Self-purification capacity of a river is a significant indicator for the river health and it is in great importance in polluted water. Tanjero River lies southwest of Sulaimani city formed by linking two streams (Qiliasan and Kani-Ban streams) along its path the sewage of wastewater is discharged into the river that causes serious pollution and threatens the quality of water. Samples of water were taken from six stations (S1, S2, S3, S4, S5 and S6) along the Tanjero river. The data obtained from sample locations include velocity, depth, river discharge, water temperature, pH, electrical conductivity (EC), total dissolved solids (TDS), turbidity, dissolved oxygen (DO) and BOD. The De-oxygenation coefficient (k1) and re-oxygenation coefficient (K2) are then used to estimate the deficit value of predicted oxygen using the Streeter Phelps equation. The maximum de-oxygenation rate (K1) and reaeration (K2) rate (8.259541 day−1) and (15.22917day−1) were recorded in site (4) respectively. The fair ratio (f) or self-purification factor, for the Tanjero river was determined. The maximum fair ratio (f) value of (2.219) was recorded at site (2). The average fair ratio (f) was found to be (1.507) which classifies the river into large streams of low to normal velocities. This study revealed that using Streeter-Phelps method the natural self-purification occurred along the river as a result of continuous increasing of DO value and decreasing BOD value.

The main goal of this study was to see how water-soluble fractions of light crude oil from the Taq taq refinery influenced those physicochemical parameters in drinking water from the Dukan River and Sarchnar spring sources. According to statistical analysis, water quality parameters such as pH, electrical conductivity, temperature, turbidity, color, total solids, total dissolved solids, total suspended solids, ammonium, sulfide, and phosphorus have all been impacted by this crude oil when compared to controls (water resources) and drinking water quality standards. The results showed that the values of turbidity, color, ammonium, sulfide, and phosphorus in water samples that have been treated with various percent of crude oil water-soluble fractions are increased due to the high effects of crude oil on the physical and chemical characteristics of water resources (% 0 controls). According to our findings, the effect of crude oil contamination on water quality has been linked to a variety of factors.