DESIGN OF SEWAGE TREATMENT PLANT WITH

UASB TECHNOLOGY

PRESENTED BY :JAINAB NAZMA

M.MAHESHWARIA.SUNITHA

CONTENTSo OVERVIEWo INTRODUCTIONo SOURCE OF THE SEWAGE WATERo CHARACTERISTICS OF SEWAGE

WATERo SEWAGE WATER TREATMENT

PLANTo PREMILINARY TREATMENT o PRIMARY TREATEMENTo SECONDARY TREATMENT

o SLUDGE TREATMENT DISPOSAL AND UTILIZATION

o DESIGN OFSEWAGE WATER TREATMENT PLANT WITH UASB TECHNOLOGY

o CONCLUSION

INTRODUCTIONSewage treatment is not a cheap

proposition. Public bodies have to think twice before

making substantial investments particularly in developing countries where environmental issues could not be given priority due to financial constraints.

Over the years, treatment related issues are becoming expensive as governments are not only giving emphasis to treat wastewater in order to protect their resources but the concept of reuse & recycling is also becoming an important aspect.

Sewage is the liquid waste of community. It includes the wastes from water

closets, urinals, and bath rooms, kitchens of the residences and waste water from industries and also storm water.

The liquid waste from the residential areas is called as Domestic sewage and that from industries is called industrial sewage.

Sewage contains 99.9% of water only. But the small portion of solids and other materials present in sewage which causes nuisance and pollution.

Generally sewage water is treated in four treatment steps namely :

Preliminary & Primary Treatment : Is used to remove the covers, papers, oil & grease

Secondary Treatment : Is used to remove the suspended solids, COD and BOD.

Tertiary Treatment : Is used to remove coli form bacteria’s present in the water. In the case of sewage treatment different methods like physical, chemical, biological processes are used to treat wastewater. In this, biological method is divided into two categories.

1.Aerobic 2. Anaerobic process methods.

APPROACH AND DESIGN PHILOSOPHY:

The design philosophy adopted for preparing the process design has considered unit dimensions and reactor sizes in consideration with the physical limitations of the site as well as to satisfy the technical requirements.

The primary objective of the design philosophy was to prepare a sewage treatment plant, which is simple to operate, maintain and more importantly which is sustainable in the long run.

The sewage treatment scheme includes, primary treatment in the form of screening, grit removal, followed by UASB and facultative type of aerated lagoon.

OBJECTIVES OF PROJECT :

To avoid the pollution of receiving water bodies and thus preventing the health hazards.

To create hygienic environment around the town.

To protect the fish and other aquatic life. To avoid the sewage sickness of land on to

which it is disposed. To production of methane, which is used as

energy resources like power generation, used as bio gas.

Utilization of sludge like fertilizers for agriculture field and for making cement.

Reuse of waters in agriculture lands, domestic purpose and in industries for cooling.

Reduce the impact of water pollution on environment

SOURCE OF SEWAGE WATERWe should always be mindful of whether or not we

are polluting the water around us. We need to take care of our water, not abuse it.

Every town and city, whether small or big, uses water.

Cities use water for firefighting, street cleaning, and watering public areas such as parks, grass, trees, shrubs, and flowers.

Water is also used to fill public drinking fountains, including those at schools and libraries.

All of the All of the different businesses in our community also use water.

Think about all the water that is used by restaurants, hospitals, laundries, dry cleaners, golf courses, hotels, car washes, beauty shops, barber shops, gas stations, and health clubs as well as all of the other businesses in town.

The map shows the usage of water by various industries.

In this present situation due to the lack of water it is very hard to use clean water for each and every basic needs.

So we have to reuse the waste water to reduce the usage of clean water which is generated from homes, industries, hospitals, beverages etc. as mentioned above.

In this the waste water which is to be treated is mainly taken from residential homes, commercial buildings, hospitals, industries etc.

The diagram Shows usageOf water byHousehold residential building

CHARACTERISTICS OF SEWAGE WATER

Sewage is a dilute mixture of various types of wastes from the residential, public and industrial places.

The Characteristics of sewage depends on source of water mainly. Sewage contains organic and inorganic matters which may be dissolved, suspension, and colloidal state.

