Effectiveness of Ferric, Ferrous, and Aluminum (Hydr)Oxide Coprecipitation to Treat Water Contaminated with Arsenate.

Coprecipitation of Fe and Al (hydr)oxides has been considered a low-cost process to remove As from wastewater. Arsenate is the most stable form of As in aerobic environments such as surface water, soils, and sediments and can be removed from water through methods based on this process. Iron/aluminum molar ratios of 100:0, 80:20, and 60:40 were used to treat water contaminated with As at concentrations of 50 and 500 mg L. Aluminum, ferrous, and ferric sulfates were used to coprecipitate Al and Fe (hydr)oxides at high pH. Maghemite, magnetite, lepidocrocite, and goethite were detected in precipitates from Fe(II), whereas hematite and ferrihydrite were identified in Fe(III) treatments. Segregation of Al (hydr)oxides as gibbsite and bayerite as well as the Al isomorphic substitution in Fe (hydr)oxides were detected in the presence of Al. The precipitates were classified as nonhazardous according to the leaching test based on Brazilian Technical Standard NBR 10005. The presence of Al increased the stability of the sludge from Fe(II) treatments but did not affect the stability of precipitates from Fe(III) treatments. High efficiencies for As removal from water were obtained for all treatments, but concentrations of soluble As were, in general, lower for Fe(III) treatments especially, in the absence of Al. Treatments were efficient in reaching the threshold to effluent discharge (0.5 mg L), but only treatments with initially 50 mg L of As reached the threshold for drinking water (10 µg L).

Arsenite removal from contaminated water by precipitation of aluminum, ferrous and ferric (hydr)oxides.

Several methods to remove arsenic from water have been considered, including co-precipitation with Fe and Al (hydr)oxides. Such compounds are considered very effective to remove As from contaminated water due to strong bindings between them. Three Fe:Al molar ratios (100:0, 80:20, and 60:40) were used to synthesize aluminum, ferrous, and ferric (hydr)oxides by precipitation in water highly contaminated with arsenite (50 and 500 mg L-1). The method was very efficient for all treatments (> 93%) at the beginning of the incubation period, excepted the one with 60:40 Fe(II):Al molar ratio at the higher As concentration (500 mg L-1) in which gibbsite was identified in precipitated phases. In spite of the high efficiency, however, the threshold for drinking water was not attained, mainly to the higher As concentration, even 84 days after precipitation. At this high concentration of arsenite, even the required threshold for effluent discharge was not attained in some treatments. The sludge resulting from treatments with higher As concentration were considered hazardous according to results from leaching test and corroborated by BCR extractions. Arsenic associated with Al and adsorbed phases were also assessed by extractions with NH4F and KH2PO4, respectively. In general, the presence of Al increased the efficiency as well as the stability of the sludge resulting from Fe (II) treatments, but did not affect Fe (III) treatments, which were more efficient for As removal.

Ubiquitous giants: a plethora of giant viruses found in Brazil and Antarctica.

BACKGROUND: Since the discovery of giant viruses infecting amoebae in 2003, many dogmas of virology have been revised and the search for these viruses has been intensified. Over the last few years, several new groups of these viruses have been discovered in various types of samples and environments.In this work, we describe the isolation of 68 giant viruses of amoeba obtained from environmental samples from Brazil and Antarctica. METHODS: Isolated viruses were identified by hemacolor staining, PCR assays and electron microscopy (scanning and/or transmission). RESULTS: A total of 64 viruses belonging to the Mimiviridae family were isolated (26 from lineage A, 13 from lineage B, 2 from lineage C and 23 from unidentified lineages) from different types of samples, including marine water from Antarctica, thus being the first mimiviruses isolated in this extreme environment to date. Furthermore, a marseillevirus was isolated from sewage samples along with two pandoraviruses and a cedratvirus (the third to be isolated in the world so far). CONCLUSIONS: Considering the different type of samples, we found a higher number of viral groups in sewage samples. Our results reinforce the importance of prospective studies in different environmental samples, therefore improving our comprehension about the circulation anddiversity of these viruses in nature.

Geochemistry and spatial variability of metal(loid) concentrations in soils of the state of Minas Gerais, Brazil.

Since 2009 a policy has been implemented in Brazil to establish the natural concentrations of potentially toxic substances in soil for each state. Historically a 'mining state', Minas Gerais established a Quality Reference Value for metal(loid)s for all of the soils in the state. To successfully establish these values it is important to study the spatial geochemical diversity for the state. In this context, the objectives of this work are: (1) to evaluate the natural concentrations of metal(loid)s in pristine Minas Gerais soils and (2) to interpret the spatial variability in concentration of these elements. The 0-20 cm layer of soils was sampled for 697 georeferenced sites including the main geological materials and soil groups. Soil properties were analyzed according to methodologies suitable for Brazilian soils. The concentration of metal(loid)s was determined by acid extraction according to EPA 3051A. Descriptive statistics, Pearson correlation and spatial variability analyses were performed. The dominance of acidic pH and low CEC values reflects the pervasive deep acid weathering. The variability of metal(loid) concentrations for soils of the state may be attributed to geological diversity and different pedogenesis. Correlation and spatial analysis indicated that the Fe concentration is strongly associated with metal(loid) concentrations in topsoil. According to the spatial geochemical diversity of the state, a k-means cluster analysis was performed which identified four clusters. A significant difference in the mean values of metal(loid) concentrations between the clusters confirmed that the single Quality Reference Value established does not represent the geochemical diversity of soils in Minas Gerais.

The role of Al-goethites on arsenate mobility.

The geochemical fates of Fe and As are so closely correlated that methods of As removal from contaminated water are in general based on the high affinity of this metalloid for Fe (hydr)oxides. Dissimilatory Fe reducing bacteria, however, play a fundamental role in catalysing the redox transformations that ultimately control the mobility of As in anoxic environments. The potential of Al-goethites in adsorbing As(V) compared with hematite, goethite, ferrihydrite, and gibbsite, and the stability of As retained by the Fe compounds under anoxic conditions were investigated in this study. The (hydr)oxides were synthesised, and adsorption isotherms and As(V) adsorption maxima at different pH were measured. Arsenic loaded samples were anaerobically incubated in the presence of Shewanella putrefaciens, and periodically sampled to evaluate the contents of soluble As and Fe. The As(V) adsorption maxima decreased in the following order: Fh > AlGt(13) > AlGt(20) > AlGt(23) > Gb > Hm > Gt. In terms of surface area, Gb, Gt, and Hm showed higher As(V) loading capacity than Fh, suggesting available reactive sites not fully occupied by arsenate on Fh. The same hypothesis can be considered for Al-goethites, as they showed even lower arsenate loading capacity per surface area. The presence of structural Al in the goethites enhanced considerably the As uptake capacity and stability under reducing conditions. Therefore, the Al-goethites showed good potential as adsorbents to remove As from water. S. putrefaciens cells were able to utilise both noncrystalline and crystalline Fe (hydr)oxides as electron acceptors, releasing As into solution. Al-goethites showed a decrease in Fe and As mobilisation as structural Al increased.