Date of Award
Master of Science (MS)
Environmental Engineering and Earth Sciences
David A Ladner
In today’s world, 844 million people lack a basic water service and 2.1 billion lack accessible, readily available, and clean water on the premises of their home (UN-Water, 2018). Data show that rural areas of developing countries like Haiti are far behind the rest of the world when it comes to water, sanitation, and hygiene (WASH) infrastructure (Joint Monitoring Progamme (JMP), 2017a). Treating water in this context comes with many challenges; however, chlorination using calcium hypochlorite tablets proves to be a suitable solution as tablets are effective, inexpensive, and simple to use. Calcium hypochlorite systems have been in service for several years with increasing degrees of success in the municipal water treatment system in the rural village of Cange, Haiti. Since the installation of the newest chlorinator, free chlorine residuals at the water system fountains have met at least the minimum desired level (0.5 mg/L) 69% of the time. This is an increase from only 27% with previous chlorinators but still leaves room for improvement. One theory for why residual chlorine levels fluctuated in the system is that the chlorinator could be producing variable concentrations as the tablets dissolve.
The objective of this work is to characterize the relationship between chlorine tablet dissolution and the hydrodynamics of the chlorinator currently installed in the Cange water system. The effects of flow rate, number of chlorine tablets, and the inlet/outlet location on the chlorinator body were examined with both computational fluid dynamics (CFD) modeling and experiments.
Initial CFD models indicated that the inlet and outlet location played a role in the variation of the chlorinator’s effluent concentration and helped to design experiments that would further investigate this relationship. The effects of varying flow rate and varying number of tablets were also explored. Experiments revealed that there was an elevated chlorine level at the beginning, but usually after about half an hour the concentrations stabilized and remained relatively constant through the end of each seven-hour test. This was true regardless of inlet and outlet location, number of tablets used, or the system flow rate, though it is important to mention that the experiments did not last long enough to let the tablets dissolve below 50% of their initial mass. Data also showed that for the chlorinator setup used in Cange, higher flow rates led to lower effluent concentrations due to dilution, but the mass dissolution rate of the tablet was independent of flow rate. Experiments also show that the concentration of the effluent was proportional to the number of chlorine tablets. Different outlet locations impacted the chlorine concentration dramatically, leading to further CFD analysis to explore how flow patterns affected tablet dissolution. Models with different outlet locations supported the idea that dissolution was affected by the pattern of flow, as experimental results that showed low effluent concentrations were characterized by low flow and eddies in the portion of the chlorinator containing the tablets.
The results from this work suggest that the current chlorination setup used in the Cange water system is effective at providing a constant mass flux of chlorine over time and is likely not a major reason for the variability seen in free chlorine levels at the point of delivery. The knowledge gained here will be useful in designing future upgrades for the Cange system and/or other disinfection systems for resource-constrained communities.
Martin, Ashley Caroline, "Evaluation of Tablet Chlorinator for a Rural Haitian Water Treatment System—Computational Modeling and Laboratory Testing" (2020). All Theses. 3426.