Sewage also contains various types of bacteria, virus, protozoa, algae, fungi etc.

The characteristics of sewage can be classified as: Physical characteristics :

◦ Color : With the time of the colour of sewage begins to get black as the decomposition starts. Fresh sewage has yellowish, grey or light brown colour. The colour of septic sewage is more or less black.

◦ Odour :Fresh domestic sewage has a slightly soapy or oily odour, but the stale sewage has offensive odour of hydrogen sulphide and other sulphur compounds

◦ Temperature : The biological activities increase with the rise in the temperature up to about 60degcel.

◦ Turbidity : The turbidity of the sewage directly depends on the quantity of solid matters present in it suspension state.

◦ Solids : The sewage contains more than 99.9 percentage of water and only 0.1 percentage of solids. These solids are present in sewage in suspended, dissolved and colloidal states.

Biological characteristics : ◦ Sewage contains large quantity of bacteria which

come from excremental matter◦  All the bacterias present in sewage are not

harmful ◦ Only pathogenic bacteria which are discharged

by the sick persons having infectious disease such as cholera, typhoid dysentery, diarrhea etc. are harmful to the human health and give difficulties at the treatment plants

◦ The sewage has following biological characteristics: Bacteria  Algae Fungi Protozoa

Chemical characteristics : ◦ Sewage contains complex organic matters

derived from urine, faces etc and inorganic chemicals .

◦ Normally fresh sewage is alkaline in nature but tends to acidity as it becomes stale.

SEWAGE TREATMENT PLANTSewage Treatment Plant is a facility designed to

receive the waste from domestic, commercial and industrial sources and to remove materials that damage water quality and compromise public health and safety when discharged into water receiving systems.

The Principal objective of waste water treatment is generally to allow human and industrial effluents to be disposed of without danger to human health or unacceptable damage to the natural environment.

Its objective is to produce an environmentally safe fluid waste stream (or treated effluent) and a solid waste (or treated sludge) suitable for disposal or reuse (usually as farm fertilizer)

CLASSIFICATION OF TREATMENT PROCESSES :

Sewage can be treated in different ways. Treatment processes often classified as:◦Preliminary treatment

Preliminary devices are designed to remove or cut up the larger suspended and floating solids, to remove the heavy inorganic solids, and to remove excessive amounts of oils or greases.

The objective of preliminary treatment is the removal of coarse solids and other large materials often found in raw wastewater.

◦Preliminary devices used are Screens -- rack, bar or fine Grit chambers   Pre-aeration tanks

SCREENS GRIT REMOVAL

PREAREATOIN TANKS

PRIMARY TREATMENT :◦ In the primary sedimentation stage, sewage flows

through large tanks, commonly called "pre-settling basins", "primary sedimentation tanks" or "primary clarifiers".

◦ In this treatment, most of the settle able solids are separated or removed from the wastewater by the physical process of sedimentation.

◦ The purpose of primary treatment is to reduce the velocity of the wastewater sufficiently to permit solids to settle and floatable material to surface

SECONDARY TREATMENT :◦ Secondary treatment involves further treatment

of the effluent, coming from the primary sedimentation tank. Filters (intermittent sand filters and trickling filters) Aeration tanks Oxidation ponds and Aerated lagoons

AERATED LAGOONS

TRICKLING FILTERS

TERTIARY TREATMENT ◦ Tertiary treatment consists in removing the

organic load left after the secondary treatment, particularly to kill the pathogenic bacteria.

◦ This treatment, normally carried out by chlorination, is generally not carried out for the disposal of sewage in water, but is carried out , while using the river stream for collecting the water for re use or for the water supplies.

◦ It may, however, sometimes be adopted, when the out fall of the sewage is very nearer to the water intake of some nearby town.

◦ A complete treatment system may consist of the application of a number of physical, chemical and biological processes to the wastewater.

PRILIMINARY TREATMENT Preliminary devices are designed to remove or cut

up the larger suspended and floating solids, heavy inorganic solids, and excessive amounts of oils or greases. Preliminary treatment consists of screenings, grit channels, detritus tank, and pre aeration tank and grease removals etc.

