Application of seaweeds for the removal of lead from aqueous solution

Ten different seaweed species were compared on the basis of lead uptake at different pH conditions. The brown seaweed, Turbinaria conoides, exhibited maximum lead uptake (at pH 4.5) and hence was selected for further studies. Sorption isotherms, obtained at different pH (4–5) and temperature (25–35 °C) conditions were fitted using Langmuir and Sips models. According to the Langmuir model, the maximum lead uptake of 439.4 mg/g was obtained at optimum pH (4.5) and temperature (30 °C). The Sips model better described the sorption isotherms with high correlation coefficients at all conditions examined. Various thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated indicating that the present system was a spontaneous and endothermic process. Through potentiometric titrations, number of binding sites (carboxyl groups) and pK₁ were determined as 4.1 mmol/g and 4.4, respectively. The influence of co-ions (Na⁺, K⁺, Mg²⁺ and Ca²⁺) on lead uptake was well pronounced in the case of divalent ions compared to monovalent ions. The solution of 0.1 M HCl successfully eluted all lead ions from lead-loaded T. conoides biomass. The regeneration experiments revealed that the alga could be successfully reused for five cycles without any loss in lead biosorption capacity. A glass column (2 cm i.d. and 35 cm height) was used to study the continuous lead biosorption performance of T. conoides. At 25 cm (bed height), 5 ml/min (flow rate) and 100 mg/l (initial lead concentration), T. conoides exhibited lead uptake of 220.1 mg/g. The column was successfully eluted using 0.1 M HCl, with elution efficiency of 99.7%.     

Modeling studies on mono and binary component biosorption of phenol and cyanide from aqueous solution onto activated carbon derived from saw dust

Biosorption is an effective treatment method for the removal of phenol and cyanide from aqueous solution by saw dust activated carbon (SDAC). Batch experiments were achieved as a function of several experimental parameters, i.e. influence of biosorbent dose (5–60 g/L) contact time (2–40 h), pH (4–12), initial phenol concentration (100–1000 mg/L) and initial cyanide concentration (10–100 mg/L) and temperature (20–40 °C). The biosorption capacities of the biosorbent were detected as 178.85 mg/g for phenol with 300 mg/L of initial concentration and 0.82 mg/g for cyanide with 30 mg/L of initial concentration. The optimum pH is found to be 8 for phenol and 9 for cyanide biosorption. The mono component biosorption equilibrium data for both phenol and cyanide were well defined by Redlich–Peterson model and binary component adsorption equilibrium data well fitted by extended Freundlich model. The percentage removal of phenol and cyanide using SDAC was 66.67% and 73.33%, respectively. Equilibrium established within 30 h for phenol and 28 h for cyanide. Kinetic studies revealed that biosorption of phenol followed pseudo second order indicating adsorption through chemisorption and cyanide followed pseudo first order kinetic model indicating adsorption through physisorption. Thermodynamic studies parameters, i.e., enthalpy (Δh₀), entropy (ΔS₀) and Gibb’s free energy (ΔG₀) have also been considered for the system. Thermodynamic modeling studies revealed that the process of cyanide biosorption was endothermic and phenol biosorption was exothermic in nature.     

Hexavalent chromium removal from aqueous solution by adsorption on treated sawdust

The studies on adsorption of hexavalent chromium were conducted by varying various parameters such as contact time, pH, amount of adsorbent, concentration of adsorbate and temperature. The kinetics of adsorption of Cr(VI) ion followed pseudo second order. Langmuir adsorption isotherm was employed in order to evaluate the optimum adsorption capacity of the adsorbent. The adsorption capacity was found to be pH dependant. Sawdust was found to be very effective and reached equilibrium in 3 h (adsorbate concentration 30 mg l⁻¹). The rate constant has been calculated at 303, 308, 313 and 318 K and the activation energy (E_a) was calculated using the Arrhenius equation. Thermodynamic parameters such as standard Gibbs energy (ΔG°) and heat of adsorption (ΔH_r) were calculated. The ΔG° and ΔH_r values for Cr(VI) adsorption on the sawdust showed the process to be exothermic in nature. The percentage of adsorption increased with decrease in pH and showed maximum removal of Cr(VI) in the pH range 4.5–6.5 for an initial concentration of 5 mg l⁻¹.     

