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?

Water softening

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.

Softening salts

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.

Softeners maintenance

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.

Ion Exchange

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

Reverse Osmosis

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.

As the world has industrialized and its population has grown, the problem of water pollution has intensified. With numerous factories having no choice, inject untreated effluents directly into the ground, contaminating underground aquifers. Another cause of water contamination is improper strategy of sewage treatment. Since human waste contain bacteria that can cause disease. Once water becomes infected with these bacteria, it becomes a health hazard. There are following sources of sewerage effluent as: Residential apartment Commercial complex Public amenities/convenience Labour camp/Defence/Refugee camp Resorts & clubs Factories/Industries Waste management is the collection, transport, processing, recycling or disposal, and monitoring of waste materials, without affecting humans and other life systems and without disturbing the environment. The term usually relates to materials produced by human activity either at home / office / industry / agricultural fields / mines etc., and is generally undertaken to reduce their effect on health, the environment or aesthetics. Waste Management is also carried out to recover resources from it. Sewage / Effluent Treatment Plant is a facility designed to receive the waste from domestic, commercial and industrial sources and to remove materials (containing physical, chemical and biological contaminants) that damage water quality and compromise public health and safety when discharged into water receiving systems. Key Components : Sewage / Effluent collection tank: Where preliminary, effluent is collected. Screening: Any solid materials like; iron particles, stones, plastic items, grass weed, polythene paper, cloth etc are checked through bar screen filter to avoid any damages of the transferring pump. Screening: Any solid materials like; iron particles, stones, plastic items, grass weed, polythene paper, cloth etc are checked through bar screen filter to avoid any damages of the transferring pump. Equalization tank: In which, suspended materials are mixed properly to make a homogeneous mixture. An steering arrangement is employed in the tank. Neutralization tank: Some chemicals are added for maintaining Ph, and for quick flocculation. Sludge tank: After neutralization and flocculation of effluent, the suspended matter undergoes settling which is called sludge. The tank is used for sludge collection. Aeration tank: A mechanical aeration system is adopted in the tank for growth of biomass which are easily coagulates suspended and dissolved particle. Bio reactor: Where biomass is developed in aerobic condition. Lamella filtration: After aeration of effluent, it allows to further settling with certain contact time. Gradually all solids matter deposits at the bottom while the liquid water passed to PSF Pressure sand filter (PSF): Used to remove suspended impurities from the water. Activated carbon filter (ACF): De-odorize any smell in the water. UV/chlorination disinfection: After de-odorizing of water, it is disinfected by either UV (ultraviolet radiation) or with chlorine. So that all types of micro-organisms, pathogens are killed before going to further use. Final water discharge: The discharged water is used for various purpose like, gardening, cleaning, irrigation, car washing

Bacteria and other microorganisms are removed from water through disinfection. This means that certain substances are added to kill the bacteria, these are called biocides. Sometimes disinfection can also be done with UV-light.

When bacteria are used for water purification there are two sorts of transfer; one of these is aerobic transfer. This means, that bacteria that are oxygen dependent are converting the contaminants in the water. Aerobic bacteria can only convert compounds when plenty of oxygen is present, because they need it to perform any kind of chemical conversion. Usually the products they convert the contaminants to are carbon dioxide and water.

Our package sewage treatment plant has a relatively low odor profile. Our treatment reactors are all sealed and installed below grade. This limits the amount of odor that can escape. In addition we can install an activated carbon scrubber system to clean the collected off gasses before releasing them to the atmosphere. We can also use sludge bagging systems to dewater wasted solids before disposal thus eliminating another possible source of odor.

Wasted solids (sludge & screenings) can be collected and dewatered for removal by a licensed sewage hauling company. Sludge holding tanks can be emptied by a septic hauler for disposal.

Whatever levels are needed. The design and equipment selection for our facilities is based on the treatment levels required by the wastewater treatment plant permit and local regulatory agencies. We have facilities that meet the strictest effluent limits in many states and climates. Whatever treatment level you need, we can accomplish it.

Yes. Our facilities can be built in phases with the being constructed to the full build out capacity and only the necessary tanks and equipment being installed for the current capacity. When additional capacity is needed, the additional tanks and equipment can be added to expand the capacity of your facility. Wastewater Treatment Plant Phasing is an effective way to lower upfront costs.

