Ignacio T. Vargas

Culture dependent and independent analyses of bacterial communities involved in copper plumbing corrosion.

Aims:  This study used culture‐dependent and culture‐independent approaches to characterize bacterial communities in copper plumbing corrosion and to assess biofilm formation and copper resistance of heterotrophic bacteria isolated from copper pipes.

Natural attenuation process via microbial oxidation of arsenic in a high Andean watershed

Rivers in northern Chile have arsenic (As) concentrations at levels that are toxic for humans and other organisms. Microorganism-mediated redox reactions have a crucial role in the As cycle; the microbial oxidation of As (As(III) to As(V)) is a critical transformation because it favors the immobilization of As in the solid phase. We studied the role of microbial As oxidation for controlling the mobility of As in the extreme environment found in the Chilean Altiplano (i.e., > 4000 meters above sea level (masl) and < 310 mm annual rainfall), which are conditions that have rarely been studied. Our model system was the upper Azufre River sub-basin, where the natural attenuation of As from hydrothermal discharge (pH 4-6) was observed. As(III) was actively oxidized by a microbial consortium, leading to a significant decrease in the dissolved As concentrations and a corresponding increase in the sediments As concentration downstream of the hydrothermal source. In-situ oxidation experiments demonstrated that the As oxidation required biological activity, and microbiological molecular analysis confirmed the presence of As(III)-oxidizing groups (aroA-like genes) in the system. In addition, the pH measurements and solid phase analysis strongly suggested that the As removal mechanism involved adsorption or coprecipitation with Fe-oxyhydroxides. Taken together, these results indicate that the microorganism-mediated As oxidation contributed to the attenuation of As concentrations and the stabilization of As in the solid phase, therefore controlling the amount of As transported downstream. This study is the first to demonstrate the microbial oxidation of As in Altiplano basins and its relevance in the immobilization of As.

Multi-technique approach to assess the effects of microbial biofilms involved in copper plumbing corrosion

Microbially influenced corrosion (MIC) is recognized as an unusual and severe type of corrosion that causes costly failures around the world. A microbial biofilm could enhance the copper release from copper plumbing into the water by forming a reactive interface. The biofilm increases the corrosion rate, the mobility of labile copper from its matrix and the detachment of particles enriched with copper under variable shear stress due to flow conditions. MIC is currently considered as a series of interdependent processes occurring at the metal-liquid interface. The presence of a biofilm results in the following effects: (a) the formation of localized microenvironments with distinct pH, dissolved oxygen concentrations, and redox conditions; (b) sorption and desorption of labile copper bonded to organic compounds under changing water chemistry conditions; (c) change in morphology by deposition of solid corrosion by-products; (d) diffusive transport of reactive chemical species from or towards the metal surface; and (e) detachment of scale particles under flow conditions. Using a multi-technique approach that combines pipe and coupon experiments this paper reviews the effects of microbial biofilms on the corrosion of copper plumbing systems, and proposes an integrated conceptual model for this phenomenon supported by new experimental data.

Modeling MIC copper release from drinking water pipes.

Copper is used for household drinking water distribution systems given its physical and chemical properties that make it resistant to corrosion. However, there is evidence that, under certain conditions, it can corrode and release unsafe concentrations of copper to the water. Research on drinking water copper pipes has developed conceptual models that include several physical-chemical mechanisms. Nevertheless, there is still a necessity for the development of mathematical models of this phenomenon, which consider the interaction among physical-chemical processes at different spatial scales. We developed a conceptual and a mathematical model that reproduces the main processes in copper release from copper pipes subject to stagnation and flow cycles, and corrosion is associated with biofilm growth on the surface of the pipes. We discuss the influence of the reactive surface and the copper release curves observed. The modeling and experimental observations indicated that after 10h stagnation, the main concentration of copper is located close to the surface of the pipe. This copper is associated with the reactive surface, which acts as a reservoir of labile copper. Thus, for pipes with the presence of biofilm the complexation of copper with the biomass and the hydrodynamics are the main mechanisms for copper release.