A comparative performance evaluation of jute and eggshell matrices to immobilize pancreatic lipase

A pancreatic lipase was immobilized on readily available and inexpensive jute and eggshell matrices. The purity of extracted enzyme was confirmed by SDS-PAGE. The maximum protein load for eggshell was 10.23 mg/g, and for jute, it was 5.7 mg/g. The free enzyme activity retention was greater than 80% for eggshell and 43% for jute. The immobilized lipase was stable over a pH range from 7 to 8 for eggshell and 7.5 to 8.5 for jute with over a temperature range from 25 to 45 °C for eggshell and 37 to 40 °C for the jute. FTIR data indicated new bonds on the jute upon immobilization. Although no new bond was observed, immobilization data on eggshell fit well with the Langmuir adsorption isotherm model. The model constants, Γ_max and K_l, were 13.92 mg/g and 0.382 mL/mg, respectively. Mixed adsorption with both ionic and hydrophobic interactions was observed. Lipase adsorption was reduced significantly in presence of Tween 80, whereas the effect was less in case of ionic strength, pH and temperature. For both matrices, scanning electron microscopy (SEM) was used to demonstrate the changes in surface morphology after immobilization. The performance of eggshell was better than that of jute as a matrix for immobilizing pancreatic lipase.     

Biosorption kinetics and isotherm studies of Acid Red 57 by dried Cephalosporium aphidicola cells from aqueous solutions

Equilibrium, kinetics and thermodynamic studies on the removal of Acid Red 57 (AR57) by biosorption onto dried Cephalosporium aphidicola (C. aphidicola) cells have been investigated in a batch system with respect to pH, contact time and temperature. The results showed that the equilibrium time was attained within 40 min and the maximum biosorption capacity of AR57 dye onto C. aphidicola cells was 2.08 × 10⁻⁴ mol g⁻¹ or 109.41 mg g⁻¹ obtained after contact with 0.4 g dm⁻³ biosorbent concentration, pH₀ of 1 and at a temperature of 20 °C. The pseudo-second-order kinetic model was observed to provide the best correlation of the experimental data among the kinetic models studied. Biosorption isotherm models were developed and the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were conformed well to the experimental data. The changes of free energy, enthalpy and entropy of biosorption were also evaluated for the biosorption of AR57 dye onto C. aphidicola cells.     

Thermodynamic and kinetic studies for environmentaly friendly Ni(II) biosorption using waste pomace of olive oil factory

The objective of this study is to assess the environmentaly friendly Ni(II) adsorption from synthetic wastewater using waste pomace of olive oil factory (WPOOF). Batch kinetic studies were performed in order to investigate the adsorbent and adsorbate dose, solution pH, agitating speed and temperature. The maximum Ni(II) adsorption was obtained at pH 4.0. The equilibrium nature of Ni(II) adsorption at different temperature was described by the Freundlich, Langmuir and Temkin isotherms. The equilibrium data fit well the Temkin and Langmuir isotherm. The monolayer adsorption capacities of WPOOF as obtained from Langmuir isotherm at 60 °C was found to be 14.80 mg/g. The adsorption mechanism was examined by the FTIR technique. The results of the thermodynamic investigations indicated that the adsorption reactions were spontaneous (ΔG < 0), slightly endothermic (ΔH > 0) and irreversible (ΔS > 0). The pseudo first-order, pseudo second-order, Elovich and intraparticle diffusion kinetic models were used to describe the kinetic data.     

