The effect of temperature,pH, and initial glucose concentration on the kinetics of ethanol production by Zymomonas mobilis in batch fermentation

Summary Zymomonas mobilis, strain ATCC 10988, was used to evaluate the effects of pH (5.0 to 8.0), temperature (30°C to 40°C), and initial glucose concentration (75 g/l to 150 g/l) on the kinetics of ethanol production from glucose using batch fermentation. Specific ethanol production rate was maximum and nearly constant over a pH range of 6.0 to 7.5. End-of-batch ethanol yield and specific growth rate were insensitive to pH in the range of 5.0 to 7.5. End-of-batch ethanol yield was maximum and nearly constant between 30°C and 37°C but decreased by 24% between 37°C and 40°C. All other kinetic parameters are greatest at 34°C. End-of-batch ethanol yield is maximum at an initial glucose concentration of 100 g/l. Specific growth rate reaches a maximum at 75 g/l, but specific ethanol production rate decreases throughout the range. The optimum initial glucose concentration of 100 g/l gives the highest ethanol yield at a specific ethanol production rate less than 10% below the maximum observed.     

Production of arachidonic acid byMortierella alpina ATCC 32222

Summary WhenMortierella alpina ATCC 32222 was incubated in a glucose salts medium at 25°C the biomass (17.5 g/l) contained 9.62% arachidonic acid which amounted to 54% (w/w) of total biomass lipids. When the glucose concentration in the medium was varied from 0 to 150 g/l, the percentage of arachidonic acid in biomass and in lipids was highest at a glucose concentration of 30 g/l, but highest yield of arachidonic acid per litre of culture broth was observed at a glucose concentration of 100 g/l. While production of biomass reached a plateau of 17 g/l after a 3-day incubation at 25°C, the percentage of arachidonic acid in lipids and biomass increased dramatically from 3 to 6 days with a concurrent arachidonic acid yield increase from 0.89 to 1.63 g/l. Optimum initial culture pH for arachidonic acid production was in the range 6.0–6.7. By increasing the concentration of the glucose salts medium three-fold, yields of biomass and arachidonic acid were increased to 35.8 g/l and 3.73 g/l, respectively.     

Response surface optimization of the removal of nickel from aqueous solution by cone biomass of Pinus sylvestris

Response surface methodology was applied to optimize the removal efficiency of Ni(II). Pinus sylvestris ovulate cones were used in this study. A 2(3) full-factorial central composite design was employed for experimental design and analysis of the results. The initial Ni(II) concentration (10-30 mg/l), pH (2.5-6.5) and biomass concentration (5-25 g/l) were the critical components of the removal optimized. The optimum pH, m (biomass concentration) and C0 (initial Ni(II) concentration) were found to be 6.17, 18.8 g/l and 11.175 mg/l, respectively. Under these conditions, removal efficiency of Ni(II) was 99.91%.     

Biosorption of reactive dye by waste biomass of Nostoc linckia

Potential of spent biomass of a cyanobacterium, Nostoc linckia HA 46, from a hydrogen bioreactor was studied for biosorption of a textile dye, reactive red 198. The waste biomass was immobilized in calcium alginate and used for biosorption of the dye from aqueous solution using response surface methodology (RSM). Kinetics of the dye in aqueous solution was studied in batch mode. Interactive effects of initial dye concentration (100-500 mg/L), pH (2-6) and temperature (25-45 °C) on dye removal were examined using Box-Behnken design. Maximum adsorption capacity of the immobilized biomass was 93.5 mg/g at pH 2.0, initial concentration of 100 mg/L and 35 °C temperature, when 94% of the dye was removed. Fourier transform infrared (FT-IR) studies revealed that biosorption was mainly mediated by functional groups like hydroxyl, amide, carboxylate, methyl and methylene groups present on the cell surface.     

