Ball milling biochar iron oxide composites for the removal of chromium (Cr(VI)) from water: Performance and mechanisms.

As the first of its kind, a novel biochar/iron oxide composite (BM-Fe-HC) was successfully prepared by simply ball milling iron-laden biochar (Fe-HC). The performance and mechanisms of Cr(VI) removal by BM-Fe-HC were investigated. Ball milling effectively reduced particle size, increased specific surface area, more importantly, enhanced the distribution and increased the exposure of iron oxides on biochar surface. As a result, Cr(VI) removal by BM-Fe-HC showed fast kinetics and large adsorption capacity with the Langmuir maximum capacity of 48.1 mg/g, higher than that of other biochar/iron composites reported in the literature. Acidic pH promoted Cr(VI) removal while competition ions (Cl-, SO42- and PO43-) inhibited Cr(VI) removal by BM-Fe-HC. Comparison of pre- and post-adsorption samples revealed that iron oxides of the BM-Fe-HC played the dominant role in the adsorption and reduction of Cr(VI) during the removal. After adsorption, part of adsorbed Cr(VI) was reduced by Fe(II) and then stabilized by Fe(III) in the form of amorphous CrxFe1-x(OH)3 on the composite surface. All the results demonstrate that novel ball-milled biochar/iron oxide composites can be used as an effective adsorbent to remove Cr(VI) from water.

Chromium(VI) bioreduction and removal by Enterobacter sp. SL grown with waste molasses as carbon source: Impact of operational conditions.

A technology utilizes bacteria Enterobacter sp. SL grown in an anaerobic reactor with waste molasses as carbon source to bio-reduce hexavalent chromium [Cr(VI)] in wastewater and then remove total chromium has been developed. The performance was elucidated through different initial and operating experiments conditions, and the associated mechanism of Cr(VI) reduction was explained. Results show that Cr(VI) removal is 99.91% at 25 h in the anaerobic reactor initially containing bacteria of 5% (v/v), (NH4)2Fe(SO4)2·6H2O of 0.5 g·L-1, waste molasses of 2.5 g·L-1, Cr(VI) of 100 mg·L-1, pH of 6.0, and with the operational temperature of 45 °C. After 120 h reaction, Cr(total) removal reached 91.10%. The major reduction products [FeS, Cr2O3, Cr(OH)3, S0 granules] together with microbes was removed by sludge separation with Cr(VI) in the supernatant (0.027 mg·L-1) being much lower than that (not excess 0.2 mg·L-1) of Electroplating Pollutant Emission Standard.

Eficiencia en la reducción de Cromo por una bacteria silvestre en un tratamiento tipo Batch utilizando como sustrato agua residual del municipio de Pasto, Colombia / Efficiency in the reduction of chromium by a wild bacterium in a Batch treatment type using residual water substrate from the municipality of Pasto, Colombia

Resumen Objetivo: Evaluar la eficiencia en la reducción de Cromo en un tratamiento tipo Batch, utilizando como sustrato agua residual municipal inoculada con una bacteria silvestre. Materiales y métodos: Se verificó a escala de laboratorio el porcentaje de reducción de Cromo hexavalente de tres bacterias silvestres previamente aisladas de agua residual del Río Pasto (Bacillus thuringiensis, Bacillus amyloliquefaciens y Paenibacillus sp.); se seleccionó el aislado que presentó mayor porcentaje de reducción de Cr y fue sometido a diferentes tratamientos. El análisis de los resultados se hizo mediante estadística descriptiva. Resultados: B. thuringiensis, B. amyloliquefaciens, y Paenibacillus sp., presentaron porcentajes de reducción de Cr (VI) de 82,01%; 80,85% y 79,27%, respectivamente. Se determinó que el tercer tratamiento (agua sin esterilizar del Río Pasto con B. thuringiensis) presentó diferencias significativas respecto a los demás (p = 0,0001 α = 0,05), concluyendo que B. thuringiensis reduce en mayor proporción el Cr (VI), los resultados encontrados en esta investigación son promisorios en el campo de la biorremediación de efluentes contaminados con Cromo ya que pueden ser tomados como base para implementar estrategias de biorremediación a gran escala. Conclusión: La bacteria B. thuringiensis presentó alta eficiencia en la reducción de Cromo hexavalente (99,42%), cuando fue implementada en un tratamiento a escala de laboratorio de agua residual sin esterilizar.

Abstract Objective: To evaluate the efficiency in the reduction of chromium in a Batch treatment type, using municipal residual water substrate inoculated with a wild bacterium. Materials and methods: The reduction percentage of hexavalent chromium of three wild bacteria previously isolated from residual water from the Pasto River was verified at laboratory scale (Bacillus thuringiensis, Bacillus amyloliquefaciens and Paenibacillus sp.); the isolated that showed the highest percentage of reduction of Cr was selected and was subjected to different treatments. The analysis of results was done using descriptive statistics. Results: B. thuringiensis, B. amyloliquefaciens, and Paenibacillus sp., presented percentages of reduction of Cr (VI) of 82,01%; 80,85% and 79,27%, respectively. It was determined that the third treatment (nonsterile water from the Pasto River with B. thuringiensis) presented significant differences with regard to the other (p = 0.0001 α = 0.05), concluding that B. thuringiensis reduces in greater proportion the Cr (VI). The results found in this research are promising in the field of bioremediation of contaminated effluents with Chrome since they may be taken as the basis for implementing strategies of bioremediation on a large scale. Conclusion: The bacteria B. thuringiensis presented high efficiency in the reduction of hexavalent chromium (99.42%) when implemented in a treatment at laboratory scale of residual nonsterile water.