Start-up performance and granular sludge features of an improved external circulating anaerobic reactor for algae-laden water treatment

The microbial characteristics of granular sludge during the rapid start of an enhanced external circulating anaerobic reactor were studied to improve algae-laden water treatment efficiency. Results showed that algae laden water was effectively removed after about 35 d, and the removal rates of chemical oxygen demand (COD) and algal toxin were around 85% and 92%, respectively. Simultaneously, the gas generation rate was around 380 mL/gCOD. The microbial community structure in the granular sludge of the reactor was complicated, and dominated by coccus and filamentous bacteria. Methanosphaera, Methanolinea, Thermogymnomonas, Methanoregula, Methanomethylovorans, and Methanosaeta were the major microorganisms in the granular sludge. The activities of protease and coenzyme F₄₂₀ were high in the granular sludge. The intermittent stirring device and the reverse-flow system were further found to overcome the disadvantage of the floating and crusting of cyanobacteria inside the reactor. Meanwhile, the effect of mass transfer inside the reactor can be accelerated to help give the reactor a rapid start.     

Effects of physico-chemical factors on the viscosity evolution of anaerobic granular sludge

The rheological properties of anaerobic granular sludge samples from four full-scale and one lab-scale anaerobic bioreactors were characterized by determining their “limit viscosity” values. These values were deducted from the evolution of the apparent viscosity of granular sludge samples (20 mL) at steady shear rate (200 s⁻¹) recorded using rotation tests with a wings type measurement cell stirrer Anton-Parr reference: ST24-1D/2V-Q0. The limit viscosity values depended on the applied shear rate, indicating a non-Newtonian behavior of the anaerobic granular sludge types investigated. The effect of variations of physico-chemical parameters such as pH (involving surface charge change), size, surface roughness and TSS content on the evolution of the limit viscosity of an anaerobic granular sludge suspension was investigated. This showed the importance of both quantitative (number of particles in a given volume) as well as qualitative (surface charge or shape) granule-granule interactions on this rheological parameter. Moreover, the origin of the granular sludge strongly influenced the limit viscosity value according with different granules characteristics. This work confirms the ability of the rheological parameter “limit viscosity” as an overall parameter to describe the physico-chemical characteristics (TSS, granulometry, origin, and charge) of anaerobic granular sludge and showed this holds for both sieved (500 μm) and unsieved sludges.     

Distribution of anammox bacteria in domestic WWTPs and their enrichments evaluated by real-time quantitative PCR

Enrichment of anaerobic ammonium oxidation (anammox) bacteria using five activated sludges in three domestic wastewater treatment plants (WWTPs) were processed in a short term of 70 days and evaluated by real-time quantitative PCR (RTQ-PCR). Before the enrichment, building phylogenetic trees of Planctomycetes phylum in four reactors of sequencing batch reactor (SBR), anoxic and oxic reactors of anaerobic–anoxic–oxic (A2O) process, and rotating biological contactor (RBC) revealed six groups of distantly relative genera of Planctomyces, Pirellula, Gemmata, Isophaera, Candidatus and putative anammox bacteria. All clones of Candidatus sp. were affiliated with anammox bacteria and the majority of anammox clones were related to Planctomycete KSU-1 (AB057453). The discovery of anammox bacteria in raw activated sludges provided a partial rationale for the utilization of activated sludge as a seeding source of the anammox process. To verify the activity of anammox bacteria in the activated sludges, enrichment cultivations were conducted using SBRs. The enrichment of anammox bacteria resulted in the significant anammox activity of three samples. Quantification of 16S rRNA gene of anammox bacteria using RTQ-PCR showed the highest concentration of anammox bacteria of 2.48 ± 0.22 × 10⁹ copies of 16S rRNA gene/mg-volatile suspended solids (VSS), which was the same order of magnitude as that of the referential granular anammox sludge, 6.23 ± 0.59 × 10⁹ copies of 16S rRNA gene/mg-VSS, taken from an anammox upflow anaerobic sludge blanket (UASB) reactor. The doubling time of anammox bacteria enriched in this study was 1.18 days. The growth yield of anammox bacteria enriched in this study was 4.75 ± 0.57 × 10⁶ copies of 16S rRNA gene/mg of ammonium- and nitrite-nitrogen, which was similar to 4.50 ± 0.61 × 10⁶ copies of 16S rRNA gene/mg of ammonium- and nitrite-nitrogen for the referential anammox sludge. Substrate uptake rates of three successful enrichments at the end of the enrichment were comparable to those of granular and suspended anammox sludges. Rapid enrichment of anammox bacteria using activated sludge could offer an alternative method for obtaining a large volume of seeding anammox sludge.     

Structural analysis and molecular modeling of the RvH2-e functional unit of Rapana venosa hemocyanin

Rapana venosa hemocyanin (RvH), a circulating glycoprotein of the marine snail, has a complex structure. To provide details on the stability of the protein, one functional unit, RvH2-e, was compared with the native molecule and the structural subunits, RvH1 and RvH2, via pH–T diagrams, typical phase portraits for stability and denaturation reversibility. By analyzing the T transition curves of RvH2-e at different pH values, several parameters of the thermodynamic functions were obtained. Increasing the temperature from 25 °C to 55 °C, the reversibility of the molecule of protein also increases, opening a reversibility window within the range of pH 4.0–8.0. On analyzing the pH transition curves, the start of the acid denaturation (below pH 6) and alkaline denaturation (above pH 9) was determined to be between 20 °C and 35 °C. For this range, the thermodynamic functions ΔH° and ΔG° for a standard temperature of 25 °C were calculated.     

Characterization of aerobic granular sludge at various organic loading rates

Aerobic granular sludge was cultivated from activated sludge with two types of supports, namely bivalve shell carrier (BSC) and anaerobic granules (ANG). Granules were characterized at different organic loading rates (OLRs) ranging from 2.5 to 15 kg COD/m³ d and these granules were observed to withstand high OLRs. The physico-chemical characteristics of the aerobic granules were better than those of seed sludge. The granule formation with ANG support was found to be similar to that of non-support cultivation, i.e. formation from activated sludge only. By contrast, BSC support showed better performance in terms of faster settleability, compactness and especially resistance against organic shock loading. It also enabled self-cleaning effect by removing biofilm attached on the reactor wall during the start-up phase resulting rapid granulation process.     

Biosorption of Fe3+ from aqueous solution by a bacterial dead Streptomyces rimosus biomass

The iron biosorption capacity of a Streptomyces rimosus biomass treated with NaOH was studied in batch mode. After pretreatment of biomass at the ambient temperature, optimum conditions of biosorption were found to be: a biomass particle size between 50 and 160 μm, an average saturation contact time of 4 h, a biomass concentration of 3 g/l and a stirring speed of 250 rpm. The equilibrium data could be fitted by Langmuir isotherm equation. Under these optimal conditions, 122 mg _Fe/g_biomass were fixed.     

The Molten Globule of β2-Microglobulin Accumulated at pH 4 and Its Role in Protein Folding

The acid transition of β₂-microglobulin (β2m) was studied by tryptophan fluorescence, peptide circular dichroism, and NMR spectroscopy. The protein exhibits a three-state transition with an equilibrium intermediate accumulated at pH 4 (25 °C). The pH 4 intermediate has typical characteristics of the molten globule (MG) state; it showed a native-like secondary structure without specific side-chain tertiary structure, and the hydrodynamic radius determined by pulse field gradient NMR was only 20% larger than that of the native state. The accumulation of the pH 4 intermediate is very analogous to the behavior of apomyoglobin, for which the pH 4 MG has been well characterized, although β2m, a β-protein, is structurally very different from α-helical apomyoglobin. NMR pH titration of histidine residues of β2m has also indicated that His84 has an abnormally low pK_a value in the native state. From the pH dependence of the unfolding transition, the protonations of this histidine and 10 weakly abnormal carboxylates triggered the transition from the native to the MG state. This behavior is again analogous to that of apomyoglobin, suggesting a common mechanism of production of the pH 4 MG. In contrast to the folding of apomyoglobin, in which the MG was equivalent to the burst-phase kinetic folding intermediate, the burst-phase refolding intermediate of β2m, detected by stopped-flow circular dichroism, was significantly more structured than the pH 4 intermediate. It is proposed that the folding of β2m from its acid-denatured state takes place in the following order: denatured state → MG → burst-phase intermediate → native state.     

