Journal of Environmental Engineering

A dried biomass wasted from biotrickling filters has been prepared for removing lead [Pb(II)] ions from aqueous solutions. The kinetics, isotherms, and thermodynamics of Pb(II) ion biosorption by the dried biomass were investigated. The results showed that the maximum Pb(II) ion biosorption capacity of a dried biomass was $160.0\mathrm{mg}/\mathrm{g}$ at 25°C according to an evaluation using the Langmuir equation, which was fitted well to the adsorption data. The results of the kinetic studies revealed that the adsorption process followed the pseudo second-order model. The calculated thermodynamic parameters of $\mathrm{\Delta }S°$, $\mathrm{\Delta }H°$, and $\mathrm{\Delta }G°$ suggested that the adsorption of Pb(II) ion was endothermic and spontaneous. Fourier transform infrared spectroscopy (FT-IR) analysis illustrated that the amide group and the hydroxide group affected Pb(II) ion removal significantly. This study demonstrated that a dried biomass wasted from biotrickling filters for the removal of $n$-hexane could be successfully used as adsorbent for the treatment of Pb(II) ion from aqueous solutions and had a higher adsorption capacity.

Biosorption of mercury ions from aqueous solution using activated sludge was investigated through parametric experiments. The influence of process variables like initial solution pH, adsorbent dose, initial mercury concentration, agitation speed, and temperature were studied on the metal removal performance of the selected sorbent. The optimal pH was identified as 7.0 and the removal efficiency was found to decrease with an increase in mercury concentration, confirming the limitation on the availability of active sites. An empirical relationship between metal uptake and sorbent dose was proposed. The exothermic nature of the sorption process was observed with a decrease in mercury uptake at high temperatures. A Langmuir isotherm was used to fit the equilibrium data, confirming the presence of monolayer sorption, and the maximum uptake capacity obtained was $57.803\mathrm{mg}/\mathrm{g}$ with $100\mathrm{mg}/\mathrm{L}$ mercury solution at 35°C after 180 min of equilibrium time. Pseudo-second-order and power function models were fitted to the kinetic data. The surface morphology of the activated sludge was studied using scanning electron microscope studies and the functional groups were characterized using Fourier transform infrared spectroscopic method.

A huge amount of effluents contaminated with heavy metals and metal complex dyes are generated every day from various industries. Biological treatment using various microorganisms (bacteria, algae, and fungi) is considered to be a potentially cost-effective and environmental friendly technique for the removal of heavy metals and metal complex dyes from effluents. This review focuses on the recent studies on bioremediation of metals and metal complex dyes conducted in various modes of operation. The types of metals and metal complex dyes, microorganisms, the mechanism of bioremediation suggested through various analytical techniques, and the technical problems associated with the bioremediation processes that need to be considered for the scale-up of the process are discussed.

The present study reports that microbes from marine sediments can reduce noble metal ions (Au, Ag, and Pt) to their nanoparticles (NPs). The microbes were initially screened for the synthesis of gold (Au) NPs through bioreduction. The cell-free extracts (CFE) of the most promising strain, Photobacterium sp. (MB 8), was further subjected to the synthesis of Ag, Au, and Pt NPs. The resulting metal NPs were characterized by UV-Vis spectrophotometry and transmission electron microscopy (TEM). The TEM results revealed the presence of well-dispersed NPs in the presence of CFE. The residual concentration of metal ions was measured by inductively coupled plasma mass spectrometry (ICP-MS). X-ray diffraction (XRD) analysis of the NPs confirmed the presence of crystalline Au and AgCl NPs. However, no peaks for the presence of crystalline Pt were observed. X-ray photon spectrometry (XPS) analysis of NPs obtained from synthetic wastewater confirmed the formation of nano-sized zero-valent Au and Ag. The consortium of microbes was found to be more efficient in bioreduction of ionic metals to zero-valent form than an individual strain.

