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My first task this semester was to design and set up assemble the main experimental apparatus for the Arsenic experimentexperiments, a sand column filter. Once we decided about the design parameters with the team we obtained a half-inch PVC pipe which I turned into an upflow sand filter with two openings and an intermediate tube coupling that allowed access to the sand in case the shear of the walls prevented the sand from settling during backwashI had to find the minimum value of the parameters to assemble a filtration unit that would produce minor Arsenic contaminated waste and could still be back-washed effectively. Assembling the filter, I learned a lot along the way about tubing, preventing leaks and keeping air out and these lessons required a decent amount of failure, pressure meters and more.
Furthermore, our experimental procedure suggested pretreating the sand with coagulant, therefore we first had to understand I performed some bench experiments to evaluate the behavior of coagulant under at different conditions and evaluate how well it stuck on the sand. For this reason we assembled a manometer to see head loss as it was building. After running a few experiments with coagulant and analyzing the results, I suggested the final experimental procedure for the Arsenic experiment which was performed towards the end of the semesterpH and used these observations to devise experimental procedures for Arsenic. The semester ended with a continuous flow experiment using a 100 ppb Arsenic groundwater solution in a filter pre-treated with coagulant and co-currently treated with PACL at 1 mg/L. The effluent obtained was safe to drink by the strictest water standards and the experiment suggests that aluminum based coagulants can be very effective at binding Arsenic. Further experimentation will shed more light on the exact mechanism and to ways to optimize the procedure.
Contribution to Arsenic Research during Summer of 2014
Picking up from the successful results of this spring, the goal is to evaluate the optimal procedure to remove Arsenic from groundwater for longer runs. Different treatment methods will be evaluated and the mechanism of As removal shall be better understood.
More emphasis is placed on the chemistry of Arsenic, first to understand how removal is affected at different chemical regimes and secondly to devise ways that backwash water can be treated in-situ.
The first task this summer was to improve the experimental apparatus and automatize the controls and procedures using software developed within Agua Clara. This not only improves safety but it also simplifies operation and allows more accurate measurements of head loss.
Another continuous responsibility is to run the Graphite furnace atomic absorption spectrometer (GFAAS) and ensure the best accuracy of As detections at concentrations below 10 ppb.