In this article we will discuss about the reuse of sewage effluents for irrigation.
Atta. F. El-Wakeel and Bauomy M. El-Nashar
Soil, Water & Environment Research Institute Agricultural, Research, Centern, Giza, Egypt
O.A. Al-Hamad
Faculty of Agriculture
Aleppo University, Syria
Abstract:
Since water is a critical component for sustainable development, it is clearly indicate that Egypt has to depend for many years to come on non-traditional water resources and their rational use.
With the progressive coverage of urban water supply and sewage services, increasing quantities of wastewater are being produced with a potentially heavier impact on the receiving water quality. On the other hand, with water demand approaching natural limitations, any potential new sources of water, such as treated wastewater, are being regarded with great interest in order to increase total water availability, especially for the agricultural sector.
It has been estimated that, in Egypt, about 3.1. billion cubic meter of sewage effluent will be potentially, available by the year 2000, and that is being enough to irrigate up to 150,000 acres.
The use of treated wastewater for irrigation is an attractive option. Sound planning and effective management of irrigation and fertilization regimes can minimize the disadvantages so that there are insignificant health risks and environmental pollution.
Introduction:
Most countries in the Near East region, are arid or semiarid. They have little rainfall which is mostly seasonal and erratically distributed. In these countries, water has always been regarded as a valuable commodity. During the last few decades, these countries have witnessed a rapid development of their urban and rural domestic water supplies to the extent that conventional water resources are inadequate to meet increasing water demand.
Furthermore, the rising population and continuing urbanization have generated increasing amounts of municipal wastewater, and its disposal create a serious problem. The need, therefore, to conserve water and protect the environment and public health necessitates the development of more efficient irrigation systems and, further, the use of marginal quality water.
Reclamation and reuse of municipal wastewater for irrigation is an easy and useful way to dispose of such wastewater, an attractive alternative to meet the increasing demand for water. Moreover, in arid and semiarid zones there are only a few streams with sufficient capacity to serve as natural repositories for even well treated wastewater effluent.
Thus, wastewater reuse in agriculture has provided almost be only feasible, relatively low-cost alternative for be sanitary dispose of wastewater from municipal areas. It also minimizes pollution of the waterway in the region. All these factors, coupled with the rapid urban growth and the need to increase agricultural production, helped to revive, interest in reusing wastewater for irrigation.
As a substitute for freshwater in irrigation, wastewater is an important source for potable water and other priority uses. Wastewater reuse contributes to water conservation and takes on an economic dimension. Moreover, wastewater reuse schemes, if properly planned and managed, can have positive environmental impact, besides providing increased agricultural yields.
Benefits and Limitations of Wastewater Use for Irrigation:
Environmental improvement and benefits accrue as a result of several factors including:
1. Prevention of surface water pollution, which would or their occur if the wastewater were not used but were discharged into rivers or lakes;
2. Conservation of freshwater resources, by their rational usage, especially in arid and semiarid areas. Freshwater for urban demand, and wastewater for agriculture use;
3. Reduction the degree of ground water exploitation, seawater intrusion in coastal areas;
4. Reduction in the requirements for artificial fertilizers, with a concomitant reduction in energy expenditure and industrial pollution elsewhere, those plant nutrients that may eventually pollute the environment if raw wastewater or treated effluent were discharged directly into the environment may serve as usable plant nutrients when applied as irrigation water;
5. Prevention of land erosion and soil conservation because the organic matter added through wastewater irrigation serves as a soil conditioner, increasing its water holding-capacity;
6. Desertification and desert reclamation, through the irrigation and fertilization of green belts; and
7. Improvement in urban amenities through irrigation and fertilization of green spaces for recreation.
Reuse of waste water way has a potentially adverse impact on the environment, largely depending on the wastewater characteristics, the degree of purification and the method and location of reuse. Soil, groundwater and surface water pollution are among the most important potential disadvantages of wastewater reuse.
However, sound planning and effective management of the irrigation and fertilization regime can minimize these disadvantages to such a level that they are insignificant environmental hazards.
Wastewater Quality Evaluation:
The physical properties, and the chemical and biological constituents are important parameters in the design and operation of collection, treatment and disposal facilities and in the engineering management of environmental quality. The constituents of concern in wastewater treatment and wastewater irrigation are listed in Table 1.
For evaluating the hazards associated with wastewater use, the establishment of the relative importance of the various toxic materials and pathogens eventually present in effluent in needed.
In recent guidelines four problem categories, namely, salinity, infiltration, toxicity and miscellaneous problems are used for evaluating conventional sources for irrigation (Table 2). Irrigation water may classified into three categories namely not restricted, slightly to moderately restricted and severely restricted for use.
The guidelines presented in Table 2 could also be used to evaluate the suitability of treated and untreated wastewater for irrigation in terms of its chemical constituents. The corresponding guidelines in Egypt are given in Table 3. The recommended maximum concentration of trace and heavy metals are presented in Table 4.
Guidelines are presented in Tables 5 and 6 to help in the evaluation of the suitability of wastewater for use with a drip irrigation system.
Health problems associated with the use of raw or partially treated wastewater are well documented. As a consequence, water reuse standards and guidelines are principally directed at public health protection and are generally based on the control of pathogenic organisms. In 1989, a Scientific Group formulated new guidelines for wastewater use in agriculture which are summarized in Table 7. The corresponding guidelines for Egypt are given in Table 8.
Strategy to Protect Human Health and the Environment:
The success of using treated wastewater for crop production will depend greatly on the adoption of appropriate strategies to optimize crop yields and quality, maintain soil productivity and safeguard public health and the environment.