Process optimization of batch biosorption of lead using <Emphasis Type="Italic">Lactobacillius bulgaricus</Emphasis> in an aqueous phase system using response surface methodology

Response surface methodology (RSM) based on central composite rotatable design was used to investigate the effects of operating variable, mainly, pH, weight of biomass, and initial lead ion concentration on the lead adsorption capacity at ambient temperature using dried cells of Lactobacillius bulgaricus. Using RSM, quadratic polynomial equation was obtained for predicting the percent of lead ion removal. Analysis of variance showed that the effects of pH and weight of dried biomass were concluded to be the key factors influencing the capacity of lead ion removal. At pH lower than 2 (high acidic condition) and in alkaline condition, there is no significant biosorption. The optimum percent of lead ion removal was found at pH of 6.78, biomass concentration of 6.58 g/l and initial lead concentration 36.22 ppm. In this condition, percent of lead ion removal was 86.21%. This study showed RSM effectiveness for modeling of biosorption process.     

Characterization of Desmodesmus pleiomorphus isolated from a heavy metal-contaminated site: biosorption of zinc

Microalgae have been proven efficient biological vectors for heavy metal uptake. In order to further study their biosorption potential, a strain of Desmodesmus pleiomorphus (L) was isolated from a strongly contaminated industrial site in Portugal. Under different initial Zn²⁺ concentrations, metal removal by that strain reached a maximum of 360 mg Zn/g biomass after 7 days, at 30 mg Zn/l, after an initial rapid phase of uptake. Comparative studies were carried out using a strain of the same microalgal species that is commercially available (ACOI 561): when exposed to 30 mg Zn/l, it could remove only 81.8 mg Zn/g biomass. Biosorption experiments using inactivated biomass of the isolated strain reached a maximum Zn²⁺ uptake of 103.7 mg/g. Metal removal at various initial pH values was studied as well; higher removal was obtained at pH 5.0. The microalga strain L, isolated from the contaminated site, exhibited a much higher removal capacity than the commercial strain, and the living biomass yielded higher levels of metal removal than its inactivated form.     

Biosorption of chromium(VI) by spent cyanobacterial biomass from a hydrogen fermentor using Box-Behnken model

The study explores utilization of waste cyanobacterial biomass of Nostoc linckia from a lab-scale hydrogen fermentor for the biosorption of Cr(VI) from aqueous solution. The biomass immobilized in alginate beads was used for removal of the metal in batch mode optimizing the process conditions adopting response surface methodology (RSM). Kinetic studies were done to get useful information on the rate of chromium adsorption onto the cyanobacterial biomass, which was found to follow pseudo second-order model. Four important process parameters including initial metal concentration (10-100 mg/L), pH (2-6), temperature (25-45 °C) and cyanobacterial dose (0.1-2.0 g) were optimized to obtain the best response of Cr(VI) removal using the statistical Box-Behnken design. The response surface data indicated maximum Cr(VI) biosorption at pH 2-4 with different initial concentrations of the metal in the aqueous solution. The biosorbent could remove 80-90% chromium from solutions with initial metal concentration of 10-55 mg/L. Involvement of the surface characteristics of the biomass was studied through its scanning electron micrographs and Fourier transform infrared (FTIR) analysis.     

Waste biomass of Nostoc linckia as adsorbent of crystal violet dye: Optimization based on statistical model

The potential of spent biomass of a hydrogen producing cyanobacterial strain Nostoc linckia from a hydrogen fermentor was studied for decolorization of a tri-phenylmethane dye, crystal violet. The waste cyanobacterial biomass immobilized in calcium alginate was used as a biosorbent and the process variables were optimized for maximum dye removal using the statistical response surface methodology (RSM). Batch mode experiments were performed to determine the kinetic behavior of the dye in aqueous solution allowing the computation of kinetic parameters. Influence of interacting parameters like temperature (25-35 °C), pH (4-8), initial dye concentration (100-200 mg/L) and cyanobacterial dose (0.2-0.4 g) on dye removal were examined using central composite design (CCD) which included two additional levels for each parameter. Second-order polynomial regression model, was applied which was statistically validated using analysis of variance. Ability of the immobilized biomass to decolorize the dye was maximum (72%) at pH 8.0, temperature 35 °C, 200 mg/L initial dye concentration and 0.2 g cyanobacterial dose. Adsorption of the dye on cell surface was further confirmed by scanning electron micrographs of the biomass before and after dye loading. FT-IR studies revealed that decolorization was due to biosorption mediated mainly by functional groups like hydroxyl, amide, carboxylate, methyl and methylene groups present on the cell surface.     