Newer technology does not mean it is better. MBRs can cost substantially more to operate and maintain than extended aeration systems. Our treatment process is time tested, effective and reliable.

Package plants are predesigned, prefabricated and preassembled. They arrive completed on a flatbed truck. There is little to no flexibility in regards to configuration. Aquila ‘s facilities are custom designed and constructed specifically for your project to meet your needs. In addition, finding replacement parts is easier as the equipment used in facilities are widely available on the open market from many different suppliers.

We almost always begin with effluent disposal. The method of effluent disposal will dictate the required treatment level and therefore the equipment that will be necessary to achieve it.

All stages. Most of our clients contact us during the early design stage of a project. Because of the potential length of the permitting process, it is beneficial that we become involved at a very early stage of a development. We can however begin our involvement at any point.

Yes. We at Aquila, will usually provide a basic site plan based on a past facility we have completed that is the same or similar to what we anticipate you will need. Once we enter into a contract and the details of the project get worked out, we will develop a plan specific to your project.

Yes. We can contract a local operator to run your facility. The certification and staffing levels required vary by region. We will usually take a supporting role performing inspections and responding to any issues that may arise.

YES, We does operate wastewater treatment plants. We provide plant startup, operations training, consulting and will even contract operations staff as a service to our clients but we do operate the plants ourselves.

Wastewater Treatment Purpose: To manage water discharged from homes, businesses, and industries to reduce the threat of water pollution. Wastewater Treatment Pre-treatment Occurs in business or industry prior to discharge Prevention of toxic chemicals or excess nutrients being discharged in wastewater Preliminary Treatment removes large objects and non-degradable materials protects pumps and equipment from damage bar screen and grit chamber Bar Screen catches large objects that have gotten into sewer system such as bricks, bottles, pieces of wood, etc. Grit Chamber removes rocks, gravel, broken glass, etc. Mesh Screen removes diapers, combs, towels, plastic bags, syringes, etc. Measurement and sampling at the inlet structure a flow meter continuously records the volume of water entering the treatment plant water samples are taken for determination of suspended solids and B.O.D Suspended Solids the quantity of solid materials floating in the water column B.O.D. = Biochemical Oxygen Demand a measure of the amount of oxygen required to aerobically decompose organic matter in the water Measurements of Suspended Solids and B.O.D. indicate the effectiveness of treatment processes Both Suspended Solids and B.O.D. decrease as water moves through the wastewater treatment processes Primary Treatment a physical process wastewater flow is slowed down and suspended solids settle to the bottom by gravity the material that settles is called sludge or biosolids Sludge from the primary sedimentation tanks is pumped to the sludge thickener. more settling occurs to concentrate the sludge prior to disposal Primary treatment reduces the suspended solids and the B.O.D. of the wastewater. From the primary treatment tanks water is pumped to the trickling filter for secondary treatment. Secondary treatment will further reduce the suspended solids and B.O.D. of the wastewater Secondary Treatment Secondary treatment is a biological process Utilizes bacteria and algae to metabolize organic matter in the wastewater In Cape Girardeau secondary treatment occurs on the trickling filter the trickling filter does not “filter” the water water runs over a plastic media and organisms clinging to the media remove organic matter from the water From secondary treatment on the trickling filter water flows to the final clarifiers for further removal of sludge. The final clarifiers are another set of primary sedimentation tanks.

Before we go in to the discussions of various aerobic biological treatment processes, it is important to briefly discuss the terms aerobic and anaerobic. Aerobic, as the title suggests, means in the presence of air (oxygen); while anaerobic means in the absence of air (oxygen). These two terms are directly related to the type of bacteria or microorganisms that are involved in the degradation of organic impurities in a given wastewater and the operating conditions of the bioreactor. Therefore, aerobic treatment processes take place in the presence of air and utilize those microorganisms (also called aerobes), which use molecular/free oxygen to assimilate organic impurities i.e. convert them in to carbon dioxide, water and biomass. The anaerobic treatment processes, on other hand take place in the absence of air (and thus molecular/free oxygen) by those microorganisms (also called anaerobes) which do not require air (molecular/free oxygen) to assimilate organic impurities. The final products of organic assimilation in anaerobic treatment are methane and carbon dioxide gas and biomass. The pictures in Fig. 1 and 2 depict simplified principles of the

