Kinetic,thermodynamic, and equilibrium biosorption of Pb(II), Cu(II), and Ni(II) using dead mushroom biomass under batch experiment

In this study, a low-cost biosorbent, dead mushroom biomass (DMB) granules, was used for investigating the optimum conditions of Pb(II), Cu(II), and Ni(II) biosorption from aqueous solutions. Various physicochemical parameters, such as initial metal ion concentration, equilibrium time, pH value, agitation speed, particles diameter, and adsorbent dosage, were studied. Five mathematical models describing the biosorption equilibrium and isotherm constants were tested to find the maximum uptake capacities: Langmuir, Freundlich, Redlich-Peterson, Sips, and Khan models. The best fit to the Pb(II) and Ni(II) biosorption results was obtained by Langmuir model with maximum uptake capacities of 44.67 and 29.17 mg/g for these two ions, respectively, whereas for Cu(II), the corresponding value was 31.65 mg/g obtained with Khan model. The kinetic study demonstrated that the optimum agitation speed was 400 rpm, at which the best removal efficiency and/or minimum surface mass transfer resistance (MSMTR) was achieved. A pseudo-second-order rate kinetic model gave the best fit to the experimental data (R² = 0.99), resulting in MSMTR values of 4.69× 10^?5, 4.45× 10^?6, and 1.12× 10^?6 m/s for Pb(II), Cu(II), and Ni(II), respectively. The thermodynamic study showed that the biosorption process was spontaneous and exothermic in nature.     

Copper flotation waste from KGHM as potential sorbent for heavy metal removal from aqueous solutions

Sorption affinity of copper flotation waste from KGHM toward Cd(II), Cr(III), Cu(II), and Pb(II) ions was investigated in this work. Batch sorption studies, using single-element synthetic aqueous solutions at various pH (2–12), contact time (10–300 min), initial concentration (100–5000 mg dm^?3; 1–100 mg dm^?3 for Cd(II)) and adsorbent dose (25–200 g dm^?3), were performed. Bonding strength of adsorbed metals was tested from the degree of desorption. The maximum metal removal was observed at pH 5–8, ≥120 min reaction time, and 25 g dm^?3 adsorbent dose. Maximum sorption capacities of studied material were 41.6, 58.8, and 83.8 mg g^?1 for Cr(III), Cu(II), and Pb(II), respectively, for 5000 mg dm^?3 initial concentration, and 0.86 mg g^?1 for Cd(II) for initial concentration of 50 mg dm^?3. Sorption isotherms were very well fitted to Langmuir (Cd, Cr, Pb) and Freundlich (Cu) models. Sorption kinetics was nearly ideally fitted to pseudo-second-order kinetic model. Desorption studies showed that most of Cr(III) (98.5%) and Pb(II) (67.3%) ions remained bound to the surface, indicating that the chemisorption dominated as a controlling process. On the other hand, mostly desorbed were Cd(II) (98.5%) and Cu(II) (90.3%) ions, which indicated that processes like physisorption or precipitation were prevailing.     

Peptidic models for the binding of Pb(II), Bi(III) and Cd(II) to mononuclear thiolate binding sites