SCREENINGS ◦ Screening is the first unit operation used at

waste water treatment plants (WWTPs). Screening removes objects such as rags, paper, plastics, and metals to prevent damage and clogging of downstream equipment, piping, and appurtenances.

COARSE SCREENS :◦ Coarse screens are also known as Racks.

Coarse screens remove large solids, rags, and debris from wastewater, and typically have openings of 50 mm (0.25 in) or larger.

◦ Types of coarse screens include mechanically and manually cleaned bar screens, including trash racks.

FINE SCREENS◦ Fine screens are typically used to remove

material that may create operation and maintenance problems in downstream processes, particularly in systems that lack primary treatment.

◦ Typical opening sizes for fine screens are 1.5 to 6 mm (0.06 to 0.25 in).Very fine screens with openings of 0.2 to 1.5 mm (0.01 to 0.06 in) placed after coarse or fine screens can reduce suspended solids to levels near those achieved by primary clarification.

The efficiency of the screening operation depends of the spacing between screen bars:◦ Fine screening, for a spacing under 10 mm ◦ Medium screening, for spacing of 10 to 40 mm ◦ Coarse screening, for spacing of over 50 mm

GRIT REMOVAL BASINS◦ Grit removal basins, such as grit channels or grit

chamber or detritus tanks are the sedimentation basins placed in front of the waste water treatment plant to remove the inorganic particles such as sand, gravel, grit, egg shells, bones, and other non-putrescible materials that may clog channels or damage pumps due to abrasion, and to prevent their accumulation in sludge digesters.

◦ Grit chambers artifact, nothing but like sedimentation tanks.

DETRITUS TANKS◦ Detritus tanks are nothing but rectangular grit

chamber , design to flow with a smaller flow velocity and longer detention periods (about 3to 4 minutes)so as to separate out not only the larger grit, etc., but also to separate out the very fine sand particles, etc.

◦ Due to this, a large amount of organic matter will also settle out along with the inorganic grit, sand, etc.

PRE-AERATION TANKS :◦ Pre-aeration of wastewater, that is aeration

before primary treatment is sometimes provided for the following purposes:  To obtain a greater removal of suspended solids in

sedimentation tanks. To assist in the removal of grease and oil carried

in the wastewater. To freshen up septic wastewater prior to further

treatment. BOD reduction.

PRIMARY TREATMENTSEDIMENTATION OR CLARIFIERS

◦ The screens and grit chambers to remove most of the floating materials like paper, rags, cloth, wood etc. and the heavy inorganic settleable solids from the sewage.

◦ However, a part of the suspended organic solids which are too heavy to be removed as floating matters, and too light to be removed by grit chambers, are generally removed by the sedimentation tank.

TYPES OF SEDIMENTATION TANKS◦ Sedimentation tanks may function either.

Intermittently. continuously.

The intermittent settling tanks called quiescent type tanks are simple settling tanks which store sewage for a certain period and keep it in complete rest.

In a continuous flow type of sedimentation of tanks, which is generally used in modern days, the flow velocity only reduced, and sewage is not brought complete rest, as is done in an intermittent type.

The working of such a tank is simple, as the water enters from one end, and comes out from the other end.

SECONDARY TREATMENT Secondary treatment involves further treatment of

the effluent, coming from the primary sedimentation tank.

This is generally accomplished through the biological decomposition of organic matter, which can be carried out either under aerobic or anaerobic conditions.

 .In these biological unit, bacteria will decompose the fine organic matter, to produce clearer effluent

The treatment reactors, in which the organic matter destroyed and stabilized by anaerobic bacteria, known as anaerobic biological units and may consists of anaerobic lagoons, septic tanks, Imhoff tanks.

ANAEROBIC TREATMENT PROCESS :◦ There are two methods for treatment of sewage

and removing methane in sewage treatment plant. They are aerobic and anaerobic process.

◦ Nowadays anaerobic is widely used in many sewage plants. The anaerobic process is in many ways ideal for waste treatment

ADVANTAGES BY USING ANAEROBIC TREATMENT◦ As much as 80 to 90 percent of the degradable

organic portion of a waste can be stabilized in anaerobic treatment by conversion to methane gas, even in highly loaded systems.