Parameter Aerobic Treatment Anaerobic Treatment
Process Principle
  • • Microbial reactions take place in thepresence of molecular/ free oxygen
  • • Reactions products are carbondioxide, water and excess biomass
  • • Microbial reactions take place in the absence of molecular/ free oxygen
  • • Reactions products are carbon dioxide, methane and excess biomass
Applications Wastewater with low to medium organicimpurities (COD < 1000 ppm) and forwastewater that are difficult to biodegradee.g. municipal sewage, refinery wastewateretc. Wastewater with medium to high organicimpurities (COD > 1000 ppm) and easily biodegradable wastewater e.g. food and beverage wastewater rich in starch/sugar/alcohol
Reaction Kinetic Relatively fast Relatively Slow
Net Sludge Yield Relatively high Relatively low (generally one fifth to one tenth of aerobic treatment processes)
Post Treatment Typically direct discharge or filtration/disinfection Invariably followed by aerobic treatment
Foot-Print Relatively large Relatively small and compact
Capital Investment Relatively high Relatively low with pay back
Example Technologies Activated Sludge, Extended Aerations, Oxidation Ditch , MBR Fixed Film Process Continuously Stirred Tank Reactor, digester, up flow , anaerobic Sludge Blanket


Comparison of Aerobic Biological Treatment Options

Parameter Conventional ASP Sequencing batch reactor (SBR) Integrated Fixed Film Activated Sludge (IFAS) System MBR
Treated Effluent Quality Meets specifieddischarge standardswith additional Filtration Step Meets specifieddischarge standardswith additional Filtration Step Meets/ exceeds specifieddischarge standards withadditional filtration step Exceeds specified discharge standards without additional filtration step. Very good for recycle provided TDS level permits
Ability to adjust to variable hydraulic and pollutant loading Average Very good Very good Very good
Pretreatment Requirement Suspended impurities e.g. oil & grease and TSS removal Suspended impurities e.g. oil & grease and TSS removal Suspended impurities e.g. oil & grease and TSS removal Fine screening for suspended impurities like hair and almost complete oil & grease removal
Ability to cope with ingress of oil Average Good Average Poor & detrimental to membrane
Secondary Clarifier Requirement Needed Aeration Basin actsas clarifier Needed Clarifier is replaced byMembrane filtration
Complexity to operate & control Simple, but not operator friendly Operator friendly Operator friendly Requires skilled operators
Reliability & Proven-ness of Technology Average Very good Very good Limited references in industrial applications
Capital Cost Low Low High Very High
Operating Cost Low Low High Very High
Space Requirement High Low Average Low

Specifications MBR Plant MBBR Plant
Capital Investment High Low
Footprint Low Low
Flow Tolerance Low High
Aeration Blowers Required Required
Recirculation Pumps Required Not Required
Air Scouring Blowers Required Not Required
Screening Requirements High Low
Chemical Usage High N/A
Operational Difficulty High Low

Comparison: 800 m3/day

MBBR RBC Activated Sludge SBR
No residualsuspended solids No residual suspendedsolids Requires residualsuspended solids(MLSS) Requires residualsuspended solids(MLSS)
Self regulating, nooperator adjustments Self regulating, nooperator adjustments Operator adjusts MLSSLevels Operator adjusts MLSSLevels
Single pass flowthrough Single pass flowThrough MLSS sludge recycledback through plant May or may not requireMLSS recycle
1 hour retention time(based on 800m3/d) 4 hours retention time 4 hours retention time 5 hours retention time(includes clarification)
8.25 m2 treatmentArea 64 m2 treatment area 33.75 m2 treatment area 31.5 m2 treatment area(includes clarification)
Not affected by highFlows Biology stripped ofmedia with high flows MLSS can be flushedout with high flows Rarely affected by highFlows
Low mechanicalequipment High mechanicalequipment Moderate mechanicalequipment Low mechanicalEquipment
Stable nutrientremoval Unstable nutrientremoval Unstable nutrientremoval Stable nutrient removal

3.1 Physical impurities:

(i) Colour: Yellowish thing indicates the presence of chromium and appreciable amount of organic matter. Yellowish red colour indicates the presence of iron, while red brown colour indicates the presence of peaty matter.

(ii) Turbidity: It is due to the colloidal ,extermely fine suspension such as clay, slit,finely divided matters(organic and inorganic) micro organisms like plankton etc.