Herein, we evaluate the binding of Pb(II) and Bi(III) to cysteine-substituted versions of the TRI peptides [AcG-(LKALEEK)₄G-NH₂] which have previously been shown to bind Hg(II) and Cd(II) in unusual geometries as compared with small-molecule thiol ligands in aqueous solutions. Studies of Pb(II) and Bi(III) with the peptides give rise to complexes consistent with the metal ions bound to three sulfur atoms with M–S distances of 2.63 and 2.54 Å, respectively. Competition experiments between the metal ions Pb(II), Cd(II), Hg(II) and Bi(III) for the peptides show that Hg(II) has the highest affinity, owing to the initial formation of the extremely strong HgS₂ bond. Cd(II) and Pb(II) have comparable binding affinities at pH > 8, while Bi(III) displays the weakest affinity, following the model, M(II) + (TRI LXC)₃ ^3? → M(II)(TRI LXC)₃ ^?. While the relevant equilibria for Hg(II) binding to the TRI peptides corresponds to a strong first step forming Hg(TRI LXC)₂(HTRI LXC), followed by a single deprotonation to give Hg(TRI LXC)₃ ^?, the binding of Cd(II) and Pb(II) is consistent with initial formation of M(II)(TRI LXC)(HTRI LXC)₂ ⁺ at pH < 5 followed by a two-proton dissociation step (pK _a2) yielding M(II)(TRI LXC)₃ ^?. Pb(II)(TRI LXC)(HTRI LXC)₂ ⁺ converts to Pb(II)(TRI LXC)₃ ^? at slightly lower pH values than the corresponding Cd(II)–peptide complexes. In addition, Pb(II) displays a lower pK _a of binding to the “d”-substituted peptide, (TRI L12C, pK _a2 = 12.0) compared with the “a”-substituted peptide, (TRI L16C, pK _a2 = 12.6), the reverse of the order seen for Hg(II) and Cd(II). Pb(II) also showed a stronger binding affinity for TRI L12C (K _bind = 3.2 × 10⁷ M^?1) compared with that with TRI L16C (K _bind = 1.2 × 10⁷ M^?1) at pH > 8.     

Counter-Current Attrition Process (CCAP) to Remove Metals,Pentachlorophenol (PCP), Dioxins and Furans (PCDDF) from the 1-4-mm Fraction of Contaminated Soil

The objective of this study was to evaluate the potential of a counter-current attrition process (CCAP) over 15 cycles for removing metals, pentachlorophenol (PCP) and polychlorinated dibenzo-p-dioxins and -furans (PCDDF) from contaminated soil. The CCAP, applied to the 1–4-mm fraction of a contaminated soil, included five attrition steps (pulp density (PD) = 40% (w w^?1), surfactant [BW] = 2% (w w^?1), t = 20 min, T = 20°C) followed by one rinsing step. The water emerging from the first attrition step was treated using flocculation in the presence of 0.04 g CMX 123 (commercial flocculent) L^?1 before being reintroduced into the CCAP. The CCAP including the treatment of attrition wastewater (ATW) by flocculation achieved a removal of 44 ± 5% As, 26 ± 6% Cr, 24 ± 5% Cu, 49 ± 4% PCP and 45 ± 3% PCDDF. Moreover, the CCAP enabled a significant reduction (78%) in the amount of water required (around 14.5 m³ of water per ton of the 1–4-mm soil fraction). The high removal yields obtained after 15 attrition cycles of the CCAP for PCP and PCDDF and the significant reduction of water consumption confirm that this CCAP can be considered for industrial applications.     

Anoxybacillus sp. SO B1–Immobilized Amberlite XAD-16 for Solid-Phase Preconcentration of Cu(II) and Pb(II) and Their Determinations by Flame Atomic Absorption Spectrometry

A new method for the determination of Cu(II) and Pb(II) by flame atomic absorption spectrometry (FAAS) after preconcentrating on a column containing Anoxybacillus sp. SO B1–immobilized Amberlite XAD-16 was developed. The functional groups of Anoxybacillus sp. SO B1 immobilized on Amberlite XAD-16 were characterized in KBr tablets by Fourier transform infrared (FT-IR) spectrometry. Various parameters such as pH, amount of the adsorbent, eluent type and volume, and flow rate of the sample solution were studied. The optimum pH values of quantitative sorption for Cu(II) and Pb(II) were found to be pH 7.0 and 5.0 and Cu(II) and Pb(II) ions could be quantitatively eluted with 5.0 ml of 1.0 mol L^?1 HCI and 10.0 ml of 0.25 mol L^?1 HNO₃, respectively. Recoveries of Cu(II) and Pb(II) were found to be 100.9 ± 1.57% and 100.3 ± 0.49% (N = 5), the limits of detection of Cu(II) and Pb(II) in the determination by FAAS (3 s, N = 10) were found to be 0.8 and 1.6 μg L^?1, respectively. The proposed enrichment method was applied for metal ion determination from water samples such as two parts of Tigris River water in Diyarbak?r and Elaz??, Lake of Hazar in Elaz??, and tap water in Diyarbak?r. Furthermore, the accuracy of the proposed method was verified by studying the analytical recovery and by analyzing certified reference material (NCS-DC 73350 leaves of poplar).     

