2.2. Chlorine demand
Concentrations of free and total residual chlorine (FRC and TRC) in overlying water in each sediment tube were analyzed at 0, 6, 24, 48 and 144 h after chlorine application. At each time interval, triplicate water samples were taken from four sets of tubes in one concrete tank by siphoning 100-ml water into 120-ml plastic bottles. Free and total residual chlorine were analyzed by DPD titration method (APHA, 1998). Chlorine demand of the soil was calculated as follows: