Literature Review
Freshwater is gradually turning out to be a scarce commodity globally especially in the arid and semi-arid regions like the Middle East. As a result of the massive growth of populace in most of the metropolises in the arid and semi-arid regions, the demand for fresh water keeps on inclining, which is making the reuse of wastewater a fascinating activity. Thus, most of the municipalities are struggling to ensure that there is an equilibrium in the usage of water amongst industrial, municipal, recreational as well as in industrial consumers. Furthermore, the upsurge in population has not only led to the incline in population but also resulted in an amplified amount of wastewater generation. Consequently, the only option that has been left is the consumption of recycled or treated wastewater which appears to the source the only source of water which is on the rise as other sources shrink (Jacobs et al., 2018, p. 103).
Therefore, the consumption of treated water for irrigating the landscapes has become the most appropriate alternative that could be used to maximise the prevailing sources of water. In light of this statement, the major concern regarding the reuse of treated domestic water in irrigation is its probability for undesirable impacts that this practice could have on the soil. Accordingly, the standards as well as guidelines put forward over years for reuse of treated water by (Corey et al. (2018); Ganjegunte, Ulery, Niu, and Wu, 2017)) does not safeguard against likely environmental consequences on the characteristics of the soil like sodicity and salinity, microbial community structure, hydraulic conductivity and hydrophobicity. Despite the fact that these phenomena have been researched in irrigated soils with domestic wastewater treated in massive, centralised treatment industries, limited studies have centred on domestic wastewater treatment on-site environments.
The use of domestic wastewater is an age-old practice. Ultimately, since domestic wastewater contains heavy loads of micro as well as macronutrients it is regarded a probable source for the enrichment of fertility in the soil. Consequently, for agricultural practices, the irrigation water quality can impact the soil features that in turn contribute to the potential yield of crops. The raw domestic wastewater contains rich organic matter as well as vital nutrients. Accordingly, a greater percentage of the municipality water majorly consists of water in addition to relatively small amounts of concentration of industrial and suspended effluent discharge which contain toxic metals in huge amounts (Corey et al., 2018, p. 27). Nevertheless, the composition of treated wastewater keeps on varying from time to time based on the intensity as well as the nature of human beings practices in the region and the collection method and the involved treatment process undertaken. In the context of this literature pertaining to the impact of domestic wastewater irrigation on the characteristics of the soil is reviewed based on the following subheadings.
Characteristics of Domestic Wastewater
According to Balkhair, and Ashraf, (2016) analysis of domestic wastewater of Melbourne city for an interval of two weeks for a period of two years (2009-2011) has shown that domestic wastewater differs greatly regarding the composition during dissimilar seasons of the year. In general, the concentration was found to be more during the summer as compared to the monsoon. During this
Research has shown that long-term domestic wastewater irrigation destructs the state of balance of nature resulting in ecological weakening of the landscape (Becerra-Castro et al., 2015, p. 118). The major impact of domestic wastewater irrigation on the soil physical aspects is the destruction of the soil structure, soil hardening, and functional disruption. The soil bulk density is among the leading indicators measure for physical soil properties. Certainly, this illustrates the soil compaction extent which has a significant impact on the soil aeration, infiltration, absorption capability, soil water holding capacity solute migration and soil resistance to erosion. Bedbabis et al. (2015) state that the soil porosity is subjected to a modification in the density of the soil. Research undertaken on recurrent irrigation in the calcareous soil of India revealed that long-standing domestic wastewater irrigation significantly modified the soil arrangement. Accordingly, soil bulk density and porosity showed a close relationship with domestic wastewater period. With the increase in time, the soil porosity was declining whereas the soil bulk density was increasing.
Moreover, permeation by effluents consisting of greatly saline made easy soil secondary salinization, which improved the aggregate alkalinity as well as sodium alkalinity upsurge in the soil. As a result, this led to a hardening of the soil leading to the decline in soil permeability. In addition, Todeshki et al. (2015) claim that the microorganism, sediments, organic matter and fibre originating from domestic wastewater when disposed on the soil surface it exerts deleterious effects on the physical characteristics of the soil. Consequently, this leads to soil permeability destruction and occurrence of soil compaction. The most evident outcome of soil hardening is the resistance of the soil to infiltration that is a significant index for determining crop root extension resistance. Ultimately, this is associated with the aggregate of the soil traits and distinct arrangement of the soil.
The influence of domestic wastewater irrigation on the chemical composition of the soil is shown through the soil’s acidity-alkalinity. Indeed, this is one of the significant aspects which influence the fertility of the soil. According to Ganjegunte, Ulery, A., Niu, and Wu, (2017) soil formation and variation of acidity and alkalinity of the soil means the comparative strength of the base constituents accumulation and leaching progression. The level of acidity or alkalinity of the soil is majorly articulated by pH value. The soil has a specific buffering function which makes the pH value to be comparatively unwavering. Research has found that once the soil pH level changes drastically, it greatly influences the soil chemical properties. In this sense, this process greatly influences the soil structure which results in a direct variation in the availability of soil nutrients. Therefore, modification in the soil pH is associated with the types of irrigation water as well as the soil group. In accordance to Pettygrove, (2017) the theorist showed that soil pH value declines with the upsurge in recurrence in the times of irrigation utilising wastewater.
