brine tank, unless the salt product being used is high in water-insoluble matter, or there is a serious malfunction of some sort. If there is a build-up of insoluble matter in the resin, the reservoir should be cleaned out to prevent softener malfunction.

The Water Quality Association has performed studies on this subject. These studies have indicated that a properly placed septic tank that works adequately cannot be damaged by brine that is discharged from a water softener. And softened water can sometimes even help reduce the amount of detergents discharged into a septic tank.

Lead pipe systems have to be replaced, before softened water can flow through them. Although lead pipe systems in hard water areas may not cause a problem, it is advisable to replace them anyway. When naturally or artificially softened water ends up in these lead pipe systems, it may cause the pickup of lead.

Yes, although the measurement system is mainly applied in industrial water softeners.

Feed water is water added to a boiler to replace evaporation and blow down. In many cases, condensed steam returned to the boiler through the condensate system constitutes much of the feed water. Make-up is any water needed to supplement the returned condensate. The make-up water is usually natural water, either in its raw state or treated by some process before use. Feed water composition therefore depends onthe quality of the make-up water and the amount of condensate returned.

Feed water purity is a matter both of quantity of impurities and nature of impurities. Some impurities such as hardness, iron and silica, for example, are of more concern than sodium salts. Feed water purity requirements depend on boiler pressure, design and application. Feed water purity requirements can vary widely. Low-pressure, fire tube boilers require less stringent feed water control than modern high pressure boilers.

Dissolved bicarbonates of calcium and magnesium break down under heat to give off carbon dioxide and form insoluble carbonates. These carbonates may precipitate directly on the boiler metal or form sludge in the boiler water that may deposit on boiler surfaces. Calcium sulfate, upon heating, becomes less soluble. Sulfate and silica generally precipitate directly on the boiler metal and ordinarily do not form sludge. For this reason they are much harder to condition and may cause more difficulties. Silica is usually not present in very large quantities in water, but under certain conditions it can form an exceedingly hard scale. Suspended or dissolved iron coming in with the feed water will also deposit on the boiler metal. Oil and other process contaminants can form deposits as well as promote deposition of other impurities. Sodium compounds do not deposit under normal circumstances. Sodium deposits can form under unusual circumstances: in a starved tube, a stable steam blanket or under existing porous deposits.

• Boiler water carryover is the contamination of steam with boiler water solids. There are several common causes of boiler water carryover:
• Bubbles form on the surface of the boiler water and leave with the steam. Thisfoaming can be compared to the stable foam of soap suds.
• Spray or mist is thrown up into the steam space by the bursting of rapidly risingbubbles at the steam release surface. This phenomenon is like the effervescence of champagne. No stable foam forms, but droplets of liquid burst from the liquid surface.
• Priming is a sudden surge of boiler water caused by a rapid change in load. (Uncapping a bottle of charged water produces an effect like this.)
• Steam contamination may also occur from leakage of water through improperly designed or installed steam-separating equipment in a boiler drum.

Very high concentrations of soluble or insoluble solids in boiler water will cause foaming. Specific substances such as alkalis, oils, fats, greases and certain types of organic matter and suspended solids cause foaming.

Stated simply, general corrosion is the reversion of a metal to its ore form. Iron for example, reverts to iron oxide as a result of corrosion. The process of corrosion, however, is a complex electro-chemical reaction. Corrosion may produce general attack over a large metal surface or may result in pinpoint penetration of the metal.

Basic corrosion in boilers results primarily from the reaction of oxygen with the metal. Stresses, pH conditions and chemical corrosion have an important influence and produce different forms of attack.

Corrosion may occur in the feed water system as a result of low pH water and the presence of dissolved oxygen and carbon dioxide. On-line boiler corrosion occurs when boiler water alkalinity is too low or too high. When oxygen-bearing water contacts metal, often during idle periods, corrosion can occur. High temperatures and stresses in the boiler metal tend to accelerate the corrosive mechanisms. In the steam and condensate system, corrosion is generally the result of contamination with carbon dioxide and oxygen. Additional contaminants such as ammonia or sulfur-bearing gases may increase attack on copper alloys in the system.

Excessive chelate residuals (in excess of 20 ppm as CaCO3) or improperly applied chelate programs may produce boiler system corrosion. Concentrating boiler solids at ahigh heat input area might also produce boiler corrosion. To minimize the chance of corrosion, follow the recommendations of your Nalco water treatment consultant.

