decentralised methods of sewage disposal

7/30/2019 Decentralised Methods of Sewage Disposal

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DECENTRALISED METHODSOF SEWAGE DISPOSAL

WHY ??


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THE DECENTRALIZED APPROACH TO WASTEWATER TREATMENT

IS SEEN AS BENEFICIAL FOR A NUMBER OF REASONS WHEN

COMPARED TO THE CONVENTIONAL SEWAGE SYSTEM

SAVES MONEY BY DECIDING ON A STRATEGY TO MANAGE

WASTEWATER BEFORE A CRISIS OCCURS, THEREBY AVOIDING

UNNECESSARY COST;

ALLOWS HOMEOWNERS TO CONTINUE TO USE THEIR

PROPERLY FUNCTIONING SEPTIC SYSTEMS;

BETTER WATERSHED MAINTENANCE BY ELIMINATING THE

LARGE TRANSFERS OF WATER FROM ONE WATERSHED TO

ANOTHER THAT HAPPENS WITH CENTRALIZED TREATMENT;

MOST COST-EFFECTIVE TREATMENT STRATEGY FOR RURALCOMMUNITIESWITH SPARSE POPULATIONS

ISAPPROPRIATE FOR VARYING SITE CONDITIONS INCLUDING

ECOLOGICALLY SENSITIVE AREASTREATMENT METHODS CAN

BE TAILORED TO SUIT DIFFERENT SITE CONDITIONS.


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DECENTRALISED TECHNIQUES ARE

DECENTRALIZED EVEN TO SINGLE HOUSEHOLD LEVELS

OPERABLE WITH SEMI SKILLED/ UNSKILLED LABOUR

NO MECHANICAL PARTS

REQUIRES LITTLE SPACE

NO SMELL

LESS EXPENSIVE THAN COMPARABLE CONVENTIONAL

TREATMENT SYSTEMS AND

VERY LOW MAINTENANCE COSTS

WATER CAN BE TREATED TO DISCHARGE STANDARDS AND

RECYCLED FOR IRRIGATION.


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EXAMPLES OF DECENTRALISED SEWAGE

TREATMENT

DEWATS

CESSPOOLS / DRY POOLS

SEPTIC TANKS

IMHOFF TANK

SAND FILTERS

ROOTZONE METHOD

AT-GRADE AND MOUND SYSTEM

CLUSTER SYSTEM


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CESSPOOLS/DRY POO tank, or covered cistern which can be used for or refuse.

a deep cylindrical chamber dug into the earth, having

approximate dimensions of 1 meter diameter and 2-

3 meters depth. similar to that of a hand-dug water

well.WORKING

Waste flows from the home into the cesspool.

Organic solids float to the top and inorganic solids sink to thebottom of the tank.Natural occurring bacteria in the cesspool converts the organic

solids to liquid.The clear liquid flows out the sides of the tankand into the surrounding soil.


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CESSPOOLS/DRY POOLS


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THE MAJOR PROBLEM WITH

CESSPOOLSOver time, grease, oils, soap scum, small solid particles (gunk)

build up on the walls of the cesspools.

These layers of scum buildup prevent the water from filtering

through the walls of the cesspool at the normal rate.

As a result, the cesspool starts to fill up with water. When the cesspool

fills up with water, it must be pumped out to avoid backups into the

household.

In extreme cases the walls of cesspools do not allow water to pass

through at all.

The cesspool is essentially a holding tank, requiring pumping every two t

three months, because the cesspool is not draining, and needs to be

emptied of water frequently.


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LIMITATIONS

..A cesspool should be located downhill from a well;

in any case, a distance of 50 ft. will prevent bacterial pollution of the well.

..To prevent chemical pollution, too, the distance between a well and a

cesspool placed directly uphill from it should be not less than 150 ft.

..Cesspools of the leaching type should be located at least 20 ft. away

from dwelling foundations.

..Their construction is not permitted by health authorities in densely

inhabited communities where wells are used as sources

of drinking-water supply


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DECENTRALISED WASTE WATER

SYSTEM


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DEWATS is based on four treatment systems:

Sedimentation and primary treatment in settlers,septic

tanks or Imhoff tanks.

Secondary Anaerobic Treatment in fixed bed filtersor

Baffled Reactors.

Secondary and tertiary aerobic/anaerobic treatment

in

Planted Gravel Filters.

