Assessment of agricultural drainage water for safe reuse in irrigation purposes and discharge to environment (Case study: unit F4 of Sefiedrod irrigation and drainage network)

Reducing fresh water resources and the quality of water in the agricultural has led to importance of the finding new sources of water for irrigation. In this regard, the use of non-conventional waters is one of the options. Using of drainage water as a non-conventional water source is one of the solutions to solve the water deficiency problem in agriculture. The present study was carried out to evaluate and simulate the quality of the drainage water of the rice fields in the city of Soumatserra, located in the F4 unit of Sefidrud Irrigation and Drainage Network for reuse in irrigation and evacuated to the environment. In order to investigate the quality of drainage water for discharge to surface water resources and reuse in irrigation, the concentration of the nitrate, orthophosphate, ammonium, biological oxygen demand, dissolved oxygen, total dissolved solids and acidity was measured in nine points in May-July 2017 and was compared with the standards of the Environmental Protection Agency, the Environmental Protection Agency of Iran, Institute of Standards and Industrial Research of Iran. The highest concentration of nitrate, orthophosphate, ammonium, and biological oxygen demand were 1.25, 0.184, 2.91 and 89 mg/ l in May and the lowest concentration of dissolved oxygen and the highest concentration of total dissolved solids were 3.6 and 289 mg/l in July. Also, the highest and lowest value of pH was 8.23 in May and 7.26 in June. Drainage water in terms of nitrate, orthophosphate, total dissolved solids and acidity, according to the mentioned standards was allowed in reuse in irrigation and discharge to surface water resources. But in terms of dissolved oxygen, biological oxygen demand and ammonium was diagnosed over the limit for reuse in irrigation and discharge to surface water resources. According to estimation of the pollution load of the drain to the Anzali wetland, it was found that the highest amount of pollution during the sampling period was occurred in May.