Effects of the domestic sewage physically treated on crop yield, yield components of cotton (Gossypium hirsutum L.) and soil pollution

In this study, cotton crop was grown irrigated by physically treated domestic sewage water in the tanks similar drainage type lisimeters in 2011 and 2012 under Diyarbakır conditions. Cotton variety of Stonville-453 was used for this experiment. The experiments were undertaken using randomized blocks with split plots and four replications. The main plots had fertilized and non-fertilized with sub-plots with different sewage water levels. The treated sewage water was provided from the discharge point of the reservoir in which operated as anaerobic + stabilization in Dicle University Campus. The recommended amount of fertilizers and no commercial fertilizer for cotton together with treated sewage water and sewage water + fresh water were used as the treatments. The content of suspended solids (28-60 mg l-1), biological oxygen demand (29-30 mg l-1) and chemical oxygen demand (71-112 mg l-1) decreased significantly compared to those in the sewage water. There was no pollution of heavy metals in both sewage and treated sewage water. In addition, it was not found significantly amounts in the treated sewage water while the levels of coliform bacteria (>1100 Kob ml-1), fecal coliform (1.1-1.5x103 EMS ml-1) and Escherichia coli were significantly higher in the untreated sewage water. In the first year, seed-cotton yield (31.8 g plant-1) in the tanks without commercial fertilizers were considerably higher compared to the seed-cotton yield (17.2 g plant-1) in the tanks fertilized. However, there was no any significantly differences between the yields irrigated by treated sewage water and fresh water. All these could be attributed to the fact that the treated sewage water might provide appropriate nutrients to the plants. There were no significantly differences between the values of soil pH before the experiment (7.8-7.9) and after the experiment (7.8-8.2). Soil electrical conductivity (EC) after the experiment increased from 0.8-1.0 dS m-1 to 0.9-1.8 dS m-1. The content of organic matter (OM) in the soil was not increased considerably because it was quite low at the beginning of the experiment. The heavy metal pollution did not occurred in the soils and plants because there was no heavy metal in both sewage and treated sewage water. As a result it could be concluded that treated domestic sewage water could be used for the crops grown in which not used directly in human nutrient such as cotton. However, use of all the waste and/or sewage water must be controlled and monitored continuously, since quality of those could vary depending on climate, population and habits of the inhabitants, industrial or domestic conditions. Key Words:, Domestic sewage water, Water Pollution, Cotton, Irrigation, Soil Pollution