Impact of Domestic Wastewater Irrigation on Physical Soil Properties
On the other hand, a contrary deduction was reached stating that the soil pH value of the soil reduced when irrigation was done by discharges originating from paper-making plants to relatively dishonored saline-alkaline soil. Additionally, it has also been established that there was no observable impact on plant field pH when domestic wastewater was coming from livestock breeding. Consequently, the difference in the pH value can be clarified by the dissimilarity in the amount of ammonium as well as nitrification of the soil organic matter, release, and enrichment of metallic ions, and anaerobic decomposition of organic matter. Certainly, biological matter is a vital element of the soil together with its content and is often considered to be a significant index for measuring soil fertility (Lu et al., 2015, p. 6). The build-up of biological matter in the soil is associated with both inputs of biological matter through all means and natural environmental conditions.
The source of heavy metals in the soil fall under a wide range such as agricultural wastes, industrial, sewage effluent gas emission from industries and vehicles only to mention but a few. Accordingly, heavy metals exists naturally in the soil from geological source, though it is majorly in the form that is unavailable to living organisms. Even though the movement of heavy metals in the soil has been regarded as slow and practically non-existent, research by Ma et al., 2015; and Balkhair, and Ashraf, (2016) reveals that metals are able to move down in substantial volumes to the subsoil and past the root zone over a long period of time with a continuous input of metal containing wastewater. Therefore, irrigation with polluted water result in the incline in the concentration of heavy metals in the soil. Ultimately, studies shows that at the entrance of polluted water utilised for irrigation contained approximately 6.0 ppm Cd in the topmost soils. However, the content of Cd keeps on falling by approximately 1 ppm with the increase in the distance from the entrance point.
Soil microorganism play a significant role in maintaining the structure of the soil by taking part in most of the soil biochemical as well as biological activities. Consequently, this has a high sensitivity which echo the variance in the quality of the soil. The most sensitive biological indicator is shown by the soil composition, quantity, sand microbial activities which keep on changing with changes happening in the environment. Therefore, sewage irrigation could result in the microhabitat which to a certain extent causing a great effect on the soil microbial activities. According to research it has shown that bacterial, fungal and actinomycetes are the primary types of microorganisms which are used to reflect the total amount of soil microorganisms (Becerra-Castro et al., 2015, p. 119). The soil microorganism play an essential role in transforming the soil organic matter as well as inorganic matter. However, as a result of sewage irrigation the number of actinomycetes sand bacteria has been gradually declining whereas the number of fungi has been inclining slowly. A similar research undertaken in Fushun and Shenyang in China has found that sewage irrigation changed the amount of soil nutrients as well as the multiring hydrocarbons. Certainly, this has had a direct impact on the number of microbial organisms in the soil. The research found that the aggregate nitrogen had a significant constructive relationship with the nitrogen-fixing bacteria (Lu, Wang, and Pei, 2016, p. 298). Consequently, domestic wastewater has to a certain extent an impact to the amount of soil microorganisms.
Effect of Domestic Wastewater Irrigation on Chemical Soil Properties
The questions that this research attempts to answer include:
- What are the advantages of domestic wastewater to the chemical, physical and microbial characteristics of the soil around treatment plant?
- What are the disadvantages of domestic wastewater to the chemical, physical and microbial characteristics of the soil around treatment plant?
- What is the impact of sewage irrigation on soil properties?
The aim of this study is to investigate the impact of sewage irrigation on crops.
Domestic wastewater is utilised as a probable source of irrigation for raising fodder as well as vegetables around the sewage treatment plants. These fodder and vegetables are either directly or indirectly consumed by people. According to recent research sewage is a rich source of both organic and inorganic nutrients for the growth of plants hence sewage farming has become a common practice in most of the built-up areas. However, some of the municipalities where industrial effluent is discharged in addition with other toxic metals in huge volumes (Bedbabis, Rouina, Boukhris, and Ferrara, 2014, p. 47). Thus the composition of domestic waste water keep on varying depending on the industrial discharge. Accordingly, domestic wastewater when used for irrigation purposes has numerous positive impacts to the physiochemical properties of the soil unlike the use of ground water. In the light of the above statement it led to the formulation of the following hypotheses.
H1: The use of sewage water enhances the physiochemical properties of the soil unlike ground water
H2: sewage irrigation results in high crop yield with enhanced sol fertility status
Experimental Set-up
The research was conducted by conducting a laboratory setup where the investigation was performed. The experiment was undertaken to investigate the effect of applying domestic wastewater for irrigation on the soil. In the case of this context, agricultural soil was gathered from around a water treatment plant within Sidney City. During the experiment soil parameters such as K, P, N, and pH were determined prior to applying domestic wastewater.
The water was collected from water treatment plant from within Sidney City and ground water used for irrigation was also collected from within Sidney City.
