Effect of treated grey water reuse in irrigation on soil and plants
Introduction
Wastewater and grey water (GW) reuse is emerging as an integral part of water demand management, promoting the preservation of high quality fresh water and reducing both environmental pollution and overall supply costs. Recent developments in technology and changes in attitudes towards wastewater reuse suggest that there is a potential for GW reuse in the developing world [1]. Grey water is defined as wastewater generated from domestic activities such as dish washing, laundry and bathing, whereas black water consists of toilet water. GW represents the largest potential source of water savings in domestic residences, accounting for as much as 50–80% of the total water use [2], [3], [4], [5].
The most common application for GW reuse in urban areas is toilet flushing which can reduce water demand within dwellings by up to 30% [6], [7]. However, other applications such as irrigation of green areas in parks, school yards, cemeteries, golf areas, car wash, and fire protection are practiced [8]. The use of GW for irrigation is one of the methods which is currently widely used. This is particularly important in arid zones, where water is scarce and reuse of GW for irrigation could reduce potable water use by up to 50% [9]. In some arid and semi-arid areas municipal water consumption typically increases by 40–60% in summer months due to landscape irrigation [3]. Although irrigation with treated GW and treated wastewater effluents can mitigate the utilization of natural water resources, it may also result in environmental problems. One particular concern is long-term sustainability issue (e.g. the increase of salinity and sodium content in soil). Sodium content is the ratio of sodium concentration (detrimental element) to the concentrations of calcium and magnesium (beneficial elements) which is also known as sodium adsorption ratio (SAR). High values of soil salinity and SAR cause soil structure deteriorations, decrease of soil permeability and reduction of crop yields due to toxic and osmotic effects [10], [11], [12], [13], [14], [15], [16]. Many researches had conducted to study the impact of reused GW quality on soil. A study conducted by Travis et al. [17], suggests that oil and grease from GW can accumulate in soils and affect the ability of the soils to absorb water essentially making it water repellent. Another study conducted by Gross et al. [18] found evidence that, long-term irrigation of arid loess soil with GW may result in accumulation of salts and surfactants in the soil, causing changes in soil properties and toxicity to plants. In his research [19], Patterson showed that loss of soil permeability commenced as low as SAR 3 when the electrical conductivity was about the same from domestic wastewater. Internationally, SAR 6 is accepted as a level above which soil permeability and structural stability may be affected [19]. According to reference [20], SAR 8 was suggested as the higher limit for irrigation of non-tolerant plants. According to the data presented in reference [21], long-term irrigation using water with SAR higher than 4 can negatively alter the soil properties. Madyiwa et al. [22], investigated the effect of using treated effluent for irrigation of pasture for over 30 years. The results showed that Pb and Cd were taken up by plants from the soil, thereby making plants as potential sources of contamination for humans and animals.
Recently in some rural areas of Jordan, GW is being used for irrigation in home gardens to provide additional water source. In the year 2003, the Ministry of Planning and International Cooperation of Jordan provided more than 750 low-income households in more than 90 villages in rural areas of Jordan with GW treatment units for home garden irrigation [23]. Although GW was used for irrigation purposes, the effect of their use on the properties of irrigated soil and plants was not fully investigated. This study involves evaluation of the environmental impact of GW reuse project in Al-Amer villages, Jordan. The project included 110 GW treatment units and aimed to help the local population preserve fresh water and protect the environment. The objectives of this study are to:
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estimate the average production rates of GW in the study area.
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evaluate the suitability of treated GW produced from 4-barrel and confined trench (CT) units for irrigating olive trees and vegetable crops according to Jordanian standards.
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study the impact of treated GW reuse for irrigation on some chemical properties of the irrigated soil and plants.
Section snippets
Treatment of grey water
Many new technologies have been developed to treat GW [24], [25], [26], [27], [28], [29], [30]. The major difficulty presented for treatment of GW is the large variation in its composition. Reused GW should fulfill four criteria: hygienic safety, aesthetics, environmental tolerance, and technical and economical feasibility [9].
In this study 4-barrel and confined trench (CT) units developed by Inter-Islamic Network on Water Resources Development and Management (INWRDAM) were used for GW
Study area
The study area was at Al-Amer villages in Karak governorate in the middle part of Jordan. The area is dominated by the Mediterranean climate, that is characterized by dry and hot summer seasons from May to September with a max temperature of 34 °C and wet winter season extending from October to April with a mean temperature of 14 °C. The mean annual rainfall is about 340 mm, the average wind speed is about 7.2 km/h and the evaporation average is 13.3 mm/day. The population in the study area was
Methodology
The research methods involved collection of GW, soil and plant samples and analyzing them for selected parameters.
Results and discussion
The estimated average GW generation rate was 30 ± 3.6 L/c.d. This rate is low compared with average rates reported for Amman (59 L/c.d.) [29], and European communities ranged between 66 and 274 L/c.d. [36], [37], [38], [39]. However, the rate in the study area was higher than the reported value (15 L/c.d.) for Um Alquttain, Mafraq area [40]. The low water consumption rate in the study area was responsible for producing GW characterized by high BOD, COD, and TSS values (Table 1). In comparisons these
Conclusions
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The average GW production rate in the study area was found to be 30 L/c.d. and the quality of treated GW complies with Jordanian standard for irrigation of fodder crops (category C) and tree crops (category B), but does not meet the standard for irrigation cooked vegetables (category A).
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Irrigation of olive trees and vegetable crops with treated GW did not show any adverse effect on the chemical properties of the fruits and leaves.
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Soil leaching with fresh water is highly recommended because it
Acknowledgement
The grey water treatment and reuse methods mentioned in this paper were possible through a financial assistance provided by the International Development Research Centre (IDRC), Ottawa, Canada to the Inter-Islamic Network on Water Resources Development and Management (INWRDAM), Amman, Jordan.
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