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Tropical Environmental Health

Sanitation 2

Elevated Toilet:

For use in areas with high water table!

We have examined methods for disposal of

faecalmatter: Now consider what happens with the effluent

• In any system using water, the effluent must be disposed

• Effluent consists of sullage water (i.e. laundry, kitchen, cleaning.

• Toilet water containing faeces, urine and other effluent.

• Real engineering principles apply; however in many developing countries this is left to providence….

The Septic TankSchematic of conventional septic tank

Inspection opening150 mm diameter

Inlet

At least 75 mm

At least 25 mm

Access opening near side wall at least 600 mm diameter

Inspection opening 150 mm diameter

Liquid level20% of

Liquid depth Water line

40% ofLiquid depthScum clear space

(75 mm, minimum)

Scum clear space(300 mm, minimum)

20% of Liquid depth(150 mm, minimum)

Scum

Clear space

Sludge Sludge

Outlet

40% ofLiquid depth

Liq

uid

dept

h

First compartment 2/3 length second compartment 2/3 length

Total length equals two to three times width

Liq

uid

dept

h (D

)

0.2D 0.4D

InletOutlet

Scum

Sludge Sludge

Liquid

Solids Solids

Manhole

Two compartment septic tank

Compartmentbaffle

Role of the septic tank

Anaerobic fermentation of solidsReduce the load of pathogens in the effluentHold the effluent for 2-3 days for improved

safetyRetain solid material to prevent blockage of

further disposal system

The soak-away

Absorption field treatment of septic tank effluent

septic tank

Absorption trench system

Distribution box

Absorption trench

1/2 to 1 meter

backfill

Gravel or crushed rocks

Drainage tile(100 mm diameter)

1/2 to1 1/2 meter

150 mm

The field requires periodic maintenance, diversion of the flow at distribution box and repacking of the rock fill, removal of plant roots etc.

Absorption field treatment of septic tank effluent

septic tank

Absorption trench system

Distribution box

Connection to a sewage system:what are the alternatives?

• Conventional sewage connection…expensive• Small bore sewage system: less expensive• use road-side drains, and hope for the best….• Unfortunately this is the common outcome

Comparison between the sewage systems

Storm sewer

combined sewer

sanitary sewer

Small bore is near surface, and runs full

Small bore

Conventional

Small bore is PVC pipe, conventional is made from concrete

Conventional

Small bore

Conventional requires heavy machinery and regular pumping stations to

maintain flow

small bore installation is simpler, and as the pipes are light and fit in small

trenches

Sewer lines can rise or fall, the system operates under slight pressure

There is a BIG –but! Small bore systems cannot handle solids. So all connections

MUST be to septic tanks

House connection

Interceptortank

Small bare sewer

Where do we go from here:

• The effluent must be disposed of in a sanitary manner

• The system should be inexpensive and easy to manage

• Tropical areas do have long hours of sunlight, why not exploit this.

• We can by using oxidation ponds…

Lay out of an oxidation pond systemStabilization pond layout and details

Aerobic pond

Aerobic pond

Aerobic pond

Interpond connection

Facultative pond

Inlet

OutletAnaerobic

pond

Plan layout(not to scale)

5,400 4,000 Varies

Water line

300300

Precast concrete

slabs 3

1

Var

ies Water line

1,80

01,2 0

0

100 mm ofSelected fill

Precast concrete slabs for

Protection against wave erosion

Detail of a typical embankment

Newcells

Algae

O2 CO2

nutrients

Light

Organicmatter

Newcells

Bacteria

Three processes of stabilization: anaerobic

Anaerobic Facultative Maturation

Suspended &Soluble solidsSettleable solids

Sludge layer

The second process is facultative

Anaerobic Facultative Maturation

Suspended &Soluble solidsSettleable solids

Sludge layer

In the maturation pond, pathogens are reduced: the water an be released to a river

Anaerobic Facultative Maturation

Organic matter

Pathogenic organisms