Introduction to Water and Wastewater Treatment Processes
Pure water (H20) is colorless, tasteless, and odorless. It is composed of hydrogen and oxygen. Because water becomes contaminated by the substances with which it comes into contact, it is not available for use in its pure state. To some degree, water can dissolve every naturally occurring substance on the earth. Because of this property, water has been termed a “universal solvent.” Although beneficial to mankind, the solvency power of water can pose a major threat to industrial equipment. Corrosion reactions cause the slow dissolution of metals by water. Deposition reactions, which produce scale on heat transfer surfaces, represent a change in the solvency power of water as its temperature is varied. The control of corrosion and scale is a major focus of water treatment technology.
Waste Water Treatment
Water treatment is an important industry requirement and comes under 4 main branches which include boiler water treatment, cooling water treatment, water purification and the treatment of wastewater effluent. It is considered that these cover the majority of Water treatment processes across the globe. water treatment can be hugely beneficial to your business not least because it can save you tens of thousands of Rupees per year in operating costs but because of reduced maintenance it can also increase efficiency and output. It is an industry which can quickly pay for itself and give back in spades. In addition to the financial benefits it is also important to remember operating efficiently and safely of your employees is too, efficiency and safety come hand in hand.
Sewage treatment Plant is the process of removing contaminants from wastewater, primarily from household sewage. It includes physical, chemical, and biological processes to remove these contaminants and produce environmentally safe treated wastewater (or treated effluent).
Impurities in water and their sanitary significance
3.1 Physical impurities:
- (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.
- 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.
- 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.
- Odour: It is in water due to undesirable for domestic as well as industrial purposes.
3.2 Chemical impurities in water:
- 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.
- 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.
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.
Name the factors that affect water quality
4.1 Boiler Water Treatment
Boiler water treatment is a popular treatment process in industrial plants because of the problem caused by scale formation and corrosion within the system which comes with stream. This at best can cause increased energy costs and a much decreased level of efficiency and a shorter plant life. At worst this can lead to a catastrophic failure with the damage of machinery and more seriously injury and loss of life. Boilers have to work with incredible pressures as water heated in to steam expands in volume over 1000 times and has to travel down narrow steam pipes at over 100 kilometres an hour. Water treatment is an important aspect in making sure this process is kept safe and efficient.
4.1..1 Low pressure Boiler Water Treatment
Lower pressure Boiler & its Use
In a low-pressure boiler the pressure does not exceed 15 psi, and hot water heating boilers are not designed to exceed over 260 psig. The temperature in a low-pressure boiler will not rise above 250 degrees F. Because these types of boilers operate at lower pressures, they don’t need to be monitored regularly and only have to be checked when the appliance begins to break down.
Low-pressure boilers are often used in buildings and designed to heat rooms through radiators. Types of buildings may include restaurants, hospitals, office buildings and schools. The boilers are able to heat the water used in bathrooms and use steam to heat the different rooms throughout the building, allowing them to become warm.
4.1.2 High pressure Boiler Water Treatment
High-Pressure Boiler Definition
High-pressure boilers will heat steam above 15 psi and water at pressures that exceed 160 psig. Temperatures in high-pressure boilers will exceed 250 degrees F. Because of the elevated pressure at which these boilers operate, they need to be monitored to ensure safety at all times. High-pressure boiler operators must inspect switches, valves, safety devices and leaks on a regular basis. Any malfunctions need to be fixed immediately to prevent further damage from occurring.
High-Pressure Boiler Uses
High-pressure boilers are used in industries and designed to generate the steam found in power plants, dry cleaners and laundromats. These boilers were also used in locomotive steam engines to give them the necessary power to run. Individuals who maintain these boilers need to follow certain precautions to avoid burns, shocks and other hazardous conditions.
Boiler Water Treatment
The treatment and conditioning of boiler feed water must satisfy three main objectives:
Continuous heat exchange
Production of high quality steam
The primary function of a boiler water treatment program is to keep heat transfer surfaces (stream generating and associated tubes) free from scale and deposition. The second requirement is corrosion inhibition. Boiler deposits are problematical, as they typically contain undesirable levels of metal oxides, mineral scale, sludge, or various combinations.
The components of boiler tube deposits and the mechanisms by which they form are varied and can be complex. Corrosion generally occurs because of excessive levels of dissolved oxygen but can also develop under tube deposits. Deposits and corrosion can lead to boiler tube failures that result in costly repairs and downtime. Boiler systems require effective chemical treatment, accurate monitoring and control
External treatment is the reduction or removal of impurities from water outside the boiler. In general, external treatment is used when the amount of one or more of the feed water impurities is too high to be tolerated by the boiler system in question. There are many types of external treatment (softening, evaporation, deaeration, membrane contractors etc.) which can be used to tailor make feed-water for a particular system. Internal treatment is the conditioning of impurities within the boiler system. The reactions occur either in the feed lines or in the boiler proper. Internal treatment may be used alone or in conjunction with external treatment. Its purpose is to properly react with feed water hardness, condition sludge, scavenge oxygen and prevent boiler water foaming.
