Biosorption of Methylene Blue from Aqueous Solutions by Hazelnut Shells: Equilibrium, Parameters and Isotherms

This paper presents a study on the batch adsorption of a basic dye, methylene blue (MB), from aqueous solution onto ground hazelnut shell in order to explore its potential use as a low-cost adsorbent for wastewater dye removal. A contact time of 24 h was required to reach equilibrium. Batch adsorption studies were carried out by varying initial dye concentration, initial pH value (3–9), ionic strength (0.0–0.1 mol L^?1), particle size (0–200 μm) and temperature (25–55°C). The extent of the MB removal increased with increasing in the solution pH, ionic strength and temperature but decreased with increase in the particle size. The equilibrium data were analysed using the Langmuir and Freundlich isotherms. The characteristic parameters for each isotherm were determined. By considering the experimental results and adsorption models applied in this study, it can be concluded that equilibrium data were represented well by Langmuir isotherm equation. The maximum adsorption capacities for MB were 2.14?×?10^?4, 2.17?×?10^?4, 2.20?×?10^?4 and 2.31?×?10^?4 mol g^?1 at temperature of 25, 35, 45 and 55°C, respectively. Adsorption heat revealed that the adsorption of MB is endothermic in nature. The results indicated that the MB strongly interacts with the hazelnut shell powder.     

Preparation, Characterization, and Adsorption Behavior of Cu(II) Ions onto Alkali-Treated Weed (Imperata cylindrica) Leaf Powder

The adsorption of Cu(II) ions by sodium-hydroxide-treated Imperata cylindrica (SoHIC) leaf powder was investigated under batch mode. The influence of solution pH, adsorbent dosage, shaking rate, copper concentration, contact time, and temperature was studied. Copper adsorption was considered fast as the time to reach equilibrium was 40–90 min. Several kinetic models were applied and it was found that pseudo-second-order fitted well the adsorption data. In order to understand the mechanism of adsorption, spectroscopic analyses involving scanning electron microscope (SEM) coupled with energy-dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectrophotometer were carried out. Ion exchange was proven the main mechanism involved as indicated by EDS spectra and as there was a release of light metal ions (K⁺, Na⁺, Mg²⁺, and Ca²⁺) during copper adsorption. Complexation also occurred as demonstrated by FTIR spectra involving hydroxyl, carboxylate, phosphate, ether, and amino functional groups. The equilibrium data were correlated with Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. Based on Langmuir model, the maximum adsorption capacity was recorded at the highest temperature of 310 K, which was 11.64 mg g^?1.     

Equilibrium and Kinetic Studies on Biosorption of Heavy Metals by Leaf Powder of Paper Mulberry (Broussonetia papyrifera)

Paper mulberry (Broussonetia papyrifera) leaf powder was used to remove heavy metal ions from aqueous solutions. The specific uptakes of Cu (II), Pb (II), and Cd (II) by the leaf powder were 43.40?±?0.2, 43.9?±?0.5, and 30.65?±?0.9 mg g^?1, respectively, when 500 mg L^?1 of the metal solutions were used. The data fitted well to the Langmuir isotherm. The process followed the pseudo-second-order kinetic equation and intraparticle diffusion played an important role in the adsorption process. On the basis of the calculated thermodynamic parameters such as standard enthalpy (??H°), entropy (??S°) and free energy change (??G°), it was inferred that the sorption process was endothermic and spontaneous in nature. The surface properties of the leaf powder (revealed by scanning electron microscopic observations) were suitable for the metal adsorption process. Energy dispersive X-ray fluorescence analysis confirmed the sequestration of the metal ions by the leaf powder. Fourier transform infrared spectroscopy implicated that different functional groups on the leaf powder were involved in the metal adsorption process. The results obtained from this study implicated that the B. papyrifera leaf powder was a good choice as a metal adsorbent. This abundantly available natural and eco-friendly biosorbent could be effectively used to develop a technology in the future.     