Corrosion causes difficulty from two respects. The first is deterioration of the metal itself and the second is deposition of the corrosion products in high heat release areas of the boiler. Uniform corrosion of boiler surfaces is seldom of real concern. All boilers experience a small amount of general corrosion. Corrosion takes many insidious forms, however, and deep pits resulting in only a minimal total iron loss may cause penetration and leakage in boiler tubes. Corrosion beneath certain types of boiler deposits can so weaken the metal that tube failure may occur. In steam condensate systems, replacement of lines and equipment due to corrosion can be costly.

With the trend toward higher heat fluxes in today’s modern boilers, corrosion has become an important factor in power plant operation. When iron corrodes, hydrogen gas, which can be measured in the steam, is released. Measuring the amount of hydrogen gas released can detect immediate fluctuations in load, boiler water conditions or fuel changes. This information when interpreted by an experienced, well trained engineer can indicate if corrosive conditions exist in an operating boiler.

The most common methods for prevention of corrosion include:

• Removing dissolved oxygen from the feedwater
• Maintaining alkaline conditions in the boiler water
• Keeping internal surfaces clean
• Protecting boilers during out-of-service intervals
• Counteracting corrosive gases in steam and condensate systems with chemical treatment

The selection and control of chemicals for preventing corrosion require a thorough understanding of the causes and corrective measures. Your Nalco representative provides this expertise.

Clarification is the removal of suspended matter and color from water supplies. The suspended matter may consist of large particles that settle out readily. In these cases, clarification equipment merely involves the use of settling basins or filters. Most often, suspended matter in water consists of particles so small that they do not settle out, but instead pass through filters. The removal of these finely divided or colloidal substances therefore requires the use of coagulants.

Coagulation is charge neutralization of finely divided or colloidal impurities. Colloidal particles have large surface areas that keep them in suspension. In addition, the particles have negative electrical charges, which cause them to repel each other and resist adhering together. Coagulation requires neutralization of the negative charges, providing an agglomeration point for other suspended particles. Flocculation is thebridging together of the coagulated particles.

In precipitation processes, the chemicals added react with dissolved minerals in the water to produce a relatively insoluble reaction product. Precipitation methods reduce dissolved hardness, alkalinity and, in some cases, silica. The most common example of chemical precipitation in water treatment is lime-soda softening.

When minerals dissolve in water, they form electrically charged particles called ions. Calcium bicarbonate, for example, forms a calcium ion with positive charges (a cation) and a bicarbonate ion with negative charges (an anion).Certain natural and synthetic materials have the ability to remove mineral ions from water in exchange for others. For example, calcium and magnesium ions can be exchanged for sodium ions by simply passing water through a cation exchange softener.

There are two types of ion exchange resins: cation and anion. Cation exchange resins react only with positively charged ions such as Ca+2 and Mg+2. Anion exchange resins react only with the negatively charged ions such as bicarbonate (HCO3-) and sulfate (SO4-2).

Although there are several types of cation exchange resins, they usually operate on either a sodium or hydrogen “cycle”. A “sodium cycle” exchanger replaces cation with sodium; a “hydrogen cycle” exchanger replaces cation with hydrogen. The two types of anion resins are: weak base and strong base. Weak base resins will not take out carbon dioxide or silica (actually carbonic acid and siliceous acid), Strong base anion resins, on the other hand, can reduce silica and carbon dioxide as well as strong acid anions to very low values. Strong base anion resins are generally operated on a hydroxide cycle. Dealkalization reduces alkalinity through chloride anion exchange.

Ion exchange resins have only a limited capacity for removing ions from water. Reversing the ion exchange process, regeneration, returns the resin to its original condition. Regeneration involves taking the unit off line and treating it with a concentrated solution of the regenerate. The ion exchange resin releases ions previously removed; these ions are rinsed out of the resin vessel. The ion exchange unit is then ready for further service. In the case of cation exchangers operating on the sodium cycle, salt (NaCl) replenishes the sodium capacity or acid (H2SO4 or HCl) replenishes the hydrogen capacity. Anion exchangers are regenerated with caustic (NaOH) or ammonium hydroxide (NH4OH) to replenish the hydroxide ions. Salt (NaCl) may be used to regenerate anion resins in the chloride form for de alkalization.

