The Use of Domestic Wastewater for Irrigation of Vegetable Crops: The Health Implications
This work examined the effects of domestic wastewater used for irrigation of vegetables. Ever increasing population; urbanization and industrialization have led to generation and indiscriminate discharge of large volume of water from domestic agricultural zones of the country. Discharged from industries, domestic sewage, abattoir and other non-point sources of pollution with high concentration of vegetable farmers using wastewater. The use of sewage water for irrigation is a matter of major concern due to the presence of toxic metals and other pollutants. Physicochemical parameters of irrigation water were observed to be higher than acceptable limits. Consumption of vegetables has positive impact on the health of man, the presence of faecal-indicator bacteria in the irrigation water and vegetable samples suggests faecal pollution raising the possibility of the presence of pathogenic microorganisms in these vegetables and a threat to public health. We recommend adequate treatment of effluents before discharge. The need for proper disinfection of raw vegetables before consumption cannot be overemphasized.
1.0 Introduction- – – – – – – – – – 1
2.0 Process of irrigation of vegetables with wastewater- – – – 5
2.1 Economic importance of irrigating vegetables with
domestic wastewater- – – – – – – – 7
2.2 Environmental benefits of irrigating vegetables with domestic wastewater- – – – – – – – – – 12
3.0 Health implication of irrigation of vegetables with domestic wastewater
Human Health Risks- – – – – – – – 14
3.1Risks from Heavy metal intake by consumers- – – – – 16
3.1.1Estimation of Daily Intake of Heavy Metals- – – – – 19
3.2 Risks to consumers from pathogens in wastewater – – – – 20
4.0 Appropriate low-cost methods of wastewater treatment for
Irrigation- – – – – – – – – – 35
4.2 Recommendation- – – – – – – – – 39
4.1 Conclusions- – – – – – – – – – 40
Plate 1 – – – – – – – – – – 3
Plate 2- – – – – – – – – – – 9
Plate 3 – – – – – – – – – – 9
Plate 4- – – – – – – – – – – 25
Plate 5- – – – – – – – – – – 38
The population of Nigeria is always on the increase, with the World Bank estimating the population of Nigeria to hit over a 300 million in the year 2035, the gap between the supply and demand for water is widening and is reaching such alarming levels that in some parts of the world it is posing a threat to human existence. Since 1950 the world population has doubled while water consumption has increased six- fold. By 2025, it is expected that 3.4 billion people will be living in countries defined as water-scarce. Scientists around the globe are working on new ways of conserving water. It is an opportune time to refocus on one of the ways to recycle water-through the use of wastewater for irrigation and other purposes.
Wastewater refers to water whose quality might pose a threat to sustainable agriculture and/or human health, but which can be used safely for irrigation provided certain precautions are taken. It describes water that has been polluted as a result of mixing with Waste or agricultural drainage (Cornish et al 1999). Pierce and Turner (1990) defined wastewater as water that possesses certain characteristics which have the potential to cause problems when it is used for an intended purpose. In this work, it is assumed that wastewater may be a combination of some or all of the following:
Storm water and other runoff.
Domestic effluent consisting of black water (excreta, urine and associated sludge) and grey water (kitchen and bathroom wastewater).
Wastewater from farm houses and fish ponds.
Reserved wastewater from residences.
Water from commercial establishments and institutions, e.g. hospitals.
The main sources of wastewater are domestic and industrial. As a general rule 80-85% of water used is wasted (Spore 2002).
Plate 1: Vegetables farm irrigated with domestic wastewater Ghana
Source: PEASEY A (2000)
On the other hand, wastewater use in crop production is not without some risks. The main risk associated with wastewater irrigation is infection with intestinal helminthes. Also, depending on the source of the wastewater it might contain chemical pollutants and heavy metals that can accumulate in the soil and crops thereby posing a threat to human health. However, a major drive towards wastewater use is the fact that it contains high levels of nutrients, reducing the need for and cost of fertilizers. Consequently, many farmers using wastewater are better able to support themselves and their families and often create extra employment (Spore 2002). Furthermore, the continuous demand for certain crops especially vegetables has increased the need to cultivate these crops all year round. This in effect leads to the dependence on wastewater during the dry seasons or during periods of drought. Also, due to the light water requirement of some crops, the use of wastewater to augment the freshwater, if any, becomes inevitable. In many areas, the few freshwater supply stations (boreholes) are owned by individuals, and the water is sold to others who cannot afford to set up one. In such a situation, the resource poor farmers are forced to resort to a cheaper alternative – wastewater. However, unregulated use of wastewater poses some risks to human health and the environment. Because of these risks, the prevailing scientific approach to wastewater irrigation advocates treatment before use. But the reality is that many developing countries lack the resources to build and maintain treatment facilities.