A new aerobic chemolithoautotrophic arsenic oxidizing microorganism isolated from a high Andean watershed

Biological arsenic oxidation has been suggested as a key biogeochemical process that controls the mobilization and fate of this metalloid in aqueous environments. To the best of our knowledge, only four aerobic chemolithoautotrophic arsenite-oxidizing (CAO) bacteria have been shown to grow via direct arsenic oxidation and to have the essential genes for chemolithoautotrophic arsenite oxidation. In this study, a new CAO bacterium was isolated from a high Andean watershed evidencing natural dissolved arsenic attenuation. The bacterial isolate, designated TS-1, is closely related to the Ancylobacter genus, in the Alphaproteobacteria class. Results showed that TS-1 has genes for arsenite oxidation and carbon fixation. The dependence of bacterial growth from arsenite oxidation was demonstrated. In addition, a mathematical model was suggested and the kinetic parameters were obtained by simultaneously fitting the biomass growth, arsenite depletion curves, and arsenate production. This research increases the knowledge of chemolithoautotrophic arsenic oxidizing microorganisms and its potential role as a driver for natural arsenic attenuation.

Copper Corrosion and Biocorrosion Events in Premise Plumbing

Corrosion of copper pipes may release high amounts of copper into the water, exceeding the maximum concentration of copper for drinking water standards. Typically, the events with the highest release of copper into drinking water are related to the presence of biofilms. This article reviews this phenomenon, focusing on copper ingestion and its health impacts, the physicochemical mechanisms and the microbial involvement on copper release, the techniques used to describe and understand this phenomenon, and the hydrodynamic effects. A conceptual model is proposed and the mathematical models are reviewed.

Electrochemically active microorganisms from an acid mine drainage-affected site promote cathode oxidation in microbial fuel cells

The limited database of acidophilic or acidotolerant electrochemically active microorganisms prevents advancements on microbial fuel cells (MFCs) operated under low pH. In this study, three MFCs were used to enrich cathodic biofilms using acid mine drainage (AMD) sediments as inoculum. Linear sweep voltammetry showed cathodic current plateaus of 5.5 (±0.7) mA at about -170mV vs Ag/AgCl and 8.5 (±0.9) mA between -500mV to -450mV vs Ag/AgCl for biofilms developed on small graphite fiber brushes. After gamma irradiation, biocathodes exhibited a decrease in current density approaching that of abiotic controls. Electrochemical impedance spectroscopy showed six-fold lower charge transfer resistance with viable biofilm. Pyrosequencing data showed that Proteobacteria and Firmicutes dominated the biofilms. Acidithiobacillus representatives were enriched in some biocathodes, supporting the potential importance of these known iron and sulfur oxidizers as cathodic biocatalysts. Other acidophilic chemolithoautotrophs identified included Sulfobacillus and Leptospirillum species. The presence of chemoautotrophs was consistent with functional capabilities predicted by PICRUSt related to carbon fixation pathways in prokaryotic microorganisms. Acidophilic or acidotolerant heterotrophs were also abundant; however, their contribution to cathodic performance is unknown. This study directs subsequent research efforts to particular groups of AMD-associated bacteria that are electrochemically active on cathodes.

Arsenic removal mediated by acidic pH neutralization and iron precipitation in microbial fuel cells