Biosorption and Desorption of Lead(II) by Hydrilla verticillata

The potential of nonliving biomass of Hydrilla verticillata to adsorb Pb(II) from an aqueous solution containing very low concentrations of Pb(II) was determined in this study. Effects of shaking time, contact time, biosorbent dosage, pH of the medium, and initial Pb(II) concentration on metal-biosorbent interactions were studied through batch adsorption experiments. Maximum Pb(II) removal was obtained after 2 h of shaking. Adsorption capacity at the equilibrium increased with increasing initial Pb(II) concentration, whereas it decreased with increasing biosorbent dosage. The optimum pH of the biosorption was 4.0. Surface titrations showed that the surface of the biosorbent was positively charged at low pH and negatively charged at pH higher than 3.6. Fourier transform infrared (FT-IR) spectra of the biosorbent confirmed the involvement of hydroxyl and C?O of acylamide functional groups on the biosorbent surface in the Pb(II) binding process. Kinetic and equilibrium data showed that the adsorption process followed the pseudo-second-order kinetic model and both Langmuir and Freundlich isothermal models. The mean adsorption energy showed that the adsorption of Pb(II) was physical in nature. The monolayer adsorption capacity of Pb(II) was 125 mg g^?1. The desorption of Pb(II) from the biosorbent by selected desorbing solutions were HNO₃ > Na₂CO₃ > NaOH > NaNO₃.     

pH effects on growth and lipid accumulation of the biofuel microalgae Nannochloropsis salina and invading organisms

Biofuels derived from non-crop sources, such as microalgae, offer their own advantages and limitations. Despite high growth rates and lipid accumulation, microalgae cultivation still requires more energy than it produces. Furthermore, invading organisms can lower efficiency of algae production. Simple environmental changes might be able to increase algae productivity while minimizing undesired organisms like competitive algae or predatory algae grazers. Microalgae are susceptible to pH changes. In many production systems, pH is kept below 8 by CO₂ addition. Here, we uncouple the effects of pH and CO₂ input, by using chemical pH buffers and investigate how pH influences Nannochloropsis salina growth and lipid accumulation as well as invading organisms. We used a wide range of pH levels (5, 6, 7, 8, 9, and 10). N. salina showed highest growth rates at pH 8 and 9 (0.19?±?0.008 and 0.19?±?0.011, respectively; mean ± SD). Maximum cell densities in these treatments were reached around 21 days into the experiment (95.6?×?10⁶?±?9?×?10⁶ cells mL^?1 for pH 8 and 92.8?×?10⁶?±?24?×?10⁶ cells mL^?1 for pH 9). Lipid accumulation of unbuffered controls were 21.8?±?5.8 % fatty acid methyl esters content by mass, and we were unable to trigger additional significant lipid accumulation by manipulating pH levels at the beginning of stationary phase. Ciliates (grazing predators) occurred in significant higher densities at pH 6 (56.9?±?39.6?×?10⁴ organisms mL^?1) than higher pH treatments (0.1–6.8?×?10⁴ organisms mL^?1). Furthermore, the addition of buffers themselves seemed to negatively impact diatoms (algal competitors). They were more abundant in an unbuffered control (12.7?±?5.1?×?10⁴ organisms mL^?1) than any of the pH treatments (3.6–4.7?×?10⁴ organisms mL^?1). In general, pH values of 8 to 9 might be most conducive to increasing algae production and minimizing invading organisms. CO₂ addition seems more valuable to algae as an inorganic carbon source and not as an essential mechanism to reduce pH.     

