Previous Page Table of Contents Next Page

3.2 Wastewater reuse

Once freshwater has been used for an economic or beneficial purpose, it is generally discarded as waste. In many countries, these wastewaters are discharged, either as untreated waste or as treated effluent, into natural watercourses, from which they are abstracted for further use after undergoing "self-purification" within the stream. Through this system of indirect reuse, wastewater may be reused up to a dozen times or more before being discharged to the sea. Such indirect reuse is common in the larger river systems of Latin America. However, more direct reuse is also possible: the technology to reclaim wastewaters as potable or process waters is a technically feasible option for agricultural and some industrial purposes (such as for cooling water or sanitary flushing), and a largely experimental option for the supply of domestic water. Wastewater reuse for drinking raises public health, and possibly religious, concerns among consumers. The adoption of wastewater treatment and subsequent reuse as a means of supplying freshwater is also determined by economic factors.

In many countries, water quality standards have been developed governing the discharge of wastewater into the environment. Wastewater, in this context, includes sewage effluent, stormwater runoff, and industrial discharges. The necessity to protect the natural environment from wastewater-related pollution has led to much improved treatment techniques. Extending these technologies to the treatment of wastewaters to potable standards was a logical extension of this protection and augmentation process.

Technical Description

One of the most critical steps in any reuse program is to protect the public health, especially that of workers and consumers. To this end, it is most important to neutralize or eliminate any infectious agents or pathogenic organisms that may be present in the wastewater. For some reuse applications, such as irrigation of non-food crop plants, secondary treatment may be acceptable. For other applications, further disinfection, by such methods as chlorination or ozonation, may be necessary. Table 18 presents a range of typical survival times for potential pathogens in water and other media.

Table 18 Typical Pathogen Survival Times at 20 - 30°C (in days)

Pathogen

Freshwater and sewage

Crops

Soil

Viruses

< 120 but usually <50

<60 but usually < 15

<100 but usually <20

Bacteria

<60 but usually <30

<3 0 but usually < 15

<70 but usually <20

Protozoa

<30 but usually <15

<10 but usually <2

<70 but usually <20

Helminths

Many months

<60 but usually <30

Many months

Source: U.S. Environmental Protection Agency, Process Design Manual: Guidelines/or Water Reuse. Cincinnati, Ohio, 1992 (Report No. EPA-625/R-92-004).

A typical example of wastewater reuse is the system at the Sam Lords Castle Hotel in Barbados. Effluent consisting of kitchen, laundry, and domestic sewage ("gray water") is collected in a sump, from which it is pumped, through a comminutor, to an aeration chamber. No primary sedimentation is provided in this system, although it is often desirable to do so. The aerated mixed liquor flows out of the aeration chamber to a clarifier for gravity separation. The effluent from the clarifier is then passed through a 16-foot-deep chlorine disinfection chamber before it is pumped to an automatic sprinkler irrigation system. The irrigated areas are divided into sixteen zones; each zone has twelve sprinklers. Some areas are also provided with a drip irrigation system. Sludge from the clarifier is pumped, without thickening, as a slurry to suckwells, where it is disposed of. Previously the sludge was pumped out and sent to the Bridgetown Sewage Treatment Plant for further treatment and additional desludging.

Extent of Use

For health and aesthetic reasons, reuse of treated sewage effluent is presently limited to non-potable applications such as irrigation of non-food crops and provision of industrial cooling water. There are no known direct reuse schemes using treated wastewater from sewerage systems for drinking. Indeed, the only known systems of this type are experimental in nature, although in some cases treated wastewater is reused indirectly, as a source of aquifer recharge. Table 19 presents some guidelines for the utilization of wastewater, indicating the type of treatment required, resultant water quality specifications, and appropriate setback distances. In general, wastewater reuse is a technology that has had limited use, primarily in small-scale projects in the region, owing to concerns about potential public health hazards.

Wastewater reuse in the Caribbean is primarily in the form of irrigation water. In Jamaica, some hotels have used wastewater treatment effluent for golf course irrigation, while the major industrial water users, the bauxite/alumina companies, engage in extensive recycling of their process waters (see case study in Part C, Chapter 5). In Barbados, effluent from an extended aeration sewage treatment plant is used for lawn irrigation (see case study in Part C, Chapter 5). Similar use of wastewater occurs on Curaçao.