The ability of Terrabacter tumescens to precipitate carbonate minerals has been demonstrated for the first time. Biomineralization of nickel, copper, lead, cobalt, zinc, cadmium and calcium by T. tumescens and mineral precipitations in both liquid and porous media were investigated. T. tumescens produced the enzyme urease which can hydrolyze urea. Due to this enzymatic reaction, soil pH increased and carbonate was produced, which results in mineralization of the soluble heavy metal ions present in soil water and their ultimate conversion to carbonates. And we studied the process of calcium carbonate precipitation induced by T. tumescens in sand column. The precipitated minerals were studied by scanning electron microscopy and X-ray diffraction, bioaccumulated divalent metal cation were deposited around the cell envelope as rhombohedral, sphere and needle shaped crystalline carbonate compounds. T. tumescens can play important role in heavy metal bioremediation and increase the strength and stiffness of sand and stone in civil engineering applications.

The effectiveness of biobarrier for leachate containment was investigated through continuous flow column studies. Landfill leachate collected from Ariyamangalam open dumping site was used as the source for microorganism isolation. Isolated organisms were enriched in the presence of lead to selectively obtain lead-tolerant microorganisms. The biochemical analysis results confirmed that the isolated strain is gram positive and rod shaped, Bacillus insolitus. Synthetic leachate was inoculated with different cultures of bacteria and was aerated to an initial dissolved oxygen level of $7.8\mathrm{mg}/\mathrm{L}$. In the batch reactor, chemical oxygen demand (COD) and lead removal was higher for lead-enriched cultures (62 and 28%) when compared with the nonenriched cultures (57 and 13%). The initial hydraulic conductivity of $1.99\times {10}^{-2}\mathrm{cm}/\mathrm{s}$ was reduced to $1.1\times {10}^{-3}\mathrm{cm}/\mathrm{s}$ at the end of 36 days of continuous study of the microbial sand column (MC), whereas negligible reduction was observed in blank column without microbes (BC). A reduction of 74% COD and 51% lead concentration were obtained at the end of 36 days in continuous flow study. The biobarrier is very effective for the reduction of hydraulic conductivity and removal of organic pollutants and heavy metals from landfill leachate. Thus, biobarrier can be used as a primary layer in landfills.

In this paper, eight Penicillium species (P. brasilianum, P. citrinum, P. funiculosun, P. janczewskii, P. janthinellum, P. mineoluteum, P. pinophilum, and P. sclerotiorum), isolated from Brazilian soil, were evaluated for their ability to remove metallic ions as cadmium, cobalt, copper, lithium, lead, and nickel present in aqueous residues. Two bioremediation methodologies were used: growing cells or resting cells. Some of the tested species showed outstanding potential for metallic ions bioremediation. Lead removal was achieved in good yields by using both growing and resting cells methodologies. Using growing cells, in 24 h, removal of nickel by P. janthinellum reached 20.8%. This species was also extremely efficient (91.2%) at biosorption of lead. Using resting cells method, Penicillium species targeted in the present study reached rates of almost 60% removal in only 1 h, being therefore of interest when preferential removal of lead in aqueous solutions is desired. An extraordinary bioremediation was detected using P. brasilianum because 74.4% of lead ion has been removed when this metal was present in a binary mixture containing lithium. Regarding copper, bioremediation using P. sclerotiorum was accomplished in 18.5%. Species P. citrinum and P. janczewskii were able to remove 26% of the copper ions present in the solution. The results show the potential of Penicillium species, a very accessible natural bioresource isolable from soil, water, and plants, to be used in lead and other metals biosorption.

Experiments were conducted to study the Selenium (Se) biosorption and recovery by marine Aspergillus terreus in an upflow bioreactor for a period of 8 days. The Se tolerance of the marine fungus was initially confirmed by visual and microscopic observations that evinced intact fungal cells in an Se-amended medium with sparse changes in the spore texture and cellular number by the seventh day of biosorption studies in the upflow bioreactor. Further, the effect of pH and contact time on the percentage of Se biosorption, in an upflow bioreactor containing fungal pellets, was investigated. It was analyzed that pH ranges of 6–7 and a contact time of 5 days resulted in 85–87% biosorption of Se by the fungal biomass. The interaction of the fungus with the induced Se stress in the medium was monitored regularly for studying the uptake of the metalloid and the possible biosynthesis of Se nanoparticles. Analyses using ultraviolet visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) studies revealed the formation of crystalline Se nanocrystals with an average diameter of 500 nm on the fungal cell wall. Fourier transform infrared (FTIR) spectroscopic analysis indicated the possible involvement of fungal protein groups that aid the binding of the biosorbed Se nanoparticles on to the fungal cell wall.