Cardiolipin modulates allosterically the nitrite reductase activity of horse heart cytochrome c

Upon cardiolipin (CL) liposomes binding, horse heart cytochrome c (cytc) changes its tertiary structure disrupting the heme-Fe-Met80 distal bond, reduces drastically the midpoint potential, binds CO and NO with high affinity, displays peroxidase activity, and facilitates peroxynitrite isomerization. Here, the effect of CL liposomes on the nitrite reductase activity of ferrous cytc (cytc-Fe(II)) is reported. In the absence of CL liposomes, hexa-coordinated cytc-Fe(II) displays a very low value of the apparent second-order rate constant for the NO₂ ^?-mediated conversion of cytc-Fe(II) to cytc-Fe(II)-NO (k _on = (7.3 ± 0.7) × 10^?2 M^?1 s^?1; at pH 7.4 and 20.0 °C). However, CL liposomes facilitate the NO₂ ^?-mediated nitrosylation of cytc-Fe(II) in a dose-dependent manner inducing the penta-coordination of the heme-Fe(II) atom. The value of k _on for the NO₂ ^?-mediated conversion of CL-cytc-Fe(II) to CL-cytc-Fe(II)-NO is 2.6 ± 0.3 M^?1 s^?1 (at pH 7.4 and 20.0 °C). Values of the apparent dissociation equilibrium constant for CL liposomes binding to cytc-Fe(II) are (2.2 ± 0.2) × 10^?6 M, (1.8 ± 0.2) × 10^?6 M, and (1.4 ± 0.2) × 10^?6 M at pH 6.5, 7.4, and 8.1, respectively, and 20.0 °C. These results suggest that the NO₂ ^?-mediated conversion of CL-cytc-Fe(II) to CL-cytc-Fe(II)-NO could play anti-apoptotic effects impairing lipid peroxidation and therefore the initiation of the cell death program by the release of pro-apoptotic factors (including cytc) in the cytoplasm.     

An evaluation of phycoremediation potential of cyanobacterium Nostoc muscorum: characterization of heavy metal removal efficiency

The present study relates to the use of cyanobacterium Nostoc muscorum as a model system for removal of heavy metals such as Pb and Cd from aquatic systems. The effects of various physicochemical factors on the surface binding and intracellular uptake of Pb and Cd were studied to optimize the metal removal efficiency of the living cells of N. muscorum. Results demonstrated that a significant proportion of Pb and Cd removal was mediated by surface binding of metals (85 % Pb and 79 % Cd), rather than by intracellular accumulation (5 % Pb and 4 % Cd) at the optimum level of cyanobacterial biomass (2.8 g L^?1), metal concentration (80 μg mL^?1), pH (pH 5.0–6.0), time (15–30 min), and temperature (30–40 °C). N. muscorum has maximum amounts of metal removal (q _max) capacity of 833 and 666.7 mg g^?1 protein for Pb and Cd, respectively. The kinetic parameters of metal binding revealed that adsorption of Pb and Cd by N. muscorum followed pseudo-second-order kinetics, and the adsorption behavior was better explained by both Langmuir and Freundlich isotherm models. The surface binding of both the metals was apparently facilitated by the carboxylic, hydroxyl, and amino groups as evident from Fourier transform infrared spectra.     

The nitrite reductase activity of horse heart carboxymethylated-cytochrome <Emphasis Type="Italic">c</Emphasis> is modulated by cardiolipin

