Geochemical and mineralogical changes in magnetite Fe-ore tailings induced by biomass organic matter amendment.

Direct phytostabilization of alkaline and finely textured Fe-ore tailings is a key challenge for sustainable rehabilitation of tailings landscapes, due to limited topsoil resources available for constructing functional root-zones. The eco-engineering of soils (i.e. technosol) from tailings through the deliberate combination of technic materials with ecological inputs (e.g. biomass, water, topsoil and organisms) may provide a cost-effecctive and sustainable alternative to topsoil-based option for tailings rehabilitation. This approach purposefully accelerates in situ mineral weathering and the development of soil-like physicochemical and biological properties and functions in the tailings. The present study aimed to characterize mineralogical and geochemical changes associated with soil formation in Fe-ore tailings, by admixing biomass organic matter (BOM) and soil inoculum under well-watered conditions. Magnetite Fe-ore tailings (pH ~9.5) were amended with 3% (w/w) BOM (Lucerne hay) and natural soil microbial communities and incubated for 68 days in a microcosm study. BOM amendment with soil inoculum resulted in a rapid neutralization of alkaline pH conditions in the tailings. The weathering of magnetite and biotite-like phyllosilicates were accelerated, resulting in increased concentrations of soluble Mg, K, Fe, Ca, and Si in porewater. Evidence of the accelerated weathering was verified by synchrotron-based Fe K-edge X-ray absorption fine structure (XAFS) spectroscopy analysis, showing the presence of possibly Fe (III)-oxalates. The weathering resulted in eroded morphological surfaces of Fe-bearing minerals in the BOM treated tailings. This study confirmed the expected geochemical and mineralogical changes in the magnetite Fe-ore tailings induced by BOM amendment, providing a fundamental basis for eco-engineering tailings into soil-like technosol.

Granule formation mechanisms within an aerobic wastewater system for phosphorus removal.

Granular sludge is a novel alternative for the treatment of wastewater and offers numerous operational and economic advantages over conventional floccular-sludge systems. The majority of research on granular sludge has focused on optimization of engineering aspects relating to reactor operation with little emphasis on the fundamental microbiology. In this study, we hypothesize two novel mechanisms for granule formation as observed in three laboratory scale sequencing batch reactors operating for biological phosphorus removal and treating two different types of wastewater. During the initial stages of granulation, two distinct granule types (white and yellow) were distinguished within the mixed microbial population. White granules appeared as compact, smooth, dense aggregates dominated by 97.5% "Candidatus Accumulibacter phosphatis," and yellow granules appeared as loose, rough, irregular aggregates with a mixed microbial population of 12.3% "Candidatus Accumulibacter phosphatis" and 57.9% "Candidatus Competibacter phosphatis," among other bacteria. Microscopy showed white granules as homogeneous microbial aggregates and yellow granules as segregated, microcolony-like aggregates, with phylogenetic analysis suggesting that the granule types are likely not a result of strain-associated differences. The microbial community composition and arrangement suggest different formation mechanisms occur for each granule type. White granules are hypothesized to form by outgrowth from a single microcolony into a granule dominated by one bacterial type, while yellow granules are hypothesized to form via multiple microcolony aggregation into a microcolony-segregated granule with a mixed microbial population. Further understanding and application of these mechanisms and the associated microbial ecology may provide conceptual information benefiting start-up procedures for full-scale granular-sludge reactors.

Initial development and structure of biofilms on microbial fuel cell anodes.

BACKGROUND: Microbial fuel cells (MFCs) rely on electrochemically active bacteria to capture the chemical energy contained in organics and convert it to electrical energy. Bacteria develop biofilms on the MFC electrodes, allowing considerable conversion capacity and opportunities for extracellular electron transfer (EET). The present knowledge on EET is centred around two Gram-negative models, i.e. Shewanella and Geobacter species, as it is believed that Gram-positives cannot perform EET by themselves as the Gram-negatives can. To understand how bacteria form biofilms within MFCs and how their development, structure and viability affects electron transfer, we performed pure and co-culture experiments. RESULTS: Biofilm viability was maintained highest nearer the anode during closed circuit operation (current flowing), in contrast to when the anode was in open circuit (soluble electron acceptor) where viability was highest on top of the biofilm, furthest from the anode. Closed circuit anode Pseudomonas aeruginosa biofilms were considerably thinner compared to the open circuit anode (30 +/- 3 microm and 42 +/- 3 microm respectively), which is likely due to the higher energetic gain of soluble electron acceptors used. The two Gram-positive bacteria used only provided a fraction of current produced by the Gram-negative organisms. Power output of co-cultures Gram-positive Enterococcus faecium and either Gram-negative organisms, increased by 30-70% relative to the single cultures. Over time the co-culture biofilms segregated, in particular, Pseudomonas aeruginosa creating towers piercing through a thin, uniform layer of Enterococcus faecium. P. aeruginosa and E. faecium together generated a current of 1.8 +/- 0.4 mA while alone they produced 0.9 +/- 0.01 and 0.2 +/- 0.05 mA respectively. CONCLUSION: We postulate that this segregation may be an essential difference in strategy for electron transfer and substrate capture between the Gram-negative and the Gram-positive bacteria used here.