(iii) Taste: It is due to the prsence of dissloved mineral in water produces taste, but not odour. Bitter taste can be due to the prsence of iron, alumminium, maganese, sulphate or excess of lime.Soapy taste can be due to the presence of large amount of sodium bi carbonate.Brackish taste is due to the presence of unusual amount of salts.Polatable Taste is due to the presence of dissolved gases and minerals like nitrates in water.

(iv) Odour: It is in water due to undesirable for domestic as well as industrial purposes.

3.2 Chemical impurities in water:

(i) Acidity: It is not any specific pollutant and it simply determines the power to neutralise hydroxyl ions and is, usually expressed in terms of ppm( or mg/L) of calcium carbonate equivalent.Surface waters and ground waters attain acidity from industrial wastes like acid, mine, drainage, pickling liquors etc.

(ii) Gases: All natural waters contain dissolved atmosphere Co2. Its solubility depends upon temperature, pressure and dissolved mineral content of water.
On the other hand dissolved oxygen in water is essential to the life of aquatic organisms such as fishes. Polluted waters and sewages contains nitrogen in the form of nitrogenous organic compounds and urea, which are partially converted in to NH3.

3.3 biological Impurities:

Bacteria, fungi and algae are found in most surface waters. Bacteria are measured by culturing a sample and counting the colony forming units per milliliter (CFU/ml). City water treatment facilities commonly add chlorine to kill microorganisms. This chlorine is removed in the first step of most water purification systems which allows bacteria to multiply in the system. Distillation effectively kills microorganisms, reverse osmosis removes them and UV light can control their growth. All ultrapure water systems must have a 0.2 micron or smaller absolute filter on the outlet to prevent bacteria from contaminating the ultrapure product water. In addition, all water pathways in the system should be regularly sanitized.

Gaseous Impurities:

CO2 dissolves in water to form weakly acidic carbonic acid (H2CO3). This gas can be measured with a conductivity/resistivity meter. CO2 is only removed by strong base anion exchange resins. Oxygen is the most common non-ionized gas and is monitored with oxygen sensing electrodes. Oxygen may cause corrosion of metal surfaces and is removed by anion exchange resins in the sulfide form.

5.1 Membranes & separation

5.1.1 Reverse Osmosis Plant

5.1.2 Ultra Filtration Plant

5.1.3 Nano Filtration Plant

5.1.4 Micro Filtration Plant

Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane. This membrane-technology is not properly a filtration method. In RO, an applied pressure is used to overcome osmotic pressure, a colligative property, that is driven by chemical potential, a thermodynamic parameter. RO can remove many types of molecules and ions from solutions and is used in both industrial processes and in producing potable water. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be “selective,” this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.

In the normal osmosis process, the solvent naturally moves from an area of low solute concentration (High Water Potential), through a membrane, to an area of high solute concentration (Low Water Potential). The movement of a pure solvent is driven to reduce the free energy of the system by equalizing solute concentrations on each side of a membrane, generating osmotic pressure. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, there are key differences between reverse osmosis and filtration. The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration. Moreover, reverse osmosis involves a diffusive mechanism so that separation efficiency is dependent on solute concentration, pressure, and water flux rate.[1] Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and othereffluent materials from the water molecules.

Ultrafiltration (UF)

Ultrafiltration (UF) is a variety of membrane filtration in which forces like pressure or concentration gradients leads to a separation through a semipermeable membrane. Suspended solids andsolutes of high molecular weight are retained in the so-called retentate, while water and low molecular weight solutes pass through the membrane in the permeate. This separation process is used in industry and research for purifying and concentrating macromolecular (103 – 106 Da) solutions, especially protein solutions. Ultrafiltration is not fundamentally different from microfiltration,nanofiltration or membrane gas separation, except in terms of the size of the molecules it retains – it is defined by the Molecular Weight Cut Off (MWCO) of the membrane used. Ultrafiltration is applied in cross-flow or dead-end mode.

Industries such as chemical and pharmaceutical manufacturing, food and beverage processing, and waste water treatment, employ ultrafiltration in order to recycle flow or add value to later products. But also blood dialysis belongs to ultrafiltration.


