 |
|||||||
| About UNEP | UNEP offices | News centre | Publications | Calendar | Awards | Milestones | UNEP Store |
|
|||||||
|
 |
|
|
|
||
| UNEP>DTIE>IETC | |
|
|
Promoting the adoption and use of environmentally sound technologies for water and wastewater treatment is central to IETC's mandate. In addition to supporting the efforts and initiatives underway within the Global Program of Action (GPA), IETC are pursuing specific initiatives related to:
Small Wastewater Treatment Systems IETC is preparing a computer-based sourcebook on various treatment processes available for small wastewater treatment systems. The selection and design of such standard rural wastewater disposal systems as septic tank - tile fields would be examined and discussed, as would "package" treatment plant design and operation. The intention of this sourcebook would not be to develop instant experts in the field of wastewater treatment for small communities, but rather to inform concerned individuals of the importance of in-depth study of problem situations and to describe methods of investigating wastewater management alternatives. The detailed design of a treatment system can be very complex; therefore it is recommended that final design, or review of the final design, be undertaken by qualified persons with experience in this field. The long term benefits from experienced advice and review will outweigh the costs incurred for the service. Small wastewater treatment systems can be defined as the collection, treatment and disposal facilities associated with domestic wastewaters generated by homes, apartment complexes, restaurants, institutions and communities with populations of up to 2,500 people. Basic information and recommended practices would be provided for the design, implementation and operation of systems that will be the most economic and efficient in particular situations. The sourcebook would be intended for engineers, architects, technologists and contractors who are frequently confronted with the task of providing small scale sewage treatment facilities, but who are not wastewater treatment specialists. The selection of a particular wastewater management system for a small community involves review of three principal alternatives:
In many instances, the selection of one of these major alternatives may become obvious upon review of regulatory requirements, inspection of site location and conditions, and/or review of regional development plans. Otherwise, the relative merits of each alternative must be reviewed on the basis of cost effectiveness, i.e., the unit cost of a system relative to such tangibles as public health protection, the protection afforded the receiving environment, aesthetics, energy conservation, reliability and operational requirements. The rationale used in the decision-making process will vary from situation to situation. The proposed sourcebook would provide sufficient information to permit the analysis of waste management problems with an awareness of the solutions that are available. Of increasing importance in the design and selection of waste management systems is the conservation of energy. The proposed sourcebook would address systems which minimize the use of energy, while maintaining an acceptable standard of effluent quality and operational simplicity. This may entail the selection of a system with design modifications over an otherwise off-the-shelf package. Energy conservation is of particular importance in isolated areas where power must be generated on-site using fossil fuels. Water Reclamation and Reuse Water reclamation and non-potable water reuse only require conventional water and wastewater treatment technology already practiced and readily available in most countries throughout the world. Furthermore, because properly implemented non-potable reuse does not entail significant health risks, it has generally been accepted and endorsed by the public in the urban and agricultural areas where it has been introduced. Demands on water resources for household, commercial, industrial and agricultural purposes are increasing greatly. This situation is being exacerbated by growing urbanization. Although rural populations may be able to find the water they need locally, urban populations need to draw water from large drainage areas or extensive aquifers. Most cities have already fully exploited the readily available water resources and are now obliged to develop and treat sources of lower quality or go great distances to develop new supplies, both of which are costly options. Furthermore, while people in rural communities can often dispose of their wastewaters satisfactorily on site, cities must generally discharge their wastewaters into nearby water courses, which require adequate treatment prior to disposal to prevent water quality degradation and to protect public health. The use of reclaimed water for non-potable purposes offers the potential to exploit a "new" resource that can be substituted for existing sources. By "source substitution" - replacing the potable water used for non-potable purposes - a larger population can be served from an existing source. Source substitution is not a new idea. In 1958, the United Nations Economic and Social Council enunciated a policy that "No higher quality water, unless there is a surplus of it, should be used for a purpose that can tolerate a lower grade" (United Nations, 1958). Many urban residential, commercial and industrial uses can be satisfied with water of less than potable water quality: irrigation of lawns, parks, roadway borders and medians; air conditioning and industrial cooling towers; stack gas scrubbing; industrial processing; toilet and urinal flushing; construction; cleansing and maintenance, including vehicle washing; scenic waters and fountains; and environmental and recreational purposes. Usually, public water supplies are designed to provide water of potable quality to serve all these purposes. The economics of source substitution with reclaimed water are site specific, depending on the marginal costs of new sources of high quality water and the costs of treatment and disposal of wastewaters. The reclamation and reuse of wastewaters will likely be most attractive in serving new residential, commercial and industrial areas of a city, where the installation of dual distribution mains and dual building services would be far more economical than in already developed areas. Reuse of reclaimed water for agricultural purposes near urban areas can also be economically attractive. Agricultural users are usually willing to make long term commitments, often for as many as 20 years, to use large quantities of reclaimed water instead of fresh water sources. IETC is developing guidelines for water reclamation and reuse to assist decision makers in evaluating the requirements and potential benefits of water reuse. These guidelines will address the key issues needed to evaluate water reclamation and reuse opportunities, assess the costs and benefits of reuse alternatives, and plan and implement a water reuse system. Major technical and non-technical issues will be identified and discussed, drawing upon the experience of those with water reuse programs. |