Sodium hydrosulfide (NaSH), which is utilized for recovering rare metals, was synthesized in a laboratory-scale batch reactor by absorbing a simulated flue gas containing ${\mathrm{H}}_2\mathrm{S}$ into NaOH solution. The effects of ${\mathrm{H}}_2\mathrm{S}$ flow rate, NaOH concentration, and reaction time on the synthesis of NaSH were examined. With an increase in the ${\mathrm{H}}_2\mathrm{S}$ flow rate, the absorption ratio, conversion ratio, and total NaSH productivity showed a decreasing tendency. On the other hand, a higher concentration of NaSH could be synthesized with a higher concentration of NaOH. Most of the ${\mathrm{Na}}_2\mathrm{S}$ (the intermediate product) were produced at a $\mathrm{pH}>12$, and the NaSH synthesis reaction was feasible at a pH 11.5. Contrary to the increased ${\mathrm{H}}_2\mathrm{S}$ flow rate, increased NaOH concentration resulted in an enhanced ${\mathrm{Na}}_2\mathrm{S}/\mathrm{NaSH}$ ratio. With a maximum equivalent ratio of ${\mathrm{NaOH}/\mathrm{H}}_2\mathrm{S}$ at 0.88, the chemical composition of the product could maintain equilibrium with the highest NaSH concentration and less than 1% weight-to-weight ratio (w/w) ${\mathrm{Na}}_2\mathrm{S}$ concentration.

Biological sulfate reduction is an alternative and emerging technique to treat metal containing sulfate-rich wastewater. In this study, the potential of anaerobic biomass from three different wastewater treating systems was evaluated for heavy metal removal under sulfate-reducing conditions. Among the three different biomass sources tested in the study, the biomass from a lab-scale upflow anaerobic-packed bed reactor (UFAR) showed maximum sulfate reduction ($>90\%$) within 96 h with a maximum wastewater chemical oxygen demand (COD) removal of up to 92.8%. The heavy metal removal efficacy was in the order $\mathrm{Cu}>\mathrm{Fe}>\mathrm{Ni}>\mathrm{Pb}>\mathrm{Cd}>\mathrm{Zn}$. Metal removal by the biomass was further established due to its precipitation with sulfide formed by the sulfate-reducing bacteria. The field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) of the metal-loaded biomass showed that the precipitates formed during the process consist of mainly the metal sulfides. The transmission electron microscopy (TEM) along with energy dispersive spectroscopy (EDS) confirmed that the metal precipitates were confined to the exterior and interior surface of the bacterial cells. The Fourier transmission infrared spectroscopy (FTIR) spectra of the biomass, obtained during its growth, clearly established the presence of sulfate ions.

The corrosion and odor caused by hydrogen sulfide formation are serious problems in sewer operations, and the cost to prevent these problems is high. Understanding the sulfur cycle mechanism and controlling the sulfur cycle in sediment biofilm are essential to solve these problems. In this review, the reaction mechanisms of the sulfur cycle in sediment biofilm in sewer systems revealed by using in situ microelectrode measurements and molecular biological technologies are summarized. The results indicated that the profile of the reaction process of the sulfur cycle in sediment biofilm was primarily affected by the substrate concentration change in the liquid phase and the various substrate penetrations in sediment biofilm. The biological community’s distribution and shifting of sulfate reduction bacteria and sulfide oxidation bacteria across the sediment biofilm were in response to the substrate change of the microenvironment in sediment biofilm. The influence of flow fluctuation on the profile of the sulfur cycle in the sediment biofilm of field sewers, the advantageous biological techniques of pyrosequencing and metagenome analyses combined with novel in situ microelectrode measurements, and the new concept model–related control technology of the sulfur cycle in sediment biofilm should be promoted in future studies.