Nanofiltration is a relatively recent membrane filtration process used most often with low total dissolved solids water such as surface water and fresh groundwater, with the purpose of softening (polyvalent cation removal) and removal of disinfection by-product precursors such as natural organic matter and synthetic organic matter.[1] [2]

Nanofiltration is also becoming more widely used in food processing applications such as dairy, for simultaneous concentration and partial (monovalent ion) demineralisatio

Nanofiltration is a membrane filtration based method that uses nanometer sized cylindrical through-pores that pass through the membrane at a 90°. Nanofiltration membranes have pore sizes from 1-10 Angstrom, smaller than that used in microfiltration and ultrafiltration, but just larger than that in reverse osmosis. Membranes used are predominantly created from polymer thin films. Materials that are commonly used include polyethylene terephthalate or metals such as aluminum.[3] Pore dimensions are controlled by pH, temperature and time during development with pore densities ranging from 1 to 106 pores per cm2. Membranes made from polyethylene terephthalate and other similar materials, are referred to as “track-etch” membranes, named after the way the pores on the membranes are made.[4] “Tracking” involves bombarding the polymer thin film with high energy particles. This results in making tracks that are chemically developed into the membrane, or “etched” into the membrane, which are the pores. Membranes created from metal such as alumina membranes, are made by electrochemically growing a thin layer of aluminum oxide from aluminum metal in an acidic medium.

Range of applications

Sr NoIndustryUses
1Fine chemistry and PharmaceuticalsNon-thermal solvent recovery and management
Room temperature solvent exchange
2Oil and Petroleum chemistryRemoval of tar components in feed
Purification of gas condensates
3Bulk ChemistryProduct Polishing
Continuous recovery of homogeneous catalysts
4Natural Essential Oils and similar productsFractionation of crude extracts
Enrichment of natural compounds Gentle Separations
5MedicineAble to extract amino acids and lipids from blood and other cell culture


Microfiltration (commonly abbreviated to MF) is a type of physical filtration process where a contaminated fluid is passed through a special pore-sized membrane to separate microorganismsand suspended particles from process liquid. It is commonly used in conjunction with various other separation processes such as ultrafiltration and reverse osmosis to provide a product stream which is free of undesired contaminants.

Microfiltration usually serves as a pre-treatment for other separation processes such as ultrafiltration, and a post-treatment for granular media filtration. The typical particle size used for microfiltration ranges from about 0.1 to 10 µm.[1] In terms of approximate molecular weight these membranes can separate macromolecules generally less than 100,000 g/mol.[2] The filters used in the microfiltration process are specially designed to prevent particles such as, sediment, algae, protozoa or large bacteria from passing through a specially designed filter. More microscopic, atomic or ionic materials such as water (H2O), monovalent species such as Sodium (Na+) or Chloride (Cl-) ions, dissolved or natural organic matter, and small colloids and viruses will still be able to pass through the filter.[3]

The suspended liquid is passed though at a relatively high velocity of around 1–3 m/s and at low to moderate pressures (around 100-400 kPa) parallel or tangential to the semi-permeable membrane in a sheet or tubular form.[4] A pump is commonly fitted onto the processing equipment to allow the liquid to pass through the membrane filter. There are also two pump configurations, either pressure driven or vacuum. A differential or regular pressure gauge is commonly attached to measure the pressure drop between the outlet and inlet streams. See Figure 1 for a general setup.

Figure 1: Overall setup for the Microfiltration system

The most abundant use of microfiltration membranes are in the water, beverage and bio-processing industries (see below). The exit process stream after treatment using a micro-filter has a recovery rate which generally ranges to about 90-98 %.[6]

Membrane filtration processes can be distinguished by three major characteristics; Driving force, retentate stream and permeate streams. The microfiltration process is pressure driven with suspended particles and water as retentate and dissolved solutes plus water as permeate. The use of hydraulic pressure accelerates the separation process by increasing the flow rate (flux) of the liquid stream but does not affect the chemical composition of the species in the retentate and product streams.[14]

A major characteristic that limits the performance of microfiltration or any membrane technology is a process known as fouling. Fouling describes the deposition and accumulation of feed components such as suspended particles, impermeable dissolved solutes or even permeable solutes, on the membrane surface and or within the pores of the membrane. Fouling of the membrane during the filtration processes decreases the flux and thus overall efficiency of the operation. This is indicated when the pressure drop increases to a certain point. It occurs even when operating parameters are constant (pressure, flow rate, temperature and concentration) Fouling is mostly irreversible although a portion of the fouling layer can be reversed by cleaning for short periods of time.

Microfiltration membranes can generally operate in one of two configurations.

