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6.2 Reuse of wastewater from on-site systems

Many options are open to a householder who wishes to reuse wastes on-site. One option is separation of all wastes. Urine can be separately collected and stored for later use as a liquid fertiliser, rich in nitrogen, phosphorus and potassium. Toilet wastes can be composted and used as a soil conditioner, rich in organic carbon, nitrogen and phosphorus. Greywater can be treated in a constructed wetland and used for sub-surface irrigation of the garden beds (Figure 37). This option may be suitable for a householder who is interested in managing wastes for beneficial uses in the garden. Sufficient garden area needs to be available for this purpose.

Another option is the use of an evapotranspiration system for growing shrubs and trees (see Section 4.1.4). This is a passive system, not requiring household attention on a regular basis, except desludging of the septic tank every 3 to 5 years. There is a fairly wide choice of shrubs and trees to choose from depending on local soil and climatic conditions.

6.3 Stormwater reuse

Stormwater is generally of a higher water quality than wastewater. Reuse (or strictly useE of stormwater can take place at two levels (household and municipal) or even at a larger (regional) scale if desired. Use at the household and municipal levels is described below.

6.3.1 Household level

Householders can use stormwater by collecting roof run-off in a tank for use as drinking water (common in arid regions), flushing toilets or for irrigation of the garden. The first flush of roof run-off can be contaminated by dust particles, leaf litter and animal droppings. The first flush can be simply diverted using a simple diverter (Figure 38). A screen can be placed at the inlet to the tank to filter gross particles. Water for drinking will still need to be boiled to denature pathogens.

Water from the roof can be directed to the garden beds directly rather than through soakways, and in this way shallow rooted vegetation can benefit from the water, especially in arid regions.

6.3.2 Municipal level

At the municipal level stormwater can be stored in ponds for use for irrigation of parks and gardens and for fire-fighting purposes. This is in addition to employing the ponds for flood control and for improving the amenity value of the water as described in Section 4.3. Other uses are for groundwater recharge, either as a means of storing water, e.g. during the rainy season, for withdrawal in the dry season. Groundwater recharge can also be used to prevent encroachment of seawater near the coast where there is heavy groundwater withdrawal in excess of natural replenishment by precipitation.

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