Before the feed water enters the boiler, oxygen must be removed. Feed water deaeration removes dissolved oxygen by heating the water with steam in a de aerating heater or deaerators. A steam vents transports the oxygen out of the deaerator.There are two basic types of steam deaerators: spray and tray. In the spray deaerator,a jet of steam mixes intimately with the feed water being sprayed into the unit. In the tray type, the incoming waterfalls over a series of trays, where it is broken into small droplets and mixed with the steam. Tray-type deaerators also increase the residence time in the deaerators section

To understand reverse osmosis (RO), one must first understand osmosis. Osmosis uses a semi-permeable membrane that allows ions to pass from a more concentrated solution to a less concentrated solution without allowing the reverse to occur. Reverse osmosis overcomes the osmotic pressure with a higher artificial pressure to reverse the process and concentrate the dissolved solids on one side of the membrane. Normal operating pressures are 300 to 900 psi. Reverse osmosis will reduce the dissolved solids of the raw water, making the final effluent ready for further pretreatment. Although sometimes expensive, this process can be used on any type water.

Reverse Osmosis, commonly referred to as RO, is a process where you demineralize or deionize water by pushing it under pressure through a semi-permeable Reverse Osmosis Membrane.

To understand the purpose and process of Reverse Osmosis you must first understand the naturally occurring process of Osmosis.

Osmosis is a naturally occurring phenomenon and one of the most important processes in nature. It is a process where a weaker saline solution will tend to migrate to a strong saline solution. Examples of osmosis are when plant roots absorb water from the soil and our kidneys absorb water from our blood.

Below is a diagram which shows how osmosis works. A solution that is less concentrated will have a natural tendency to migrate to a solution with a higher concentration. For example, if you had a container full of water with a low salt concentration and another container full of water with a high salt concentration and they were separated by a semi-permeable membrane, then the water with the lower salt concentration would begin to migrate towards the water container with the higher salt concentration.

Reverse Osmosis works by using a high pressure pump to increase the pressure on the salt side of the RO and force the water across the semi-permeable RO membrane, leaving almost all (around 95% to 99%) of dissolved salts behind in the reject stream. The amount of pressure required depends on the salt concentration of the feed water. The more concentrated the feed water, the more pressure is required to overcome the osmotic pressure.

The desalinated water that is dematerialized or deionized, is called permeate (or product) water. The water stream that carries the concentrated contaminants that did not pass through the RO membrane is called the reject (or concentrate) stream.

Reverse Osmosis is capable of removing up to 99%+ of the dissolved salts (ions), particles, colloids, organics, bacteria and pyrogens from the feed water (although an RO system should not be relied upon to remove 100% of bacteria and viruses). An RO membrane rejects contaminants based on their size and charge. Any contaminant that has a molecular weight greater than 200 is likely rejected by a properly running RO system (for comparison a water molecule has a MW of 18). Likewise, the greater the ionic charge of the contaminant, the more likely it will be unable to pass through the RO membrane. For example, a sodium ion has only one charge (monovalent) and is not rejected by the RO membrane as well as calcium for example, which has two charges. Likewise, this is why an RO system does not remove gases such as CO2 very well because they are not highly ionized (charged) while in solution and have a very low molecular weight. Because an RO system does not remove gases, the permeate water can have a slightly lower than normal pH level depending on CO2 levels in the feed water as the CO2 is converted to carbonic acid.

Reverse Osmosis is very effective in treating brackish, surface and ground water for both large and small flows applications. Some examples of industries that use RO water include pharmaceutical, boiler feed water, food and beverage, metal finishing and semiconductor manufacturing to name a few.

The industrial world relies on a lot of different processes to keep things operating smoothly. With so much machinery, chemicals and other materials involved over such a wide range of industries, every single process has its place and plays a role. Filtration is one process that is evident in many different industries and is crucial for removing unwanted particles from water and other substances. The filtration process may differ slightly from plant to plant and industry to industry, but will typically include elements of absorption, sedimentation, interception, diffusion and straining. Industrial water filtration is one area of filtration that is quite important for a variety of different reasons.

In an industrial setting, water filtration refers to the removal of particles or suspended solids from water or wastewater. The particles that need to be removed are typically larger than 0.5 microns and the action is accomplished using commercial industrial filters. Depending on the scope of the operation, one filter may be sufficient or you may need several. Sometimes, a combination of filters in a specific sequence or order is necessary to remove all of the solids and keep the process running smoothly.