Table 19 Guidelines for Water Reuse

Type of Reuse

Treatment Required

Reclaimed Water Quality

Recommended Monitoring

Setback Distances

AGRICULTURAL

Secondary Disinfection

pH = 6-9

pH weekly

300 ft from potable water supply wells

Food crops commercially processed

BOD £ 30 mg/l

BOD weekly

SS = 30 mg/l

SS daily

Orchards and Vinerds

FC £ 200/100 ml

FC daily

100 ft from areas accessible to public

Cl2 residual = 1 mg/l min.

Cl2 residual continuous

PASTURAGE

Secondary Disinfection

pH = 6-9

pH weekly

300 ft from potable water supply wells

Pasture for milking animals

BOD £ 30 mg/l

BOD weekly

SS £ 30 mg/l

SS daily

Pasture for livestock

FC £ 200/100 ml

FC daily

100 ft from areas accessible to public

Cl2 residual = 1 mg/l min.

Cl2 residual continuous

FORESTATION

Secondary Disinfection

pH = 6-9

pH weekly

300 ft from potable water supply wells

BOD £ 30 mg/l

BOD weekly

SS £ 30 mg/l

SS daily

FC £ 200/100 ml

FC daily

100 ft from areas accessible to the public

Cl2 residual = 1 mg/l min.

Cl2 residual continuous

AGRICULTURAL

Secondary Filtration Disinfection

pH = 6-9

pH weekly

50 ft from potable water supply wells

Food crops not commercially processed

BOD £ 30 mg/l

BOD weekly

Turbidity £ 1 NTU

Turbidity daily

FC = 0/100 ml

FC daily

Cl2 residual = 1 mg/l min.

Cl2 residual continuous

GROUNDWATER RECHARGE

Site-specific and use-dependent

Site-specific and use-dependent

Depends on treatment and use

Site-specific

Source: USEPA, Process Design Manual: Guidelines for Water Reuse, Cincinnati, Ohio, 1992, (Report No. EPA-625/R-92-004).

In Latin America, treated wastewater is used in small-scale agricultural projects and, particularly by hotels, for lawn irrigation. In Chile, up to 220 l/s of wastewater is used for irrigation purposes in the desert region of Antofagasta. In Brazil, wastewater has been extensively reused for agriculture. Treated wastewaters have also been used for human consumption after proper disinfection, for industrial processes as a source of cooling water, and for aquaculture. Wastewater reuse for aquacultural and agricultural irrigation purposes is also practiced in Lima, Peru. In Argentina, natural systems are used for wastewater treatment. In such cases, there is an economic incentive for reusing wastewater for reforestation, agricultural, pasturage, and water conservation purposes, where sufficient land is available to do so. Perhaps the most extensive reuse of wastewater occurs in Mexico, where there is large-scale use of raw sewage for the irrigation of parks and the creation of recreational lakes.

In the United States, the use of reclaimed water for irrigation of food crops is prohibited in some states, while others allow it only if the crop is to be processed and not eaten raw. Some states may hold, for example, that if a food crop is irrigated in such a way that there is no contact between the edible portion and the reclaimed water, a disinfected, secondary-treated effluent is acceptable. For crops that are eaten raw and not commercially processed, wastewater reuse is more restricted and less economically attractive. Less stringent requirements are set for irrigation of non-food crops.

International water quality guidelines for wastewater reuse have been issued by the World Health Organization (WHO). Guidelines should also be established at national level and at the local/project level, taking into account the international guidelines. Some national standards that have been developed are more stringent than the WHO guidelines. In general, however, wastewater reuse regulations should be strict enough to permit irrigation use without undue health risks, but not so strict as to prevent its use. When using treated wastewater for irrigation, for example, regulations should be written so that attention is paid to the interaction between the effluent, the soil, and the topography of the receiving area, particularly if there are aquifers nearby.

