Tertiary Treatment And Low Cost Treatment Of Waste Water

Tertiary Treatment And Low Cost Treatment Of Waste Water Presented by Mohammed Aamir Hussain1GC07CV029CONTENTSIntroduction

Stages Of Treatment Preliminary TreatmentPrimary Treatment Secondary Treatment Tertiary Treatment

Tertiary TreatmentFiltrationLagooningNutrient RemovalDisinfectionOdour Control

Low Cost Water TreatmentSeptic TankOxidation PondsOxidation DitchesAerated Lagoons

Sewage is created by residential, institutional, commercial establishments.It also includes household waste liquid from toilets, bathroom, kitchen etc., which are disposed through sewers.Sewage treatment is a process of removing contaminants from domestic as well as industrial waste water.It includes physical, chemical and biological processes to remove their respective contaminants.The main objective is to produce environmentally safe fluid which is reusable. IntroductionPreliminary TreatmentScreeningGrit Removal

Primary TreatmentSaponification

Secondary TreatmentActivated SludgeSurface Aerated BasinsFilter BedsSecondary Sedimentation

Tertiary TreatmentFiltrationLagooningNutrient RemovalDisinfectionOdour Control

Sewage treatment involves 4 stagesPreliminary treatment removes materials that can be easily collected from the raw waste water before they damage or block the pumps and skimmer the primary treatment clarifiers.

Screening: The sewage water is screened to remove objects like cans, sticks, rags etc., in the sewage stream.

Grit Removal: Pretreatment may include a sand or grit chamber to adjust the velocity of incoming waste water where the settlement of solids take place. Solids can damage the pumps, so they are removed.Preliminary TreatmentIn the primary treatment, sewage flows through a large tank called primary sedimentation tank, where settlement of sludge takes place, oil and grease are raised to the surface and are skimmed off.Sludge is removed towards the hopper in the base of the tank where it is pumped to sludge treatment.

Saponification: It is the chemical process that produces soap from fatty acid derivatives. Generally, it involves hydrolysis of ester to from alcohol and salt of carboxylic acid. In this process, grease and oil can sometimes be recovered.

Primary TreatmentSecondary treatment is designed to substantially degrade the biological content of the sewage which are derived from human waste, food waste, soaps and detergents. Activated Sludge: In this process, dissolved oxygen is used to promote the growth of biological flocs that removes organic material. The process traps particulate matter under ideal condition, where ammonia is converted to nitrogen gas.

Surface Aerated Basin: Most biological oxidation process for treating industrial waste water have in common the use of oxygen and microbial action. Secondary TreatmentFilter Bed: In older plants, tickling filter beds are used where the sewage liquor is spread onto the surface of bed up of coke. The liquor is typically distributed through perforated spray arms. The distributed liquor tickles through the bed and collected at the basin.

Secondary sedimentation: The final step in the secondary treatment is to settle out the filtered material through secondary clarifier and to produce sewage water containing low level of organic material and suspended matter.Surface aerated basins achieve 80-90% removalof BOD with retention time of 1-10 days.The basin may range in depth from 1.5-5mand motor driven aerators floating on the surface of waste water.

Tertiary treatmentThe purpose of tertiary treatment is to provide a final treatment stage to raise the effluent quality before it is discharged to the receiving environment.

More than one tertiary treatment process may be used at any treatment plant.

It involves: Filtration: Filtration removes much of the suspended matter. Filteration over activated carbon also called carbon absorption removes residual toxins.

Lagooning: Lagooning provides settlement and further biological improvement through storage in large man made ponds or lagoons. These lagoons are highly aerobic and colonized by native macrophyte especially reeds is often encouraged.

Sewage treatment plan and lagoon in unitedstates.Nutrient removal: Waste water may contain high levels of nutrient nitrogen and phosphorous. Nutrient removal basically involves removal of phosphorous and nitrogen. Excessive release of nitrogen and phosphorous leads to eutrophication, which can lead to the overgrowth of weeds and algae. This can cause a rapid bloom i.e., the rapid growth in the population of algae. The decomposition of algae by bacteria uses up so much of oxygen that most of the aquatic animals die. It causes deoxygenation. Different treatment processes are required to remove nitrogen and phosphorous, they are:Nitrogen removalPhosphorous removal