Sulfate-reducing bacteria (SRB)–based technologies have gained a lot of attention in the field of wastewater treatment, especially to treat metal-contaminated wastewaters. An inverse fluidized bed (IFB) bioreactor is a versatile bioreactor configuration that uses SRB technology for metal removal and recovery from wastewater. Apart from sulfate, which is commonly used as an electron acceptor, thiosulfate is another potential candidate for this process. In this study, the performance of two IFB bioreactors that were operated at pH 7.0 (R1) and 5.0 (R2) using sulfate and thiosulfate as the electron acceptors were evaluated. The electron donor used in this study was ethanol and the chemical oxygen demand (COD) to electron acceptor ratio (${\mathrm{SO}}_4^{2-}$ or ${\mathrm{S}}_2{\mathrm{O}}_3^{2-}$) was kept constant at 1.0. By using sulfate as the electron acceptor, the average COD removal efficiency was 75.0 and 58.0% at pH 7.0 and 5.0, respectively, while the sulfate removal efficiency was 74.4 and 50.4%, respectively. The average sulfide production was 246.3 and $150.7\mathrm{mg}/\mathrm{L}$ at pH 7.0 and pH 5.0, respectively. Using thiosulfate as the electron acceptor, slightly higher sulfate reduction activities were achieved when compared to sulfate at pH 5.0. The maximum COD removal efficiency was 54.8% and $162.7\mathrm{mg}/\mathrm{L}$ sulfide was produced. The COD and sulfate removal efficiencies as well as the total sulfide production profiles in the IFB reactor fed with sulfate were modeled using a three-layered artificial neural network (ANN). The results showed that the developed ANN model with a topology of 3-7-3 was able to give good predictions of the performance variables. Moreover, the sensitivity analysis from ANN showed that this process is mainly pH dependent.

Ordered mesoporous MCM-48 ceramic composite membrane was synthesized on a macroporous ceramic support using tetraethyl orthosilicate (TEOS) and cetyltrimethyl ammonium bromide (CTAB) as source materials by an in situ hydrothermal crystallization technique. The repeated multiple coating of MCM-48 on a circular-shaped ceramic support reduces the pore size and porosity of the membrane from 1.0 to 0.142 μm and from 47 to 22%, respectively. The hydraulic permeability of the fabricated MCM-48 ceramic composite membrane is evaluated by permeation of pure water at various applied pressures ranging between 69 and 345 kPa. Various solvent flow tests through MCM-48 ceramic composite membrane demonstrate that permeability of the solvent is mainly controlled by the chemical nature of the liquids. Further, the performance of the MCM-48 ceramic composite membrane is evaluated by separation of Cr(VI) from aqueous solution at various operating pressures, feed concentrations, and pH of the solution. The highest rejection of 81% is observed at an operating pressure of 207 kPa for the feed concentration of 1,000 ppm at pH 2.

The adsorption kinetics of cadmium (Cd) from wastewater onto coffee grounds and wheat straw was ascertained under various process conditions. Batch tests were performed to study the effect of pH, adsorbent concentration, contact time, and initial metal concentration on the removal of Cadmium. The adsorption kinetics was envisaged by fitting the experimental data to the pseudo-first-order and pseudo-second-order kinetic models; and based on linear regression analysis, the best fit was found to be for the pseudo-second-order kinetic model for both adsorbents. Equilibrium conditions were achieved in less than 30 min. Two isotherm equations, namely Langmuir and Freundlich models, were also used to fit the experimental adsorption equilibrium data. The results showed that both physisorption and chemisorption mechanisms controlled the adsorption rate and capacity. The maximum adsorption capacity of coffee grounds and wheat straw was calculated to be 16.2 and $31.6\mathrm{mg}/\mathrm{g}$, respectively.