Operation and Maintenance

The operation and maintenance required in the implementation of this technology is related to the previously discussed operation and maintenance of the wastewater treatment processes, and to the chlorination and disinfection technologies used to ensure that pathogenic organisms will not present a health hazard to humans. Additional maintenance includes the periodic cleaning of the water distribution system conveying the effluent from the treatment plant to the area of reuse; periodic cleaning of pipes, pumps, and filters to avoid the deposition of solids that can reduce the distribution efficiency; and inspection of pipes to avoid clogging throughout the collection, treatment, and distribution system, which can be a potential problem. Further, it must be emphasized that, in order for a water reuse program to be successful, stringent regulations, monitoring, and control of water quality must be exercised in order to protect both workers and the consumers.

Level of Involvement

The private sector, particularly the hotel industry and the agricultural sector, are becoming involved in wastewater treatment and reuse. However, to ensure the public health and protect the environment, governments need to exercise oversight of projects in order to minimize the deleterious impacts of wastewater discharges. One element of this oversight should include the sharing of information on the effectiveness of wastewater reuse. Government oversight also includes licensing and monitoring the performance of the wastewater treatment plants to ensure that the effluent does not create environmental or health problems.

Costs

Cost data for this technology are very limited. Most of the data relate to the cost of treating the wastewater prior to reuse. Additional costs are associated with the construction of a dual or parallel distribution system. In many cases, these costs can be recovered out of the savings derived from the reduced use of potable freshwater (i.e., from not having to treat raw water to potable standards when the intended use does not require such extensive treatment). The feasibility of wastewater reuse ultimately depends on the cost of recycled or reclaimed water relative to alternative supplies of potable water, and on public acceptance of the reclaimed water. Costs of effluent treatment vary widely according to location and level of treatment (see the previous section on wastewater treatment technologies). The degree of public acceptance also varies widely depending on water availability, religious and cultural beliefs, and previous experience with the reuse of wastewaters.

Effectiveness of the Technology

The effectiveness of the technology, while difficult to quantify, is seen in terms of the diminished demand for potable-quality freshwater and, in the Caribbean islands, in the diminished degree of degradation of water quality in the near-shore coastal marine environment, the area where untreated and unreclaimed wastewaters were previously disposed. The analysis of beach waters in Jamaica indicates that the water quality is better near the hotels with wastewater reuse projects than in beach areas where reuse is not practiced: Beach #1 in Table 20 is near a hotel with a wastewater reuse project, while Beach #2 is not. From an aesthetic point of view, also, the presence of lush vegetation in the areas where lawns and plants are irrigated with reclaimed wastewater is further evidence of the effectiveness of this technology.

Table 20 Water Quality of Beach Water in Wastewater Reuse Project in Jamaica

Site

BOD

TC

FC

NO3

Beach # 1

0.30

<2

<2

0.01

Beach # 2

1.10

2.400.00

280.00

0.01

Source: Basil P. Fernandez, Hydrogeologist and Managing Director, Water Resources Authority, Kingston, Jamaica.

Suitability

This technology has generally been applied to a small-scale projects, primarily in areas where there is a shortage of water for supply purposes. However, this technology can be applied to larger-scale projects. In many developing countries, especially where there is a water deficit for several months of the year, implementation of wastewater recycling or reuse by industries can reduce demands for water of potable quality, and also reduce impacts on the environment.

Large-scale wastewater reuse can only be contemplated in areas where there are reticulated sewerage and/or stormwater systems. (Micro-scale wastewater reuse at the household or farmstead level is a traditional practice in many agricultural communities that use night soils and manures as fertilizers.) Urban areas generally have sewerage systems, and, while not all have stormwater systems, those that do are ideal localities for wastewater reuse schemes. Wastewater for reuse must be adequately treated, biologically and chemically, to ensure the public health and environmental safety. The primary concerns associated with the use of sewage effluents in reuse schemes are the presence of pathogenic bacteria and viruses, parasite eggs, worms, and helminths (all biological concerns) and of nitrates, phosphates, salts, and toxic chemicals, including heavy metals (all chemical concerns) in the water destined for reuse.

Advantages

· This technology reduces the demands on potable sources of freshwater.