Equilibrium, Kinetics, and Thermodynamics of Methylene Blue Adsorption by Pine Tree Leaves

The adsorption capacity of pine tree leaves for removal of methylene blue (MB) from aqueous solution was investigated in a batch system. The effects of the process variables, such as solution pH, contact time, initial dye concentration, amount of adsorbent, agitation speed, salt concentration, and system temperature on the adsorption process were studied. The extent of methylene blue dye adsorption increased with increase in initial dye concentration, contact time, agitation speed, temperature, and solution pH but decreased with increased in amount of adsorbent and salt concentration. Equilibrium data were best described by both Langmuir isotherm and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine tree leaves biomass was 126.58?mg/g at 30?°C. The value of separation factor, R _L , from Langmuir equation and Freundlich constant, n, both give an indication of favorable adsorption. The intrapartical diffusion model, liquid film diffusion model, double exponential model, pseudo-first and second order model were used to describe the kinetic and mechanism of adsorption process. A single stage bath adsorber design for the MB adsorption onto pine tree leaves has been presented based on the Langmuir isotherm model equation. Thermodynamic parameters such as standard Gibbs free energy (??G ⁰), standard enthalpy (??H ⁰), and standard entropy (??S ⁰) were calculated.     

Catalytic effect of various metal ions on the methylation of mercury in the presence of humic substances

Methylation of Hg²⁺ (Hg(NO₃)₂) in the presence of fulvic acid (FA) and various metal ions has been studied. The concentrations of Hg²⁺ and FA ranged from 5 to 20 mg L^?1 and 171 to 285 mg L^?1 DOC, respectively. The pH range was 3 to 6.5. FA was isolated from an acid brown-water lake by XAD-8 polymeric adsorbent. Methylmercury production in the dark during 2 to 4 days incubation at 30 °C increased with increasing concentrations of Hg²⁺ ion and FA as well as with additions of metal ions (5 to 10 × 10^?5 mole L^?1 The observed catalytic activity of metal ions followed the order Fe³⁺ (Fe²⁺) > Cu²⁺ ≈ Mn²⁺, > Al³⁺. The production of methylmercury had a pH-optimum around 4 to 4.5 at the conditions tested.     

Removal of Pb2+ Ions from Water by Poly(Acrylamide-co-Sodium Methacrylate) Hydrogels

The application of poly(acrylamide-co-sodium methacrylate) (AAm/SMA) hydrogel for the removal of Pb²⁺ ions from aqueous solutions has been investigated using batch adsorption technique. The extent of adsorption was investigated as a function of pH, adsorbent dose, and temperature. The Fourier transform infrared (FTIR) spectra showed that ?CNH₂ and ?CCOOH groups are involved in Pb²⁺ ion adsorption. The obtained results were analyzed by pseudo-first-order, pseudo-second?Corder, and intraparticle diffusion models using both linear and nonlinear methods. It was found that the Pb²⁺ ion adsorption followed pseudo-first-order kinetics. Nonlinear regression analysis of six isotherms, Langmuir, Freundlich, Redlich-Peterson, Toth, Dubinin-Radushkevich, and Sips, have been applied to the sorption data, while the best interpretation was given by Redlich-Peterson. Based on the separation factor, R _L, the Pb²⁺ ion adsorption is favorable, while the negative values of ?G indicates that the Pb²⁺ ion adsorption on the investigated hydrogel is spontaneous.     

Copper Ions Adsorption from Aqueous Medium Using the Biosorbent Sugarcane Bagasse In Natura and Chemically Modified

This study evaluated the copper ion adsorption capacity of sugarcane bagasse in natura and chemically modified with citric acid and sodium hydroxide. Adsorption analyses in batch system were carried out in function of contact time with the adsorbent and adsorbate concentration. Flame atomic absorption spectrometry was used to determine the copper concentrations. Adsorption experimental data were fitted to Langmuir and Freundlich linear models, and the maximum adsorption capacity was estimated for copper ions in function of modifications. The chemical modifications were confirmed at 1,730 cm^?1 peak in infrared spectra, referring to the carboxylate groups. The required time for the adsorption to reach equilibrium was 24 h and the kinetics follows the behavior described by the pseudo-second order equation. Besides, a significant improvement of the copper adsorption has been observed after the bagasse treatment, where the maximum adsorption capacity was 31.53 mg g^?1 for copper using modified bagasse with nitric acid according to Langmuir isotherm linear model. The high uptake of copper ions from aqueous medium verified by chemically modified sugarcane bagasse makes this material an attractive alternative for effluent treatment and avoids environmental contamination.     

