Waste Stabilsation Ponds

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WASTE STABILIZATION PONDS

GROUP 02

BCH 1

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DEFINITION

They are large, shallow basins in which raw

sewage is treated entirely by natural processes

involving both algae and bacteria

They are used for sewage treatment in

temperate and tropical climates

Sunlight energy is the only requirement for their

operation

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WASTESTABILIZATIONPONDS13/04/2013

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LAGOONS

They are man-made outdoor earthen basins in which

waste is stored and undergoes anaerobic respiration

as part of a system designed to manage and treat

waste

They are effective in on-site waste water treatment

and they are relatively easy to maintain

They should be constructed in positions where trees

will not restrict sunlight exposure and free air

movement

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SEPTICTANKWITHLAGOON (OXIDATIONPOND)

Septic tank

Lagoon

Dyke

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MAINTENANCE OF LAGOONS

A permanent vegetative cover should be established on the

lagoon dike as soon as possible to prevent erosion of the dyke

Vegetative growth should be controlled to assure necessarysunlight exposure and air movement

No trees should be allowed to grow around the lagoon.

They should be fenced

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ADVANTAGES OF LAGOONS

Low operational and maintenance cost

Lagoons provide effective treatment withminimal threat to the environment

Work well in clay soils where conventionalsubsurface on-site absorption fields will

not work

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DISADVANTAGES OF LAGOONS

Lagoons must be constructed in clay soil or be lined to preventleakage

May overflow occasionally during extended periods of heavy rainfall

Offensive odours may occur

Can not be installed on a small lot.

Some people consider lagoons unsightly and unsafe

As with any other open body of water, there is some potentialdanger

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TYPES OF WASTE STABILISATION PONDS

Anaerobic ponds; Are commonly 2 5 m deep andreceive wastewater with high organic loads

Facultative ponds; Are usually 1-2 m deep and are oftwo types i.e. Primary facultative ponds andsecondary facultative ponds

Maturation ponds; Are usually 1-1.5 m deep andthey receive the effluent from the facultative ponds.Their primary function is to remove excretedpathogens

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PROCESSES IN WASTE STABILIZATIONS POUNDS

Anaerobic ponds; Biochemical Oxygen Demand (BOD)

removal is achieved by sedimentation of solids, and

subsequent anaerobic digestion in the resulting

sludge

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PROCESSES IN WSPS

Facultative ponds; The process of oxidation of organic matter

by aerobic bacteria is usually dominant in primary facultative

ponds and secondary facultative ponds

Pathways of BOD removal in primary facultative ponds (After Marais, 1970)

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PROCESSES IN WSPS

Maturation ponds; Faecal bacterial die-off in ponds

increases with both time and temperature. High pH

values ( >9) occur in ponds, due to rapid photosynthesis

by pond algae

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MAINTENANCE OF WSPS

There is need for periodic vegetation, plants, algae

and scum control

Control of odour, if any

Monitor volume and BOD of the sewage

Desludging of Anaerobic Pond (say 2 to 5 years)

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ADVANTAGES OF WSPS

Simple to build, reliable and easy to maintain

Provides pathogen removal which is better than the

conventional treatment

Used in small communities

Low in construction and operating cost

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DISADVANTAGES OF WSPS

Large area requirement

Poor quality of treated effluent

May promote breeding of vectors in the ponds

Needs to be located far from communities

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REFERENCES

Waste stabilization ponds and constructed wetlands

design manual by S. Kayombo, T.S.A. and N. Ladegaard,

WSP & CW Research Project

Oklahoma Department of Environmental quality

Philippines Sanitation Sourcebook and Decision Aid

Environmental Health Engineering in the Tropics by Sandy

Caircross and Richard Feachem

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Documents

Waste Stabilsation Ponds