The two samples of water were separately discharged into the soil for a period of 5 days, 10 days, 15 days, 20 days and 30 days for application of domestic wastewater soil parameters K, P, N, and pH in the two soil samples containing sewage was determined.
The following tests were conducted on the soil and domestic wastewater:
Determining the soil parameters (K, P, N and pH) prior to application of domestic wastewater.
Determining the pH, alkalinity, turbidity, hardness, chlorine content total solids and B.O.D of the two samples of waste water.
Determining the soil constraints (K, P, N, and pH) of both samples of soil after 5 days, 10 days, 15 days, 20 days and 30 days.
Impact of Domestic Wastewater Irrigation on the Distribution of Heavy Metals in the Soil
In this experiment, the researcher was analysing the physiochemical aspects of domestic wastewater and ground water shown in the table one and two below respectively. The soil constituents were analysed prior to applying the sewage shown in table three. The following stage the soil was irrigated by applying domestic wastewater and ground water and the soil constituents measured after 10 days, 15days, and 20 days. The experiment found existence of opportunities as well as challenges with both sewage and ground water used for irrigation. Consequently, use of recycled domestic wastewater for irrigating crops aid to conserve water and also recycles soil nutrients (Assouline, Narkis, Gherabli, and Sposito, 2016). A variation in the soil constituents after discharging domestic wastewater on the soil in assessed. The results shows a variation in the pH in the soil irrigated with ground water and that irrigated with organic carbon (OC) in the soil against time shown in figure two and three respectively. Also, the changes in potassium (K), phosphorous (P), nitrogen (N) in the soil with the change in time as illustrated in figures 4, 5 and 6 respectively.
Conclusion
According to the results, the value of P and N keeps on rising until day ten and thereafter start falling while the value of K keep on increasing until the fifteenth day and then decline thereafter. Organic carbon declines until the tenth day then start increasing from the tenth day to the fifteenth day and then slowly start to decline until the twentieth day. Accordingly, utilisation of domestic wastewater proves to be of benefit between 10 and 15 days in certain crops (Bardhan, Russo, Goldstein, and Levy, 2016, p. 3). Also, use of domestic wastewater amplified the crop produce unlike ground water, which also increases the content of K, P, N, and organic carbon in the soil. Therefore, domestic wastewater can be utilised for irrigation purposes because of the scarcity in fresh water sources as an alternative approach management of wastewater.
Assouline, S., Narkis, K., Gherabli, R. and Sposito, G., 2016. Combined effect of sodicity and organic matter on soil properties under long-term irrigation with treated wastewater. Vadose Zone Journal, 15(4).
Balkhair, K.S. and Ashraf, M.A., 2016. Field accumulation risks of heavy metals in soil and vegetable crop irrigated with sewage water in western region of Saudi Arabia. Saudi journal of biological sciences, 23(1), pp.S32-S44.
Balkhair, K.S. and Ashraf, M.A., 2016. Field accumulation risks of heavy metals in soil and vegetable crop irrigated with sewage water in western region of Saudi Arabia. Saudi journal of biological sciences, 23(1), pp.S32-S44.
Bardhan, G., Russo, D., Goldstein, D. and Levy, G.J., 2016. Changes in the hydraulic properties of a clay soil under long-term irrigation with treated wastewater. Geoderma, 264, pp.1-9.
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Becerra-Castro, C., Lopes, A.R., Vaz-Moreira, I., Silva, E.F., Manaia, C.M. and Nunes, O.C., 2015. Wastewater reuse in irrigation: A microbiological perspective on implications in soil fertility and human and environmental health. Environment international, 75, pp.117-135.
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Bedbabis, S., Trigui, D., Ahmed, C.B., Clodoveo, M.L., Camposeo, S., Vivaldi, G.A. and Rouina, B.B., 2015. Long-terms effects of irrigation with treated municipal wastewater on soil, yield and olive oil quality. Agricultural water management, 160, pp.14-21.
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Jacobs, L.W., O’Connor, G.A., Overcash, M.A., Zabik, M.J., Rygiewicz, P., Machno, P., Munger, S. and Elseewi, A.A., 2018. Effects of trace organics in sewage sludges on soil-plant systems and assessing their risk to humans. In Land application of sludge (pp. 101-143). CRC Press.
Lu, S., Wang, J. and Pei, L., 2016. Study on the effects of irrigation with reclaimed water on the content and distribution of heavy metals in soil. International journal of environmental research and public health, 13(3), p.298.
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Ma, S.C., Zhang, H.B., Ma, S.T., Wang, R., Wang, G.X., Shao, Y. and Li, C.X., 2015. Effects of mine wastewater irrigation on activities of soil enzymes and physiological properties, heavy metal uptake and grain yield in winter wheat. Ecotoxicology and environmental safety, 113, pp.483-490.
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Todeshki, A.R.S., Vanani, H.R., Shayannejad, M. and Askari, K.O.A., 2015. Effects of magnetized municipal effluent on some chemical properties of soil in furrow irrigation. International Journal of Agriculture and Crop Sciences, 8(3), p.482.
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