Preconcentration/Cleanup Studies of Tin from Environmental Water Samples by Oxidized Multiwall Carbon Nanotubes Packed Column and its Determination by ETAAS

The use of multiwall carbon nanotubes (MWCNT) as an efficient solid extractor in preconcentration/cleanup studies for tin determination in water samples by electrothermal atomic absorption spectrometry (ETAAS) is proposed. In the proposed method, tin adsorption onto MWCNT was carried out by percolating the solution previously buffered (pH 4.79 with 0.24 mol?L^?1 acetic acid/acetate buffer) at 4.0-mL?min^?1 flow rate, followed by elution with 1.0 mL of 2.7 mol?L^?1 HNO₃. Factors such as sample pH, preconcentration/cleanup flow rate, type and concentration of eluent, and buffer concentration were appraised and optimized from chemometric tools based on fractional factorial design and Doehlert design. A limit of detection of 0.73 ??g?L^?1 and precision (n?=?8) assessed as relative standard deviation of 8.6% and 7.0% for tin concentration of 8.0 and 43.0 ??g?L^?1, respectively, were achieved. Foreign metallic ions (Ni²⁺, Pb²⁺, Co²⁺, Zn²⁺, Cd²⁺, Mn²⁺, and Fe³⁺) were checked as potential interferents, and no interference was observed up to an analyte/interference ratio of 1:10 (m/v). Direct tin determination by ETAAS in water samples containing high salt amount is drastically affected by background signal. However, previous cleanup of sample by MWCNT has promoted a significant improvement and makes the method useful for tin monitoring in water samples (mineral, lake, mine, and natural waters) by ETAAS. Quantitative recovery values ranging from 91.5% to 103.0% attested the applicability of the proposed preconcentration/cleanup for tin determination in water samples.     

Adsorption of deoxyribonucleic acid (DNA) by willow wood biochars produced at different pyrolysis temperatures

Adsorption of DNA by biochars was investigated in the present study. Biochars were produced from air-dried willow wood chips at 300, 400, 500, and 600 °C under limited oxygen supply. The resulting products, referred to as BC300, BC400, BC500, and BC600, respectively, were characterized for their elemental composition, cation exchange capacity (CEC), specific surface areas (SSA), and microporosity. According to a Langmuir isotherm, maximum DNA adsorption capacity of biochars was ranked as BC500?>?BC600?>?BC400?>?BC300. Increasing solution pH (from 4.0 to 9.0) faintly decreased DNA adsorption onto biochars. The addition of Na⁺, Mg²⁺, and Ca²⁺ slightly increased the adsorption of DNA, and the effect decreased by increasing the pyrolysis temperature of biochars, indicating that electrostatic interaction was not the main driving force for DNA adsorption onto those biochars. Correlation analysis showed that SSA and micropore surface area were the main factors influencing DNA adsorption on biochars.     

Equilibrium, Kinetics and Mechanism of Removal of Methylene Blue from Aqueous Solution by Adsorption onto Pine Cone Biomass of Pinus radiata

The kinetics and mechanism of methylene blue adsorption onto raw pine cone biomass (Pinus radiata) was investigated under various physicochemical parameters. The extent of the methylene blue dye adsorption increased with increases in initial dye concentration, contact time and solution pH but decreases with the amount of adsorbent, salt concentration and temperature of the system. Overall the kinetic studies showed that the methylene blue adsorption process followed pseudo-second-order kinetics among various kinetic models tested. The different kinetic parameters including rate constant, half-adsorption time and diffusion coefficient are determined at different physicochemical conditions. Equilibrium data were best represented by Langmuir isotherm among Langmuir and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine cone biomass was 109.89 mg/g at 30°C. The value of separation factor, R _L, from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. Thermodynamic parameters such as standard Gibbs free energy (?G ⁰), standard enthalpy (?H ⁰), standard entropy (?S ⁰) and the activation energy (A) were calculated. A single-stage batch absorber design for the methylene blue adsorption onto pine cone biomass has been presented based on the Langmuir isotherm model equation.     

