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Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

8.2 Environmental considerations

Achievement of protection of environmental quality is implicitly assumed when we consider technologies for wastewater and stormwater management. These considerations are (i) the need to protect the environment and (ii) the imperative of recycling/reusing the water and nutrients in the water. The first factor is usually taken into account by making sure that standards for discharge of wastewater are met. Standards alone should not be relied upon, because it is the capacity of the environment to assimilate the wastes that should not be exceeded. Each local environment has its own capacity depending amongst others on the natural throughflow of water, climatic, vegetation and soil conditions.

Reuse of the water and nutrients conserve these resources in a world where water will in the future be a precious resource for growing food and maintain ecosystems for the world’s increasing population and standard of living. Reuse of water can in fact fulfil the objective of protecting the environment, because reuse has standards which have to be met prior to the water being able to be reused. A corollary to the above two factors is the need to exclude toxic and hazardous chemicals from being mixed and discharged with human excreta. Treatment, reuse or disposal of wastewater and stormwater containing toxic and hazardous chemicals will be considerably more difficult than treating the toxic and hazardous wastes separately.

Table 2.5: Technologies for wastewater and stormwater management (with relative costs, environmental impact and maintenance requirement)

Wastewater management technologies
Technology Capital cost Operation &
maintenance cost		 Environmental impact
On-site technology
Pit latrine Low Low Pollution of groundwater
Composting toilet Low Low Reuse of nutrients
Pour flush toilet Low Low Pollution of groundwater
Improved on site treatment unit Medium to high Low to medium Reuse of water and nutrients
Off-site technology
Collection technology
Conventional sewerage High High Dependent on treatment
Simplified sewerage Medium to high Medium Dependent on treatment
Settled sewerage Medium Low Dependent on treatment
 
Treatment technology
Activated sludge High High Nutrients may need removal
Trickling filtration Medium Medium Nutrients may need removal
Lagoons Low to medium
(dependent on cost of land)		 Low Nutrients may need removal; aquaculture can be incorporated
Land-based treatment Low to medium
(dependent on cost of land)		 Low to medium Reuse of water and nutrients
Constructed wetland Low to medium
(dependent on cost of land)		 Low Amenity value
Anaerobic treatment Medium Medium Produces biogas; further aerobic treatment needed

 

Stormwater management technologies*
Technology Source control Site control Regional control
Filter strips and swales O
Filter drains and permeable surfaces O
Infiltration devices O
Basins and ponds O
*Cost increases from source control to regional control technology.

Conservation of resources needs to consider water conservation at the point of its use. Less water used means less wastewater produced. The hierarchy of waste management discussed in Section 1 (4) emphasises this point, and should be seriously considered in achieving sound technology practice.

 

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