Waste Water Treatment
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
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
Wastewater Treatment Purpose: To manage water discharged from homes, businesses, and industries to reduce the threat of water pollution. Wastewater 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
|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|
Air Scouring Blowers
Comparison: 800 m3/day
|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|
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.
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?
Before the purification process begins some contaminants, such as oil, can be settled in a settling tank. They can then be removed easily, after they have reached the bottom of the tank.
Removal of dangerous microorganisms
Often polluted water has to be freed from microorganisms. The water is than disinfected, usually by means of chlorination.
Removal of dissolved solids
Microorganisms are not only a threat to water; they can also be an advantage when it comes to water purification processes. They can convert harmful contaminants to harmless substances. This biological purification process usually takes a long time and it is only used for water that is polluted with contaminants that the microorganisms, usually bacteria, can convert.
Physical/ chemical techniques
When treatment by microorganisms is not an option we often use different treatment techniques, called physical/ chemical treatment techniques. Chemical treatment often deals with the addition of certain chemicals, in order to make sure that the contaminants change structure and can then be removed more easily. Fertilizers such as nitrates are removed this way. Removal of contaminants can also be done through more difficult specific chemical processes. It takes a lot of education to fully understand these purification steps. Physical treatment usually deals with purification steps such as filtration.
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).
For water softening, three types of salt are generally sold:
– Rock salt
– Solar salt
– Evaporated salt
- Rock salt as a mineral occurs naturally in the ground. It is obtained from underground salt deposits by traditional mining methods. It contains between ninety-eight and ninety-nine percent sodium chloride. It has a water insolubility level of about 0.5-1.5%, being mainly calcium sulphate. Its most important component is calcium sulphate.
- Solar salt as a natural product is obtained mainly through evaporation of seawater. It contains 85% sodium chloride. It has a water insolubility level of less than 0.03%. It is usually sold in crystal form. Sometimes it is also sold in pellets.
- Evaporated salt is obtained through mining underground salt deposits of dissolving salt. The moisture is then evaporated, using energy from natural gas or coal. Evaporated salt contains between 99.6 and 99.99% sodium chloride.
Rock salt contains a lot of matter that is not water-soluble. As a result, the softening reservoirs have to be cleaned much more regularly, when rock salt is used. Rock salt is cheaper than evaporated salt and solar salt, but reservoir cleaning may take up a lot of your time and energy.
Solar salt contains a bit more water-insoluble matter than evaporated salt. When one makes a decision about which salt to use, consideration should be given to how much salt is used, how often the softener needs cleanout, and the softener design. If salt usage is low, the products could be used alternately.
If salt usage is high, insoluble salts will build up faster when using solar salt. Additionally, the reservoir will need more frequent cleaning. In that case evaporated salt is recommended.
It is generally not harmful to mix salts in a water softener, but there are types of softeners that are designed for specific water softening products. When using alternative products, these softeners will not function well.
Mixing evaporated salt with rock salt is not recommended, as this could clog the softening reservoir. It is recommended that you allow your unit to go empty of one type of salt before adding another to avoid the occurrence of any problems.
Salt is usually added to the reservoir during regeneration of the softener. The more often a softener is regenerated, the more often salt needs to be added.
Usually water softeners are checked once a month. To guarantee a satisfactory production of soft water, the salt level should be kept at least half-full at all times.
Before salt starts working in a water softener it needs a little residence time within the reservoir, since the salt is dissolving slowly. When one immediately starts regeneration after adding salt to the reservoir, the water softener may not work according to standards.
When the water softening does not take place it could also indicate softener malfunction, or a problem with the salt that is applied.
When the water does not become soft enough, one should first consider problems with the salt that is used, or mechanical malfunctions of softener components. When these elements are not the cause of the unsatisfactory water softening, it may be time to replace the softener resin, or perhaps even the entire softener.
Through experience we know that most softener resins and ion exchanger resins last about twenty to twenty-five years.
If there is a build-up of insoluble matter in the resin, the reservoir should be cleaned out to prevent softener malfunction.
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.
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.
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.
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.
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.
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.
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 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:
- Food and Beverage
- Oil and Gas
- Air and Gas
- Pulp and Paper
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.
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 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.