· It may reduce the need for large wastewater treatment systems, if significant portions of the waste stream are reused or recycled.

· The technology may diminish the volume of wastewater discharged, resulting in a beneficial impact on the aquatic environment.

· Capital costs are low to medium, for most systems, and are recoverable in a very short time; this excludes systems designed for direct reuse of sewage water.

· Operation and maintenance are relatively simple except in direct reuse systems, where more extensive technology and quality control are required.

· Provision of nutrient-rich wastewaters can increase agricultural production in water-poor areas.

· Pollution of seawater, rivers, and groundwaters may be reduced.

· Lawn maintenance and golf course irrigation is facilitated in resort areas.

· In most cases, the quality of the wastewater, as an irrigation water supply, is superior to that of well water.

Disadvantages

· If implemented on a large scale, revenues to water supply and wastewater utilities may fall as the demand for potable water for non-potable uses and the discharge of wastewaters is reduced.

· Reuse of wastewater may be seasonal in nature, resulting in the overloading of treatment and disposal facilities during the rainy season; if the wet season is of long duration and/or high intensity, the seasonal discharge of raw wastewaters may occur.

· Health problems, such as water-borne diseases and skin irritations, may occur in people coming into direct contact with reused wastewater.

· Gases, such as sulfuric acid, produced during the treatment process can result in chronic health problems.

· In some cases, reuse of wastewater is not economically feasible because of the requirement for an additional distribution system.

· Application of untreated wastewater as irrigation water or as injected recharge water may result in groundwater contamination.

Cultural Acceptability

A large percentage of domestic water users are afraid to use this technology to supply of potable water (direct reuse) because of the potential presence of pathogenic organisms. However, most people are willing to accept reused wastewater for golf course and lawn irrigation and for cooling purposes in industrial processes. On the household scale, reuse of wastewaters and manures as fertilizer is a traditional technology.

Further Development of the Technology

Expansion of this technology to large-scale applications should be encouraged. Cities and towns that now use mechanical treatment plants that are difficult to operate, expensive to maintain, and require a high skill level can replace these plants with the simpler systems; treated wastewater can be reused to irrigate crops, pastures, and lawns. In new buildings, plumbing fixtures can be designed to reuse wastewater, as in the case of using gray water from washing machines and kitchen sinks to flush toilets and irrigate lawns. Improved public education to ensure awareness of the technology and its benefits, both environmental and economic, is recommended.

Information Sources

Contacts

Carlos Solís Morelos, Centro Interamericano de Recursos de Agua de la Universidad Autónoma del Estado de México (UAEM), Facultad de Ingeniería, Código Postal 50 110, Cerro de Coatepec, Toluca, México. Tel. (52-72)20-1582. Fax (52-72)14-4512.

Basil P. Fernandez, Managing Director, Water Resources Authority, Hope Gardens, Post Office Box 91, Kingston 7, Jamaica. Tel. (809)927-1878. Fax (809)977-0179.

Armando Llop and Graciela Fasciolo, Instituto Nacional de Ciencia y Técnica Hídrica (INCYTH/CELAA), Belgrano 210 Oeste, 5500 Mendoza, Argentina. Tel. (54-61)28-7921. Fax (54-91)28-5416.

Guillermo Navas Brule, Codelco Chile, Div. Chuquicamata, Calama, Chile. Tel. (56-56)32-2207. Fax (56-56)32-2207.

Alberto Cáceres Valencia, Gerente de Ingenieria, Empresa de Servicios Sanitarios de Antofagasta S.A., Manuel Verbal 1545, Santiago, Chile. Tel. (56-55)26-7979. Fax (56-55)22-4547.

Vincent Sweeney, Caribbean Environment Health Institute (CEHI), Post Office Box 1111, Castries, St. Lucia. Tel. (809)452-2501. Fax (809)453-2721. E-mail: cehi@isis.org.lc.

Ernesto Pérez, P.E., Technology Transfer Chief, Water Management Division, USEPA Region IV, 345 Courtland Street N.E, Atlanta, Georgia 30365, U.S.A.. Tel. (404) 347-3633.