Co(II) Adsorption in Aqueous Media by a Synthetic Fe–Mn Binary Oxide Adsorbent

Co(II) adsorption on high-purity amorphous Fe?CMn binary oxide adsorbent was investigated. The Co(II) adsorption behavior of this synthetic material was studied and discussed as a function of contact time, pH and initial concentration. The Langmuir and Freundlich isotherm models were applied to fit the Co(II) adsorption data on Fe?CMn binary oxide with mesoporous particles of irregular surface morphology and a specific surface area of 201.8?m²?g^?1 with a maximum capacity of 32.25?mg?g^?1. Various kinetic models applied to the adsorption rate data of the Co(II) ion were evaluated. The results show that the pseudo-second order and the intra-particle mass transfer diffusion models correlated best with the experimental rate data. The adsorption activation energy was found to be 9.07?kJ?mol^?1 indicating that it corresponds to a physical adsorption. The evaluated thermodynamics parameters of the adsorption values indicated the endothermic and spontaneous nature of the adsorption. The results obtained confirmed that Fe?CMn binary oxide had the potential to be utilized as a low-cost and relatively effective adsorbent for Co(II) removal from wastewater.     

Cadmium Uptake by Yeast, Candida tropicalis, Isolated from Industrial Effluents and Its Potential Use in Wastewater Clean-Up Operations

This study is aimed at assessing the ability of metal-resistant yeast, Candida tropicalis, to uptake cadmium from the liquid medium. The minimum inhibitory concentration of Cd²⁺ against C. tropicalis was 2,800 mg L^?1. The yeast also showed tolerance towards Zn²⁺ (3,100 mg L^?1), Ni²⁺ (3,000 mg L^?1), Hg²⁺ (2,400 mg L^?1), Cu²⁺ (2,300 mg L^?1), Cr⁶⁺ (2,000 mg L^?1), and Pb²⁺ (1,200 mg L^?1). The yeast isolate showed typical growth curves, but low specific rate of growth was observed in the presence of cadmium. The yeast isolate showed optimum growth at 30°C and pH 7. The metal processing ability of the isolate was determined in a medium containing 100 mg L^?1 of Cd²⁺. C. tropicalis could decline Cd²⁺ 57%, 69%, and 80% from the medium after 48, 96, and 144 h, respectively. C. tropicalis was also able to remove Cd²⁺ 56% and 73% from the wastewater after 6 and 12 days, respectively. Cd produced an increase in glutathione (GSH) and non-protein thiol levels by 146.15% and 59.67% at 100 mg L^?1 concentration, respectively. Metal tolerance and accumulation together with changes in the GSH status and non-protein thiols under Cd exposure were studied in C. tropicalis.     

Magnetic Solid-Phase Extraction Based on Modified Iron Oxide Nanoparticles for the Preconcentration of Ultra-Trace Amounts of Copper Ions in the Environmental and Plant Samples and its Determination Using FAAS

In the present work, magnetic iron oxide nanoparticles (MIONPs) coated with sodium dodecyl sulfate (SDS) and modified with 1-(2-pyridylazo)-2-naphthol (PAN) as a new nanoparticle were prepared and used as an adsorbent for the extraction and preconcentration of copper ions. After adsorption, copper ions were desorbed with nitric acid (HNO₃), followed by determination with flame atomic absorption spectrometry (FAAS). The extraction conditions0. were investigated systematically. The linear range 3.0–500.0 ng mL^?1 and the detection limit of 0.6 ng mL^?1 were obtained. The relative standard deviation (RSD) of the method for seven replicate determinations of 0.1 µg mL^?1 of Cu(II) was 2.2%. The method was applied for the determination of Cu(II) in different water samples with good trueness. The accuracy was also evaluated through analyses of a certified reference material (CRM TMDW-500).     

Removal of Rhodamine-B by biogas waste slurry from aqueous solution

The ability of biogas waste slurry to adsorb a basic dye (Rhodamine-B) has been investigated. The parameters include agitation time, initial dye concentration, pH and adsorbent dosage. The rate controlling step is mainly intraparticle diffusion. The adsorption rate constant was found to be 2.9 × 10^?2 min^?1 at 20 mg L^?1 initial dye concentration. The adsorption conforms with Freundlich isotherm. Removal of the dye was at least 90% in the entire pH range from 2.3 to 11.2. Desorption of the dye in 50% (v/v) acetic acid to the extent of 69.7% indicates that most of the dye is held by the adsorbent by chemisorption.     