Removal of hexavalent chromium by fungal biomass of <Emphasis Type="Italic">Mucor racemosus</Emphasis>: influencing factors and removal mechanism

This study reported the hexavalent chromium removal by untreated Mucor racemosus biomass and the possible mechanism of Cr (VI) removal to the biomass. The optimum pH, biomass dose, initial Cr (VI) concentration and contact time were investigated thoroughly to optimize the removal condition. The metal removal by the biomass was strongly affected by pH and the optimum pH ranged from 0.5 to 1.0. The residual total Cr was determined. It was found that dichromate reduction occurred at a low very low pH value. At biomass dose 6 g/l, almost all the Cr (VI) ions were removed in the optimum condition. Higher removal percentage was observed at lower initial concentrations of Cr (VI) ions, while the removal capacity of the biomass linearly depended on the initial Cr (VI) concentration. More than half of Cr (VI) ions were diminished within 1 h of contact and removal process reached a relative equilibrium in approximately 8 h. Almost all of the Cr (VI) ions were removed in 24 h when initial concentrations were below 100 mg/l. The equilibrium data were fitted in to the Langmuir and the Freundlich isotherm models and the correlated coefficients were gained from the models. A Fourier transform infrared spectra was employed to elucidate clearly the possible biosorption mechanism as well.     

Biosorption of Cr (VI) from aqueous solution by Rhizopus nigricans

The study was aimed to quantify the Cr sorption ability of powdered biomass of Rhizopus nigricans at the best operating conditions. The influence of solution pH, agitation, Cr (VI) concentration, biomass dosage, contact time, biomass particle size and temperature were studied. The optimum pH for biosorption of Cr (VI) was found to be 2.0. Higher adsorption percentage was noted at lower initial concentrations of Cr ions, while the adsorption capacity of the biomass increased with increasing concentration of ions. Optimum biomass dosage was observed as 0.5% (w/v). More than 75% of the ions were removed within 30 min of contact and maximum removal was obtained after 8 h. Biomass particles of smaller size (90 microm) gave maximum adsorption (99.2%) at 100 mg/l concentration. The adsorption capacity increased with increase in temperature and agitation speed and the optimum were determined as 45 degrees C at 120 rpm. Freundlich and Langmuir isotherms were used to evaluate the data and the regression constants were derived. The adsorption rate constant values (Kad) were calculated for different initial concentration of Cr ions and the sorption was found to be higher at lower concentration (100 mg/l) of metal ion.     

The kinetics and mechanism of lead (II) biosorptionby powderized Rhizopus oligosporus

The kinetics and mechanism of lead biosorption by powderized Rhizopus oligosporus were studied using shake flask experiment. The optimum biomass concentration and initial solution pH for lead sorption at initial lead concentrations ranging from 50–200 mg/l was obtained at 0.5 g/l and pH5, respectively. In term of the ratio of initial lead concentration to biomass concentration ratio, the highest lead adsorption was obtained at 750 mg/g which gave the maximum lead uptake capacity of 126 mg/g. The experimental data of lead sorption by R.oligosporus fitted well to the Langmuir sorption isotherm model, indicating that the sorption was similar to that for an ion-exchange resin. This means that the sorption is a single layer metal adsorption that occurred as a molecular surface coverage. This assumption was confirmed by the examination of lead sorption using transmission electron microscope and energy dispersive X-ray analysis, which showed that during sorption most of the lead was adsorbed on the surface of cell.     

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.     

Bioremoval of lead from water using Lemna minor

This study examined the ability of duckweed (Lemna minor) to remove soluble lead from water. The duckweed was obtained from the Devils Lake wastewater treatment plant in North Dakota. The viable aquatic plants were exposed to a single dose of lead (from Pb(NO₃)₂) at a concentration of 5.0 mg/l for a time period of 21 days. Lead concentrations were measured in the water daily and in the biomass at the conclusion of the experiment. All measurements were done in triplicate and performed in accordance with standard methods. These data were used to calculate the removal efficiency with respect to time, and to provide the necessary empirical constants to model the removal behavior. Viable biomass removed 85–90% of the lead, viable duckweed previously exposed to lead removed 70–80% of the lead, non-viable biomass (control group) removed 60–75% of the lead, and there was no removal in the ‘no-biomass' control group. Based on these results we conclude that the viable biomass is effective in removing lead present at sub-lethal levels.     

