The Study of Self Purification Capacity Based on Biological Oxygen Demand (BOD) and Dissolved Oxygen (DO) Parameters

Jajar River is geographically located between Demak and Grobogan Regency area. For most part, Jajar River which lies on lowland area is mainly utilized for agricultural purposes. The utilization of the land around the area of Jajar River might potentially cause several environmental problems such as river water contamination, causing degradation of river water quality. Generally, river has the capacity to purify itself by decomposing any pollutants blended in the water. This capacity is called self-purification. The aim of this study is to determine the level of self-purification capacity (time and distance of water purification) using Streeter-Phelps equation, by obtaining data about organic pollutant concentrations DO and BOD at a certain pollutant point in a river. By using Streeter-Phelps equation, it is expected to find oxygen reduction curve toward time and distance. Deoxygenation and reaeration constants are needed to draw the curve. Moreover, Streeter-Phelps equation can generate the oxygen reduction curve which shows self-purification distance. The results showed that there was no natural purification process in Jajar River. In other word, the water sample test in each segment showed the existence of waste input, which was indicated by unacceptable results of DO and BOD parameters. In this condition, the river ecosystem had not been able to purify the water from BOD input. It supposedly happened due to the inability of DO concentration to return to the ideal condition of anaerobic river from waste contamination in the extended segments.