Secondary and tertiary anaerobic /aerobic

treatment in


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Half-ball-shaped fixed dome plant

Suitable for rather thick and

homogenous substrate like sludge

from aerobic treatment tanks, liquid

animal excreta and excrements

Basically principled on

sedimentation tank in which settled

sludge is stabilized by anaerobic

digestion Mechanical treatment by

sedimentation

Biological treatment by contact

between fresh water and active

sludge compete with each other in

the septic tank

Biogas plant

Septic Tank


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Treatment by forcing incoming waste water to pass through active

bacteria sludge in each compartment. The settler in front prevents

larger solids to enter the baffle section

Baffled Reactor


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Treatment of non- settleable and

dissolved solids by bringing

them in close contact with a

surplus of active bacterial mass

Provides continuous oxygen supply to the upper layers

Treatment by permanently soaked sand or gravel filter with water

and operates partly aerobic, partly anoxic, and partly anaerobic

Anaerobic Filter

Horizontal Filter


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Vertical Planted Filters


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Apartments can opt for DEWATS

Minimum space requirement does not eat up precious

ground space

Can be accommodated underground

below paved

pathways / parking lots or even under service buildings etc.

No need for skilled maintenance.

Minimum operation costs.

Civic responsibility to prevent soil and ground water

contamination.

Housing Colonies / Townships

Can be decentralized thereby reducing plumbing and

pumping costs.

Possibility of safe reuse of water for gardening open

spaces.

Can be integrated as part of the landscape.

Low energy & operation costs.

Civic Responsibility.


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DEWATS for Commercial Establishments

Offices,

Shops, Hotels, Resorts etc.

Can be scaled to any size.

Adaptability to varying load conditions.

Adaptability to varying climatic conditions. Can treat waste water with high fat, suspended solids and

BOD.

Safe reuse of water for non potable end uses.

System cannot be switched off so ensures efficient

working irrespective of external factors.


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SEPTIC TANK

is a small scale sewage treatment system common in areaswith no connection to main sewage

Indianapolis is an example of a large city where many of

the city's neighborhoods are still on separate septic systems).

The term "septic" refers to the

ANAEROBIC BACTERIALenvironment that develops in the tank and which decomposes or

mineralizes the waste discharged into the tank.

Septic tanks can be coupled with other on-site waste watertreatment units such as biofilters or aerobic systems involving

artificial forced aeration.


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SEPTIC TANK


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consists of a tank of between 1,000 and 2,000 gallons (4000 - 7500

litres) in size connected to an inlet wastewater pipe at one end and a

septic drainage field at the other.

pipe connections made via a T pipe which allows liquid entry and exitwithout disturbing any crust on the surface.

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 liquidthen draining in a relatively clear condition from the outlet into the

leach field or drain field, or seepage field.

remaining impurities are trapped and eliminated in the soil, with the

excess water eliminated through Percolation into the soil.SEPTIC

TANK


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A piping network, laid in a stone filled trench distributes the

wastewater throughout the field with multiple drainage holes in thenetwork.

The size of the leach field is proportional to the volume of wastewater

and inversely proportional to the porosity of the drainage field.

entire septic system can operate by gravity alone, or where

topographic considerations require, with inclusion of a lift pump.

Certain septic tank designs include siphons or other methods of

increasing the volume and velocity of outflow to the drainage field.

This helps to load all portions of the drainage pipe more evenly and

improvesthe drainage field life by preventing premature clogging.

SEPTIC

TANK


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THE SEPTIC TANK IS A

BIOREACTOR

WHERE MICROORGANISMS BREAK DOWN ORGANIC MATTER IN

THE WASTEWATER TO LIQUIDS, GASES AND SOLIDS.

GASES ARE VENTED OFF THROUGH THE HOUSE VENT STACK.

SOLIDS ARE COMPOSED OF BOTH SCUM AND SLUDGE.SCUM IS LIGHTER THAN WATER AND FL OATS TO THE SURFACE IN THE SEPTIC

TANK. SOLID PARTS ARE HEAVIER THAN WATER AND SINK TO THE BOTTOM OFTHE TANK.

BACTERIA FEED ON THE WASTES AND THE FRACTION THAT CANT BE

DECOMPOSED IS SLUDGE. SLUDGE ACCUMULATES IN THE BOTTOMOF THE SEPTIC TANK AND MUST BE REMOVED PERIODICALLY.

THE SEPTIC TANK AND SOIL ABSORPTION UNIT


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THE SEPTIC TANK AND SOIL ABSORPTION UNITat least 100 feet away from any private well that is less than 100 feet

deep,

and at least 50 feet away from wells more than 100 feet deep.


