a - 1. It is desired to design a bromide chloride contact tank to be used to disinfect a secondary-treated sewage discharge. To determine the contact time, an experiment was conducted producing the following results: HCl Dosage (mg/L) Contact time (min) residual fecal coliform (No/100 mL) 4.7 23.0 51 15 20,000 950 380 30 5,000 530 180 60 600 320 85 Determine the equation of contact time & concentration to be used in design, if it is desired to have a log 3 removal efficiency for fecal coliforms. The original concentration of fecal coliforms is 50,000 per/100 mL