(529f) Investigating the Mechanisms of Arsenic Removal by Microbial Layer In a Bio-Sand Filter

The present study addresses the enormous global demand for safe drinking water in developing countries, and focuses on the removal of  arsenic and bacterial pathogens from potable water supplies using a bio-sand filter.  The bio-sand filter was constructed of a transparent polyethyl resin to facilitate visual observation  of microbial activity and  reactor flows.  The filter medium essentially  consisted of a supporting gravel layer, large sand layer, and biofilm layer containing a diverse microbial population, acclimated to a natural surface water source.  Our work showed that  the bio-sand filter r in-tandem with a pre-treatment column of iron-oxide-coated sand were effective in eliminating  these contaminants.  The present work  focuses on determining the actual mechanisms of arsenic removal within the filter medium.  In this study, the  previous filter design was adapted to include a layer of iron-oxide-coated sand.  Four sampling ports were strategically located to separately quantify arsenic removals in the biofilm and iron-oxide-coated-sand layers.   Both sodium arsenate and sodium arsenite were spiked in the filter influent to determine whether arsenic removal was attributable to redox reactions. 

              The study is also directed at determining the actual mechanisms of arsenic removal within the filter, and the microbial strains primarily responsible for arsenic removal.  Four sampling ports were strategically located in the bio-sand filter to separately quantify arsenic removals in the biofilm and iron-oxide-coated-sand layers.   Both sodium arsenate and sodium arsenite were spiked in the filter influent to determine whether arsenic removal was attributable to redox reactions.  The total arsenic removal was determined using the inductively coupled plasma –mass spectrometry (ICP-MS) technique.  The bacterial removals were determined by the  If arsenic removal occurred within the biofilm layer, the implications would be important,  highlighting the ability of bacteria to store or process harmful forms of arsenic.  Samples of schmutzdecke (biofilm layer) were obtained from the filter for microbial community analysis.  Identification of dominant bacterial strains was accomplished by DNA isolation, PCR techniques, and DGGE fingerprinting. The DNA materials were isolated from these bio-layer samples, and the bacterial rRNA sequences were amplified by polymerase chain reaction (PCR) techniques.  The PCR products were subsequently separated by denaturing gradient gel electrophoresis (DGEE), and sequenced for fingerprinting identification of dominant bacterial strains, before and after exposure to arsenic.  Similar samples were also collected for scanning electron microscopy analysis to morphologically distinguish the microbial species associated with arsenic removal.  Elemental analysis was undertaken to determine the locations of any immobilized arsenic species.  The removals of bacterial pathogens (coliform used as surrogates for bacteria) in the bio-sand filter easily exceeded 5-logs (99.999%).  The presentation would  discuss the removals of arsenic and bacteria in the bio-sand filter at various depths of the filter.  More importantly, it would  address the mechanisms and interactions and mechanisms of arsenic removal in the bioactive filter.