Iron oxide–coated sand (IOCS) and granular ferric hydroxide (GFH) were used to study the effect of ${\mathrm{Ca}}^{2+}$ and pH on the adsorptive removal of ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Cd}}^{2+}$ from groundwater using batch adsorption experiments and kinetic modeling. It was observed that ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Cd}}^{2+}$ were not stable in synthetic waters. The extent of precipitation increased with increasing pH. Removal of ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Cd}}^{2+}$ was achieved through both precipitation and adsorption, with IOCS showing higher adsorption efficiency. Increase of pH (from 6 to 8) resulted in a higher overall removal efficiency of both ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Cd}}^{2+}$, with precipitation as predominant removal mechanisms at higher pH values, especially for ${\mathrm{Cu}}^{2+}$. An increase in ${\mathrm{Ca}}^{2+}$ concentration increased the precipitation of ${\mathrm{Cu}}^{2+}$ [as ${\mathrm{Cu}}_2{(\mathrm{OH})}_2{\mathrm{CO}}_3$ and ${\mathrm{Cu}}_3{(\mathrm{OH})}_2{({\mathrm{CO}}_3)}_2$] and ${\mathrm{Cd}}^{2+}$ [as $\mathrm{Cd}{(\mathrm{OH})}_2$ and ${\mathrm{CdCO}}_3$]. In addition, ${\mathrm{Ca}}^{2+}$ competes with ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Cd}}^{2+}$ for surface adsorption sites on IOCS and GFH, and reduces their adsorption capacity. The kinetic modeling revealed that the adsorption of ${\mathrm{Cd}}^{2+}$ onto IOCS is a complex process, with limited contribution of chemisorption that increases in the presence of ${\mathrm{Ca}}^{2+}$.

A novel nanobiocomposite, hydrous cerium oxide nanoparticles impregnated Enteromorpha sp. (HCONIE) was used effectively for the adsorption of Cr(VI) from aqueous solutions. The chemical and structural characteristics of the nanobiocomposite were investigated using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analysis. Adsorption studies were determined as a function of pH, contact time, initial concentration of Cr(VI), HCONIE dose, and temperature. The equilibrium adsorption data were modeled using two parameter isotherms, including Langmuir, Freundlich, Dubinin–Radushkevich (D–R), Temkin, Jovanovic, Halsey, and Harkin–Jura. Adsorption data were well described by the Freundlich and Halsey isotherm. The kinetics data were analyzed using adsorption kinetic models like the pseudo-first-order, pseudo-second-order and intraparticle diffusion equation. Kinetic data showed good agreement with the pseudo-second-order kinetic model. The obtained thermodynamic parameters showed that the adsorption of Cr(VI) onto the HCONIE was exothermic in nature. The presence of foreign ions showed a decreased effect on the adsorption capacity of HCONIE towards Cr(VI) removal. The desorption study was carried out with 0.1 and 0.5 M of three different desorbing agents. The study suggests that HCONIE nanobiocomposite could be used for the removal of Cr(VI) from aqueous solution.

Hydrogen has been recognized globally as an energy carrier that fulfills all the environmental quality, energy security and economic competitive demands. In the present study, batch experiments were performed using confectionery wastewater to examine the influence of initial substrate and iron concentrations on hydrogen production. For the different initial substrate concentrations of 1,000, 3,000, 5,000, 7,000, and $\mathrm{9,000}\mathrm{mg}\mathrm{COD}/\mathrm{L}$, the obtained cumulative hydrogen production were 600, 1,325, 1,565, 1,825, and 915 mL, respectively. It was observed that the maximum cumulative hydrogen production of 1,825 mL was obtained at $\mathrm{7,000}\mathrm{mg}\mathrm{COD}/\mathrm{L}$. On this basis, further experiments were intended to study the role of iron concentration on hydrogen production by varying the iron concentration from 0.0, 0.05, 0.10, 0.15, 0.20 to $0.25\mathrm{g}/\mathrm{L}$ at constant $\mathrm{7,000}\mathrm{mg}\mathrm{COD}/\mathrm{L}$ of initial substrate concentration and initial pH of 5.5. It was inferred that the maximum cumulative hydrogen production of 2,475 mL was obtained at optimized conditions of $0.15\mathrm{g}/\mathrm{L}$, $\mathrm{7,000}\mathrm{mg}\mathrm{COD}/\mathrm{L}$ and pH of 5.5. PCR-DGGE and 16S rRNA analysis of dominant hydrogen producing microbes revealed that Corynebacterium kutscheri YMAU-13 played a wide role in fermentation of confectionery wastewater into hydrogen.