◦ This is in contrast to aerobic systems, where only about 50 percent of the waste is actually stabilized even at conventional loadings

UPFLOW ANAEROBIC SLUDGE BLANKET REACTOR :◦ The UASB reactor maintains a high concentration

of biomass through the formation of highly settleable microbial sludge aggregates.

◦ The wastewater flows upwards through a layer of very active sludge to cause anaerobic digestion of organics of the waste water.

◦ At the top of reactor, three phase separation between gas-solid-liquid takes place.

Top view of UASB reactor

This reactor consists of an up flowing treatment tank, provided with a feed inlet distribution system at the tank bottom.

A gas solid liquid separator device is provided at the top to help provide a quiescent zone at the top of the reactor.

Top view of feed inlet boxes cross section UASB reactor

ADVANTAGES◦ Lower energy requirement combined with the

production of biogas ◦ Low nutrient requirement ◦ High degree of waste stabilization ◦ Handling high organic loading rates ◦ Lower production of excess sludge, which in

addition, is well-stabilized and therefore easier to dispose.

DISADVANTAGES◦ requires skilled operation. ◦ Capital cost is high.

IMPACT OF TEMPERATURE ON UASB REACTORS

◦ At higher temperatures, rates of reaction proceed much faster, resulting in more efficient operation and smaller tank sizes.

◦ Two optimum temperature levels for anaerobic treatment have been reported one in the mesophilicrange from 85 to 100F, and the other in the thermophilic range from 120 to 135F.

◦ Although treatment proceeds much more rapidly at thermophilic temperatures, the additional neat required to maintain such temperatures may offset the advantage obtained.

METHANE FORMATION◦ The methane producing bacteria have proven to

be very difficult to isolate and study. ◦ The conversion of organic matter into methane no

doubt proceeds through a long series of complex biochemical steps.

◦ Although almost nothing is known of the individual steps involved.

◦ One source of methane is the direct cleavage of acetic acid into methane and carbon dioxide.

◦ Major Mechanisms of Methane Formation

Acetic Acid Cleavage: C*H3COOH -> C*H4 + C02 Carbon Dioxide Reduction C02 + 8H - CH4 +

2H20

COLLECTING OF METHANE GAS◦ GAS COLLECTORS : Methane gas is produced in the

reactors which is collected by using the gas collectors from these gas collectors gas pumped through the various pipes of high durability and leak proof s like PVC

◦ GAS HOLDERS : Three floating type of gas holders will be provided floating in a concrete tank with a holding capacity of biogas production in the reactor. It will be provided with inlet, gas outlet, water drain, pressure vacuum relief valves arrangements.

GAS FLARING SYSTEM : A gas flaring system will be provided consisting of following;◦ Pressure regulate and water seal, ◦ Flame check, Pilot gas flame and valve along with electronic

lighter, ◦ Gas flare at 6m height from ground level, and Moisture trap.

Gas flaring system

LAGOONS ◦ Lagoons are one of the most popular methods for

wastewater treatment around the world they are also among the simplest and least expensive.

◦ Lagoons are especially well suited to small communities because they can cost less to construct, operate, and are simpler to maintain than other systems.

◦ They require more land than other wastewater treatment methods, but land is usually more available and less expensive in rural areas

LAGOON SYSTEMS◦ Lagoons are pond-like bodies of water or basins

designed to receive, hold, and treat wastewater for a predetermined period of time.

◦ If necessary, they are lined with material, such as clay or an artificial liner, to prevent leaks to the groundwater below

ANAEROBIC LAGOONS ◦ The word anaerobic means "without oxygen", which

describes the conditions inside this type of lagoon. ◦ Anaerobic lagoons are most often used to treat

animal wastes from dairies and pig farms, commercial or industrial wastes, or as the first treatment step in systems using two or more lagoons in a series.

AEROBIC LAGOONS◦ Dissolved oxygen is present throughout much of the

depth of aerobic lagoons. ◦ They tend to be much shallower than other lagoons,

so sunlight and oxygen from air and wind can better penetrate the wastewater.