Cross-flow filtration: where the fluid is passed through tangentially with respect to the membrane.[16] Part of the feed stream containing the treated liquid is collected below the filter while parts of the water are passed through the membrane untreated. Cross flow filtration is understood to be a unit operation rather than a process. Refer to Figure 2 for a general schematic for the process.

Dead-end filtration; all of the process fluid flows and all particles larger than the pore sizes of the membrane are stopped at its surface. All of the feed water is treated at once subject to cake formation.[17] This process is mostly used for batch or semicontinuous filtration of low concentrated solutions,

Power plant

A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fossil fuelresources generally used to heat the water. Some prefer to use the term energy center because such facilities convert forms of heat energy into electrical energy.[1] Certain thermal power plants also are designed to produce heat energy for industrial purposes of district heating, ordesalination of water, in addition to generating electrical power. Globally, fossil fueled thermal power plants produce a large part of man-made CO2emissions to the atmosphere, and efforts to reduce these are varied and widespread

Textile industry and water treatment

The textile industry is very water intensive. Water is used for cleaning the raw material and for many flushing steps during the whole production. Produced waste water has to be cleaned from, fat, oil, color and other chemicals, which are used during the several production steps. The cleaning process is depending on the kind of waste water (not every plant use the same way of production) and also on the amount of used water. Also not all plants uses the same chemicals, especially companies with a special standard (environmental) try to keep water cleaned in all steps of production. So the concepts, to treat the water can differ from each other.

Water treatment with different kind of pollutants, is large-scale, because of many cleaning and removing steps involved.

The diagram above shows a general overview over the several steps in water treatment in the textile industry.

Screening, straining

This first step of treatment is to remove small particles from the process water. In this way the water will cleaned from fibres, fluff and cotton flock. Fore these filter steps drum- and bag filters are used.

Oil removal (if required)

If during the step of wool treatment, solvents like white spirit or others are used they have to be removed from the waste water. Membranes or oil removers are useful. Because of oil or other organic solvents in the water, microorganisms can be killed.


This step is useful to mix the water. With this step, the pollution is better distributed. That makes it more easy for microorganisms to treat the water. Result is a more effective biological cleaning step.


After homogenization, the solution has a pH of around 9 to 10. Neutralization of the water can be done by acid or air flow injector depending on the pH value.

Physical- chemical- treatment

If the concentration of dissolved solids is very high (sulfides, chromates, etc.) and/ or color is also in the water, the kind of treatment is various.
Possible are the following procedures:

  • catalyzed oxidation of sulfides
  • flocculation
  • decoloring with flotation
  • Biological purification

    The type of biological treatment depends on the concentration and kind of pollutant. Two biological steps are used:

    trickling filter

    The construction is a great reservoir, which is filled with plastic “pieces”, crushed siliceous rocks or other materials which have a very large surface. The large surface gives microorganisms an easy chance to grow. The trickling apparatus sprinkles the waste water over the loaded material. Air is blowing into the pool from top or from below to give the aerobe bacteria the right living conditions. With the growing of the bacteria the biologic dismantlement particles in the waste water will be treated.

    This easiest step of biological treatment is reducing the BOD5 between 50 and 70%. A disadvantage is a very good filtrated water without particles which could clog the spray nozzles. Depending on this fact a flocculation process before trickling is necessary.

    Activated sludge

    With this kind of procedure the waste water does not have to be flocculated because the bacteria live in the sludge. The principle is easy, waste water is filled into a pool where the bacteria are living. By a fan air is blowing into the water to give the aerobe bacteria the right growing conditions. The sludge, together with the bacteria are the activated sludge. BOD5removal rates reach 90 to 95%.

    To dump the sludge, it has to be thicken. This can be done by different procedures, depending on the amounted sludge, which have to be dumped.


    If it is necessary this last step of treatment will remove the color by oxidation, adsorption or other procedures.

  • Demineralization Plant:
  • Demineralization or Deionisation is the process of removing mineral salts from water by using the ion exchange process. Impurities that remains dissolved in water dissociate to form positive and negative charged particles known as ions. An ion-exchange vessel holds ion-exchange resin of the required type through which water is allowed to pass. The selective ions in the water are exchanged with ions or radicals loosely held by the resin. In this way, the water is passed through several vessels or a mixed bed vessel so that both positive and negative ions are removed and water is dematerialized.