Three types of CueR proteins were anchored on the surface of Saccharomyces cerevisiae cells via surface display technology. The surface-engineered cells showed enhanced adsorption capacity and specificity toward Ag (I) in aqueous phase than control groups. A series of experiments were conducted to investigate the resistance of the surface-engineered cells toward environmental changes including pH, temperature, and eluent. The surface-engineered Saccharomyces cerevisiae cells had the highest adsorption capacity of $2.799\mathrm{mg}/\mathrm{g}$, which was 87.3% higher than original cells. The engineered cells were able to tolerate an acidic environment ($\mathrm{pH}=3.0$ to 5.0) and high temperature (up to 50°C) with relatively stable adsorption performance. Desorption efficiency was 11% ($\mathrm{pH}=5.0$, 1 mM eluent), which implied the absorbed Ag (I) ions bonded to the cells with high affinity.

Surface modification of titanium dioxide, ${\mathrm{TiO}}_2$, by codoping with nitrogen and iron to get the photocatalyst active under ordinary visible light was investigated for the photocatalytic degradation of methylene blue. The sol-gel method was used in preparing the modified titanium dioxide. Titanium tetraisopropoxide (TTIP), ammonium nitrate and ferric nitrate were used as precursors with the dopant concentration of 1% and calcination temperature at 600°C. The prepared photocatalyst samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area, ultraviolet (UV)–visible diffusive reflectance spectra (DRS), and X-ray photoelectron spectroscopy (XPS) in order to study their physical properties. The results from XRD confirmed that all prepared photocatalyst were of the anatase phase whereby the codoping photocatalyst perfectly fitted with the standards and also found with high BET surface area. The analysis of band gap energy from UV-visible DRS was observed by a decrease through codoping nitrogen and iron into the ${\mathrm{TiO}}_2$ crystal structure. XPS analysis revealed that the nitrogen atom existed as interstitial N sites, whereas some Fe ions replaced ${\mathrm{Ti}}^{4+}$ ions due to their similarities in ionic radii. The efficiency of photocatalysts was tested by performing a standard batch photocatalytic degradation experiment under visible light. The result showed that 1.0% N, 1.0% Fe-codoped ${\mathrm{TiO}}_2$ photocatalyst yielded a maximum of 80.50% methylene blue degraded within 5 h of irradiation time.

The biofilm matrix is a complex of secreted polymers, absorbed nutrients and metabolites, cell lysis products, and even particulate material. Being polyanionic in nature, this matrix plays a crucial role in the biosorption of metal cations. In this work, the adsorption process of heavy metals in biofilms is modeled in one space dimension. The mathematical model is a free-boundary value problem for nonlinear hyperbolic and parabolic partial differential equations. Biomass and extracellular polymeric substances (EPS) growth is governed by hyperbolic equations, and substrate evolution by parabolic equations. All equations are mutually connected. The model is general and can work for any number of microbial species, EPS, and substrates. In numerical analysis, heterotrophic–autotrophic competition for space with oxygen as common substrate is considered. The model can describe biofilm growth dynamics including spatial distribution of microbial species, substrate concentrations, EPS formation, and, in particular, is able to simulate heavy metal diffusion and adsorption into biofilm. Numerical simulations for representative examples are obtained by the method of characteristics. Results indicate that model is able to capture the main features of heavy metal adsorption process on EPS.