Horse heart carboxymethylated cytc (CM-cytc) displays myoglobin-like properties. Here, the effect of cardiolipin (CL) liposomes on the nitrite reductase activity of ferrous CM-cytc [CM-cytc-Fe(II)], in the presence of sodium dithionite, is reported between pH 5.5 and 7.6, at 20.0 °C. Cytc-Fe(II) displays a very low value of the apparent second-order rate constant for the NO₂ ^?-mediated conversion of cytc-Fe(II) to cytc-Fe(II)-NO [k _on = (7.3 ± 0.7) × 10^?2 M^?1 s^?1; at pH 7.4], whereas the value of k _on for NO₂ ^? reduction by CM-cytc-Fe(II) is 1.1 ± 0.2 M^?1 s^?1 (at pH 7.4). CL facilitates the NO₂ ^?-mediated nitrosylation of CM-cytc-Fe(II) in a dose-dependent manner, the value of k _on for the NO₂ ^?-mediated conversion of CL–CM-cytc-Fe(II) to CL–CM-cytc-Fe(II)-NO (5.6 ± 0.6 M^?1 s^?1; at pH 7.4) being slightly higher than that for the NO₂ ^?-mediated conversion of CL–cytc-Fe(II) to CL–cytc-Fe(II)-NO (2.6 ± 0.3 M^?1 s^?1; at pH 7.4). The apparent affinity of CL for CM-cytc-Fe(II) is essentially pH independent, the average value of B being (1.3 ± 0.3) × 10^?6 M. In the absence and presence of CL liposomes, the nitrite reductase activity of CM-cytc-Fe(II) increases linearly on lowering pH and the values of the slope of the linear fittings of Log k _on versus pH are ?1.05 ± 0.07 and ?1.03 ± 0.03, respectively, reflecting the involvement of one proton for the formation of the transient ferric form, NO, and OH^?. These results indicate that Met80 carboxymethylation and CL binding cooperate in the stabilization of the highly reactive heme-Fe atom of CL–CM-cytc.     

Biological evaluations of newly-designed Pt(II) and Pd(II) complexes using spectroscopic and molecular docking approaches

To perform biological evaluations of newly-designed Pt(II) and Pd(II) complexes, the present study was conducted with targeted protein human serum albumin (HSA) and HCT116 cell line as model of human colorectal carcinoma. The binding of Pt(II) and Pd(II) complexes to HSA was analyzed using fluorescence spectroscopy and molecular docking. The thermal stability and alterations in the secondary structure of HSA in the presence of Pt(II) and Pd(II) complexes were investigated using the thermal denaturation method and circular dichroism (CD) spectroscopy. The cytotoxicity of the Pt(II) and Pd(II) complexes was studied against the HCT116 cell line using MTT assay. The binding analysis revealed that the fluorescence findings were well in agreement with docking results such that there is only one binding site for each complex on HSA. Binding constants of 8.7?×?10³ M^?1, 2.65?×?10³ M^?1, 0.3?×?10³ M^?1, and 4.4?×?10³ M^?1 were determined for Pd(II) and Pt(II) complexes (I–IV) at temperature of 25?°C, respectively. Also, binding constants of 1.9?×?10³ M^?1, 15.17?×?10³ M^?1, 1.9?×?10³ M^?1, and 13.1?×?10³ M^?1 were determined for Pd(II) and Pt(II) complexes (I–IV) at temperature of 37?°C, respectively. The results of CD and thermal denaturation showed that the molecular structure of HSA affected by interaction with Pt(II) and Pd(II) complexes is stable. Cytotoxicity studies represented the growth suppression effect of the Pt(II) and Pd(II) complexes toward the human colorectal carcinoma cell line. Therefore, the results suggest that the new designed Pt(II) and Pd(II) complexes are well promising candidates for use in cancer treatment, particularly for human colorectal cancer.

Communicated by Ramaswamy H. Sarma     

Design of hybrid PVA–CA–Jania rubens biomatrix for removal of lead

Polyvinyl alcohol–sodium alginate (PVA–SA) matrix was fabricated and red algae Jania rubens was embedded for removal of lead from aqueous solutions. The Pb(II) uptake rate was rapid primarily at 1 h and equilibrium was achieved within 2 h. The optimum pH was 5, the data were well fitted by Langmuir and Freundlich models, and R_L values are in the range of 0.1–0.38. The sorption capacity (q_e) of PVA–calcium alginate (CA)–J. rubens matrix increased from 10.77 to 37.195 mg g^?1 with increasing Pb(II) concentration from 24.86 to 98.75 mg L^?1 at the temperature of 30°C and pH 5. The sorption capacity (q_e) and maximum biosorption (q_m) were noted as 37.179 ± 0.32 and 71.43 mg/g, respectively. The adsorption process was well described by pseudo-second-order model. The reaction is endothermic, is spontaneous, and increases in randomness. The functional groups present on matrix, i.e., –OH, –C–N, –C–O,–CO–NH, –NH₂, –SH, and –C–OH, were intensely involved in the process. Scanning electron microscopy results revealed the morphological changes due to adsorption of Pb(II) on and inside of PVA–CA–J. rubens matrix. Desorption study indicates the efficient regeneration of PVA–CA–J. rubens biomass matrix for three cycles and is a promising matrix for removal of Pb(II) and can be used in continuous systems.     