The water treatment facilities purify and deaerate make-up water or feed water. Water is sometimes pretreated by evaporation to produce relatively pure vapor, which is then condensed and used for boiler feed purposes. Evaporators are of several different types, the simplest being a tank of water through which steam coils are passed to heat the water to the boiling point. Sometimes to increase the efficiency the vapor from the first tank is passed through coils in a second tank of water to produce additional heating and evaporation. Evaporators are suitable where steam as a source of heat is readily available. They have particular advantages over demineralization, for example, when the dissolved solids in the raw water are very high.
4.2 Cooing Tower Water Treatment
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 up and 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 depends on the type of process being cooled, the characteristics of the water and environmental considerations.
4.3 Pharmaceutical Water Treatment (High Purity)
4.3.1 Water For Injection (EFI)
4.3.2 Water For other process.
Pharmaceutical water treatment requires removing contaminents from municipal drinking water to meet USP standards. There are two basic types of pharmaceutical water; water for topical use or cleaning (sterle purified water, or PW), or water for injection(WFI) which includes sterile water for irrigation and most sterile water for inhalation.
For PW, USP guidelines require a conductivity limit of 0.6–4.7 µS/cm, a total organic carbon or total oxidizable carbon (TOC) limit of 500 ppb (µg/L), and a bacteria-count limit of 100 cfu/mL.
For WFI, the USP guidelines require a conductivity limit of 0.6–4.7 µS/cm, a TOC limit of 500 ppb (µg/L), an endotoxin limit of 0.25 end toxin units/mL and a bacteria-count limit of 10 cfu/100 mL.
The main difference between PW and WFI is the amount of bacterial contamination allowed, measured by colony count and by endotoxin level.
Every water treatment plant is unique, but may include a combination of these methods:
Multimedia filtration: Multimedia filters are designed to remove the bulk of suspended contaminants whose size exceeds 10–30 µm.
Activated carbon (AC): AC beds, also known as activated carbon filters, most commonly are used to remove chlorine and chloramine compounds from feed water. This filtration process protects downstream equipment such as RO membranes and IX resin beads from the damaging oxidizing action of chlorine and chloramine compounds.
Ion Exchange (IX) units: IX technology exchanges undesirable feed water cations and anions with desirable cations and anions. Cations are positively charged atoms and molecules. Anions are negatively charged atoms and molecules. Cation IX units exchange undesirable feed water cations such as calcium, magnesium, lead, and copper with desirable hydrogen ions. Anion IX units exchange undesirable feed water anions such as chloride, sulfate, phosphate, and nitrate with desirable hydroxide ions. The resulting hydrogen and hydroxide ions then combine to form water.
Distillation: Distillation units heat the feed water to its boiling point. Most dissolved and suspended contaminants remain in the water phase. The steam that is produced is condensed and typically meets WFI and PW standards.
Reverse Osmosis (RO) water treatment: RO water treatment has become the standard at many pharmaceutical water treatment plants. RO technology can be a costeffective replacement for dual cation and anion IX units. RO systems reduce the need to use costly chemicals, especially those that are caustic, and they curtail the ever-increasing cost of regeneration waste disposal. The payback that results from using an RO system can be achieved in less than two years in some situations. An RO membrane system can remove as much as 98–99% or more of all dissolved contaminants and can remove essentially all suspended (particulate) contaminants. However, RO units require pretreatment to prevent scaling, fouling with living and nonliving particulate materials, and chemical attack, commonly by oxidizing agents.
Softening: A softener is a type of IX technology that controls scaling in downstream equipment. A softener controls scaling by removing hard scale–forming cations such as calcium and magnesium and exchanging (i.e., replacing) these ions for nonscale- forming sodium ions. An older term, sodium zeolite softening, frequently is used to describe water softening.
Cartridge filtration: Cartridge filtration or other prefiltration technology is used ahead of RO units to protect against fouling from suspended particles in the feed water. RO membrane systems may become fouled if sufficient suspended solids (particulate) removal is not accomplished. Typically, 1–5-µm nominally rated filter cartridges are used.
Mixed-bed IX units usually are positioned after an RO subsystem. The effluent from a mixed-bed IX unit meets USP conductivity limits for PW and WFI.
UV irradiation may be used for bacterial control.
Electrodeionization (EDI): EDI units in many cases can cost-effectively replace mixed-bed IX units. The resin beads in EDI units do not require chemical regeneration by acid and caustic. EDI units are continuously regenerated electrically.
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