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Nanoparticles have excellent catalytic, adsorptive, and reactive properties, which led to their application for wastewater treatment. The current study focuses on silver nanoparticle synthesis using neem leaf and banana peel extract and its application as an antimicrobial and dye degrading agent for wastewater treatment. The use of these extracts led to a rapid, simple, and environment-friendly method for the biosynthesis of silver nanoparticles (AgNPs). UV-Vis spectroscopy showed absorption bands at 473 and 423 nm for AgNPs synthesized from neem leaf and banana peel extracts, respectively. The AgNPs were further characterized using XRD, FTIR, ESEM, EDX, and DLS methods. XRD data confirmed the crystalline nature of the synthesized AgNPs. ESEM images revealed the synthesized nanoparticles were spherical. From DLS analysis the average diameter of the AgNPs was found to be 168.7 nm from banana peel and 206.4 nm from neem leaf extract. Antibacterial activity of synthesized nanoparticles at 0.025 mg/ml concentration was tested against Escherichia coli (E.coli), Bacillus subtilis (B.subtilis), Staphylococcus aureus (S.aureus), and Klebsiella sp. using disk diffusion method and the zone of inhibitions observed were 10-13, 3-4, 2-3, and 1-3 nm respectively. 99% degradation of model dye malachite green was observed using banana peels-derived nanoparticles at a concentration of 0.06 mg/ml within 4.5 h. This study provides an eco-friendly and economic approach to AgNP synthesis and its potential application in the removal of hazardous dye from wastewater.

Ethanol has gained its importance as one of the highly demanded biofuels and is being produced from different food crops or food crop wastes after vigorous pretreatment compelling the production process economically incompatible to some extent. The process also becomes non-ecofriendly as the pretreatment process generally produces acid fumes and toxic effluents as well as consumes high energy. In this current study, the potential of the banana peel as a probable substrate for ethanol production was evaluated with the help of logical prediction. Moreover, a single-step ethanol production process was investigated to eliminate hazardous pretreatment processes. A potential bacterial strain SWET4 was isolated from a sewage treatment pond and was identified as a member of the Klebsiella genus by partial sequencing of the 16S rRNA gene. The isolated strain showed ethanol tolerance up to 12% and exhibited its potential as a cellulolytic strain. The bacterial strain SWET4 was found able to ferment banana peel in MSM broth without any other carbon source with a comparatively prolonged lag phase of cellular growth. Trace of ethanol in banana peel fermentation broth of SWET4 was confirmed by high-pressure liquid chromatography. The optimization study for ethanol production enlightened the fact that high temperature and pH supported higher ethanol production. However, due to the growth restriction of the bacterial cell at higher temperatures and pH, only 40 °C and pH 8 were considered optimum. At the optimum substrate concentration (40 g l−1), ethanol concentration was found to be 5.48 g l−1 after 5 days of incubation which summed as a total yield of 0.137 g of ethanol per g of dried banana peel. This current study evaluates the potential of banana peel as a probable substrate for ethanol production and emphasizes on a new possibility of single-step ethanol production without any pretreatment, although metabolic optimization of the strain SWET4 is required to make the process industrially feasible.

Dry powder of fruit wastes including pomegranate, grapes, lime, apple, and papaya was used to examine their pigment extraction capability. Solvent combination of hexane and acetone (1:1) produced the maximum extraction for lime waste with a yield of 1.65%. Gas Chromatography and Mass Spectrometry analysis of the crude pigment of lime exhibited the abundance of compounds like chlorogenic acid, caffeic acid, and coumaric acid. Three major bands were obtained in Thin Layer Chromatography. Column Chromatographic purification using ethyl acetate and hexane mixture as eluting phase showed a retention factor of 0.62 for the major band. Nuclear Magnetic Resonance revealed the final structure of the compound as chlorogenic acid. Slight inhibition was exhibited by the compound against Escherichia coli. Adsorption of arsenate by residual fruit waste revealed the highest adsorption in grapes with 92% efficiency. This study enlightens an alternative approach of fruit waste management with the production of value-added products and its utilization of residue as bioadsorbent.