Atmospheric methane removal by methane-oxidizing bacteria immobilized on porous building materials

Biological treatment using methane-oxidizing bacteria (MOB) immobilized on six porous carrier materials have been used to mitigate methane emission. Experiments were performed with different MOB inoculated in building materials at high (~20 % (v/v)) and low (~100 ppmv) methane mixing ratios. Methylocystis parvus in autoclaved aerated concrete (AAC) exhibited the highest methane removal rate at high (28.5?±?3.8 μg CH₄ g^?1 building material h^?1) and low (1.7?±?0.4 μg CH₄ g^?1 building material h^?1) methane mixing ratio. Due to the higher volume of pores with diameter >5 μm compared to other materials tested, AAC was able to adsorb more bacteria which might explain for the higher methane removal observed. The total methane and carbon dioxide-carbon in the headspace was decreased for 65.2?±?10.9 % when M. parvus in Ytong was incubated for 100 h. This study showed that immobilized MOB on building materials could be used to remove methane from the air and also act as carbon sink.     

Effect of Potassium and Nitrogen Fertilizer on Switchgrass Productivity and Nutrient Removal Rates under Two Harvest Systems on a Low Potassium Soil

Biomass demand for energy will lead to utilization of marginal, low fertility soil. Application of fertilizer to such soil may increase switchgrass (Panicum virgatum L.) biomass production. In this three-way factorial field experiment, biomass yield response to potassium (K) fertilizer (0 and 68 kg?K?ha^?1) on nitrogen (N)-sufficient and N-deficient switchgrass (0 and 135 kg?N?ha^?1) was evaluated under two harvest systems. Harvest system included harvesting once per year after frost (December) and twice per year in summer (July) at boot stage and subsequent regrowth after frost. Under the one-cut system, there was no response to N or K only (13.4 Mg?ha^?1) compared to no fertilizer (12.4 Mg?ha^?1). Switchgrass receiving both N and K (14.6 Mg?ha^?1) produced 18 % greater dry matter (DM) yield compared to no fertilizer check. Under the two-cut harvest system, N only (16.0 Mg?ha^?1) or K only (14.1 Mg?ha^?1) fertilizer produced similar DM to no fertilizer (15.1 Mg?ha^?1). Switchgrass receiving both N and K in the two-cut system (19.2 Mg?ha^?1) produced the greatest (P?<?0.05) DM yield, which was 32 % greater than switchgrass receiving both N and K in the one-cut system. Nutrient removal (biomass?×?nutrient concentration) was greatest in plots receiving both N and K, and the two-cut system had greater nutrient removal than the one-cut system. Based on these results, harvesting only once during winter months reduces nutrient removal in harvested biomass and requires less inorganic fertilizer for sustained yields from year to year compared to two-cut system.     

Mathematical modeling and analysis of the flocculation process in chambers in series

In this study, the flocculation process in continuous systems with chambers in series was analyzed using the classical kinetic model of aggregation and break-up proposed by Argaman and Kaufman, which incorporates two main parameters: K _a and K _b. Typical values for these parameters were used, i. e., K _a = 3.68 × 10^?5–1.83 × 10^?4 and K _b = 1.83 × 10^?7–2.30 × 10^?7 s^?1. The analysis consisted of performing simulations of system behavior under different operating conditions, including variations in the number of chambers used and the utilization of fixed or scaled velocity gradients in the units. The response variable analyzed in all simulations was the total retention time necessary to achieve a given flocculation efficiency, which was determined by means of conventional solution methods of nonlinear algebraic equations, corresponding to the material balances on the system. Values for the number of chambers ranging from 1 to 5, velocity gradients of 20–60 s^?1 and flocculation efficiencies of 50–90 % were adopted.     