  • Water Softening :
  • ion-exchange resins are used to replace the magnesium and calcium ions found in hard water with sodium ions. When the resin is fresh, it contains sodium ions at its active sites. When in contact with a solution containing magnesium and calcium ions (but a low concentration of sodium ions), the magnesium and calcium ions preferentially migrate out of solution to the active sites on the resin, being replaced in solution by sodium ions. This process reaches equilibrium with a much lower concentration of magnesium and calcium ions in solution than was started with.

    The resin can be recharged by washing it with a solution containing a high concentration of sodium ions (e.g. it has large amounts of common salt (NaCl) dissolved in it). The calcium and magnesium ions migrate off the resin, being replaced by sodium ions from the solution until a new equilibrium is reached. The salt is used to recharge an ion-exchange resin which itself is used to soften the water.

    Filtration :

  • Slow sand filters :
  • Slow sand filters :are used in water purification for treating raw water to produce a potable product. They are typically 1 to 2 metres deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water. The length and breadth of the tanks are determined by the flow rate desired by the filters, which typically have a loading rate of 0.1 to 0.2 metres per hour (or cubic metres per square metre per hour). Slow sand filters differ from all other filters used to treat drinking water in that they work by using a complex biological film that grows naturally on the surface of the sand. The sand itself does not perform any filtration function but simply acts as a substrate.

  • Rapid sand filter
  • The rapid sand filter or rapid gravity filter is a type of filter used in water purification and is commonly used in municipal drinking water facilities as part of a multiple-stage treatment system.[1]Rapid sand filters use relatively coarse sand and other granular media to remove particles and impurities that have been trapped in a floc through the use of flocculation chemicals—typically salts of aluminium or iron. Water and flocs flows through the filter medium under gravity or under pumped pressure and the flocculated material is trapped in the sand matrix.

    Mixing, flocculation and sedimentation processes are typical treatment stages that precede filtration. Chemical additives, such as coagulants, are often used in conjunction with the filtration system.

  • Screen Filter
  • A screen filter is a type of filter using a rigid or flexible screen to separate sand and other fine particles out of water for irrigation or industrial applications. These are generally not recommended for filtering out organic matter such as algae, since these types of contaminants can be extruded into spaghetti-like strings through the filter if enough pressure drop occurs across the filter surface. Typical screen materials include stainless steel (mesh), polypropylene, nylon and polyester.

  • Coagulation
  • Coagulation (thrombogenesis) is the process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel. Disorders of coagulation can lead to an increased risk of bleeding (hemorrhage) or obstructive clotting (thrombosis).[1]

    Coagulation is highly conserved throughout biology; in all mammals, coagulation involves both a cellular (platelet) and a protein (coagulation factor) component.[2] The system in humans has been the most extensively researched and is the best understood.[citation needed]

    Coagulation begins almost instantly after an injury to the blood vessel has damaged the endothelium lining the vessel. Exposure of the blood to proteins such as tissue factor initiates changes to blood platelets and the plasma protein fibrinogen, a clotting factor. Platelets immediately form a plug at the site of injury; this is called primary hemostasis. Secondary hemostasis occurs simultaneously: Proteins in the blood plasma, called coagulation factors or clotting factors, respond in a complex cascade to form fibrin strands, which strengthen the platelet plug.

  • Flocculation
  • Flocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flake; either spontaneously or due to the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a solution. In the flocculated system, there is no formation of a cake, since all the flocs are in the suspension.

  • Neutralization
  • In chemistry,Neutralization (or neutralisation, see spelling differences) is a chemical reaction in which an acid and a base react to form a salt.Water is frequently, but not necessarily, produced as well. Neutralizations with Arrhenius acids and bases always produce water where acid–alkali reactions produce water and a metal salt.

    Often, neutralization reactions are exothermic (the enthalpy of neutralization). For example, the reaction of sodium hydroxide and hydrochloric acid. However, forms of endothermic neutralization do exist, such as the reaction between sodium bicarbonate (baking soda) and acetic acid (vinegar).

    Neutralization reactions do not necessarily imply a resultant pH of 7. The resultant pH will vary based on the respective strengths of the acid and base reactants.

  • Sedimentation
  • Sedimentation is a physical water treatment process using gravity to remove suspended solids from water.Solid particles entrained by the turbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans. Settling basins are ponds constructed for the purpose of removing entrained solids by sedimentation. Clarifiers are tanks built with mechanical means for continuous removal of solids being deposited by sedimentation.