◦ In general, they are better suited for warm,sunny climates, where they are less likely to freeze. Wastewater usually must remain in aerobic lagoons from 3 to 50 days to receive adequate treatment

FACULTATIVE LAGOONS ◦ Like environmental conditions, conditions inside the

facultative lagoons are always changing. ◦ Lagoons experience cycles due to variations in the

weather, the composition of the wastewater, and other factors.

◦ In general, the wastewater in facultative lagoons naturally settles into three fairly distinct layers or zones.

◦ Different conditions exist in each zone, and wastewater treatment takes place in all three

Facultative lagoon

AERATED LAGOONS◦ Aerated lagoons are common in small communities. ◦ These systems use aerators to mix the contents of the

pond and add oxygen to the wastewater. ◦ They are sometimes referred to as partial-mix or complete-

mix lagoons depending on the extent of aeration. ◦ Partial-mix aerated lagoons are often anaerobic lagoons

that have been adapted and upgraded to receive more wastewater

Aerated lagoons

ADVANTAGES OF LAGOON SYSTEMS:◦ Lagoon systems can be cost-effective to design

and construct in areas where land is inexpensive. ◦ They use less energy than most wastewater

treatment methods. ◦ They are simple to operate and maintain and

generally require only part-time staff. ◦ They can handle intermittent use and shock

loadings better than many systems, making them a good option for campgrounds, resorts, and other seasonal properties.

DISADVANTAGES◦ Lagoon systems require more land than other

treatment methods. ◦ They are less efficient in cold climates and may

require additional land or longer

SLUDGE TREATMENT DISPOSAL AND UTILIZATION

The sludge accumulated in a wastewater treatment process must be treated and disposed of in a safe and effective manner.

The purpose of digestion is to reduce the amount of organic matter and the number of disease-causing microorganisms present in the solids.

◦ THICKENING : Thickening is usually the first step in sludge treatment because it is impractical to handle thin sludge, a slurry of solids suspended in water.

◦ An alternative to gravity thickening is dissolved-air flotation. In this method, air bubbles carry the solids to the surface, where a layer of thickened sludge forms.

◦ DIGESTION : Sludge digestion is a biological process in which organic solids are decomposed into stable substances.

◦ Digestion reduces the total mass of solids, destroys pathogens, and makes it easier to dewater or dry the sludge.

◦ Digested sludge is inoffensive, having the appearance and characteristics of a rich potting soil.

◦ ANAEROBIC DIGESTION : Anaerobic digestion is a bacterial process that is carried out in the absence of oxygen.

◦ The process can either be thermophilic digestion, in which sludge is fermented in tanks at a temperature of 55 °C, or mesophilic, at a temperature of around 36 °C.

◦ Though allowing shorter retention time (and thus smaller tanks), thermophilic digestion is more expensive in terms of energy consumption for heating the sludge.

◦ SLUDGE DRYING BEDS :The digested sludge from the digestion tank contains lot of water, and is, therefore, first of all, dewatering or dried up, before further disposal either by burning or dumping.

◦ In India, the water of sludge is removed by drying the sludge on drying beds.

◦ Whereas western countries, dewatering is generally done by vacuum filters or by using high speed centrifuges.

Sludge drying beds

◦ DEWATERING : Digested sewage sludge is usually dewatered before disposal.

◦ Dewatered sludge still contains a significant amount of water—often as much as 70 percent—but, even with that moisture content, sludge no longer behaves as a liquid and can be handled as a solid material.

◦ Sludge-drying beds provide the simplest method of dewatering.

SLUDGE DISPOSAL The solids that result from wastewater treatment

may contain concentrated levels of contaminants that were originally contained in the wastewater.

A great deal of concern must be directed to the proper disposal of these solids to protect environmental considerations.

DISPOSAL IN WATER This is an economical but not common method

because it is contingent on the availability of bodies of water adequate to permit it.

At some seacoast cities, sludge either raw or digested is pumped to barges and carried to sea to be dumped in deep water far enough off shore to provide huge dilution factors and prevent any ill effects along shore.