Use of hydrophobic bacterium Rhodococcus rhodochrous NBRC15564 expressed thermophilic alcohol dehydrogenases as whole-cell catalyst in solvent-free organic media

The hydrophobic bacterium Rhodococcus rhodochrous NBRC15564 was employed as a whole-cell biocatalyst to examine its potential for bioconversion in solvent-free organic media. The genes encoding two different thermostable alcohol dehydrogenases (ADH_Tt1 and ADH_Tt2) of Thermus thermophilus HB27 were expressed in R. rhodochrous cells. To inactivate indigenous mesophilic enzymes in R. rhodochrous, transformant cells were heated at 70 °C for 10 min. Heat-treated hydrophobic wet cells were used for the bioconversion of 2,2,2-trifluoroacetophenone (TFAP) to α-(trifluoromethyl) benzyl alcohol (TFMBA) as a model reaction with ADH_Tt1. NADH, which was supplied in aqueous solution, was regenerated by converting cyclohexanol to cyclohexanone by ADH_Tt2. All reactions were performed by suspending heat-treated cells in solvent-free organic media consisting of 3.7 M TFAP and 4.8 M cyclohexanol (1:1, v/v ratio) at 60 °C. When 800 mg heat-treated R. rhodochrous cells were dispersed in 2 mL of solvent-free organic media (400 mg cells/mL), the product concentration reached about 3.6 M TFMBA by 48 h with a total NADH turnover number of approximately 900. The overall productivity was 190 mol TFMBA/kg cells/h.     

Ethanol-to-methane activity of Geobacter-deprived anaerobic granules enhanced by conductive microparticles

Direct interspecies electron transfer (DIET) has been typically proposed as mechanism of electron transfer among methanogenic populations in granules during anaerobic digestion where Geobacter species play a key role. Using anaerobic granules where Geobacteraceae members were not prevalent − representing only 0.3% of total bacteria −, tests incubated with two co-substrates showed that the rate of methanogenesis from formate and hydrogen diminished in the presence of a non-methanogenic co-substrate such as ethanol. This could indicate that biological DIET occurs and competes with hydrogen and formate during methanogenesis. Moreover, the addition of conductive microparticles, such as stainless steel and granular activated carbon, was found to increase methanogenic activity in disintegrated granules by 190 ± 18% and 175 ± 22% respectively as compared to disintegrated granules devoid of microparticles. The addition of non-conductive microparticles such as porcelain however decreased methanogenic activity by 65 ± 3% of the disrupted granules without microparticle activity. These results indicate that syntrophic bacteria from anaerobic sludge excluding Geobacter species can also carry out conductive mineral mediated DIET.     

Application of dye-ligands affinity adsorbent in capturing of rabbit immunoglobulin G

The applicability of dye-ligands attached to an expanded bed chromatography quartz base matrix (Streamline™) for the affinity bioseparation of rabbit immunoglobulin G (IgG) was investigated. Reactive Green 5 (RG-5) immobilized onto adsorbent was selected for capturing of rabbit-IgG due to its higher binding capacity compared to other dye-ligands possessing similar ligand density. Adsorption parameters such as pH, temperature, ionic strength and initial rabbit-IgG concentration were optimized for the adsorption of rabbit-IgG on the RG-5-immobilized adsorbent. The highest rabbit-IgG adsorption was recorded in pH 7.0, while the maximum binding capacity for BSA was achieved at pH 4.0. The adsorption of rabbit-IgG on RG-5-immobilized adsorbent was declined as the increase of ionic strength. There is no significant influence of temperature against adsorption efficiency of RG-5-immobilized adsorbent for rabbit-IgG. The adsorption phenomenon of rabbit-IgG on RG-5-immobilized adsorbent appeared to follow the Langmuir–Freundlich adsorption isotherm model. The theoretically maximum binding capacity (q_m) of RG-5-immobilized adsorbent estimated from this isotherm was 49.3 mg ml⁻¹, which is very close to that obtained experimentally (49.0 mg ml⁻¹). About 50% of bound BSA on RG-5-immobilized adsorbent in binary adsorption system was removed with washing buffer containing 1 M NaCl.     

Purification,kinetic and thermodynamic characterization of soluble acid invertase from sugarcane (Saccharum officinarum L.)