Cr(VI) removal was investigated under batch and continuous mode using dry Litchi chinensis as the low-cost sorbent. Batch biosorption experiments displayed a maximum Cr(VI) removal of 99% with litchi peels, suggesting that the litchi peels can be utilized as a prime sorbent for removal of Cr(VI). Fourier transform infrared spectroscopy (FTIR) profiles confirmed the occurrence of ─NH, ─CH, $─{\mathrm{CH}}_3$, $─{\mathrm{CH}}_2$, and $\mathrm{C}═\mathrm{O}$ functional groups in the litchi peels for the biosorption of Cr(VI). Cr(VI) sorption thermodynamics by litchi peels indicated that the reaction is endothermic and spontaneous in nature. The effect of various co-ions on Cr(VI) biosorption in the batch experiments revealed a significant effect due to ${\mathrm{Fe}}^{2+}(p=0.021)$ and ${\mathrm{PO}}_4^{3-}$ ($p=0.043$) ions on biosorption of Cr(VI). By fitting the experimental data on Cr(VI) biosorption to different sorption isotherm models, a very high coefficient of determination ($R^2$) and very high biosorption capacity values were obtained for the Freundlich model. Cr(VI) sorption kinetic followed the pseudo-first-order kinetics with a $R^2$ value of 0.914. The breakthrough curves from the continuous flow-through column study for Cr(VI) removal demonstrated that litchi peels in the fixed-bed column are suitable for decreasing the concentration of Cr(VI) from $10\mathrm{mg}/\mathrm{L}$ to a value below the recommended detection limit of $0.02\mathrm{mg}/\mathrm{L}$. Furthermore, the sorbent regeneration followed by Cr(VI) biosorption demonstrated that litchi peels could be reused for at least two consecutive cycles without any significant change in the Cr(VI) biosorption capacity.

A rapid method for the synthesis of nanoparticles using Curculigo orchioides rhizome extracts (CoREs) with high level of polyphenols, gamma sterol, and $n$-hexadecanoic acid contents was described. The formation of the silver nanoparticles (AgNPs) was confirmed with surface plasmon resonance using ultraviolet-visible (UV) spectroscopy. The synthesized AgNPs were characterized by X-ray diffractometer (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The shape of the synthesized AgNPs was spherical morphology with 15–18 nm size. The boiled rhizome extract mediated AgNPs (CoBAgNPs) exhibited a maximum zone of inhibition against the bacterial strains tested. Larvicidal bioassay confirmed that the CoBAgNPs showed the highest mortality rate against the malarial vectors such as Anopheles subpictus and Culex quinquefasciatus. The in vitro cytotoxicity study indicated that the inhibitory concentration (${\mathrm{IC}}_{50}$) of CoBAgNPs was 18.86 and $42.43\mathrm{\mu g}{\mathrm{mL}}^{-1}$ for human breast cancer cell line (MDA-MB-231) and Vero cells line, respectively, after 48 h of incubation. The present results clearly suggested that the synthesized metallic silver nanoparticles (CoBAgNPs) could act as potential agent for antibacterial, larvicidal, and anticancer activity.

The present study describes the potential role of additional phosphorus (P) on alleviating cadmium (Cd)–induced toxicity in vetiver plants. The plant growth was significantly affected at $50\mathrm{mg}{\mathrm{L}}^{-1}$ Cd treatment compared to the control, while it increased by 13% with addition of P in the medium when compared with Cd treatment. Accumulation of Cd content in plants showed positive correlation with Cd and $\mathrm{Cd}+\mathrm{P}$ combination exposure, whereas it was slightly decreased at higher doses of $\mathrm{Cd}+\mathrm{P}$ combination treatments in roots compared to the shoot exposed to Cd. A decreased level of photosynthetic pigments was noticed with increasing the Cd concentrations, but it was slightly enhanced with Cd and P combination treatments over Cd treatment. Both hydrogen peroxide (${\mathrm{H}}_2{\mathrm{O}}_2$) and malondialhyde (MDA) contents were found to be increased with increasing Cd dose. The antioxidative enzymes such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX) activities were found to be increased at lower doses of Cd exposure, while they were slightly decreased at higher doses of Cd treatment. The ameliorating effect of P was confirmed by reduction of ${\mathrm{H}}_2{\mathrm{O}}_2$, MDA contents, and antioxidative enzyme activities in shoot and root tissues. Isozyme banding pattern revealed the appearance of additional isoforms of SOD, CAT, and POX in leaf tissues grown in $\mathrm{Cd}+\mathrm{P}$ combination. These results together suggested that the P amendment with Cd may decrease the Cd-induced toxicity that could promote seedlings growth. The present protocol could be considered as novel technology for alleviation of heavy metal stress-induced toxicity in plants including Cd ions.