Ethanol tolerant strains were isolated from the marine waters of Digha and Shankarpur of West Bengal, India and screened for ethanol production using several domestic wastes including, paper, kitchen, garden, and fruit wastes. Strain E4 was found to be the most efficient in ethanol production through fermentation of kitchen and fruit waste. Phylogenetic analysis of the 16S rRNA gene of strain E4 showed its closeness to Citrobacter sp. Production of 2.96 g/l of ethanol was obtained using fruit waste using High-Performance Liquid Chromatography (HPLC) analysis. The yield of ethanol production was obtained as 0.13 g of ethanol/g of reducing sugar present in fruit waste. Although after optimization of fermentation condition, the yield was improved to 0.30 in batch scale. The production was optimized using Central Composite Design. The production was scaled up to 4 l culture volume in the stirred tank bioreactor. Finally, a distillation of fermentation broth resulted in 16.10 ml of product with a yield of 0.30 g of ethanol from 1 g of fruit waste. Thus the isolated marine strain Citrobacter sp. E4 could be potentially used for ethanol production from fruit wastes without any pretreatment in a cost-effective and eco-friendly way.

Biosorption is an ingenious technique that uses biological materials to acquire trace metal ions from wastewater. In the present study, the ability of Colocasia esculenta stem biomass was explored for the biosorption of toxic trace metals. The maximum removal was observed for arsenate (As5+) with 58.63%, followed by chromium (Cr6+) with 56.56%, and cadmium (Cd2+) with 41.2%. However, for copper (Cu2+), nickel (Ni2+), and zinc (Zn2+), low adsorption was observed. Batch sorption tests revealed that adsorbent dosage of 0.5g, 0.5g, and 0.3g; time of 10 h, 4 h, and 10 h; room temperature range of 25–30°C; pH range of 7.0–4.5; and initial concentration of 30 μg/L, 20 mg/L, and 30 mg/L were the optimum conditions for the removal of As5+, Cr6+, and Cd2+, respectively. Scanning electron microscope and energy-dispersive X-ray spectroscopy (SEM-EDX) analysis of Colocasia esculenta stem biomass before and after adsorption revealed that the trace metals successfully get adsorbed on the surface of the biosorbent. The equilibrium data fitted well with the adsorption isotherm model of Langmuir (for As5+, Cr6+, and Cd2+), Dubinin-Radushkevich (for As5+ and Cr6+), and Flory-Huggins (for Cd2+), and the kinetic data of As5+, Cr6+, and Cd2+ biosorption were best described by pseudo-second-order kinetic model. Thermodynamic studies revealed that the adsorption process for all concerned trace metals acts in a spontaneous manner and is endothermic in nature. Thus, the use of Colocasia esculenta stem biomass proved to be an efficient and economical alternative for the treatment of effluents contaminated with these trace metals.

A superior arsenite [As (III)] oxidizing strain was isolated by enrichment technique from a shallow aquifer of Bhojpur district, Bihar, India. Along with high As (III) and arsenate [As (V)] resistance [up to 70 mM of As (III) and 1000 mM of As (V), respectively], it showed high resistance to multi-metals and a superior ability to utilize a wide range of carbon sources. The gram-negative rod-shaped strain of Delftia spp. BAs29 was characterized thoroughly for its As (III) oxidation ability. The strain showed mixed growth associated, facultative chemolithotrophic As (III) oxidation process, releasing-67 kJ/reaction of free energy in an exergonic reaction. Testing of cost-effective and natural bio-sorbents showed efficient As (V) removal from the contaminated water. Moringa oleifera showed the maximum As (V) removal capacity of 57.89% among the tested bio-sorbents. This study revealed a two-step approach for arsenic removal with 98.77% efficiency from groundwater using an indigenous As (III) oxidizing strain combined with a natural bio-sorbent.

