Urban wastewater reuse in agriculture for irrigation in arid and sem-iarid regions - A review

Purpose: In recent years, attempts have been made to compensate irrigation water shortage through widespread wastewater application as a lowquality water resource for agriculture. The existing wastewater treatment plants do not have sufficient capacity to treat such a huge volume of wastewater. In arid and semiarid region, soil type as well as climate is different from the others, so the aim of this paper is the review of literature on the effects of wastewater reuse in agriculture. Methods: An extensive literature review was conducted to evaluate urban wastewater effects on soil, plant and environment. Results: One of the best methods: for wastewater disposal is wastewater discharge into the soil. However, as it was revealed in this research, in most cases, this method would lead to increased salinity, SAR, organic matter content, permeability, and electric conductivity as well as reduced soil bulk density. Nevertheless, wastewater effect on soil physical properties depends on its characteristics and also its application period. For instance, in durations less than one year, wastewater has often no significant effect on some soil properties such as bulk density. The best wastewater usage approach is utilizing drip irrigation method, which can overcome the shortcomings resulted from its application. In most studies carried out in this field, wastewater irrigation has led to increased accumulation of heavy elements and nutrients in the soil and even sometimes in undercultivation plants. It is noteworthy that these elements’ accumulation in the fruit section is less than their accumulation in the vegetable part of the plants. Conclusion: The use of wastewater without accurate management can extremely cause adverse environmental outcomes, including soil salinization, soil degradation, reduced soil hydraulic conductivity, soil hydrophobicity, poisoning, reduced yield of the crops, and surface/groundwater resources’ contamination, and eventually the prevalence of diseases. Consequently, in order to reuse wastewater for agriculture, microbial contamination’ reduction should be seriously considered in accordance with the standards determined by the Environmental Protection Agency or the World Health Organization guidelines. It is highly emphasized that after reaching the required standards, the wastewater can be used for irrigation. In conclusion, Pharmaceuticals presence in the wastewater are a growing global concern.