Hexavalent chromium removal from water by microalgal-based materials: Adsorption, desorption and recovery studies.

The current study presents a comprehensive comparison towards the potential of different microalgal-based materials for the removal of hexavalent chromium (Cr(VI)) from water. Among the tested materials, microalgal biochar showed the highest removal efficiency (100%) of Cr(VI). The highest monolayer estimated adsorption capacities were 23.98, 25.19 and 24.27 mg/g at 5, 22 and 35 °C, respectively. Experimental data showed good compliance with pseudo-second-order kinetic model. The results of continuous column studies showed that the column removal efficiency increased from 52.33 to 57.58% by increasing the adsorbent dose from 0.125 to 0.200 g. Desorption efficiency of Cr(VI) by 0.1 M NaOH was increased from 51.16 to 59.41% by sonication bath as compared to roller shaker. More than 97% of desorbed Cr(VI) was recovered in less than 10 min by BaCl2. This study shows that non-living microalga materials are more effective than living cells in the removal and recovery of Cr(VI) from water.

Effect of sodium selenite on the bacteria growth, selenium accumulation, and selenium biotransformation in Pediococcus acidilactici.

In this study, the effect of low selenium concentrations on bacteria growth, selenium bioaccumulation, and selenium speciation in Pediococcus acidilactici was investigated. Six different sodium selenite (Na2SeO3) solutions with concentrations of 0, 0.5, 1, 2, 3, and 4 mg/L were added in MRS broth for 24 h. Then, the obtained bacterial pellets were weighed. The contents of total selenium and selenium species in the bacterial pellets were measured via optimized enzymatic hydrolysis and HPLC-ICP-MS. The maximum dried P. acidilactici biomass of 1.44 g/L was achieved by utilizing 1 mg/L Na2SeO3. By increasing sodium selenite concentrations, total selenium contents were significantly increased from 0.14 to 1.45 mg/g dry weight (p < 0.05). The findings indicated that selenium was favorably incorporated into the bacteria protein fraction and mainly formed selenocysteine. Therefore, selenium-enriched lactic acid bacterium P. acidilactici can deliver a less-toxic, more bioavailable selenium source for human and animal nutrition.