Background and Objectives: Various standards have been proposed for the application of water resources, each of which addresses some of the environmental consequences and aspects related to water, soil, plants or human health. The FAO standard, for example, emphasizes the protection of plants and soil in addition to water parameters. On the other hand, the Schuler standard emphasizes water parameters and applies only to the drinking water, but neglects water hygiene parameters. The present research was aimed at introducing the indigenous standard of wastewater application as one of the most important unconventional water resources in agriculture.
Materials and Methods: To achieve this, the national standards of some countries (Cyprus, Mexico, Australia and Jordan), international standards (WHO, FAO and EPA) and Wilcox and Schuler indexes for wastewater use (treated municipal wastewater) were collected, studied and reviewed. In the agricultural sector, a standard has been developed and proposed that, contrary to the Iranian standards, has proposed numerical values for calcium, nitrate, phosphate, sodium, EC, TDS, SS and SAR parameters, based on water quality, soil, plant, environmental protection, and human health, related to the use of wastewater and production of healthy crops. Investigation of each of the effluent parameters alone requires more extensive and detailed studies and this research can be a starting point for them. Wastewater quality monitoring data of Zahedan (2014 to 2018), Arak (2016) and Zargandeh, Tehran (2018) cities were used as case study.
Results: Results indicate that the effluent of Zahedan treatment plant is in medium risk group and Arak and Zarghandeh effluents are in good wastewater group. The results also show that the values of pH, EC, SAR, BOD5, TSS, sodium, magnesium, and mercury in the Zahedan wastewater application are above the maximum permissible level and DO is less than the minimum. In addition, all metals, except copper (0.56 mg/l), with permissible level of 0.2 mg/l, are permitted in comparing heavy metals with the aforementioned standards. Sodium content of 15.55 mg/l and TSS value of 455 mg/l exceed all standards and the recommended standard. The values of EC (2.24 dS/m), SAR (7.63), TDS (1919.6 mg/l) and pH (7.76) are within the permissible standard range. Also according to the Schuler index, the effluent is in the acceptable to medium range and according to the Wilcox index, Zahedan effluent is in the S₁-C₄ class.
Conclusion: The proposed standard of the present research completes the shortcomings of the standard of the Environmental Protection Organization of Iran as the most complete standard among the reviewed standards and includes all aspects of the protection and health of water, soil, plants and humans. In the proposed standard, the permissible range was determined for calcium, nitrate, phosphate, sodium, EC, TDS, SS, and SAR, which have not been previously defined in the national standards of Iran. Phosphorus in the form of phosphate in municipal wastewater is one of the nutrients required for plant growth. One of the most important advantages of using wastewater for agricultural irrigation is reducing the need to use phosphate and nitrogen fertilizers. Sodium is defined in WHO, EPA, University of California, Ayers and Westcott and Jordan standards. If, in the process of cation exchange with soil particles, cations of single capacity (specifically sodium) prevail, the soil structure loses its consistency and disintegrates easily. Sodium is one of the most important cations due to its effects on soil. Exchangeable sodium tends to spread in the soil and reduces the velocity of water and air infiltration in the soil.