Dental General f1519940 Strength of sewage is best expressed by A E-coli count B Suspended particles C Chemical oxygen demand D Biological oxygen demand High-Yield Explanation The most important test carried out on sewage. Sewage with a BOD value of: 300mg/I (300 ppm) or above is termed as strong. 100 mg/I (100 ppm) or below is termed as weak.