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IMHOFF TANK

IMHOFF TANK


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a two-stage septic system where the sludge is digested in a separate

tank.

This avoids mixing digested sludge with incoming sewage. Also,some septic tank designs have a second stage where the effluent

from the anaerobic first stage is aerated before it drains into the

seepage field

Waste that is not decomposed by the anaerobic digestion eventually

has to be removed from the septic tank, or else the septic tank fills upand undecomposed wastewater discharges directly to the drainage

field.

Not only is this bad for the environment, but if the sludge overflows

the

Septic tank into the leach field, it may clog the leach fieldpiping or decrease the soil porosity itself, requiring expensive

repairs.

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

IMHOFF TANK


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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 10-20 years between pumpings.

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.


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Imho

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The Imhoff tank was developed to correct the two main defects of the

septic tank.

1.IT PREVENTS THE SOLIDS ONCE REMOVED FROM THE SEWAGE

FROM AGAIN BEING MIXED WITH IT, BUT STILL PROVIDESFOR THE DECOMPOSITION OF THESE SOLIDS IN THE SAME

UNIT

2.IT PROVIDES AN EFFLUENT AMENABLE FOR FURTHER

TREATMENT.

Contact between the waste stream and the anaerobic digesting sludge is

practically eliminated and the holding period in primary settling

compartment at the tank is reduced.

The Imhoff tank may be either circular or rectangular and is divided into

three compartments:

1.the upper section or sedimentation compartment

2.the lower section known as the digestion compartment and

3.the gas vent and scum sectionImho

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It is desirable to be able to reverse the direction of flow to prevent excessive

deposition of solids at one end of the sedimentation compartment.

Periodically reversing the flow will result in an even accumulation of sludge

across the bottom of the tank.

In operation, all of the wastewater flows through the upper compartment.

Solids settle to the bottom of this sloped compartment, slide down and pass

through an opening or slot to the digestion compartment.

One of the bottom slopes extends at least six inches beyond the slot.

This forms a trap to prevent gas or digesting sludge particles in the lower

section from entering the waste stream in the upper section.

The gas and any rising sludge particles are diverted to the gas vent and

scum section.

Imho

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SAND FILTERS

consists of a septic tank, sand filter and soil absorption

bed.

in the septic tank, solids settle out of the waste stream

and anaerobic bacteria facilitate the partial breakdown of

organic matter (primary treatment).

Pressured doses of clarified effluent from the septic tankare discharged to the sand filter.

The sand filter, is a buried chamber containing at least 24

inches of sand between layers of gravel.

It serves as the fixed porous medium on which aerobicbacteria provide much of the secondary treatment.

The effluent from the sand filter is then discharged, in

pressurized doses, to a soil absorption bed.


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SAND FILTERS


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HIGH RATE SAND FILTERS

LOW RATE SAND FILTERS


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the effluent from the sand filter is treated by passage through 24

inches of sand of an approved size and consistency, the soil

absorption bed is reduced to 24 inches of suitable soil (minimum 6

inches in-situ soil).

Because the sand layer is underground, the potential landscaping

disadvantages of an above ground mound are improved.

Also, since the sand filter treats wastewater within an enclosedstructure, the sand can be replaced easily should the need arise.

ABOUT 45% OF THE HEALTH DEPARTMENTS NATIONWIDE THAT RESPONDED TO

A RECENT SURVEY STATED THAT THEY PERMITTED THE USE OF SAND FILTERS.

THE INDUSTRY ESTIMATES THAT THERE ARE APPROXIMATELY

15,000 SYSTEMS IN USE NATIONALLY.

Since wastewater leaves a sand filter system as high-quality effluent, the soil


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in the trench or mound soil treatment system may be better able to accept it,

and the system should last longer.

Because sand filters produce cleaner wastewater, they are useful for sites

that have been compacted, cut, or filled; and for environmentally sensitive

areas like those near lakes, in shallow bedrock areas, aquifer recharge areas,and wellhead protection areas.

Pretreatment may allow a reduction in the three-foot separation required

between the soil treatment system and the limiting soil layer.

Researchers in several states, including Minnesota, are testing reduced

separation distances in soil treatment systems receiving wastewater

pretreated in a sand filter.Sand filter systems may also be successfully retrofitted into drain fields that

have failed because of excessive organic loading from lack of maintenance.

SAND

FILT

ERSAPPLICATION


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Final Disposal of Wastewater

Effluent discharged from this system will be very clean, but must still

be applied to the soil for final treatment.

The design of this part of the system is still being tested and sizing

requirements are being developed.