We report for the first time kinetic and thermodynamic properties of soluble acid invertase (SAI) of sugarcane (Saccharum officinarum L.) salt sensitive local cultivar CP 77-400 (CP-77). The SAI was purified to apparent homogeneity on FPLC system. The crude enzyme was about 13 fold purified and recovery of SAI was 35%. The invertase was monomeric in nature and its native molecular mass on gel filtration and subunit mass on SDS-PAGE was 28 kDa. SAI was highly acidic having an optimum pH lower than 2. The acidic limb was missing. Proton transfer (donation and receiving) during catalysis was controlled by the basic limb having a pKa of 2.4. Carboxyl groups were involved in proton transfer during catalysis. The kinetic constants for sucrose hydrolysis by SAI were determined to be: k_m = 55 mg ml^?1, k_cat = 21 s^?1, k_cat/k_m = 0.38, while the thermodynamic parameters were: ΔH* = 52.6 kJ mol^?1, ΔG* = 71.2 kJ mol^?1, ΔS* = ?57 J mol^?1 K^?1, ΔG*_E–S = 10.8 kJ mol^?1 and ΔG*_E–T = 2.6 kJ mol^?1. The kinetics and thermodynamics of irreversible thermal denaturation at various temperatures 53–63 °C were also determined. The half -life of SAI at 53 and 63 °C was 112 and 10 min, respectively. At 55 °C, surprisingly the half -life increased to twice that at 53 °C. ΔG*, ΔH* and ΔS* of irreversible thermal stability of SAI at 55 °C were 107.7 kJ mol^?1, 276.04 kJ mol^?1 and 513 J mol^?1K^?1, respectively.     

Biosorption of Basic Orange using dried A. filiculoides

In order to understand the biosorption of Basic Organic (BO) textile dye on dried Azolla filiculoides (A. filiculoides), batch experiments were conducted under various conditions. The results show that biosorption of BO on dried A. filiculoides was dependent on the initial solution pH, biosorbent dosage, contact time and the initial BO concentration. Using the Langmuir equation, the biosorption capacity (q_m) for BO was 833 mg/g at 303 K. The kinetic study suggested that the mechanism of biosorption was due to ion-exchange physisorption via the intra-particle diffusion and chemisorption on the external surface of dried A. filiculoides. Different techniques were used to characterize dried A. filiculoides and indicated that the biomass had a high cation exchange capacity (93.6 mmol/100 g), a large specific surface area (80.35–422.89 m²/g) and contained various functional groups which may play an important role in the physisorption and chemisorption of BO on the surface of A. filiculoides. The results showed that the removal ratio of BO reached 79.3% from wastewater containing 100 mg/L BO, indicating that the biomass could be used as a potential biosorbent for the removal of BO from industrial wastewater.     

Anaerobic granule development for removal of pentachlorophenol in an upflow anaerobic sludge blanket (UASB) reactor

The granulation process using synthetic wastewater containing pentachlorophenol (PCP) in four 1.1 l laboratory scale upflow anaerobic sludge blanket (UASB) reactors was studied, and the anaerobic biotransformation of PCP during the granulation process investigated. After 110 days granular sludge was developed and up to 160 and 180 mg/l of PCP was added into the reactors R1 and R2, respectively, when they were inoculated with acclimated anaerobic sludge from an anaerobic digester of a citric acid plant. The inoculum was predominately composed of bacilli and filamentous bacteria. Granulation did not occur in reactors R3 and R4 which were inoculated with acclimated anaerobic sludge from aerobic sludge of the municipal sewage treatment plant which consisted mainly of cocci. Despite similar bacilli in the granule, the filamentous bacteria from reactor R1 were thicker than those of reactor R2. The granular sludge had a maximum diameter of 2.5 and 2.2 mm, and SMA of 1.44 and 1.32 gCOD/gTVS per day for reactors R1 and R2, respectively. Over 98% chemical oxygen demand (COD) removal rate and 99% of PCP removal rate were achieved when reactors R1 and R2 were operated at PCP and COD loading rates of 150 and 7.5 g/l per day, respectively. H₂-producing acetogens were the dominant anaerobes in the granular sludge.