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Title:Iron reduction mediated increases in carbon oxidation and phosphorus precipitation in on-site wastewater systems
Author(s):Azam, Hossain
Director of Research:Finneran, Kevin T.
Doctoral Committee Chair(s):Werth, Charles J.
Doctoral Committee Member(s):Finneran, Kevin T.; Strathmann, Timothy J.; Sims, Gerald K.
Department / Program:Civil & Environmental Eng
Discipline:Environ Engr in Civil Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Fe (III) reduction
onsite waste water
Phosphorus removal
Abstract:1.2 billion people lack access to safe drinking water, 2.6 billion have little or no sanitation, and millions of people die annually from diseases transmitted through unsafe water and human excreta. Onsite wastewater systems (OWSs), referred to as septic tanks, serve approximately 25% of the United States population. Septic systems typically operate under strictly anoxic conditions, and fermentation is the dominant process driving carbon transformation. Moreover, phosphorus, a major nutrient that causes eutrophication, accumulates in onsite wastewater systems from human and domestic wastes. Phosphate is of particular interest because of its growth limiting effects on microbes in natural aqueous environments. We proposed a novel technique to anaerobic onsite wastewater by leveraging iron reduction to oxidize more carbon and precipitate phosphorus with reduced iron as vivianite. We used carbon-14 radiolabeled acetate, lactate, propionate, butyrate, glucose, starch, xylose and oleic acid to demonstrate that short and long term carbon oxidation is increased when different forms of Fe3+ are amended to septic wastewater. The rates of carbon mineralization to 14CO2 increased 2 to 5 times (relative to un-amended systems) in the presence of Fe3+. The extent of mineralization reached 90% for some carbon compounds when Fe3+ was present, compared to levels of 50-60% in the absence of Fe3+. When methanogenesis was the dominant process present in-situ; 14CH4 was not generated due to Fe3+ amendment, demonstrating that this strategy can limit methane emissions from septic systems. Moreover, iron reduction as a terminal electron accepting process increases the microbial diversity of the wastewater. Amplified 16S rDNA restriction analysis (ARDRA) confirmed that unique Fe3+-reducing microbial communities increased significantly in iron-amended incubations. Pure culture growth experiments in ferric citrate media with Geobacter metallereducens clearly showed extensive iron reduction and subsequent phosphate (>97.5% or higher) removal in presence of electron donor. Both TEM-EDAX and XRD techniques confirm the precipitant as vivianite when additional Fe2+ was present. Ferric citrate, ferrihydrite and ferrihydrite+AQDS completely removed (>95.5% or higher) of phosphate in the original wastewater sample. Ferric citrate and ferrihydrite+AQDS performed better (>97.5 or higher) when an extreme phosphate loading condition was evaluated. The form of Fe3+ added had a significant impact on the rate and extent of mineralization with ferrihydrite and lepidocrocite favored as solid phase Fe3+ and chelated Fe3+ (with NTA or EDTA) as preferred soluble Fe3+ forms. Though chelated Fe3+ (with NTA or EDTA) removed phosphate at a significant level; ferric citrate, ferrihydrite and lepidocrocite showed quick and high phosphate removal from wastewater sample. The result clearly shows that iron reduction coupled with phosphate removal can be an effective strategy for onsite wastewater systems.
Issue Date:2012-06-27
Rights Information:Copyright 2012 Hossain Azam
Date Available in IDEALS:2014-06-28
Date Deposited:2012-05

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