Water reuse is a common fact of life. In the natural water cycle, evaporation and precipitation are forms of reuse. Similarly, humans have always used and reused water. The unplanned return of wastewaters to streams and lakes is nothing new. Planned reuse of wastewaters for beneficial purposes has been done in some areas for many years, but it is here that we need to concentrate our efforts for far greater use of our wastewaters.
In this era of chronic water scarcity, communities, farmers, and industrial water users need to recognize that not all supply water need be of the same quality, and the wastewater of a community should be considered a resource. By collecting and treating wastewater appropriately, we can recover both usable water and valuable nutrients.
Abundant supplies of clean surface and underground waters in the world have been taken for granted until recent years. Contamination of surface and ground water supplies is increasingly severe, making available water less and less usable. Adequate pollution control measures must be taken and conservation and reclamation of resources must become the rule.
The quality and quantity of wastewaters produced by a community depend upon such factors as the source of supply, population density, industrial practices, and even the attitudes of the local population. The quality of the environment can be improved by reducing polltion at the source, providing adequate treatment of wastewater, and by recycling and reusing wastewater. Since there are many different types of wastewater reuse and the term "reuse" has different meanings to different people, the following definitions are offered:
Indirect Reuse: Indirect reuse of wastewater occurs when water already used one or more times for domestic or industrial purposes is discharged into fresh surface or underground waters and is used again in its diluted form.
Direct Reuse: The planned and deliberate use of treated wastewater for some beneficial purpose such as irrigation, recreation, industry, prevention of saltwater intrusion by recharging of underground aquifers, and potable reuse.
Specific Considerations Governing Reuse
The reuse of treated effluents is most applicable where large volumes of water are used and the wastes are not highly contaminated. As wastewater--treated or untreated--has been reused in agriculture for a fairly long time, many countries have developed standards for this purpose.
One very important question is whether the reuse will result in multiple recycle. Multiple recycle produces a buildup of refractory materials, especially inorganic ions, and may require the use of demineralization or other specialized processes. In-plant reuse of industrial water, where actual consumption is small, may lead to a high degree of recycle. On the other hand reuses of municipal wastewater, except for domestic reuse, probably would not lead to multiple recycle.
Indirect Reuse
As treatment of wastewaters improves, future effluents will be less damaging to water quality. In the treatment of polluted rivers, the methods employed at present are based upon those developed over the years for the treatment of relatively unpolluted river water, and it appears that sufficient notice may not have been taken of the increasing proportion of wastes in many rivers. The unintentional reuse of wastewater also occurs widely as a result of the use of river water for agriculture, recreation, and industrial supply and for these purposes, too, there is a need for appropriate safeguards.
Direct Reuse
Treated wastewater may be deliberately used in a planned way for a variety of purposes. If the planning of wastewater treatment facilities can incorporate potential reuse options, both environmental and economic benefits may be realized.
Economics of Reuse
Pricing of water and all of the costs that go into the acquisition, purification, power and pumping, transmission and distribution and support services is vastly complicated. Subsidies and variable bookkeeping practices add to the difficulty of finding the true cost of water. The following is a checklist for determining if wastewater reuse is potentially practical:
Water-short areas of the world may not have a choice--they will have to reuse wastewaters. Planning for adequate water supply and sanitation must be considered an integral part of the development process, and overall national plans should be formulated and implemented. Efforts should be made to innovate and test treatment technologies which are appropriate for their setting. National planning efforts should serve as the framework for technology selection, institutional development, and financing/cost recovery.
HWR can help developers, local governments and wastewater treatment plant operators plan for cost-effective water reuse on any scale, from individual households and facilities to regional wastewater districts.
© 1999 Humboldt Water Resources