Modeling of Pb(II) adsorption by a fixed-bed column

Removal of Pb(II) from an aqueous environment using biosorbents is a cost-effective and environmentally benign method. The biosorption process, however, is little understood for biosorbents prepared from plant materials. In this study, the biosorption process was investigated by evaluating four adsorption models. A fixed-bed column was prepared using a biosorbent prepared from the aquatic plant Hydrilla verticillata. The effect of bed height and flow rate on the biosorption process was investigated. The objective of the study was to determine the ability of H. verticillata to biosorb Pb(II) from an aqueous environment and to understand the process, through modeling, to provide a basis to develop a practical biosorbent column. Experimental breakthrough curves for biosorption of 50 mg L^?1 aqueous Pb(II) using a fixed-bed column with 1.00 cm inner diameter were fitted to the Thomas, Adams-Bohart, Belter, and bed depth service time (BDST) models to investigate the behavior of each model according to the adsorption system and thus understand the adsorption mechanism. Model parameters were evaluated using linear and nonlinear regression methods. The biosorbent removed 65% (82.39 mg g^?1 of biosorbent) of Pb(II) from an aqueous solution of Pb(NO₃)₂ at a flow rate of 5.0 ml min^?1 in a 10 cm column. Na₂CO₃ was used to recover the adsorbed Pb(II) ions as PbCO₃ from the biosorbent. The Pb(II) was completely desorbed at a bed height of 10.0 cm and a flow rate of 5.0 ml min^?1. Fourier transform infrared (FT-IR) analysis of the native biosorbent and Pb(II)-loaded biosorbent indicated that the hydroxyl groups and carboxylic acid groups were involved in the metal bonding process. The FT-IR spectrum of Pb(II)-desorbed biosorbent showed an intermediate peak shift, indicating that Pb(II) ions were replaced by Na⁺ ions through an ion-exchange process. Of the four models tested, the Thomas and BDST models showed good agreement with experimental data. The calculated bed sorption capacity N₀ and rate constant k_a were 31.7 g L^?1 and 13.6 × 10^?4 L mg^?1 min^?1 for the C_t/C₀ value of 0.02. The BDST model can be used to estimate the column parameters to design a large-scale column.     

Elicitor mediated enhancement of wedelolactone in cell suspension culture of <Emphasis Type="Italic">Eclipta alba</Emphasis> (L.) Hassk

The present research focused on enhancing the production of wedelolactone through cell suspension culture (CSC) in Eclipta alba (L.) Hassk. With an aim of attaining a sustainable CSC, various plant growth regulators, elicitors and agitation speed were examined. Nodal segments of in vitro propagated plantlets induced the maximum percentage (93.47?±?0.61%) of callus inoculated on Murashige and Skoog (MS) medium fortified with picloram (2 mg L^?1). The growth kinetics of CSC exhibited a sigmoid pattern with a lag phase (0–6 days), a log phase (6–18 days), a stationary phase (18–24 days) and then death phase thereafter. The highest biomass accumulation in CSC with 7.09?±?0.06 g 50 mL^?1 fresh weight, 1.52?±?0.02 g 50 mL^?1 dry cell weight, 1.34?±?0.01?×?10⁶ cell mL^?1 total cell count and 57.00?±?0.58% packed cell volume was obtained in the liquid MS medium supplemented with 1.5 mg L^?1 picloram plus 0.5 mg L^?1 kinetin at 120 rpm. High performance thin layer chromatography confirmed that yeast extract (biotic elicitor) at 150 mg L^?1 accumulated more CSC biomass with 1.22-fold increase in wedelolactone (288.97?±?1.94 µg g^?1 dry weight) content in comparison to the non-elicited CSC (237.78?±?0.04 µg g^?1 dry weight) after 120 h of incubation. Contrastingly, methyl jasmonate (abiotic elicitor) did not alter the biomass but increased the wedelolactone content (259.32?±?1.06 µg g^?1 dry weight) to an extent of 1.09-fold at 100 µM. Complete plantlet regeneration from CSC was possible on MS medium containing N⁶-benzyladenine (0.75 mg L^?1) and abscisic acid (0.5 mg L^?1). Thus, the establishment of protocol for CSC constitutes the bases for future biotechnological improvement studies in this crop.     

