Hernández Vega, Margaret J.

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    Sand filtration and chlorination for removal and inactivation of Bacillus subtilis
    (2015) Hernández Vega, Margaret J.; Hwang, Sangchul; College of Engineering; Tarafa, Pedro J.; Bogere, Moses; Department of Civil Engineering; Ramírez, Lillian
    Sustainable water treatment and technology need to be implemented for safe-drinking water. In Puerto Rico, some rural communities do not rely on the central systems operated by the water authority but have their own small treatment systems that do not fully comply with the bacteriological standards. As such, the Río Piedras community, located in San German, Puerto Rico was chosen for the assessment of a sand filtration and chlorination system for the removal of Bacillus subtilis as the surrogate microorganisms of Giardia lamblia and Cryptosporidium parvuum. The Caín Alto River, the source water of the Río Piedras community water treatment system, was monitored for its physicochemical and bacteriological characteristics for over one year. The results from the statistical analyses showed that conductivity and total dissolved solids were highly positively related (Pearson correlation coefficient = 0.953 and P-value = 0.000) and that B. subtilis was highly positively related to turbidity (Pearson correlation coefficient = 0.720 and P-value = 0.001). Three different lab-scale rapid filtration units were evaluated for the possible packing media of the field-scale filters. Units included two sand filters connected in series, one filter with granular activated carbon incorporating sand and one filter with iron oxide coated sand (IOCS) incorporating sand. Outcomes of the comparison between systems yielded that IOCS filter showed more consistency in the removal of B. subtilis, achieving 1.1-log removal. However, IOCS preparation at large scale was neither practical nor economical. The results from the lab-scale system showed that the sand filtration inactivated 1.5-log removal of B. subtilis and disinfection as well. The treatment train achieved 3-log removal of B. subtilis, complying with the USEPA standards of Cryptosporidium and Giardia. However, further modifications were to be done on the field scale to improve the effectiveness of the system. The field-scale SEED unit was assessed for B. subtilis removal for three days at different configurations. The results showed that the SEED unit under the current hydromechanical and technical properties was not capable of removing B. subtilis. Some circumstances could have affected the efficiency of the unit including the initial condition of the system and the actual condition of the community system that made impossible to perform a backwash.