Combined Removal of Zinc (II) and Cadmium (II) from Aqueous Solutions by Adsorption onto High-Calcium Turkish Fly Ash

The aim of this work is the investigation of possible use of flyash in the removal of zinc (Zn²⁺) and cadmium (Cd²⁺) contained in aqueous solutions. Batch adsorption experiments wereperformed in order to evaluate the removal efficiency oflignite-based fly ash. The parameters studied include contact time, pH,temperature, initial concentration of the adsorbate and fly ashdosage. The contact time necessary to attain equilibrium was found to be two hours. Maximum adsorption occurred in the pH range of 7.0 to 7.5. The percent adsorption of Zn²⁺ and Cd²⁺ increased with an increase in concentration of Zn²⁺ and Cd²⁺, dosage of fly ash and temperature. Theapplicability of Langmuir isotherm suggests the formation ofmonolayer coverage Zn²⁺ and Cd²⁺ ions at the outer surface of the adsorbent. Thermodynamic parameters suggested the endothermic nature of the adsorption process. The fly ashwas found to be an metal adsorbent as effective as activated carbon.     

Adsorption features of Cu(II), Pb(II), and Zn(II) by an ordinary chernozem from nitrate,chloride, acetate,and sulfate solutions

The effect of Cl^?,SO ₄ ^2? , CH₃COO^?, and NO ₃ ^? anions on the adsorption of copper, lead, and zinc by an ordinary chernozem has been studied. The effect of the anions on the adsorption of Cu²⁺, Pb²⁺, Zn²⁺ ions is significant but uncertain. It has been shown that the attendant anions affect the shape of the adsorption isotherms, which are described by the Langmuir, Freundlich, or Henri equations. The constants of the adsorption from a nitrate solution calculated from the Langmuir equation (K _L) decrease in the following order: Cu²⁺ > Pb²⁺ >> Zn²⁺. The values of the maximum adsorption (C _max) decrease in the following order: Cu²⁺ ≥ Zn²⁺ > Pb²⁺ for acetate solutions and in the series Pb²⁺ > Zn²⁺ ≥ Cu²⁺ for nitrate solutions. The values of the Henry constants (K _H) calculated for the adsorption of the same cations from chloride solutions decrease in the same order as the values of K _L. The CH₃COO^? anion has the highest effect on the constant values. The NO ₃ ^? and Cl^? anions “switch their places” depending on the attendant cation, but their effect is always lower than that of the acetate anion. The values of C _max for copper and zinc are most affected by the CH₃COO^? anion, and the adsorption of zinc is most affected by the Cl^? and NO ₃ ^? anions. The assessment of the mobility of the adsorbed cations from the extraction with ammonium acetate (pH 4.8) has shown that the content of the desorbed metals is always lower than the content of the adsorbed cations and varies from 0.025 to 83%. According to their mobility, the adsorbed metals form the following order: Zn²⁺ > Pb²⁺ > Cu²⁺. The effect of the attendant anions on the extractability of the adsorbed cations decreases in the following order: chlorides > sulfates > acetates > nitrates.     

Adsorptive Potential of 2-Mercaptobenzimidazole-Immobilized Organophilic Hydrotalcite for Mercury(II) Ions from Aqueous Phase and Its Kinetic and Equilibrium Profiles

