A comprehensive review on removal of pollutants from wastewater through microbial nanobiotechnology -based solutions

Increasing wastewater pollution owing to the briskly rising human population, rapid industrialization, and fast urbanization has necessitated highly efficient wastewater treatment technologies. Although several methods of wastewater treatments are in practice, expensiveness, use of noxious chemicals, generation of unsafe by-products, and longer time consumption restrain their use to a great extent. Over the last few decades, nanotechnological wastewater treatment approaches have received widespread recognition globally. Microbially fabricated nanoparticles reduce the utilization of reducing, capping, and stabilizing agents, and exhibit higher adsorptive and catalytic efficiency than chemically synthesized nanomaterials. The present review comprehensively summarizes the applications of microbial nanotechnology in the removal of a wide range of noxious wastewater pollutants. Moreover, prospects and challenges associated with the integration of nanotechnology with other biological treatment technologies including algal-membrane bioreactor, aerobic digestion, microbial fuel cells, and microbial nanofiber webs have also been briefly discussed.

Insights into Thermophilic Plant Biomass Hydrolysis from Caldicellulosiruptor Systems Biology

Plant polysaccharides continue to serve as a promising feedstock for bioproduct fermentation. However, the recalcitrant nature of plant biomass requires certain key enzymes, including cellobiohydrolases, for efficient solubilization of polysaccharides. Thermostable carbohydrate-active enzymes are sought for their stability and tolerance to other process parameters. Plant biomass degrading microbes found in biotopes like geothermally heated water sources, compost piles, and thermophilic digesters are a common source of thermostable enzymes. While traditional thermophilic enzyme discovery first focused on microbe isolation followed by functional characterization, metagenomic sequences are negating the initial need for species isolation. Here, we summarize the current state of knowledge about the extremely thermophilic genus Caldicellulosiruptor, including genomic and metagenomic analyses in addition to recent breakthroughs in enzymology and genetic manipulation of the genus. Ten years after completing the first Caldicellulosiruptor genome sequence, the tools required for systems biology of this non-model environmental microorganism are in place.

Overview of microbes based fabricated biogenic nanoparticles for water and wastewater treatment

Treatment of toxic and emerging pollutants (T&EPs) is increasing the threats to the survival of conventional wastewater treatment (WWTs) technologies. The high installation and operational costs of advanced treatment technologies have shifted the research interest to the development of economical and reliable technology for management of T&EPs. Thus, recently biogenic nanoparticles (BNPs) fabricated using microbes/microorganisms are getting tremendous research interest due to their unique properties (i.e. high specific surface area, desired morphology, catalytic reactivity) for the biodegradation and biosorption of T&EPs. In addition, BNPs can be manufactured using metal contaminated water which indicates a hidden potential for resource recovery and utilization. Therefore, the present study discusses the adsorptive and catalytic performance of BNPs in the removal of T&EPs from water (W) and wastewater (WW). In addition, inspired by the superior performance of BNPs in advance WWT, a model of BNPs based WWT resource recovery and utilization process is also proposed. Finally, main issues i.e. mass production, leaching, poisoning/toxicity, regeneration, reusability and fabrication costs and process optimization are discussed which are main hinders in the transfer of BNPs based WWT technologies from laboratory to commercial scale.

Investigation of Cr(VI) reduction potential and mechanism by Caldicellulosiruptor saccharolyticus under glucose fermentation condition

This study examined the microbial reduction of hexavalent chromium [Cr(VI)] by an extremely thermophilic bacterium, Caldicellulosiruptor saccharolyticus, under glucose fermentation conditions at 70°C. Experimentation with different initial Cr(VI) concentrations confirmed that C. saccharolyticus had the ability to reduce Cr(VI) and immobilize Cr(III). At a concentration of 40mg/L, Cr(VI) was completely reduced within 12h, and 97% of the reduction product Cr(III) precipitated on the cell surface. Cr(VI) reduction was accelerated by the addition of neutral red (NR, an electron mediator), resulting in the reduction time shortened to 1h. The addition of CuCl₂, a Ni-Fe hydrogenase inhibitor, also enhanced Cr(VI) reduction. Additionally, analysis of the relationship between Cr(VI) reduction and glucose fermentation suggested that different electron sources acted during CuCl₂ and NR conditions. Hydrogen served as an electron donor under normal fermentation and NR conditions with the catalysis of Ni-Fe hydrogenase. However, when the activity of Ni-Fe hydrogenase was inhibited by CuCl₂, C. saccharolyticus directly used reduction equivalents during glucose fermentation for intracellular Cr(VI) reduction. Therefore, our findings demonstrated high Cr(VI) reduction ability and different electron transfer pathways during Cr(VI) reduction by C. saccharolyticus.

Hydraulic retention time affects stable acetate production from tofu processing wastewater in extreme-thermophilic (70°C) mixed culture fermentation

Acetate is an important industrial chemical and its production from wastes via mixed culture fermentation (MCF) is economic. In this work, the effect of hydraulic retention time (HRT) on acetate production from tofu processing wastewater (TPW) in extreme-thermophilic (70°C) MCF was first investigated. It was found that long HRT (>3days) could lead to less acetate production while stable acetate production was achieved at short HRT (3days) with the yield of 0.57g-COD/g-CODTPW. The microbial community analysis showed that hydrogenotrophic methanogens (mainly Methanothermobacter) occupied up to 90% of archaea at both HRTs of 3 and 5days. However, Coprothermobacter, the main acetate-degraders, decreased from 35.74% to 10.58% of bacteria when HRT decreased from 5 to 3days, supporting the aggravation of syntrophic acetate oxidation in long HRT. This work demonstrated that HRT was a crucial factor to maintain stable acetate production from TPW in extreme-thermophilic MCF.