Prediction of Five-day Biochemical Oxygen Demand (BOD5) from Chemical Oxygen Demand (COD) Values in Raw and Biologically Treated Domestic Sewage

The functional relationship between BOD5 and COD was evaluated using domestic sewage samples collected from a sewage treatment plant in an estate in Warri, Delta State, Nigeria. Two types of samples were collected: raw domestic sewage,(influent) and biologically treated domestic sewage (effluent).The correlation coefficient ‘r’ between the BOD5 and COD was determined and values were 0.99 and 0.94, respectively for different sewage samples. The regression analysis carried out showed very strong correlation . The linear correlation established was: COD = 1.62 BOD5 + 15.82 ; r2 = 0.978; COD = 1.58BOD5 + 9.21; r2 = 0.878. Results obtained above were also judged as significant at 95% and 99% confidence levels. Confidence intervals obtained were: 1.53£ a £1.71 at 95% and 1.49£ a £1.75 at 99% for the raw sewage; 1.37£ a £ 1.80 at 95% and 1.27£ a £1.90 at 99% for the biologically treated sewage.