To achieve this and to protect the environment and human health, the four groups of measures presented in Fig. 1 are available:
1. Wastewater treatment;
2. Restriction of crops grown;
3. Choice of methods of application of treated effluents to the crops; and
4. Control of human exposure to the waste and hygiene.
Wastewater Treatment:
The design of wastewater treatment plants has usually been based on the need to reduce organic and suspended solids loads to limit pollution of the environment. Pathogenic removal, which is the most important single parameter in irrigation, has very rarely been considered an objective. For reuse of effluent in agriculture, this must now be of concern, and treatment processes should be selected and designed accordingly.
Crop Restriction:
Even if the new guidelines for treated wastewater quality are not fully met, the wastewater may still be used to irrigate selected agricultural crops without risk to the consumer.
Crops can be grouped into three broad categories with regard to the degree to which health protection measures are required:
1. Category A includes situation which protection is needed only for field workers. Such situations include industrial crops, such as cotton, sisal, grains, and forestry, as well as food crops for canning;
2. Category B includes situations in which further measures may be needed. This applies to pasture and green fodder crops, as well as to tree crops and fruits and vegetables which are peeled or cooked before eating; and
3. Category C includes situation in which treatment to an unrestricted irrigation level is essential. This covers fresh vegetables, spray-irrigated fruit, and parks lawns and golf courses.
Irrigation which is limited to certain crops and conditions, such as is the case in category A, is commonly referred to as restricted irrigation. Crop restriction is a strategy to provide protection to the consuming public. However, it does not provide protection to frameworks or their families.
Crop restriction is, therefore, not adequate on its own; it should be complemented by other measures, such as partial wastewater treatment, controlled application of the workers, or human exposure control. Partial treatment coupled with the helminthic component of the new quality guidelines would be sufficient to protect field workers in most settings, and would be cheaper than full treatment.
Crop restrictions is feasible and is particularly called for under the following conditions:
1. A law-abiding society or strong law enforcement exists;
2. A public body controls the allocation of water;
3. An irrigation project has a central management;
4. There is adequate demand for the crops allowed under crop restriction and reasonable prices are obtained, and
5. There is little market pressure in favor of excluded crops.
Adopting crop restriction as a means of health protection in reuse schemes will require a strong institutional framework and capacity to monitor and control compliance with and enforcement of regulations.
Farmers must be informed as to why such crop restrictions are necessary, and assisted in developing a balanced mix of crops which fully utilizes the constant production of partially treated wastewater. National planning should take into account the crop production potential of restricted reuse schemes so that excesses of production are avoided.
Wastewater Application Control:
Irrigation water, including treated wastewater, can be applied to the land in general in the five following ways:
1. Flooding (border irrigation), thus wetting almost all the land surface;
2. Furrows, thus wetting only part of the ground surface;
3. Sprinklers, in which the soil is wetted in much the same way as by rainfall;
4. Subsurface irrigation, in which the surface is wetted a little, if any, but the subsoil is saturated, and
5. Localized, i.e., trickle, drip or bubbler irrigation, in which water is applied to each individual plant at an adjustable rate.
Flooding involves the least investment, but probably exposes field workers to the greatest risk.
If the effluent is not of the required category B type, sprinkler irrigation should not be used or fodder crops, and border irrigation can give the greatest degree of health protection, as well as using water more efficiency and often producing higher yields.
However, it is expensive, and a high degree of reliable treatment is required, to prevent clogging of small holes (emitters) through which water is slowly released into the soil. Bubbler irrigation, a technique developed for localized irrigation of tree crops, avoids the need for small emitter to regulate the flow to each tree.
Exposure Control through Personal and Domestic Hygiene:
Four groups of people can be identified as being at potential risk from the agricultural use of wastewater.
These are:
1. Agricultural fieldworkers and their families;
2. Crop handlers;
3. Consumers (of crops, meat and milk); and
4. Those living near the affected fields.
Agricultural fieldworker’s exposure to hookworm infection can be reduced by the continuous in field use of appropriate footwear, but this may be more difficult to achieve than it might at first appear.
Immunization is not feasible against helminthic infections, or most diarrheal diseases, but immunization of highly exposed groups against typhoid and hepatitis A may be worth considering. Additional protection may be provided by the provision of adequate medical facilities to treat diarrhoeal disease, and by regular chemotherapeutic control of intense nematode infections in children and control of anemia.
Risks to consumers can be reduced by thorough cooking and by high standards of hygiene. Food hygiene is a theme to be included in health educations campaign, although the efficiency of such campaigns may often be quite low.
Local residents should be kept fully informed about the location of all fields where wastewaters is used, so that they may avoid entering them and also prevent their children from doing so. There is no evidence that those living near wastewater irrigated fields are at significant risk from sprinkler irrigation schemes. However, sprinklers should not be used within 50 to 100 m of houses or roads.
Wastewater Production and Reuse in Egypt:
The predictions covering the period 1997 to the planned horizon 2025 for wastewater and sewage sludge are given in Table 9. It appears that about 8,650 and 15,040 x 106 m3/ day of sewage effluents and 5,320 and 9, 25 tons/day of dry solids will be available during the two years, respectively.
The planned reuse of municipal wastewater for irrigation is not a new concept, it has been practiced since 1911 on the sandy soil of El-Gabal El-Asfer Farm (25 km north-east of Greater Cairo), as well as on Abu Rawash farm (south-east of Greater Cairo). Citrus, becan, flowers, forests and field crops (i.e., corn, barley, wheat, sunflower, flax and cotton) are the main crops being cultivated.
Both positive and negative effects have been recorded. The positive ones include the increasing of organic matter in the soil with marked improvement in the soil’s properties, significant increase of nutrient absorption and yield production.
Among the negative impacts are the accumulation of heavy metals in the soil and plant organs, increases in the NO3 -N in the groundwater, and health hazards for the field workers.