Nitrogen removal: The removal of nitrogen is affected through nitrification, nitrification is oxidation of nitrogen from ammonia to nitrate, followed by denitrification I.e., the reduction of nitrate to nitrogen gas. Nitrogen gas is released to the atmosphere and thus removed from the water. Nitrification itself is a two-step aerobic process, each step facilitated by different type of bacteria, initially nitrification occurs i.e., oxidation of ammonia to nitrate which is facilitated by nitrosomonas , then denitrification occurs i.e., reduction of nitrate to nitrogen gas which is facilitated by nitrobacter. Sometimes the conversion of toxic ammonia to nitrate alone is referred as tertiary treatment.Phosphorous removal: Phosphorous removal is important as it is a limiting nutrient for algae growth in many fresh water system. I t is also particularly important for the water reuse system where high phosphorous concentration may lead to reverse osmosis. Phosphorous can be removed biologically by a process called biological phosphorous removal. In this process, a bacteria names polyphosphate enriches and accumulates large number of phosphorous within their cell. Phosphorous removal can also be achieved by chemical precipitation usually with salts of iron, aluminium or lime. They may lead to excessive sludge production. Chemical phosphorous removal requires smaller equipment than biological remover, hence it is easier to operate and is often more reliable and efficient than biological phosphorous removal type. Granular laterite is another method of phosphorous removal. Once removed phosphorous in the form of phosphate rich sludge may be stored in land fill and can be used as a fertilizer. Disinfection: The purpose of disinfection in the treatment of waste water is to substantially reduce the number of microorganisms in the water to be discharged back into the environment. the type of disinfection being used, the disinfectant dosage (concentration and time), and other environmental variables. Common methods of disinfection include ozone, chlorine, ultraviolet light, or sodium hypochlorite. Chloramines, which is used for drinking water, is not used in waste water treatment because of its persistence.

Chlorination: Chorination remains the most common form of waste water disinfection due to its low cost and long-term history of effectiveness. One disadvantage is that chlorination can generate chlorinated-organic compounds that may be harmful to the environment. . Residual chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated, adding to the complexity and cost of treatment.

Ultraviolet(UV) light: UV light can be used instead of chlorine, iodine, or other chemicals. Because no chemicals are used, the treated water has no adverse effect on organisms that later consume it, as may be the case with other methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other pathogens, making them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that the target microorganisms are not shielded from the UV radiation Ozone(O3): Ozone is generated by passing oxygen (O2) through a high voltage potential resulting in a third oxygen atom becoming attached and forming O3. Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, thereby destroying many pathogenic microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site. Ozonation also produces fewer disinfection by-products than chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the requirements for special operators.

Odour Control: Odours emitted by sewage treatment are typically an indication of an anaerobic or "septic" condition. Early stages of processing will tend to produce smelly gases, with hydrogen sulphide being most common in generating complaints. Large process plants in urban areas will often treat the odours with carbon reactors, a contact media with bio-slimes, small doses of chlorine or circulating fluids to biologically capture and metabolize the obnoxious gases. Other methods of odour control exist, including addition of iron salts, hydrogen peroxide, calcium nitrate etc. to manage hydrogen sulphide levels.

LOW COST WASTE TREATMENT The following are the major low cost treatment methods. If these are properly designed designed and treated, it is possible to get desired treatment efficiency. Its operation cost and maintenance is very cheap.

- Septic tank

- Oxidation ponds

- Oxidation ditches

-Aerated lagoons

Septic tank: A tank, usually below ground, for containing sewage to be decomposed by anaerobic bacteria. A sewage-disposal tank in which a continuous flow of waste material is decomposed by anaerobic bacteria. It is also an underground tank where faecus, urine and other waste matter is made harmless using bacteria. A septic tank generally consists of a tank of between 4000 - 7500 litres size connected to an inlet wastewater pipe at one end and a septic drain field at the other. Today the design of the tank usually incorporates two chambers which are separated by means of a dividing wall which has openings located about midway between the floor and roof of the tank. Wastewater enters the first chamber of the tank, allowing solids to settle and scum to float. The settled solids are anaerobically digested, reducing the volume of solids. The liquid component flows through the dividing wall into the second chamber where further settlement takes place, with the excess liquid then draining in a relatively clear condition from the outlet into the leach field, also referred to as a drain field or seepage field, depending upon locality. How often the septic tank has to be emptied depends on the volume of the tank relative to the input of solids, the amount of indigestible solids and the ambient temperature (as anaerobic digestion occurs more efficiently at higher temperatures). The required frequency varies greatly depending on jurisdiction, usage, and system characteristics. Some health authorities require tanks to be emptied at prescribed intervals, while others leave it up to the determination of the inspector. Some systems require pumping every few years or sooner, while others may be able to go 1020 years between pumpings. Contrary to what many believe, there is no "rule of thumb" for how often tanks should be emptied. An older system with an undersized tank that is being used by a large family will require much more frequent pumping than a new system used by only a few people. Anaerobic decomposition is rapidly re-started when the tank re-fills. A properly designed and normally operating septic system is odour free and, besides periodic inspection and pumping of the septic tank, should last for decades with no maintenance. A well designed and maintained concrete, fibreglass or plastic tank should last about 50 years.

SEPTIC TANK

A properly designed and normally operating septic system is odour free and, besides periodic inspection and pumping of the septic tank, should last for decades with no maintenance. A well designed and maintained concrete, fibreglass or plastic tank should last about 50 years.

Role of soil in septic system

- The soil's job is to filter out any remaining solids, and to kill the germs in the effluent. - The purified water flows downward through the soil to the water table and should be fit to drink once it reaches the water table.

