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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 Tank Schematic of conventional septic tank Inspection opening 150 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 level 20% of Liquid depth Water line 40% of Liquid depth Scum clear space (75 mm, minimum) Scum clear space (300 mm, minimum) 20% of Liquid depth (150 mm, minimum) Scum Clear space Sludge Outlet 40% of Liquid depth First compartment 2/3 lengthsecond compartment 2/3 length Total length equals two to three times width

Liquid depth (D) 0.2D 0.4D

Inlet Outlet Scum Sludge Liquid Solids Manhole

Two compartment septic tank Compartment baffle

Role of the septic tank Anaerobic fermentation of solids Reduce the load of pathogens in the effluent Hold the effluent for 2-3 days for improved safety Retain 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 to 1 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 Interceptor tank 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 system Stabilization pond layout and details Aerobic pond Interpond connection Facultative pond Inlet Outlet Anaerobic pond Plan layout (not to scale) 5,4004,000Varies Water line 300 Precast concrete slabs 3 1 Varies Water line 1,800 1, mm of Selected fill Precast concrete slabs for Protection against wave erosion Detail of a typical embankment

New cells Algae O2O2 CO 2 nutrients Light Organic matter New cells Bacteria

Three processes of stabilization: anaerobic AnaerobicFacultativeMaturation Suspended & Soluble solids Settleable solids Sludge layer

The second process is facultative AnaerobicFacultativeMaturation Suspended & Soluble solids Settleable solids Sludge layer

In the maturation pond, pathogens are reduced: the water an be released to a river AnaerobicFacultativeMaturation Organic matter Pathogenic organisms