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About UNEP
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United Nations Environment Programme
Division of Technology, Industry and Economics
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8. Sound Practices

8.1 Technology choice

Environmentally sound practices in wastewater and stormwater management are practices that ensure that public health and environmental quality are protected. A range of technologies exist that can achieve this objective (Sections 3 to 7). A summary is shown in Table 2 which, although it does not cover all available technologies, it does represent the major technologies for most situations. The Regional Overviews in the Source Book, published by IWA and IETC, include technologies that are modifications or variations of the listed technologies or represent practices or advances in the regions.

As mentioned before, the processes in environmentally sound technologies are largely akin to the purification and recycling processes taking place in nature. There is a scientific basis for the physical, chemical and biological processes for the removal of pathogens and pollutants from the water. Properly designed, constructed, maintained and operated these technologies can achieve protection of public health and the environment, and can recycle water and nutrients, which are beneficial to sustaining ecosystems and life.

The choice of technology is determined by environmental, economic and social factors. 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.

Table 2: 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 x    
Filter drains and permeable surfaces x    
Infiltration devices   x  
Basins and ponds     x
*Cost increases from source control to regional control technology.

Sound economic practices require that costs are optimised. An indication of relative costs of technologies is provided in Table 2. Optimising the cost of technology for wastewater management needs to consider (1) availability of land, (2) labour costs, (3) land uses and (4) economy of scale. The economics of wastewater management needs to consider the benefits of improvement to public health and long-term affordability of sanitation services to the community.

From a community’s point of view the affordability of a wastewater collection and treatment system is an important factor. A percentage of the average person's income in a community, or of the average value of housing appears to be a figure that can be used as a measure of what a community can afford. What the percentage figure should be is determined by the importance given by community members to having the wastewater system in their community. The priority given to wastewater management in turn is dependent on the community having the information that will help them decide on its importance relative to other household and community needs. Hygiene promotion and education is needed to provide this information. An example of an excellent hygiene promotion is a publication by WHO (WSSCC Working Group on Promotion of Sanitation, 1998).

8.2 Selection of technology

Procedures to consider economic and environmental factors in a systematic way have been developed. These range from a single decision-making flowsheet to a computer software package. Figure 39 illustrates a flowsheet that has been developed for the selection of wastewater technology in developing countries in both urban and rural communities. Computerised decision-making software such as SANEX and WAWTTAR are based on the same methodology as illustrated in the flowsheets. SANEX is briefly described in the following boxed sections to illustrate its advantages and limitations.

The WAWTTAR program was designed to assist financiers, engineers, planners and decision-makers in improving their strategies toward sustainable water and sanitation coverage while minimizing impacts on water resources. It was developed specifically for application at the pre-feasibility stage of project development to assist planners select suitable water and wastewater treatment processes which are appropriate to the material and manpower resources available in their particular location at particular time. A more detailed description of WAWTTAR can be found in the Source Book, published by IWA and IETC.

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