An inquiry into the relationship between water quality parameters: Biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) in Iraqi Southern region

Biological oxygen demand (BOD5) analysis is mainly used to estimate organic pollutants in water systems, it takes five days to obtain the result. The chemical oxygen demand (COD) is a fast alternative analysis that requires only (2 hours) to carried out the test. The other advantage of these tests is to evaluate the efficiency of the wastewater treatment plant. A total number of 108 Samples were taken from the Al-Gharaf river from three stations in Thi-Qar province (Al Refaae, Al Nser, and Al Shatra districts) in a period of a year and monthly sampling. The samples were tested according to ASTM D125-06 and ASTM D6238-98 for (COD) and (BOD5) respectively. The collected data were statistically analysed using the SPSS program to predict a relation between COD and BOD5 values. The analysis showed a good relationship with a value of correlation coefficient (r = 0.908) and coefficient of determination (R2 = 0.89). The predicted formula that describes the Biological oxygen demand (BOD5) is expressed by an exponential equation .The validation of the predicted formula has been tested using data from the national water quality monitoring data in Korea for four rivers (Han river, Nakdong river, Geum river, and Yeongsan river), the formula gave reasonably acceptable values. It could be used in wastewater plants to have pre-impression of the plant efficiency.