Bioremediation of a polymetallic, arsenic-dominated reverse osmosis reject stream.

The treatment of metal-laden industrial effluents by reverse osmosis is gaining in popularity worldwide due to its high performance. However, this process generates a polymetallic concentrate (retentate) stream in need of efficient post-treatment prior to environmental discharge. This paper presents results on the bioremediation (in batch mode) of a metal-laden, arsenic-dominated retentate using Shewanella sp. O23S as inoculum. The incubation of the retentate for 14 days under anoxic conditions resulted in the following removal yields: As (8%), Co (11%), Mo (3%), Se (62%), Sb (30%) and Zn (40%). The addition of 1 mmol l-1 cysteine increased the removal rate as follows: As (27%), Co (80%), Mo (78%), Se (88%), Sb (83%) and Zn (90%). The contribution of cysteine as a source of H2 S to enhancing the removal yield was confirmed by its addition after 7 days of incubations initially lacking it. Additionally, the cysteine-sourced H2 S was confirmed by its capture onto headspace-mounted Pb-acetate test strips that were analysed by X-ray diffraction. We show that real metal-laden industrial effluents can be treated to medium-to-high efficiency using a biological system (naturally sourced inocula) and inexpensive reagents (yeast extract, lactate and cysteine).

Pseudomonas moraviensis subsp. stanleyae, a bacterial endophyte of hyperaccumulator Stanleya pinnata, is capable of efficient selenite reduction to elemental selenium under aerobic conditions.

AIMS: To identify bacteria with high selenium tolerance and reduction capacity for bioremediation of wastewater and nanoselenium particle production. METHODS AND RESULTS: A bacterial endophyte was isolated from the selenium hyperaccumulator Stanleya pinnata (Brassicaceae) growing on seleniferous soils in Colorado, USA. Based on fatty acid methyl ester analysis and multi-locus sequence analysis (MLSA) using 16S rRNA, gyrB, rpoB and rpoD genes, the isolate was identified as a subspecies of Pseudomonas moraviensis (97.3% nucleotide identity) and named P. moraviensis stanleyae. The isolate exhibited extreme tolerance to SeO3(2-) (up to 120 mmol l(-1)) and SeO4(2-) (>150 mmol l(-1)). Selenium oxyanion removal from growth medium was measured by microchip capillary electrophoresis (detection limit 95 nmol l(-1) for SeO3(2-) and 13 nmol l(-1) for SeO4(2-)). Within 48 h, P. moraviensis stanleyae aerobically reduced SeO3(2-) to red Se(0) from 10 mmol l(-1) to below the detection limit (removal rate 0.27 mmol h(-1) at 30 °C); anaerobic SeO3(2-) removal was slower. No SeO4(2-) removal was observed. Pseudomonas moraviensis stanleyae stimulated the growth of crop species Brassica juncea by 70% with no significant effect on Se accumulation. CONCLUSIONS: Pseudomonas moraviensis stanleyae can tolerate extreme levels of selenate and selenite and can deplete high levels of selenite under aerobic and anaerobic conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Pseudomonas moraviensis subsp. stanleyae may be useful for stimulating plant growth and for the treatment of Se-laden wastewater.