The fractions of heavy metals in sediment cores taken from the riverine wetland located in the Huaihe River Basin, China, were analyzed using BCR (European Communities Bureau of Reference) sequential extraction techniques. The results revealed that the total concentrations of Cd, Cr, Cu, Pb, and Zn ranged from 0.09–0.38, 47.6–70.2, 14.0–92.1, 19.6–35.9, and $53.8–227.0\mathrm{mg}·{\mathrm{kg}}^{-1}$, respectively. The significant increase in the values of enrichment factors (EF) and the geoaccumulation index (${\mathrm{I}}_{\text{geo}}$) from about 4 cm depth layer and maximum values approaching 5 and 1 near the surface, respectively, indicated the rapid growth of pollutant discharge especially for Cd, Cu, and Zn in recent years. Furthermore, the proportions of the different fractions (i.e., acid extractable, reducible, oxidizable, and residual fractions) of Cd, Cr, Cu, Pb, and Zn had changed drastically. The significant increases in the proportions of reactive forms (acid extractable, reducible, and oxidizable fractions) of heavy metals from about 4 cm depth layer to top layer suggested a marked increase in the mobility and bioavailability of Cd, Pb, Cu, and Cr. Finally, significant positive correlations between total organic carbon (TOC) and reactive fractions suggested that heavy metals, especially reactive fractions, tended to be absorbed by organic materials. The most significant trend in increases indicated that Cd and Cu possessed the most conspicuous mobility and bioavailability. In addition, larger proportions of reactive fractions of Zn indicated that Zn had constant mobility and posed a significant ecological risk to aquatic organisms in the riverine wetland.

The present article intends to make a state-of-the review of removal of ${\mathrm{Hg}}^{2+}$ ions from wastewater using biofilm reactor. Preservation of mercury resistant bacteria has been identified as one of the challenges regarding commercialization of biofilm reactors for this purpose. Finally, a case study on biofilm reactor using freeze-dried Bacillus cereus (JUBT1) has been incorporated. A novel, cost-effective, and economically feasible freeze-drying protocol has been designed and optimized for JUBT1. The freeze-dried strain renders the same characteristics as that of the native strain after revival. The mercury removal efficiency of the biofilm of revived freeze-dried cells is comparable to that of the native cells with a negligible deviation (absolute) of 0.16%. Thus, the present study could prove itself sufficient to throw some light on the future prospects on demercurization of wastewater using bacterial biofilm.

In this review, recent developments pertaining to the use of fungi as biosorbent for heavy metals removal from wastewater has been presented with critical analysis of the present status of the subject. Undoubtedly fungi have emerged as an interesting biosorbent family. They are superior to other microorganisms as they can be easily grown, produce large biomass, and genetic and morphological manipulation is easily possible with them. Various aspects of this field, such as classification, general characteristics, composition and role of the cell wall, and metal uptake mechanisms have been critically analyzed. The superiority of dead biomass of fungi and immobilization was paid enough attention. The use of fungal species as biosensors for metal detection in the environment was also presented.

The biosorption properties of ethylenediaminetetraacetate (EDTA)-treated biomass of baker’s yeast (Saccharomyces cerevisiae) are studied for the removal of Cadmium(Cd), Lead(Pb), and Copper(Cu) from artificially prepared industrial wastewater. The metal ions are chosen for biosorption studies with regard to their availability in industry and potential pollution impact. The optimum biosorption capacity of these metal ions on the biomass is obtained at pH 5. It is observed that the sorption capacity of EDTA-treated biomass increases when the initial concentration of the metal ions is increased. Both Langmuir and Freundlich isotherm models are used to fit experimental biosorption equilibrium data. The maximum biosorption capacity as determined via the Langmuir isotherm is 32.26, 200.0, and $17.24\mathrm{mg}/\mathrm{g}$ for Cd(II), Pb(II), and Cu(II) ions, respectively. The kinetics of biosorption is studied using both pseudo first order and pseudo second order models. Based on a linear regression correlation coefficient, pseudo second order metal uptake rate kinetics is found to give the best fit.