Disposal on Land◦ Under land disposal the following methods may

be included: ◦ Burial ◦ Fill ◦ Application as fertilizer or soil conditioner

SLUDGE UTILIZATION ◦ Sludge Utilization for Construction Work as Cement

Ingredient About 26% of generated sludge in 2002 was utilized

as Cement Ingredient. Inorganic matter of sewage sludge comprises silica, aluminum, calcium, iron, etc. and the clay, which is used as cement ingredient, comprises the same elements.

Then, after generated sludge is dehydrated and incinerated, incinerator ash is used as cement ingredient.

Also, dewatered sludge, which contains organic matter and inorganic substance, is utilized as fuel for cement burning and cement ingredient.

◦ Sludge Utilization for Construction Work About 20% of generated sludge in 2002 was utilized

for Construction Work. In Japan, dewatered sludge is incinerated to reduce its

volume, and incinerator ash is used as soil stabilization additive, roadbed material, etc.

TERTIARY TREATMENTTertiary treatment consists in removing the

organic load left after the secondary treatment, particularly to kill the pathogenic bacteria.

This treatment, normally carried out by chlorination, is generally not carried out for the disposal of sewage in water, but is carried out , while using the river stream for collecting the water for re use or for the water supplies.

CHLORINATION SYSTEMS ◦ Chlorination system includes mainly of three units they

are Chlorine house Chlorination mix tank Chlorination contact tank

CHLORINE HOUSE : o Chlorination house will incorporate vacuum type

gaseous chlorinator along with all accessories and required number of chlorine tonner.

Chlorine house

CHLORINE MIX TANK◦ Chlorine mix tank is provided with slow speed mechanical

mixer to mix the chlorine solution with treated effluent of facultative aerated lagoon. From chlorine mix tank water will flow to chlorine contact tank.

◦ Chlorine mix tank

CHLORINE CONTACT TANK◦ In chlorine contact tank actual disinfection of treated waste water

will take place by keeping water in contact with chlorine.

Chlorine contact tank

Chlorine contact tank CHLORINATION PROCESS

◦ Chlorination of wastewater is the application of chlorine to a wastewater to accomplish some definite purpose.

◦ The purpose of chlorination may not always be disinfection and may, in fact, involve odor control or some other objective which will be noted.

◦ Chlorine may be applied in two general ways, gaseous and liquid. In general, the effective chemical form of chlorine that either destroys the microbe or acts against odor, etc., is the same

REACTIONS OF CHLORINE IN WASTEWATERS◦ When chlorine is mixed with pure water, it immediately

dissolves, forming fist hypochlorous acid and then hypochlorites:

◦ The above two forms of chlorine (hypochlorous acid and hypochlorite ion) are called "free" residual chlorine, as opposed to the reaction products of chlorine with other compounds that can also be detected using analytical techniques that are called "combined" residual chlorine.

◦ Free residual chlorine is a more effective disinfecting agent than combined residual chlorine, and generally hypochlorous acid is a much more effective disinfectant than hypochlorite ion.

DISPOSAL AND REUSE OF TREATED WATER

DISPOSAL There are two general methods of disposing of sewage effluent

Dilution i.e. disposal in water Effluent irrigation or sewage farming i.e. disposal on land

Disposal by dilution Disposal by dilution is the process whereby the treated sewage

or effluent from sewage treatment plant is discharged into a river stream, or a large body of water such as a lake or sea.

 Disposal on land In this method, the sewage effluent (treated) is generally

disposed of by applying it on land. The percolating water may either join the water table, or is collected below by a system of under drains. This method can then be used for irrigation crops.

REUSE OF TREATED WATER◦ Wastewater can be recycled/reused as a source of

water for a multitude of water demanding activities such as agriculture, aquifer recharge, aquaculture, firefighting, flushing of toilets, snow melting, industrial cooling, parks and golf course watering, formation of wetlands for wildlife habitats, recreational impoundments, and essentially for several other non-potable requirements.

REUSE OF IRRIGATION :◦ Irrigation reuse of wastewater can be for

application on: (I) agricultural crops, woodlots and pastures. (ii) Landscape and recreational areas.