Optimal operational factors for nitrite accumulation in batch reactors

The environmental factors that affected the accumulation of nitrite in nitrifying reactors were investigated using a mixed culture. A batch reactor with 50 mg-N/l of ammonia was used. The pH, temperature and dissolved oxygen concentration were varied. The concentration of unionized free ammonia also changed with the oxidation of ammonia and the variation of pH and temperature. The accumulation of nitrite was affected sensitively by pH and temperature. A higher nitrite concentration was observed at pH 8-9 or temperature around 30 °C. The dissolved oxygen also affected, giving the highest nitrite accumulation at around 1.5 mg/l. These were the favoredconditions for nitrite production. The free ammonia concentration influenced thenitrite accumulation also, by inhibiting nitrite oxidation. The inhibition becameapparent at a concentration of approximately 4 mg/l or above, but insignificant atbelow 1 mg/l. Thus, simultaneously high free ammonia concentration and maximumspecific ammonia-oxidation rate (above 15 × 10^-3 mg-N/mg-VSSh)were needed for a significant nitrite accumulation. When the two conditions were met, thenthe highest accumulation was observed when the ratio of the maximum specific oxidationrate of ammonia to the maximum specific oxidation rate of nitrite (k_a/k_n) was highest.Under the optimal operating conditions of pH 8, 30 °C and 1.5 mg/l of dissolvedoxygen, as much as 77% of the removed ammonia accumulated in nitrite.     

Hydration of cyanopyridine to nicotinamide by whole cell nitrile hydratase

Summary 3-cyanopyridine was hydrated to nicotinamide by whole cells ofBrevibacterium R-312 containing nitrile hydratase. Cells used for kinetic studies had an initial activity of 0.30 mg nicotinamide/mg cells(dry)-min and storage half-lives (pH 8) of approximately 100 days, 10 days, 5 days and less than 1 day at 4°C, 10°C, 25°C, and 30°C respectively. Temperature and pH maxima were 35°C and 8.0, respectively. Fermentations gave a maximum total hydratase activity of 1.25 mg nicotinamide/min, but at this maximum the amidase activity was unacceptably high (25% of the hydratase activity): nicotinamide was converted too rapidly to nicotinic acid. But systematic fermentation studies (7 1) showed that harvesting at mid-log phase (18–20 h) prior to the attainment of maximum total activity gave reasonably high levels of hydratase (0.3 mg nicotinamide/mg cells-min) and acceptable levels of amidase (0.03 mg nicotinic acid/mg cells-min).     

Oryza sativa L. husk as heavy metal adsorbent: optimization with lead as model solution

The effects of initial concentration of lead, temperature, biomass loading and pH were investigated for an optimized condition of lead uptake from the aqueous solution. The optimization process was analyzed using Central Composite Face-Centered Experimental Design in Response Surface Methodology (RSM) by Design Expert Version 5.0.7 (StatEase, USA). The design was employed to derive a statistical model for the effect of parameters studied on the removal of lead ion from aqueous solution. The coefficient of determination, R2 was found to be 92.36%. The initial concentration of 50.0 mg/L, temperature of 60 degrees C, biomass loading of 0.2 g and pH of 5.0 had been found to be the optimum conditions for the maximum uptake of lead ions in 98.11% batch mode. Under the optimum conditions, the lead uptake was attained to be circa 8.60 mg/g.     

