Microbial Uptake of Arsenic Lara Derchak - Civil Engineering Erin Frey - Chemical Engineering Crystal L. Mattson – Civil Engineering Oxidation and reduction.
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Microbial Uptake of Arsenic Lara Derchak - Civil Engineering Erin Frey - Chemical Engineering Crystal L. Mattson – Civil Engineering Oxidation and reduction reactions occur in sediment Anthropogenic and natural emissions Methylation processes by algae in surface waters As is consumed by certain organisms in the water Arsenic Cycling in the Environment Toxicity –Arsenic is extremely toxic causing severe health problems –LD 50 of arsenic is between 15 and 30 mg/kg of body weight –In comparison, NaCl is 3,000 mg/kg body weight and nicotine is 60 mg/kg body weight Exposure –Dermal Contact –Ingestion –Inhalation Health Effects –Immediate symptoms: vomiting, esophageal & abdominal pain and bloody diarrhea –Long term exposure: cancer, gangrene, loss of feeling in limbs, hearing impairment, diabetes, heart and circulatory problems, and affects the gastrointestinal system and liver Background Project Objectives Determine if a mixed bacteria culture is a viable treatment option Study the adsorption of arsenic by iron Identify algae species that will uptake arsenic and study the impact on growth Drinking Water Regulations USEPA Standard: 0.01 mg/L WHO Standard: 0.01 mg/L > 0.05 mg/L (50 ppb) As concentrations found throughout country Large populations exposed to As because of groundwater contamination worldwide As contaminated countries include Bangladesh, Australia, Chile, and New Zealand People used the rivers as their source of water –Began to get sick and even die because of the bacterial contamination The solution: Change to groundwater –Did not realize the arsenic problem at the time Groundwater arsenic contamination was first discovered in 1993 –Thousands of wells were already in place –5 times higher than the world standard Bangladesh Mixed Bacteria Culture Obtained bacteria from a local wastewater treatment plant Exposed bacteria to varying concentrations of arsenate (Na 2 HAsO 4 ) and arsenite (NaAsO 2 ) (0.05 mg/L – 1.5 mg/L) Second experiment had concentrations varying from 50 mg/L to 1600 mg/L. Glucose (C 6 H 12 O 6 ) used as the carbon source Conclusions MIXED CULTURE At low concentrations, significant amounts of both forms of arsenic were removed (60% average) It is apparent that low concentrations of arsenic may be removed by aerobic bacteria At high concentrations, varying removal was noted for both forms Arsenite removal 48% Arsenate removal 77% Probable cause for low arsenite removal is toxicity Probable mechanism for removal is biosorption Higher concentrations significantly impacted growth Inhibition is approximately 50% at 1600 mg/L contradicting available literature ALGAE Removal of arsenic was time dependent with major removals occurring within the first hour of experimentation. Desorption of arsenic was evident after the first hour. Algae morphology was impacted by the presence of arsenic. However the impact was not arsenic concentration dependent. Algal morphology changed to clumping at higher concentrations of arsenic. Significant differences were not noticed for arsenic uptake with the two types of algae. Use of microorganisms for arsenic removal from water may be a viable mechanism of arsenic removal. Experimental Setup HACH BODTrak measured oxygen uptake in mg/L vs. time Conducted at room temperature (22 + 0.5°C) Arsenic concentrations measured at conclusion of experiment using HACH Arsenic Test Kits Oxygen Uptake Results Arsenic Removal Algae Two methods by which algae can uptake heavy metals –Biosorption –Bioaccumulation Scenedesmus abundans and Chlorella vulgaris are both common green freshwater algae capable of metal uptake Batch experiments with algae and varying concentrations of arsenic were conducted. Arsenic concentrations were measured with time. Algae morphology was checked at end of experiments. Acknowledgements Oxygen Uptake Results Dr. Kauser Jahan Dr. Patricia Mosto Costantinos Tsoukalis