Rationally designed Shewanella oneidensis Biofilm Toilored Graphene-Magnetite Hybrid Nanobiocomposite as Reusable Living Functional Nanomaterial for Effective Removal of Trivalent Chromium.

Sustainable treatment of wastewater containing trivalent chromium (Cr3+) remains a significant challenge owing to the several limitations of the existing methodologies. Herein, combination of biosynthesis and Response Surface Methodology (RSM) for the fabrication and optimization of Shewanella oneidensis biofilm functionalized graphene-magnetite (GrM) nanobiocomposite was adopted as a 'living functional nanomaterial' (viz. S-GrM) for effective removal of Cr3+ ions from aqueous solution. In the biosynthetic process, S. oneidensis cells reduced the GO-akaganeite complex and adhered on the as-synthesized GrM nanocomposite to form S-GrM hybrid-nanobiocomposite. The process parameters for fabrication of S-GrM hybrid-nanobiocomposite was optimized by RSM based on four responses of easy magnetic separation, biofilm formation along with protein, and carbohydrate contents in extracellular polymeric substances (EPS). The morphology and chemical composition of S-GrM hybrid-nanobiocomposite were investigated using various spectroscopic and microscopic analyses and subsequently explored for removal of Cr3+ ions. The hybrid-nanobiocomposite effectively removed 304.64 ± 14.02 mg/g of Cr3+ at pH 7.0 and 30 °C, which is found to be very high compared to the previously reported values. The high surface area of graphene, biofilm biomass of S. oneidensis and plenty of functional groups provided a unique structure to the S-GrM hybrid-nanobiocomposite for efficient removal of Cr3+ through synergistic interaction. The FTIR and zeta potential studies confirmed that electrostatic and chelation/complexation reaction played key roles in the adsorption process. The fabrication of S-GrM nanobiocomposite thus creates a novel hybrid 'living functional nanomaterial' for low cost, recyclable, and sustainable removal of Cr3+ from wastewater.

Bio-reserves inventory-improving substrate management for anaerobic waste treatment in a fast-growing Indian urban city, Chennai.

India is one among the Asia's newly industrialized countries, in which urban centres generate large amount of municipal solid wastes due to the rapid urbanization. To demonstrate urban waste potentials for biogas production by anaerobic digestion, a comprehensive analysis on the availability of organic waste hotspots and its biogas potential for the exemplary case of Chennai, India, was undertaken. The identified hotspots and their biogas potential were plotted with Geographical Information System as thematic maps. The results of biogas potential tests revealed strong variations in the biogas potentials of individual waste streams from 240.2 to 514.2 mLN/g oDM (organic dry matter) with oDM reduction in the range of 36.4-61.5 wt.-%. Major waste generation hotspots were identified from the surveyed urban bio-reserves and the biogas potentials within an effective area of 5 km radius surrounding the hotspot were estimated. It was found that the biogas potential of individual hotspots ranged between 38.0-5938.7 m3/day. Further results revealed that the biogas potential during anaerobic co-digestion, by considering nearby bio-reserves in the effective areas of major hotspots, with and without residential organic waste, ranged between 4110.4-18-106.1 m3/day and 253.2-5969.5 m3/day, originating from 144.0-620.0 tons and 3.1-170.5 tons, respectively. Despite variations in the composition of the wastes, the Carbon/Nitrogen ratio, oDM reduction, biogas production and substrate availability were improved during co-digestion of nearby bio-reserves within the major hotspots, thereby improving the prevailing barriers in substrate management during anaerobic digestion of wastes.