Mechanism of Cr(VI) reduction by an indigenous Rhizobium pusense CR02 isolated from chromite mining quarry water (CMQW) at Sukinda Valley, India

Performance of surface-functionalized structured polypropylene fillers for toluene removal in biotrickling filters

Fillers significantly affect the efficient operation of biotrickling filters (BTFs). Herein, structured polypropylene fillers modified with polydopamine (PDA) and cationic polyacrylamide (CPAM) were developed to reduce pressure loss and shorten the start-up period. Based on thermodynamics and the extended Derjaguin-Landau-Verwey-Overbeek theory, both modified fillers could improve biocompatibility. BTF with CPAM-modified filler had a shorter start-up period than PDA-modified filler. The maximum elimination capacity of the BTFs packed with PDA and CPAM-modified filler was 75.52 g·m-3·h-1 and 78.62 g·m-3·h-1, respectively, at an inlet toluene loading rate of 97.26 g·m-3·h-1 and an empty bed residence time of 33 s. CPAM-modified filler biofilms exhibited higher adhesion strength and extracellular polymeric substance content during early operation. Furthermore, coating differences affected the microbial community structure on the filler surface. The CPAM-modified filler demonstrated superior performance by enriching toluene-degrading bacteria and upregulating key catabolic genes during the start-up stage.

Ultrafast removal of toxic Cr(VI) by the marine bacterium Vibrio natriegens

The fastest-growing microbe Vibrio natriegens is an excellent platform for bioproduction processes. Until now, this marine bacterium has not been examined for bioremediation applications, where the production of substantial amounts of biomass would be beneficial. V. natriegens can perform extracellular electron transfer (EET) to Fe(III) via a single porin-cytochrome circuit conserved in Vibrionaceae. Electroactive microbes capable of EET to Fe(III) usually also reduce toxic metals such as carcinogenic Cr(VI), which is converted to Cr(III), thus decreasing its toxicity and mobility. Here, the performance of V. natriegens was explored for the bioremediation of Cr(VI). At a density of 100 mg/mL, V. natriegens removed 5-20 mg/L Cr(VI) within 30 s and 100 mg/L Cr(VI) within 10 min. In comparison, the model bacterium Escherichia coli grown to a comparable cell density removed Cr(VI) 36 times slower. To eliminate Cr(VI), V. natriegens had to be metabolically active, and functional outer-membrane c-type cytochromes were required. At the end of the Cr(VI) removal process, V. natriegens had reduced all of it into Cr(III) while adsorbing more than half of the metallic ions. These results demonstrate that V. natriegens, with its fast metabolism, is a viable option for the rapid treatment of aqueous pollution with Cr.