Groundwater arsenic contamination represents a global threat to human health. Among the proposed bioremediation applications, microbial transformation of arsenite (As (III)) seems to be the most favorable approach as it can be easily coupled with several adsorption techniques, without producing lethal by-products or demanding chemical addition. This study highlights the potential contribution of a highly efficient As (III) transforming bacteria Delftia sp. BAs29 followed by the adsorption of transformed arsenate (As (V)) using neutralized red mud under suitable treatment conditions. Diverse experimental conditions elucidated (inflow As (III) concentrations, flow rate) the rate and oxidation efficiency to mediate the process. Red mud is a waste by-product from the Bayer's process of the alumina industry, which when neutralized aids the removal of As (V). The neutralized red mud was characterized using X-ray diffraction (XRD) microanalysis, Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) and Fourier-transform infrared spectroscopy (FTIR). Arsenate adsorption using neutralized red mud was also studied as a function of pH and time, adsorbent dosage, and initial As (V) concentration. The adsorption process was significantly affected by the solution pH, which on decreasing gradually increased the adsorption efficiency. The maximum monolayer capacity for adsorption of 274.1 mg/g As (V) was found at optimum conditions of pH 4.0 and a contact time of 30 min at a temperature of 30 °C, respectively. Furthermore, this process significantly contributed in fabricating a two-step bio-filter column for the removal of total arsenic from groundwater. Graphical abstract.

Arsenic endosmosis causes a severe threat to human health within the developing countries. This study assessed the levels of geogenic arsenic and other heavy metals affecting the release of As in the aquifers within the drinking water sources in Bhojpur district of Bihar, India. Eighteen water samples were collected in triplicates from hand-dug wells in six neighboring villages in proximity to the River Ganga namely Bakhorapur, Gaziapur, Parasrampur (or Kanhachhapara), Saraiya, Paiga and Gundiinin. The physicochemical parameters, ionic content and heavy metal analysis of the collected water samples indicated the region to be highly contaminated with arsenic, zinc, manganese and iron. The arsenic and iron concentration ranged between 24.3 and 168.07 μg/L and 0.17–1.16 mg/L respectively, indicating the excessive withdrawal of groundwater for domestic and irrigation purposes with a significant correlation between both the metals. Elevated concentration of zinc in the region attributed to the excessive application of chemical fertilizers and pesticides. Concentration of manganese was also in the higher range of 0.05–1.15 mg/L, primarily due to the urbanized industrial activities. Human health risk assessment within two population groups in the region indicated that the overall water quality is slightly contaminated but the risk associated with it is low. Water Quality Index ranged from 29 to 48, signifying the water quality to be poor. Residual sodium carbonate values indicated that few water sample sources are not suitable for irrigation purposes whereas, sodium adsorption ratio (SAR) values were within the acceptable limits to be used for irrigation.

High arsenic groundwater contamination causes serious health risks in many developing countries, particularly in India and Bangladesh. The arsenic fluxes in aquifers are primarily controlled by bacterial populations through biogeochemical cycle. In this present study, two gram-positive rod-shaped bacteria were isolated from shallow aquifers of Bhojpur district in Bihar during the early winter season, able to withstand arsenite (As

Bacterial community composition within the highly arsenic (As) contaminated groundwater from Kolsur, West Bengal was analyzed over a period of 3 years using 16S rRNA gene clone library and Denaturing Gradient Gel Electrophoresis (DGGE). Molecular phylogenetic study revealed abundance of α-Proteobacteria (56%) and Firmicutes (29%) along with members of β-Proteobacteria, Verrucomicrobia and Sphingobacteria as relatively minor groups. Along with consistent physicochemical environment, a stable microbial community structure comprising of bacterial genera Agrobacterium-Rhizobium, Ochrobactrum, Pseudomonas, Anoxybacillus and Penibacillus was recorded over the three years study period. Presence of cytosolic arsenate reductase (arsC) gene was observed within the microbial community. Phylogenetic analyses revealed that all the arsC sequences were closely related to the same gene from γ-proteobacterial members while the community was consisted of mainly α-proteobacterial groups. Such phylogenetic incongruence between 16S rRNA and arsC genes possibly indicated horizontal gene transfer (HGT) of the ars genes within the groundwater community. Overall, the study reported a nearly stable geomicrobial environment and genetic determinant related to As homeostasis gene, and provided a better insight on biogeochemistry of As contaminated aquifer of West Bengal.