Effect of pH,Temperature, and Lead Concentration on the Bioremoval of Lead from Water Using Lemna Minor

This study examined the ability of the aquatic plant Lemna minor (duckweed) to remove soluble lead under various laboratory conditions. In a batch process L. minor was exposed to different pH values (4.5–8.0) and temperature (15–35°C) in presence of different lead concentrations (0.1–10.0 mg L^?1) for 168 h. The amount of biomass obtained in the study period on a dry weight basis, the concentrations of lead in tissue and in medium and net uptake of lead by Lemna all have been determined in each condition. The percentages of lead uptake ratios (PMU) and bioconcentration factors (BCF) were also calculated for these conditions. Bioaccumulated lead concentrations and the PMU were obtained at lowest pH of 4.5, and at 30°C. The highest accumulated lead concentration was found at pH 4.5 as 3.599 mg Pb g^?1 in 10.0 mg L^?1. It decreased to pH 6.0, but it did not change at pH 6.0–8.0 range. The maximum lead accumulation was obtained at 30°C as 8.622 mg Pb g^?1 in 10 mg L^?1 at pH 5.0, and the minimum was at 15°C as 0.291 mg g^?1 in 0.1 mg L^?1. Lead accumulation gradually increased with increasing lead in medium, but the opposite trend was observed for PMU. Lead accumulation increased up to 50 mg L^?1, but did not change significantly in the 50.0–100.0 mg L^?1 range. The lead uptake from water was modeled and the equation fit the experimental data very well.     

Biosorption of Copper by Cyanobacterial Bloom-Derived Biomass Harvested from the Eutrophic Lake Dianchi in China

Biomass of cyanobacterial bloom from Lake Dianchi was used as a biosorbent for copper removal from aqueous solution. The maximum capacity was found at conditions of pH 4, initial concentration of copper was 10 mg/l and initial dose of biomass was 1.0 g/l. HNO₃ demonstrated the highest desorption efficiency compared with HCl, EDTA, and citric acid. Physical adsorption was assumed not to be the dominant mechanism of biosorption as revealed by scanning electron microscopy and surface area measurement of the biomass. Infrared ray spectra analysis of the biomass suggested that ion-exchange is the principal mechanism for biosorption. Considering the advantages—low cost, easy to collect, and huge in quantity—the Microcystis bloom biomass could be used as a sorbent for copper and other heavy metals removal.     

The use of flocculating brewer's yeast for Cr(III) and Pb(II) removal from residual wastewaters

The use of inexpensive biosorbents to sequester heavy metals from aqueous solutions, is one of the most promising technologies being developed to remove these toxic contaminants from wastewaters. Considering this challenge, the viability of Cr(III) and Pb(II) removal from aqueous solutions using a flocculating brewer's yeast residual biomass from a Portuguese brewing industry was studied. The influence of physicochemical factors such as medium pH, biomass concentration and the presence of a co-ion was characterised. Metal uptake kinetics and equilibrium were also analysed, considering different incubation temperatures. For both metals, uptake increased with medium pH, being maximal at 5.0. Optimal biomass concentration for the biosorption process was determined to be 4.5?g dry weight/l. In chromium and lead mixture solutions, competition for yeast binding sites was observed between the two metals, this competition being pH dependent. Yeast biomass showed higher selectivity and uptake capacity to lead. Chromium uptake kinetic was characterised as having a rapid initial step, followed by a slower one. Langmuir model describes well chromium uptake equilibrium. Lead uptake kinetics suggested the presence of mechanisms other than biosorption, possibly including its precipitation.     

Effect of dirhamnolipid on the removal of phenol catalyzed by laccase in aqueous solution

In this study, the effects of three surfactants, i.e. the anionic biosurfactant dirhamnolipid (diRL), the cationic surfactant hexadecyltrimethyl ammonium bromide (CTAB), and the anionic surfactant sodium dodecyl sulfate (SDS), on the removal of phenol catalyzed by laccase were studied first. CTAB and SDS were detrimental, while diRL improved phenol removal and was selected for detailed research. The biosurfactant increased the activity of laccase and the removal of phenol with the increase of diRL concentrations from 10.6 to 318 μM. DiRL at 318 μM improved the removal when the initial concentrations of phenol were from 50 to 400 mg/l. In particular, the removal of phenol with 318 μM diRL was 4.3–6.4 folds that of the controls within 24 h when the initial concentration of phenol was 400 mg/l. The presence of diRL at 318 μM also caused the complete removal (above 98%) of phenol at concentrations from 50 to 400 mg/l after 24 h. The enhancement of phenol removal was over a wide range of pH and temperatures, and the highest removal efficiency was obtained at pH 6.0 and 50°C. The results suggest that diRL had potential application in the enhancement of phenols removal catalyzed by laccase in water treatment or remediation.