EFFLUENT TOTAL RESIDUAL CHLORINE DECAY IN OUTFALL PIPE

Field and bench tests were conducted to determine the decay property o f effluent total residual chlorine (TRC) in an outfall pipe. The pipe conveys secondary treated effluent from the Broward County North Regio nal Wastewater Treatment Plant to the Atlantic Ocean off the east coas t of South Florida. During a field test effluent samples were taken an d TRC concentrations were measured every 15 min for 6 h at three stati ons along the inland portion of the outfall pipe. Results indicate tha t the effluent TRC decay can be described by first-order kinetics. The TRC overall decay constant is assumed to be the sum of static and dyn amic decay constants. The overall decay constant, determined from the field tests, is one order of magnitude greater than the static decay c onstant determined from the bench tests. This suggests that TRC decay in the outfall pipe is dominated by chlorine consumption by the biofil m at the pipe wall. The removal of TRC during the effluent transport i n the outfall pipe is estimated as 68% at the permitted flow rate of 2 .9 m(3)/s.