Water Treatment

Water treatment & utilization of recycled water

 General properties of water: -water is a tasteless, odourless, liquid at ambient temperature and pressure, and appears colourless. The freezing point of water is 0°C (32 f) convert in solid phase. Boiling point of water is 100 °C (212 F) convert in gas (vapours) phase Density of water is 1 it most dense at 4 °C.

Water in life: –

Water is an essential element for life. Water makes up 50-90of the weight of living things protoplasm is solution of water and carbohydrates, proteins fats and salts.it is necessary to digestion and absorption of most essential elements and excretion of body waste. Water resources are source of water that are potentially useful for agriculture, industrial and environmental activities

Water pollution: –

Water pollution van be defined as the presence in water of some foreign substances or impurities (organic, inorganic, radiological or biological) in such quantity to constitute a health hazard by lowering the water quality and making it unfit for use.

Water Treatment Technologies

Processes

Empty aeration tank for iron precipitation

Elimination of hazardous chemicals from the water, many treatment procedures have been applied.

The selection of wastewater treatment systems is contingent on several factors: The degree to which a method is necessary to raise the wastewater quality to a permissible level.

(1) The control method’s flexibility.

(2) The process’s cost; and

(3) The process’s environmental compatibility.

The processes involved in removing the contaminants include physical processes such as

settling and filtration,

chemical processes such as disinfection and coagulation,

and biological processes such as slow sand filtration.

A combination selected from the following processes is used for municipal drinking water treatment worldwide.

Chemical

 

Tanks with sand filters to remove precipitated iron (not in working condition)

Chemical approaches are used in addition to physical and biological measures to reduce the discharge of pollutants and wastewater into water bodies. Different chemical procedures for the conversion into final products or the removal of pollutants are used for the safe disposal of contaminants.

• Pre-chlorinationfor algae control and arresting biological growth.
• Aerationalong with pre-chlorination for removal of dissolved iron when present with relatively small amounts of manganese.
• Disinfection for killing bacteria, viruses and other pathogens, using chlorine, ozone and ultra-violet light.

Physical

Physical techniques of wastewater treatment rely on physical phenomena to complete the removal process, rather than biological or chemical changes.

Most common physical techniques are:

• Sedimentation:-

is one of the most important main wastewater treatment procedures. Gravity settling is a method of separating particles from a fluid. The particle in suspension remains stable in quiescent conditions due to the decrease in water velocity throughout the water treatment process, following which the particles settle by gravitational force. For solids separation that is the removal of suspended solids trapped in the floc.

• Filtration:-

is the technique of removing pollutants based on their particle size is known as filtration. Pollutant removal from wastewater permits water to be reused for a variety of purposes. The types of filters used in the procedure differ depending on the contaminants present in the water. Particle filtration and Membrane filtration are the two main forms of wastewater filtration.

• Dissolved air flotation(Degasification): –

is the process of removing dissolved gases from a solution . Degasification is a low-cost method of removing carbon dioxide gas from waste water that raises the pH of the water by removing the gas.

Physio-chemical

Also referred to as “Conventional” Treatment

• Coagulation for flocculation.

The addition of coagulants destabilizes colloidal suspensions by neutralizing their charges, resulting in the aggregation of smaller particles during the coagulation process.

• Coagulant aids or polyelectrolytes:-

is to improve coagulation and for more robust floc formation.

• Polyelectrolytes or polymers

usually consist of either a positive or negative charge. The nature of the polyelectrolyte used is purely based on the source water characteristics of the treatment plant.

• These will usually be used in conjunction with a primary coagulant such as ferric chloride, ferric sulphate, or alum.

Chemical Precipitation

Chemical precipitation is a common process of eliminating heavy metals from inorganic wastewater.

The dissolved metal ions are transformed to the insoluble solid phase by a chemical interaction with a precipitant agent such as lime after the pH is adjusted to basic conditions (pH 11).

Flotation

Flotation uses bubble attachment to separate solids or dispersed liquids from a liquid phase.

Membrane Filtration

Membrane filtration has a lot of attention for inorganic effluent treatment since it can remove not only suspended solids and organic components, but also inorganic pollutants such heavy metals. For heavy metal removal, several forms of membrane filtration,

such as

• ultrafiltration
• nanofiltration and reverse osmosis,

can be used depending on the particle size that can be maintained

Ion Exchange

Ion exchange is a reversible ion exchange process in which an insoluble substance (resin) takes ions from an electrolytic solution and releases additional ions of the same charge in a chemically comparable amount without changing the resin’s structure.

Electrochemical Treatment Techniques 

• Electrodialysis (ED)
• Membrane electrolysis (ME)
• Electrochemical precipitation (EP)

Adsorption

Adsorption is a mass transfer process in which a substance is transported from the liquid phase to the surface of a solid/liquid (adsorbent) and becomes physically and chemically bonded (adsorbate). Adsorption can be classified into two forms based on the type of attraction between the adsorbate and the adsorbent: physical and chemical adsorption, commonly known as physisorption and chemisorption.

Activated Carbon

Activated carbons are effective adsorbents for a wide variety of contaminants. The adsorptive removal of color, aroma, taste, and other harmful organics and inorganics from drinking water and wastewater is one of their industrial applications.

Both a high surface area and a large pore size can improve the efficiency of activated carbon. Activated carbon was utilized by a number of studies to remove heavy metals and other types of contaminants from wastewater.

Biological Treatment

This is the method by which dissolved and suspended organic chemical components are eliminated through biodegradation, in which an optimal amount of microorganism is given to re-enact the same natural self-purification process.

Through two distinct biological process, such as biological oxidation and biosynthesis, microorganisms can degrade organic materials in wastewater. Microorganisms involved in wastewater treatment produce end products such as minerals, carbon dioxide, and ammonia during the biological oxidation process. The minerals (products) remained in the wastewater and were discharged with the effluent. Microorganisms use organic materials in wastewater to generate new microbial cells with dense biomass that is eliminated by sedimentation throughout the biosynthesis process.

Bioremediation

Bioremediation is a biological treatment method in which micro-organisms breakdown or transform hazardous contaminants in wastewater to a less toxic or non-toxic state. The following technologies can be used to bioremediate wastewater, which can be done by autotrophs or heterotrophs .Slow sand filtration using a biofilm to metabolize organic matter, adsorb soluble components and entrap particulates.

Technologies

Technologies for potable water and other uses are well-developed, and generalized designs are available from which treatment processes can be selected for pilot testing on the specific source water. In addition, a number of private companies provide patented technological solutions for the treatment of specific contaminants. Automation of water treatment is common in the developed world. Source water quality through the seasons, scale, and environmental impact can dictate capital costs and operating costs. End use of the treated water dictates the necessary quality monitoring technologies, and locally available skills typically dictate the level of automation adopted.

Desalination

Saline water can be treated to yield fresh water. Two main processes are used, reverse osmosis or distillation. Both methods require more energy than water treatment of local surface waters and are usually only used in coastal areas or where water such as groundwater has high salinity.

Portable water purification

Living away from drinking water supplies often requires some form of portable water treatment process. These can vary in complexity from the simple addition of a disinfectant tablet in a hiker’s water bottle through to complex multi-stage processes carried by boat or plane to disaster areas.

Constituent	Unit processes
Turbidity and particles	Coagulation/ flocculation, sedimentation, granular filtration
Major dissolved inorganics	Softening, aeration, membranes
Minor dissolved inorganics	Membranes
Pathogens	Sedimentation, filtration, disinfection
Major dissolved organics	Membranes, adsorption

Standards

Main article: Drinking water quality standards

enforcement.^] Two exceptions are the European Drinking Water Directive and the Safe Drinking Water Act in the United States, which require legal compliance with specific standards.

Industrial water treatment

Processes

Two of the main processes of industrial water treatment are: –

boiler water treatment and cooling water treatment. A large amount of proper water treatment can lead to the reaction of solids and bacteria within pipe work and boiler housing. Steam boilers can suffer from scale or corrosion when left untreated.

Scale deposits can lead to weak and dangerous machinery, while additional fuel is required to heat the same level of water because of the rise in thermal resistance. Poor quality dirty water can become a breeding ground for bacteria such as Legionella causing a risk to public health.

Corrosion in low pressure boilers can be caused by dissolved oxygen, acidity and excessive alkalinity. Water treatment therefore should remove the dissolved oxygen and maintain the boiler water with the appropriate pH and alkalinity levels. Without effective water treatment, a cooling water system can suffer from scale formation, corrosion and fouling and may become a breeding ground for harmful bacteria. This reduces efficiency, shortens plant life and makes operations unreliable and unsafe.