Oscar Vélez, Ingeniero Sanitario Subinterventor, OSM - SE, Belgrano 920, 5500 Mendoza, Argentina. Tel. (54-61)25-9326. Fax (54-61)25-9326.

Pedro Mancuso, Faculdade de Saúde Pública da Universidade de São Paulo, Departamento de Saúde Ambiental, 01255-090 São Paulo, São Paulo, Brasil. Tel. (55-11)872-3464. Fax (55-11)853-0681.

Bibliography

Arjona, B. 1987. Evaluación de un Cultivo Hidropónico de Penissetus Clandestinum Hoschst (kikuyo) como Tratamiento Biológico para Aguas Residuales Domésticas. Bogotá, Universidad Nacional de Colombia. (Trabajo de grado)

Barbosa, M., and G. Sarmiento. 1988. Estudios de Tratabilidad de las Aguas Residuales de Bogotá, Colector Salitre. Bogotá, Empresa de Acueducto y Alcantarillado de Bogotá, LAN-10. (Discos Biológicos Rotatorios)

Cornejo, E., and R. Berolatti. 1991. Tratamiento de Aguas Servidas Mediante el Uso de Macrófitos Acuáticos. Puno, Peru, Convénio UNA-UBC-ACDI, IIAA.

Fair, G. 1989. Purificación de Aguas y Tratamiento de Aguas Servidas. vol II. Mexico, D.F., Limusa. Guyot, J. P. 1988. Microbiología de la Digestión Anaeróbica. Medellín, Colombia, Universidad de Antioquía.

Kraft, Harald. 1995. Draft Preliminary Report on Design, Construction and Management of a Root Zone Waste Water Treatment Plant at Hurricane Hole Hotel, Marigot Bay, Saint Lucia. Castries, CARICOM/GTZ. Environmental Health Improvement Project.

Huanacuni, V. 1991. Factores Ambientales del Tratamiento con Totora (Schoenoplectus Totora) en Aguas Servidas, Ciudad de Puno. Puno, Perú, UNA. (Tesis)

Lettinga, G., et al. 1989. "High Rate Anaerobic Waste Water Treatment Using the UASB Reactor Under a Wide Range of Temperature Conditions," Biotechnology and Genetic Engineering Review, 2.

Martínez, I. 1989. Depuración de Aguas con Plantas Emergentes. Madrid, Ministério de Agricultura, Pesca y Alimentación.

Reed, S.C., E.J. Middlebrooks, and R.W. Crites. 1988. Natural Systems for Waste Management and Treatment. New York, McGraw-Hill.

UNEP. 1993. "Re-use of Water: An Overview." Paper prepared for the WHO/FAO/UNCHS/UNEP Workshop on Health, Agriculture, and Environmental Aspects of the Use of Wastewater, Mexico City, Mexico. Nairobi.

USEPA. 1980. Process Design Manual: Onsite Wastewater Treatment and Disposal Systems. Cincinnati, Ohio. (U.S. EPA Report No. EPA-625/1-80-012)

----. 1980. Innovative and Alternative Technology Assessment Manual. Washington, D.C. ((EPA Report No. EPA-430/9-78-009)

----. 1980. Planning Wastewater Management Facilities for Small Communities. Cincinnati, Ohio. (Report No. EPA-600/8-80-030)

----. 1981. Process Design Manual: Land Treatment of Municipal Wastewater. Cincinnati, Ohio. (Report No. EPA-625/1-81-013)

----. 1983. Process Design Manual: Municipal Wastewater Stabilization Ponds. Cincinnati, Ohio. (Report No. EPA-625/1-83-015)

----.1988. Process Design Manual: Constructed Wetlands and Aquatic Plant Systems. Cincinnati, Ohio. (Report No. EPA-625/1-88-022)

----. 1990. State Design Criteria for Wastewater Treatment Systems. Washington. D.C. (Report No. EPA-430/09-90-014)

----. 1992. Process Design Manual: Wastewater Treatment/Disposal for Small Communities. Cincinnati, Ohio. (Report No. EPA-625/R-92-005)

Previous Page Top of Page Next Page