CHLORINE TRANSPORT AND DECAY STUDIES OF A PILOT-SCALE DRINKING WATER DISTRIBUTION DEAD END PIPE SYSTEM
Chlorine residual concentration in a dead end pipe varies in response to changing hydrodynamic such as Reynolds number Re, flow rate qi*, and initial chlorine concentrations C0*, and environmental factors such as biomass concentration, TOC, temperature and inorganic constituents in the water and wall conditions. These relationships were quantified in experiments using a pilot-scale dead-end pipe designed and constructed at the US EPA Test and Evaluation facility. Hydraulic dispersion, biomass population in the system, and chlorine decay and transport under continuous and intermittent flow conditions were examined. Tracer dispersion experiments were used to estimate the chlorine dispersion coefficients as a function of Reynolds number (Re). Bench scale studies of chlorine decay resulted in first-order bulk decay constants in an average of 3.5x10-3 hr-1. Chlorine decay was tested under stagnant (qi* = 0 L/min), continuous (qi* = 0.8, 3.8, 15.9 and 69.3 L/min, where, Re = 100, 550, 2300 and 10,000) and intermittent flow under various (C0* = 0.5, 1.0 and 2.0 mg/L). In stagnant water, molecular diffusion has a significant impact on residual concentrations. When qi*>0, the chlorine decay rate is inversely related to C0* and Re. Higher chlorine decay (Ct/C0) occurred at laminar flow (Re=100) and low concentrations (C0*=0.5 mg/L), and the decay was much lower at C0*>1.0 mg/L and under transitional and turbulent flow regimes. It was found that, biofilm density remains nearly constant along the test pipe and the microbial concentrations in the pipe effluent decreased at high flow rates. A computer model was used to simulate chlorine decay and transport, in which wall decay constant was estimated. This model indicates wall consumption constant ranges from 0.005 to 2.6 sec-1 inversely related to C0* and qi* or Re. A chorine decay and transport models was developed for the dead end pipe under stagnant flow condition. However, to make the models truly useful, further studies are required to refine the model.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:chlorine decay transport water quality distribution system biofilm
Date of Publication:01/01/2000