Boiler water treatment

Boiler water treatment is a type of industrial water treatment focused on removal or chemical modification of substances potentially damaging to the boiler. Varying types of treatment are used at different locations to avoid scale, corrosion, or foaming. External treatment of raw water supplies intended for use within a boiler is focused on removal of impurities before they reach the boiler. Internal treatment within the boiler is focused on limiting the tendency of water to dissolve the boiler and maintaining impurities in forms least likely to cause trouble before they can be removed from the boiler in boiler blowdown.

Cooling water treatment

Water cooling is a method of heat removal from components of machinery and industrial equipment. Water may be a more efficient heat transfer fluid where air cooling is ineffective. . Chemical additives to reduce these disadvantages may introduce toxicity to wastewater. Water cooling is commonly used for cooling automobile internal combustion engines and large industrial facilities such as nuclear and steam electric power plants, hydroelectric generators, petroleum refineries and chemical plants.

Technologies

Chemical treatment

Chemical treatments utilizes the additive of chemicals to make industrial water suitable for use or discharge. These includes processes like-

• chemical precipitation,
• chemical disinfection,
• Advanced oxidation process (AOP),
• ion exchange,
• and chemical neutralization

Physical treatment

Physical treatment involves the separation of solids form industrial wastewater either through Filtration or Dissolved air flotation. Filtration involves the use of Membrane or filters such as mechanical filters like sand filtration etc to achieve solid-liquid separation. Whereas for Dissolved air flotation,

pressurized air is pumped into the wastewater. The pressurized air then forms small bubbles which adhere to the suspended matter causing them to float to the surface of the water where they can be removed by a skimming device or an overflow.

 Biological treatment

Slow sand filters use a biological process to purify raw water to produce potable water. They work by using a complex biological film that grows naturally on the surface of sand. This gelatinous biofilm called the hypogeal layer is located in the upper few millimetres of the sand layer.

The surface biofilm purifies the water as it flows through the layer, the underlying sand provides a support medium for the biological treatment layer. The Schmutzdecke consists of bacteria, fungi, protozoa, rotifera and a range of aquatic insect larvae. As the biofilm ages, more algae may develop and larger aquatic organisms including bryozoa, snails and Annelid worms may be present. As water passes through the hypogeal layer, particles of matter are trapped in the mucilaginous matrix and soluble organic material is adsorbed. The contaminants are metabolised by the bacteria, fungi and protozoa.

Slow sand filters are typically 1–2 metres deep and have a hydraulic loading rate of 0.2–0.4 cubic metres per square metre per hour. Filters lose their performance as the biofilm thickens and reduces the rate of flow. The filter is refurbished by removing the biofilm and a thin upper layer of sand. Water is decanted back into the filter and re-circulated to enable a new biofilm to develop. Alternatively wet harrowing involves stirring the sand and flushing the biolayer through for disposal.

Physio-chemical treatment: –

Chemical flocculants are used to generate a floc in the water that traps suspended solids. Chemical polyelectrolytes are used to increase coagulation of suspended solids to improve removal.

This consist of a primary coagulant such as ferric sulphate and a coagulant aid cationic polymer being flash-mixed before it enters a Flocculation Basin.

Once the source water being treated has been flash-mixed with a primary coagulant and a polymer, they are then put into some type of flocculation basin, where slow turning or mixing of the water, mixes the chemicals together and they can then form what is called “floc” .

1. After the water has mixed and the floc has formed, it is then passed to the next stage which would be the settling The water would flow up through these tubes or plates, allowing the clear water to flow over into an effluentlaunder, which would then carry the “settled” water to the filters for further treatment.
2. The tubes/plates in the settling stage, allow a greater surface area for the “floc” to settle on. These plates are typically at a 30–45° angle, allowing the floc particles to collect in the tubes or the plates and eventually ending up in the bottom of the settling basin.
3. There is typically some sort of sludgecollection system that then will collect all of the settled floc a.k.a. sludge, and pump it or transfer the waste to a decant tank or basin, where it is later disposed of.
4. Once the settled water had travelled to the filters, and has made its way through the filters, it is then stored in a clear well, where all the filtered water gets collected for additional chemical addition: pHadjuster, chlorine or UV light.
5. After the appropriate contact timeor kill time, the water leaves the clear well and heads out to storage tanks or into the distribution, all the way to the customers faucet for us.

 

Uses of recycled or treated water: –

• after treatment the treated water may be released to a sanitary surface water in the environment.
• We can use it in the agriculture, landscape irrigation, industrial processes.
• Non portable water uses like fire protection ground water recharge, recreation, gardening, cleaning, washing purposes
• Electricity production.