Effluent leaving the sand filter is sent to a soil treatment system. The

effluent is so "clean," a biomat layer does not form the way it does in

soil treatment systems receiving effluent from septic tanks.

A pressure distribution network is needed to apply effluent evenly

throughout the system.


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ROOT ZONE METHOD


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consists of 100mm top mud layer where plants are grown

below which 100mm sand layer is provided and below the sand

layer, 300mm of gravel layer is provided for filtration.

Raw effluent after removing grit or floating material is passed

horizontally or vertically through

The water percolates through the top layer, gets absorbed by the roots

of wetland plants spread thickly and gets treated as they absorb the

pollutants present in it

the percolated water gets filtered as it passes through the sand

gravel layer.

After the gravel layer, 100mm RCC slab is provided to prevent the

infiltration of the treated water.

The treated water can be used to water the green landscapes.

The beds can serve flows ranging from 1m3/day to more.

The constructed wetlands require sizeable land area - 2 to 5

m2/person.

Me

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Aquatic plant species: the selected species should


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Aquatic plant species: the selected species should

preferably have a rapid growth rate, be tolerant to

nutrient rich feeds and be able to withstand wetland

conditions.

In India, the Phragmites species (available

locally) have been reported to be successfully used.

About 3-5 Phragmites plant saplings are planted persquare meter. At full growth, the plants may be 3-4m tall

and 100-150 reeds may exist per square meter.

The quality of the wastewater in terms of BOD (mg/L),

volume of discharge and the area available are thedeciding factors while planning for a wetland system. Since

the construction of wetland system and maintenance

involves minimum cost, it is a user friendly system for

wastewater handling.


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Advantages of root zone system

achieves the standard for tertiary level with no operating

cost.no chemical used for pH adjustment or for flocculation.

Low electricity is consumed for pumping treated water

from the collection tank to the reed bed.

From the reed bed the treated water is collected and usedfor irrigation by gradient flow.

has low maintenance cost since it involves no machinery

and its associated maintenance.

requires negligible attendance for operation and

monitoring. Ihas no sludge handling problem such as scraping of

slurry from the sludge drying beds and its disposal twice in

a week.

T sludge gets mineralized in the vertical zone of the reed


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It enhances the landscape and gives the site a green appeal.

It provides natural habitat for birds and after a few years givesan appearance of a Birds sanctuary.

It is though an effluent treatment plant, it does not have odourproblem and though

It is a green zone, it does not have mosquitoes problem.

The reeds are not grazed by ruminants.

Salinity may not be a problem for a survival or operations of

reed beds. It is recommended to combine vertical flow and then

horizontal flow of sewage with a soil having imperviousbottom.

In the horizontal flow system, the sewage percolates through

bed and that has all roots of the wetland plants spread verythickly nearly with 2500 types of bacteria and 10,000 types offungi and aerobically oxidized organic matter of the effluent.

Root zone system gives a very good performance ofremoving 90% BOD and 63% Nitrogen.

Phragmites australis has been found more efficient in

nitrogen removal compared to Typha latifolia.


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AT GRADE AND MOUND SYSTEM


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Some soil types are unsuitable for conventional septic tank soil

absorption systems. As a result, alternative systems such as the

MOUND SYSTEM can be used to overcome certain soil and site

conditions.


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Mounds are pressure-dosed sand filters that discharge

directly to natural soil. They lie above the soil surface and

are designed to overcome site restrictions such as:

Slow or fast permeability soils.

Shallow soil cover over creviced or porous bedrock.

A high water table.

The main purpose of a mound system is toprovide sufficient treatment to the natural

environment to produce an effluent equivalent to,

or better than, a conventional onsite disposal

s stem.


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Advantages

uses some sites that would otherwise be unsuitable for in-ground orat-grade onsite systems.

The natural soil utilized in a mound system is the upper most

horizon, which is typically the most permeable.

A mound system does not have a direct discharge to a ditch,

stream, or other body of water.

Construction damage is minimized since there is little excavation

required in the mound area.

Mounds can be utilized in most climates.


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Disadvantages

Construction costs are typically much higher than conventionalsystems.

Since there is usually limited permeable topsoil available at mound

system sites. Extreme care must be taken not to damage this layer

with construction equipment.

The location of the mound may affect drainage patterns and limit

land use options.

The mound may have to be partially rebuilt if seepage or leakageoccurs.

All systems require pumps or siphons.

Mounds may not be aesthetically pleasing in unless properly

landscaped.


