The increase in population growth rate as well as the growing trend of various industrial activities has increased the demand for the use of fresh water resources during the past years (Ramakrishnaiah et al., 2009). The water crisis is referred as the number one global risk based on the impact on the society and the number eight global risk based on the likelihood of occurrence within 10 years (Gap, 2017). Therefore, the world is facing with increasing water crisis day by day. In the current situation, one of the ways to deal with dry climatic conditions is the optimal use of existing water resources and also the use of unconventional waters. The use of treated wastewater for irrigation as an alternative source in agriculture has been suggested by different researchers due to the increasing shortage of fresh water in arid and semi-arid regions of the world (Ibekwe et al., 2018). Sustainable utilization of water resources necessitates the utilization of alternative water resources such as treated wastewater, especially for irrigation purposes, to minimize the damage of depleting freshwater resources (Heras et al., 2020).
The agricultural sector is the main sector that consumes fresh water, which usually accounts for more than 70% of water resources withdrawal (Officer, 2016). In arid and semi-arid agricultural area, in both developed and developing countries, irrigation of crops with treated wastewater (TWW) is already a common practice as a result of water scarcity due to climate change as well as to continuously growing population (Carter et al., 2019; Ait-Mouheb et al., 2018).
It should be noted that wastewater usually contains high values of plant nutrients and therefore reduced the need for costly mineral fertilizers and increases soil fertility and crop production (Mukherjee et al., 2007; Urbano et al., 2017; Elfanssi et al., 2018; Perulli et al., 2019; Ahmali et al., 2020; Bhunia et al., 2021). However, the long-term use of the TWW could imply potential negative impact on the soil through the accumulation of micro pollutants such as heavy metals which lead to the progressive deterioration of the physicochemical and microbiological properties of the soil-plant system (Becerra-Castro et al., 2015; Balkhair & Ashraf, 2016; Ganjegunte et al., 2017). Industrial effluents from several activities such as: (metallurgy, textile, dyeing, tanning, pharmaceuticals etc.) are the main source of environmental pollution, because they generate various types of emerging (antibiotics, steroid hormones, and personal care-based products) and inorganic (Cd, Cr, Zn, Pb, Cu etc.) pollutants (Kanwal & Rana, 2020; Chaturvedi et al., 2021; Kishor et al., 2021). These effluents end up in the wastewater since the water treatment stations are unable to remove all the recalcitrant compounds (Ezzariai et al., 2018).
Several studies have been conducted at the laboratory and field level regarding the reuse of treated wastewater for irrigation around the world. In this researches, the effects of the reuse of treated wastewater on soil, plants, crops, water and public health, as well as its economic efficiency, have been investigated.
The long-term effects of urban sewage wastewater irrigation on soil properties in Hyana, India showed that total salt and heavy metal content were higher compared to well water (Rana et al., 2010). In a research, the effect of irrigation with treated wastewater on soil chemical properties and infiltration rate were investigated. The result showed that irrigation with treated wastewater increased EC, OM, and SAR levels and decreased soil pH values (Bedbabis et al., 2014). Alghobar et al. (2014) and Alghobar & Suresha (2015), during a research under long-term irrigation with urban sewage reported an increase in EC, nitrogen, phosphorus, and potassium, as well as a decrease in soil pH in the Karnataka region of India. Farmani Fard et al. (2016) reported that the use of Kermanshah city waste water improved the physical conditions of the soil, but according to the results obtained from chemical tests and heavy metals in water and soil, the use of wastewater was not recommended for irrigation of edible crops. Choopan et al. (2018) investigated the chemical properties of soil affected by irrigation with untreated industrial wastewater. The results obtained from the statistical analysis indicated that water stress and the type of irrigation water had a significant effect on potassium, phosphorus, nitrogen, and salinity ions at the 1% probability level and on the acidity at the 5% probability level. Wang et al. (2019) showed that periodic irrigation by using of treated wastewater can improve water availability in clay soil. Also, Ofori et al. (2021) stated that wastewater may have a high organic matter content; as a result, wastewater could be a sustainable and beneficial to supply organic matter for soils and can encourage plant development. Many long-term (more than ten years) and short-term (less than 5 years) studies on the effects of irrigation with treated wastewater on soil quality in different agricultural systems have been performed around the world, with different results. The published results shown many positive effects on the physical and chemical properties of soil (Jahany & Rezapour, 2020; Chaganti et al., 2021), as well as biological properties (Jahany & Rezapour, 2020). In contrast, some studies reported that the application of treated wastewater (TWW) with a negative effect on soil health (Gharaibeh et al., 2016; Paudel et al., 2018). In explaining the contradictory results obtained from various researches, it can be stated that several factors play a role in the positive or negative effects of treated wastewater using on soil properties. Among those factors, the quantity and quality of TWW use, the du-ration of irrigation, the inherent characteristics of the soil, climatic texture and agricultural management methods can be mentioned (Libutti et al., 2018; Leuther et al., 2019).