Growth and phosphorus removal by <Emphasis Type="Italic">Synechococcus elongatus</Emphasis> co-immobilized in alginate beads with <Emphasis Type="Italic">Azospirillum brasilense</Emphasis>

This study examined the co-immobilization of the cyanobacterium Synechococcus elongatus with the plant growth-promoting bacterium Azospirillum brasilense in alginate beads and its potential application for the removal of phosphorus from aquaculture wastewater. Co-immobilization of both microorganisms significantly increased the cell density of S. elongatus (2852.5?×?10⁴ cells mL^?1) compared with that of immobilization of cyanobacteria alone (1325.2?×?10⁴ cells mL^?1). Chlorophyll a content was similar in co-immobilized (11.1?±?3.5 pg cell^?1) and immobilized S. elongatus (14.5?±?4.9 pg cell^?1). Azospirillum brasilense showed continuous growth until day 2, after which its cell concentration declined until the end of the assay. Co-immobilized S. elongatus removed more phosphorus (44.8 %) than immobilized cyanobacteria cells alone (32.0 %). In conclusion, phosphate removal was greater with free cells of S. elongatus but overlapped with the values that were obtained with the treatment of co-immobilization of cells. Our results demonstrate that A. brasilense enhances the growth of S. elongatus and improves its removal of phosphorus when they are co-immobilized in alginate beads compared with only immobilization of cyanobacteria cells alone.     

Degradation of cationic surfactants using Pseudomonas putida A ATCC 12633 immobilized in calcium alginate beads

In this study, the degradation of tetradecyltrimethylammonium bromide (TTAB) by freely suspended and alginate-entrapped cells from the bacteria Pseudomonas putida (P. putida) A ATCC 12633 was investigated in batch cultures. The optimal conditions to prepare beads for achieving a higher TTAB degradation rate were investigated by changing the concentration of sodium alginate, pH, temperature, agitation rate and initial concentration of TTAB. The results show that the optimal embedding conditions of calcium alginate beads are 4 % w/v of sodium alginate content and 2 × 10⁸ cfu ml^?1 of P. putida A ATCC 12633 cells that had been previously grown in rich medium. The optimal degradation process was carried out in pH 7.4 buffered medium at 30 °C on a rotary shaker at 100 rpm. After 48 h of incubation, the free cells degraded 26 mg l^?1 of TTAB from an initial concentration of 50 mg l^?1 TTAB. When the initial TTAB concentration was increased to 100 mg l^?1, the free cells lost their degrading activity and were no longer viable. In contrast, when the cells were immobilized on alginate, they degraded 75 % of the TTAB after 24 h of incubation from an initial concentration of 330 mg l^?1 of TTAB. The immobilized cells can be stored at 4 °C for 25 days without loss of viability and can be reused without losing degrading capacity for three cycles.     

Lead removal by Spirulina platensis biomass

In this investigation, we report on the biosorption of Pb (II) from aqueous solutions by the nonliving biomass of the micro-alga (cyanobacterium) Spirulina platensis. Propagation of the micro-alga was carried out in outside oblong raceway ponds. The biomass was cleaned, dried and used for the investigation. The effects of pH, adsorbent dose, temperature, initial concentration of Pb (II), and contact time on the adsorption of lead by the dry biomass were studied. The experiments were carried out in 250 ml conical flasks containing 100 ml of test solutions using an orbital incubator at 150 rpm. Concentrations of the metal before and after the experiments were measured using Atomic Absorption Spectrophotometer. Very high levels of Pb (II) removal (>91%) were obtained. The optimum conditions for maximal adsorption by S. platensis were found to be pH 3; 2 g of adsorbent dose; incubation at 26°C; 100 mg/l of lead initial concentration and 60 minutes of contact time. The experimental data fitted well with Freundlich isotherm equation with R² values greater than 0.97. Based on our results, we recommend the utilization of S. platensis biomass for heavy metal removal from aqueous solutions.