6.2 Reuse of wastewater from on-site systems
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.