Some of the different types of industrial filters that are used for water filtration include:

•  Bag filters
•  Cartridge filters
•  Multimedia filters
•  Dual media filters
•  Sand filters
•  Screen filters

Since filtration is such serious business, great care is usually taken to determine which kind of filter will do the best job. This often includes laboratory tests with a wide range of samples. Once the results are in, you will know if you need bag filters, cartridge filters or any of the other possible choices

Industrial water filtration is an important process across a range of different industries, for a range of different reasons. Products you use on a daily basis in your home, at work or even out in nature, may depend on industrial water filtration as part of their process. Some of the common industries that rely on industrial water filtration include:

• Chemicals
• Electronics
• Food and Beverage
• Pharmaceutical
• Oil and Gas
• Air and Gas
• Pulp and Paper
• Power
• Coolants

Just as good industrial water filtration through the proper use of bag filters and other filters will enhance the process, poor filtration can lead to a host of different problems.

• Depending on the specific industry in question, the consequences may range from regulatory to business to health.
• Poor filtration might lead to contamination of an order or entire batch of product, it might lead to recalls of particular products, or t might put a company on the wrong side of government laws and regulations.
• In industries such as the pharmaceutical industry, improper filtration could lead to serious human health consequences, which would then lead to serious legal consequences for the company in question.
• No matter the industry, it pays to take industrial water filtration very seriously and follow all the necessary guidelines to ensure that aspect is always operating at full capacity.

Ultrafiltration (UF) is a pressure-driven process that removes emulsified oils, metal hydroxides, colloids, emulsions, dispersed material, suspended solids, and other large molecular weight materials from water and other solutions. UF membranes are characterized by their molecular weightcut-off. UF excels at the clarification of solutions containing suspended solids, bacteria, and high concentrations of macromolecules, including oil and water, fruit juice, milk and whey, electrocoat paints, pharmaceuticals, poly-vinyl alcohol and indigo, potable water, and tertiary wastewater.

Cooling water systems are an integral part of process operations in many industries. For continuous plant productivity, these systems require proper chemical treatment and preventive maintenance.

Most industrial production processes need cooling water for efficient, proper operation. Refineries, steel mills, petrochemical plants, manufacturing facilities, food plants, large buildings, chemical processing plants, and electric utilities all rely on the cooling water system to do its job. Cooling water systems control temperatures and pressures by transferring heat from hot process fluids into the cooling water, which carries the heat away. As this happens, the cooling water heats upend must be either cooled before it can be used again or replaced with fresh makeup water. The total value of the production process will be sustained only if the cooling system can maintain the proper process temperature and pressure. The cooling system design, effectiveness and efficiency depend on the type of process being cooled, the characteristics of the water and environmental considerations.

Ultra filter vs. Conventional Filter

Ultra filtration, like reverse osmosis, is a cross-flow separation process. Here liquid stream to be treated (feed) flows tangentially along the membrane surface, thereby producing two streams. The stream of liquid that comes through the membrane is called permeate. The type and amount of species left in the permeate will depend on the characteristics of the membrane, the operating conditions, and the quality of feed. The other liquid stream is called concentrate and gets progressively concentrated in those species removed by the membrane. In cross-flow separation, therefore, the membrane itself does not act as a collector of ions, molecules, or colloids but merely as a barrier to these species.

Conventional filters such as media filters or cartridge filters, on the other hand, only remove suspended solids by trapping these in the pores of the filter-media. These filters therefore act as depositories of suspended solids and have to be cleaned or replaced frequently. Conventional filters are used upstream from the membrane system to remove relatively large suspended solids and to let the membrane do the job of removing fine particles and dissolved solids. In ultrafiltration, for many applications, no prefilters are used and ultrafiltration modules concentrate all of the suspended and emulsified materials

Ultrafiltration Membranes

Ultrafiltration Membrane modules come in plate-and-frame, spiral-wound, and tubular configurations. All configurations have been used successfully in different process applications. Each configuration is specially suited for some specific applications and there are many applications where more than one configuration is appropriate. For high purity water, spiral-wound and capillary configurations are generally used. The configuration selected depends on the type and concentration of colloidal material or emulsion. For more concentrated solutions, more open configurations like plate-and-frame and tubular are used. In all configurations the optimum system design must take into consideration the flow velocity, pressure drop, power consumption, membrane fouling and module cost.