Ethanol resistant bacterial strain Enterobacter sp. EtK3 was isolated from kitchen wastewater through enrichment culture. The isolated strain was found to produce ethanol by fermenting dried banana peel without any pre-treatment. Ethanol production was confirmed by High-Performance Liquid Chromatography (HPLC) analysis of the fermentation broth. Sequence analysis of the 16S rRNA gene of bacterial isolate EtK3 confirmed its relation with the Enterobacteriaceae family. The temperature of 35 °C with pH 7 utilizing 15.5 gL-1 fruit waste was found to be most favorable for ethanol production after a two-level, three-factor optimization study using Response Surface Methodology (RSM). In the optimized condition, a 23.6% yield of ethanol was obtained. Kinetic study of cell growth, ethanol production and reducing sugar utilization revealed that ethanol production was growth associated with product inhibition at the late log phase. Proximate analysis of pre and post-fermented fruit waste showed subsequent depletion of the fixed carbon content of waste indicating carbon utilization of EtK3 strain from the waste sample. Waste degradation was further confirmed by Scanning Electron Microscope with Energy Dispersive X-Ray (SEM-EDX) and Fourier Transform Infrared Spectrometer (FTIR). An empirical representation of the waste was derived to produce a complete mass balance of the whole ethanol production process from fruit waste.

Hydrocarbon-degrading bacteria were isolated from 2% hydrocarbon enriched sample collected from vehicular repairing stations, garages and petrol bunk. Incubation of the isolated non-virulent strains in Bushnell-Haas (BH) medium supplemented with hydrocarbon, showed their ability to survive on hydrocarbon thereby reducing the total organic carbon content. Based on the degradation potential, different bacterial consortia were prepared and consortium CHM1 was found to grow best with maximum degradation. 16S rRNA gene sequencing of the strains revealed their identity with Klebsiella spp., Enterobacter sp. and Pantoea sp. high to moderate affinity towards hydrocarbon of the selected strains were indicated by Bacterial Adhesion To Hydrocarbon (BATH) test and Contact Angle. Gas Chromatography-Mass Spectrometric (GC-MS) analysis of the mixed hydrocarbon containing broth revealed the presence of benzene derivatives, aliphatic acids, naphthalene, aliphatic alkanes, cyclic aliphatics as major compounds. The efficiency of the selected bacterial consortium showed an overall 16.20% degradation of the mixed hydrocarbon after 4 days, where, aliphatic cyclic compound (1-(1,5-Dimethylhexyl)-4-(4-Methylpentyl)-Cyclohexane) were completely degraded, naphthalene derivatives were reduced to 36.72%, aliphatic acids were degraded to 78.13% and benzene derivatives to 24.16%. Degradation of the long-chain aliphatic alkanes was further observed through Fourier Transform Infrared spectrometric (FTIR) analysis.

Background Hexavalent chromium (Cr(6+)) contamination is one of the mejor problems of environmental protection for its carcinogenic effect on human health. Remediation of Cr(6+) contaminated environment thus becomes highest priority. Methods A Gram positive tiny rod shaped chromate (Cr(6+)) reducing bacterium strain A1 was isolated from uranium ore collected from Jaduguda, East Singhbhum, Jharkhand. The strain was identified and characterized in terms of its potential to reduce more toxic Cr(6+) to its less toxic form for its application in bioremediation of Cr(6+) contaminated environments. Results 16S rRNA gene based phylogentic analysis identified the strain as Microbacterium oleivorans. Along with Cr(6+), the strain showed resistance to other heavy metals including Ag, Cu, Co, Hg, Ni and Zn also. Complete reduction of Cr(6+) (750 µM) was achieved within 84 h with optimum reduction at pH 9 and 30°C. Effect of different parameters including cell mass concentration, pH, induction with Cr(6+), SO4 = ion, heavy metals, etc. on Cr(6+) reduction were studied thoroughly at resting cell condition to study its potential towards Cr(6+) bioremediation. Chromate reductase gene (chrA) was detected within this strain. Conclusion Along with presence of appropriate genetic determinant, efficient Cr(6+) reduction ability of the strain indicated its potential for developing redox based Cr(6+) remediation system for varied concentrations of Cr6+ under a wide range of environmental conditions. Patent data have suggested the efficient application of Cr(6+) reducing bacteria in cleaning up of Cr(6+) contaminated environments.