Abstract High concentrations of arsenic (As) in natural waters are a growing concern worldwide. In northern Chile, fluvial systems enriched in As from natural and anthropogenic sources have been found to contain microbial communities with exoelectrogenic activity. Previous work performed with Microbial Fuel Cells (MFCs) resulted in a neutralizing microbial community developed from a consortium extracted from northern Chile. Considering that the formation of iron minerals, which have been reported as good As sorbents, would be favored by pH neutralization, the use of neutralizing MFCs could result in a sustainable alternative for Fe and As removal. In this work, we quantified the removal of As and Fe from acidic waters in air-cathode single-chamber MFCs. Our results show a removal ~80% of As and Fe and, simultaneously, a pH neutralization from ~3.7 to ~7.2. Additionally, non-MFC experiments indicate that the removal of As and Fe is dependent only on the activity of the microbial community developed during MFC operation and not on the MFC electrochemical performance. In addition, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) analysis showed spatial associations between Fe and As on the surface of cathodes, suggesting the idea that iron oxyhydroxides formation would be associated with the higher oxygen concentration near the cathodes. Powder X-ray diffraction (XRD) analysis showed the dominance of iron amorphous minerals, which may be favoring the removal of As. These results indicate that acid/metal-tolerant bacteria favor pH neutralization and consequently the removal of Fe and As by processes of surface sorption and/or As-Fe co-precipitation. Furthermore, these findings expand the possible MFC applications to the simultaneous removal of Fe and As from acidic waters, enabling its use as an energetically sustainable bioremediation alternative.

Perchlorate contamination in Chile: Legacy, challenges, and potential solutions

&NA; This paper reviews the unique situation of perchlorate contamination in Chile, including its sources, presence in environmental media and in the human population, and possible steps to mitigate its health impacts. Perchlorate is a ubiquitous water contaminant that inhibits thyroid function. Standards for drinking water range from 2 to 18 &mgr;g L−1 in United States and Europe. A major natural source of perchlorate contamination is Chile saltpeter, found in the Atacama Desert. High concentrations of perchlorate have presumably existed in this region, in soils, sediments, surface waters and groundwaters, for millions of years. As a result of this presence, and the use of Chile saltpeter as a nitrogen fertilizer, perchlorate in Chile has been found at concentrations as high as 1480 &mgr;g L−1 in drinking water, 140 &mgr;g/kg−1 in fruits, and 30 &mgr;g L−1 in wine. Health studies in Chile have shown concentrations of 100 &mgr;g L−1 in breast milk and 20 &mgr;g L−1 in neonatal serum. It is important to acknowledge perchlorate as a potential health concern in Chile, and assess mitigation strategies. A more thorough survey of perchlorate in Chilean soils, sediments, surface waters, groundwaters, and food products can help better assess the risks and potentially develop standards. Also, perchlorate treatment technologies should be more closely assessed for relevance to Chile. The Atacama Desert is a unique biogeochemical environment, with millions of years of perchlorate exposure, which can be mined for novel perchlorate‐reducing microorganisms, potentially leading to new biological treatment processes for perchlorate‐containing waters, brines, and fertilizers. HighlightsPerchlorate occurs naturally at high concentrations in Chile, for millions of years.Perchlorate contaminates soils, sediments, drinking water and food products.Trade of contaminated food products and fertilizers may affect countries worldwide.Atacama Desert can be used as a natural laboratory for bioprospecting new bacteria.Chile should evaluate population risks and mitigation strategies for perchlorate.

A New Method for Sensing Soil Water Content in Green Roofs Using Plant Microbial Fuel Cells

Green roofs have many benefits, but in countries with semiarid climates the amount of water needed for irrigation is a limiting factor for their maintenance. The use of drought-tolerant plants such as Sedum species, reduces the water requirements in the dry season, but, even so, in semiarid environments these can reach up to 60 L m−2 per day. Continuous substrate/soil water content monitoring would facilitate the efficient use of this critical resource. In this context, the use of plant microbial fuel cells (PMFCs) emerges as a suitable and more sustainable alternative for monitoring water content in green roofs in semiarid climates. In this study, bench and pilot-scale experiments using seven Sedum species showed a positive relationship between current generation and water content in the substrate. PMFC reactors with higher water content (around 27% vs. 17.5% v/v) showed larger power density (114.6 and 82.3 μW m−2 vs. 32.5 μW m−2). Moreover, a correlation coefficient of 0.95 (±0.01) between current density and water content was observed. The results of this research represent the first effort of using PMFCs as low-cost water content biosensors for green roofs.