Disadvantages of septic tankExcessive dumping of cooking oils and grease can cause the inlet drains to block. Oils and grease are often difficult to degrade and can cause odour problems and difficulties with the periodic emptying.Flushing non-biodegradable items such as cigarette butts and hygiene products such as sanitary towels and cotton buds will rapidly fill or clog a septic tank; these materials should not be disposed of in this way.The use of garbage disposers for disposal of waste food can cause a rapid overload of the system and early failure.Certain chemicals may damage the working of a septic tank, especially pesticides, herbicides, materials with high concentrations of bleach or caustic soda (lye) or any other inorganic materials such as paints or solvents.Roots from trees and shrubbery growing above the tank or the drain field may clog and/or rupture them.

Playgrounds and storage buildings may cause damage to a tank and the drainage field. In addition, covering the drainage field with an impervious surface, such as a driveway or parking area, will seriously affect its efficiency and possibly damage the tank and absorption system.Unsupervised septic tanks may cause serious injury or death to children playing nearby.Excessive water entering the system will overload it and cause it to fail. Checking for plumbing leaks and practicing water conservation will help the system's operation.Very high rainfall, rapid snow-melt, and flooding from rivers or the sea can all prevent a drain field from operating and can cause flow to backup and stop normal operation of the tankOver time biofilms develop on the pipes of the drainage field which can lead to blockage. Such a failure can be referred to as "Biomat failure".Septic tanks by themselves are ineffective at removing nitrogen compounds that can potentially cause algal blooms in receiving waters; this can be remedied by using a nitrogen-reducing technology, or by simply ensuring that the leach field is properly sited to prevent direct entry of effluent into bodies of water.

OXIDATION PONDSOxidation ponds are large shallow basins enclosed by earthen embankments in which raw sewage is treated by entirely natural processes involving both algae and bacteria. They are without doubt the most important method of sewage treatment in hot climate, were sufficient land is available and were temperature is most favourable for there operation.Types of ponds

-Aerobic ponds -Anaerobic ponds -Facultative ponds

Aerobic ponds: They are the shallow ponds of 0.3 m depth so designed to maximise the growth of algae through photosynthetic action. Their use has not been widespread in waste treatment.

Anaerobic ponds: They are those designed for higher organic loadings so that photosynthetic algae action is precluded and anaerobic conditions prevail throughout the pond volume. Anaerobic decomposition degrades organic matter through successive steps to gaseous end products like methane and carbon dioxide. Such ponds are built deeper to the depth of 2.5 to 3.7m.

Facultative ponds: These ponds are relatively shallow about 0.9 to 1.5m depth. Predominantly aerobic during sunshine hours as well as some hours of night. In the remaining few hours of night, the upper may or may not be aerobic, but bottom layers are generally anaerobic, these ponds are more common

Mechanism of the process:

The aerobic bacteria present in the pond will utilize the nutrient as their food source. Oxygen is supplied to liquid naturally by atmospheric re-aeration and the major portion of oxygen is supplied by algae produced during its photosynthesis. The bacterias utilize this oxygen in addition to nutrients, metabolises and produces CO2. The algae utilizes the CO2 produced by the bacteria and with the presence of sunlight prepares its food by photosynthesis. Thus there exist a mutual relationship between algae and bacteria, this relationship is known as symbiosis. The organic matter which was complex is broken up by bacteria and converted to stable end products of water and CO2, thus the sewage is treated entirely by the natural sources.

Oxidation ditchesThe oxidation ditch is an economical, highly efficient and simple waste treatment process. The most commonly used oxidation ditch is a trapezoidal cross section of relatively shallow depth forming a continuous circuit. The oxidation ditch process is a modified form of activated sludge process and may be classified in the complete mix long term aeration group. The shape of the ditch is generally an elongated oval. The depth of the ditch varies from 1 to 1.7m, it also consist of one or more rotors revolving at required rpm in order to keep moving the sewage inside and mixing it. So that there will not be solid settlement.The raw sewage is introduced into the ditch through properly designed inlet. Due to the revolving rotor the ditch content is well mixed uniformly and it keeps moving in addition to aeration. The sludge is allowed on sledge drying bed. The BOD removal ranges from 70 to 95% depending on the nature of sewage, aerator, detention period etc.

Aerated lagoonsAerated lagoons are complete mixing ponds, usually followed by facultative ponds, are used for first stage treatment of waste waters and for pre treatment of industrial waste. The basins are three to four meter deep and are aerated with pier mounted or floating mechanical units. The aerators are designed to provide mixing for suspension of microbial flow and to supply dissolved oxygen. The biological process does not include algae and organic stabilization depends on the mixed liquor that develops within the basin, since there is no provision for settling returning activated sludge. BOD removal is a function aeration period, temperature and nature of waste water. Design aeration periods are normally in the range of three to eight days depending on the degree of treatment desired and waste water temperature during the cold season of the year.