DOMESTIC AND INDUSTRIAL USE :◦ Reuse of wastewater for purposes other than

irrigation may be either for: Industrial reuse; Non-potable purposes; Indirect potable purposes; or Direct potable purposes

WASTE WATER REUSE ◦ Wastewater can be recycled/reused as a source of

water for a multitude of water demanding activities such as agriculture, aquifer recharge, aquaculture, firefighting, flushing of toilets, snow melting, industrial cooling, parks and golf course watering, formation of wetlands for wildlife habitats, recreational impoundments, and essentially for several other non-potable requirements

DESIGN OF SEWAGE WATER TREATMENT PLANT WITH UASB

TECHNOLOGY DESIGN CONSIDERATIONS

◦ Design of sewage water treatment plants based on the various factors they are

DESIGN PERIOD : The treatment plant, like the sewage system, is normally designed to meet the requirements over a 15 year period after its completion.

◦ The time lag between the design and the completion should not normally exceed 2-3 years, and exceptional case 5 years.

◦ Care must be taken that the plant is not considerably under loaded in the initial stages, particularly the sedimentation tank.

POPULATION FORECAST : The population are increased by births, decreased by deaths, increased by migration and increased by annexation. These all four factors change in population.

◦ The future development of the town mostly depends on trade expansion, development of industries and surrounding countries, discoveries of mines, construction of railway stations etc.

PER CAPITA DEMAND : The entire spent water of a community should normally contribute to the total flow in a sanitary sewer. ◦ However, the observed Dry Weather Flow quantities (DWF)

usually are slightly less than the per capita water consumption, since some water is lost in evaporation, seepage into ground, leakage etc.

FLOW ASSUMPTIONS : The flow in sewers varies considerably from hour to hour and also seasonally, but for the purposes of hydraulic design it is the estimated peak flow that is adopted. ◦ The peak factor or the ratio of maximum to average flow

depends upon contributory population and the following values are recommended.

DEGREE OF TREATMENT : The degree of treatment will be mostly be decided by the regulatory agencies and the extent to which the final products of treatment are to be utilized. ◦ The regulatory bodies might have laid down standards for

the effluent or might specify the conditions under which the effluent could be discharged into a natural stream, sea or disposed of on the land.

DETENTION PERIOD : The rate of removal of BOD and SS is maximum during the first 2 to 2½ hours of settling and thereafter decreases appreciably. ◦ Hence, increase in the detention time beyond 2 to

2½ hours will not increase the percentage removal of BOD or SS proportionately

LOCATION OF TREATMENT PLANT :The treatment plant should be located as near to the point of disposal possible. ◦ If the sewage is to be disposed of finally in the

river or natural streams, the treatment plant should be located on the river bank.

◦ Care should be taken while locating the site that it should be on the downward stream side of the city and tank sufficiently away from the water intake works.

LAYOUT OF TREATMENT PLANTS  The following points should be kept in mind while

giving layout of any sewage treatment plant:1. All the plant should be located in order of

sequence, so that sewage from one process should directly go into the next process.

2. If possible all the plants should be located at such elevation that sewage can flow one plant into next under its gravitational force only.

3. All the treatment units should be arranged in such a way that minimum area is required, it will also insure economy in its cost.

4. Sufficient area should be occupied for future extension, in the beginning.

5. The site of treatment plant should be very neat and very good appearance.

TOPOGRAPHY ◦ Topographic conditions e.g. the slope of an area

etc. have an influence over the type of technology chosen and these conditions change from one site to the next. Some areas have a topography that allows easier implementation of wastewater technologies then others.

◦ The types of wastewater technologies chosen with consideration of topographic conditions work more efficiently as with these technical considerations in mind they become more effective, producing better quality effluent.

◦ Topographic conditions should be considered as a criterion however is not included in the rating sheet as it is very site specific.

CONCLUSION In these days it is very essential to treat

waste water because it pollutes the environment.

The sewage treatment scheme includes, primary treatment in the form of screening, grit removal, followed by UASB and facultative type of aerated lagoon.

Historical evolution of the application of the UASB based STPs in India and subsequent modifications over the years with respect to the design, material of construction, operation and maintenance have given a new dimension to this technology.

Reduced capital costs, increased durability of the reactors and simple operation and maintenance are some of the features of these modifications.

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