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AT GRADE


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The at-grade soil absorption system accepts septic tank

effluent, treats, and disposes of it in an environmentally

acceptable manner.

It serves the same function as in-ground soil absorptiontrenches or a mound system.


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An at grade system consists of a


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An at-grade system consists of a

septic tank,

pump chamber,

pressure distribution system anda soil absorption bed.

solids settle out of the waste stream and anaerobic

bacteria facilitate the partial breakdown of organic matter

(primary treatment).Clarified effluent from the septic tank is typically

discharged via gravity to a pump chamber from which it is

pumped, in controlled pressurized doses, up to the soil

absorption bed.At-grades are unique in that the distribution piping is

placed on a prepared gravel bed at the ground surface,

literally at grade. The distribution piping is covered with

sand and soil to protect it from freezing.Thesys

tem


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The system is installed as follows:

The existing soil is tilled,

Observation tubes and aggregate are placed,

The distribution network is installed,

The fabric covering is laid on the aggregate

A soil cover is placed over the fabric and on the side

slopes.

ins

talla

tion


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Advantages:

enables use of land that may otherwise be unsuitable forconventional trenches

Less costly than a mound because there is no need for

the costly C33 sand.

The natural soil utilized in at-grade system is usually the

top layer, which is typically the most permeable.

Construction damage can be minimized since there is

little excavation required in the absorption area.

At-grade systems can be utilized in most climates


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Disadvantages:

Care must be taken to not damage the top

permeable topsoil under the absorption area.

The location of the system may affect drainagepatterns and limit land use options.

Need for electricity and mechanical equipment (in

some circumstances siphons can be used inplace of pumps).


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SEEPAGE BEDS AND LEACH


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TRENCHES


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http://www.thenaturalhome.com/infiltrator.htm


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CLUSTER DEVELOPMENT

In areas served by municipal wastewaterfacilities,

sewage is transported away from homes in large

diameter gravity sewers to a central plant where

it

is treated and discharged into a waterway.

Outside

of these areas, most individual residences must

rely on a septic tank and soil absorption field, or

on-site system, to dispose of their wastewater.

Cluster systems bridge the gap between these

two


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Components of a Cluster System

Collection Options

Pretreatment Options

Final Disposal Options

Creating a Management Structure


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Advantages

Cluster systems have a number of advantages:

Cost

Flexibility in land use

Maintenance

Environmental protection

COST


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The design and construction of the sewage collection system is often

responsible for two-thirds or more of the cost. Much of this is due to

the large-diameter gravity sewers, which must be laid on grade andcan require very deep excavations or a number of lift stations.

Small-diameter plastic pipes used in alternative systems are less

expensive and easier to install than conventional sewer pipes.

Pressurized sewers dont rely on gravity to operate, so they can be

buried at shallow depths, just below the frost line, and follow the

natural contours of the land, saving on excavation costs.

COST

Small community systems discharge to high quality, low flow streams,

local

environmental impacts can be disproportionately high.

ENVIRONMENTAL PROTECTION


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Flexibility in Land Use

Cluster wastewater systems may permit smaller lot sizes and provide

planners with a tool to better preserve the green areas and rural

character of small communities.

These features are frequently lost when large, gravity sewers are

installed and high-density development follows, or if large lot sizes are

required for individual on-site sewage disposal systems.

Maintenance

Complex sewage treatment processes require expertise often not

found in rural locations. Decentralised systems minimize the need for

process understanding and rely more on the mechanical aptitude of

an Operation and Management staff, which is more often available in

rural settings.


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DisadvantagesThe primary disadvantage of cluster systems has to do with the

amount of operation and maintenance needed. While usually not

complicated, alternative sewers have components that conventionalsewers do not have, such as septic tanks that need to be inspected

and pumped and mechanical parts and controls that use electricity.

These require more frequent and regular maintenance than

conventional sewers. They also are located on site, requiring workers

to travel to individual homes or businesses. This may, however, bemore than offset by higher operational

costs at more complex central treatment facilities. Clusters require a

somewhat complex organizational structure in order to make

community decisions such as fee collection and continuing education

of homeowners about wastewater issues. Homeowner cooperation is

much more important than with municipal systems since smaller

systems are less resilient and less tolerant of periodic large flows or

larger than normal loadings of household chemicals than in large

systems, where these peaks are averaged out over a very large user

base.


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THANK YOU

MAITREYI

NAINA

MRUNALI

SURENDRA

NIRAJRITESH

SREEKANTH

decentralised methods of sewage disposal

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