A research conducted by Dahmouni et al. (2022) with the subject of the effect of short-term irrigation of TWW on soil, groundwater and vegetation in the Cebala Borj-Touil Area (Tunisia). The published results showed a distinct decrease in soil pH and increasing of salinity, an increasing of Na+ and Cl– concentrations. Irrigation increased the heavy metals, especially in the top layer, from 0 to 30 cm. In an investigation by Tian et al. (2022), the effects of irrigation with wastewater on soil properties and accumulation of heavy metals showed that soil organic matter, total nitro-gen, available phosphorus and potassium in irrigated areas with wastewater increased around 30%, 16.5%, 322.4% and 205.5% respectively. Abou-Tammame et al. (2022) in a study under title of the impact of the reuse treated wastewater from the wastewater treatment plant in the city of Settat on the physicochemical quality of agricultural soils compared to the agricultural soils irrigated by rainwater in the region of Chaouia in Morocco, reported that despite the high fertilization value, irrigation with the treated wastewater caused a significant increase in pH, sodium, total limestone, active limestone, and salinity and a decrease in soil calcium. In addition, no significant differences were found for humidity, electrical conductivity, ammonium, nitrates, phosphorus, potassium, organic matter, total nitrogen or cation exchange capacity. Although, Irrigation with wastewater has many economic and environmental benefits, including reducing the use of natural water resources, the use of chemical fertilizers, protecting aquatic ecosystems from pollution, and improving crop performance due to the delivery of nutrients. However, it may also lead to environmental and health problems. Irrigation with wastewater may change the physical and chemical properties of the soil and cause soil salinization. Salinity, can increase, the osmotic pressure in the root zone and it is a limiting factor of land use for cultivation and plant growth (Elgallal et al., 2016).
Anyway, according to the results obtained in the mentioned previous researches, it can be concluded that the response of soil quality to treated wastewater irrigation (TWW) was specific to the study area and depends on local conditions. Because of water scarcity, wastewater reuse is essential and reliable component in the integrated and sustainable management of water resources around the world, especially in arid and semi-arid regions. In Iran, more than 90% of the total available water is used for agricultural activities (Jasim et al., 2016). Currently, in many cities of Iran, urban sewage and surface runoff of the cities are used in the downstream agricultural fields. Therefore, it is important to investigate the effects of irrigation with wastewater, in terms of its impact on the soil from different physical and chemical dimensions, and compare it with irrigation in water conditions with appropriate quality, and evaluate the results with the existing standards. Therefore, the purpose of this research was to investigate the effects of long-term irrigation (about 17 years) with the treated waste water (TWW) of Kermanshah city from the treatment refinery wastewater plant located in the west of Iran on the chemical properties of soil layers including: SAR, Cl-, HCO3-,CaCO3, total nitrogen (TN), total phosphorus (TP), K, TDS, EC and pH in the downstream covered area and its comparison with the well water (WW) used for irrigation in the same soil conditions as a control treatment in the region.