Treated municipal wastewater and sewage sludge are an important source of water for irrigation in arid and semiarid regions. It may also serve as a promising source of plant nutrients and organic material that has a potential to increase soil productivity under arid conditions. Utilization of treated wastewaters for agricultural irrigation, in addition to being a low-cost available water source, also minimizes effluent disposal problems and hence environmental contamination, and reduces the need for the input of chemical fertilizers. Disadvantages of the application of treated effluents for agricultural irrigation involve the potential for human health problems, groundwater contamination, and the need for continued follow up and control. As of now, treated wastewater in Turkey is discharged to streams and seas, and is not reused for agriculture irrigation. Environmental considerations and the predicted increase in water shortage make effluent irrigation a national priority. Recent field and pot studies demonstrate the potential of the local treated effluents for agriculture. In a pot study the effect of application of different ratios of treated waste waters and treated sludge were investigated for a range of crops including Hordeum vulgare, Sorghum bicolor, Brassica campestris, Pisum sativum, Lolium perenne, L. italicum, and Lycopersison esculentum. The data accumulated revealed that for most crops the performance was better with treated wastewater as compared to normal tap water, which can be related to increased availability of nitrogen. Treated effluents, especially of industrial sources, may contain heavy metal contaminents. Rice plants irrigated with industrial wastewater showed high levels of lead, cadmium, and chromium, and 40-45% reduction of productivity, demonstrating the need for monitoring the quality of the effluents to be used for agricultural irrigation. Although most effluents contain higher levels of salts then the water from which they were derived, in several experiments carried out in Turkey, salt damage were not apparent, seemingly due to salt leaching by rainfall.