An organophilic calcined hydrotalcite (OHTC) was prepared by treating calcined hydrotalcite (HTC) with sodium dodecylbenzene sulphonate (an anionic surfactant) to achieve a high loading of thiol functionality through the immobilization of 2-mercaptobenzimidazole (MBI) as a chelating agent. The adsorbent (MBI-OHTC) obtained was characterized using XRD, FTIR, SEM, TG/DTG, surface area analysis and potentiometric titration. The adsorption of MBI-OHTC to remove Hg(II) ions from aqueous solutions was studied as a function of pH, contact time, metal ion concentration, ionic strength and adsorbent dose. The optimum pH range for the maximum removal of Hg(II) was 6.0–8.0. The maximum value of Hg(II) adsorption was found to be 11.63 and 21.52 mg g^?1 for an initial concentration of 25 and 50 mg l^?1, respectively at pH 8.0. The equilibrium conditions were achieved within 3 h under the mixing conditions employed. A reversible pseudo-first-order used to test the adsorption kinetics. The adsorption mechanism consisted of external diffusion and intraparticle diffusion and the intraparticle mass transfer diffusion was predominated after 20 min of experiment. Extent of adsorption decreased with increase of ionic strength. The experimental isotherm was analyzed with two parameters (Langmuir and Freundlich) and three parameters (Redlich–Peterson) equations. The isotherm data were best modeled by the Freundlich isotherm equation. Complete removal (≈100%) of Hg(II) from 1.0 l of chlor-alkali industry wastewater containing 9.86 mg Hg(II) ions, was possible with 3 g of the adsorbent dose at pH 8.0. About 95.0% of Hg(II) can be recovered from the spent adsorbent using 0.1 M HCl.     

Speciation of cadmium,copper, lead,and zinc in contaminated soils

Abstract

To investigate the activity of free cadmium (Cd²⁺), copper (Cu²⁺), lead (Pb²⁺), and zinc (Zn²⁺) ions and analyze their dependence on pH and other soil properties, ten contaminated soils were sampled and analyzed for total contents of Cd, Cu, Pb, and Zn (Cd_T, Cu_T, Pb_T, and Zn_T, respectively), 0.43 MHNO₃‐extractable Cd, Cu, Pb, and Zn (Cd_N, Cu_N, Pb_N, and Zn_N, respectively), pH, dissolved organic matter (DOC), cation exchange capacity (CEC), ammonium oxalate extractable aluminum (Al) and iron (Fe), and dissolved calcium [Ca²⁺]. The activity of free Pb²⁺, Cd²⁺, Cu²⁺, and Zn²⁺ ions in soil solutions was determined using Donnan equilibrium/graphite furnace atomic absorption (DE/GFAA). The solubility of Cd in soils varied from 0.16 to 0.94 μg L^‐1, Cu from 3.43 to 7.42 μg L^‐1, Pb from 1.23 to 5.8 μg L^‐1, and Zn from 24.5 to 34.3 μg L^‐. In saturation soil extracts, the activity of free Cd²⁺ ions constituted 42 to 82% of the dissolved fraction, for Cu²⁺the range was 0.1 to 7.8%, for Pb²⁺ 0.1 to 5.1% and for Zn²⁺2 to 72%. The principal species of Cd, Cu, Pb, and Zn in the soil solution is free metal ions and hydrolyzed ions. Soil pH displayed a pronounced effect on the activity of free Cd²⁺, Cu^2t, Pb²⁺, and Zn²⁺ ions.     

Removal of Heavy Metals in Storm Water Runoff Using Porous Vermiculite Expanded by Microwave Preparation

The main objective of this study was to examine the effectiveness of vermiculite for removing heavy metals from water. Vermiculite components were analyzed by X-ray fluorescence, and the concentrations of metal ions were measured by inductively coupled plasma spectrometry. Serial batch kinetic tests and batch sorption tests were conducted to determine the removal characteristics for heavy metals in aqueous solutions. Solution pH values of tests with the inflated vermiculites generally increased and then stabilized. Equilibrium pH was generally established within 5?h. Removal rates of inflated vermiculite were tested at the initial concentration of 3?mg/L. At equilibrium concentrations, except for chromium (36.23%), most heavy metals were effectively removed (96.08?C98.54%). Finally, sorption data were correlated with both Langmuir and Freundlich isotherms. For each metal, the Q _max obtained using the Langmuir isotherm was as follows: lead, 725.4?mg?kg^?1; cadmium, 568.8?mg?kg^?1; zinc, 540.2?mg?kg^?1; copper, 457.2?mg?kg^?1; and chromium, 0.9?mg?kg^?1. The study results indicate that inflated vermiculite has outstanding removal rates and therefore can be used as an adsorbent for various heavy metals.     

Aerobic Biological Treatment of Chestnut Processing Wastewater

Chestnut agro-industrial companies consume a high volume of water for washing and processing fruit, generating a large volume of wastewater. This work studied the biodegradation of chestnut processing wastewater through aerobic assays, varying substrate, and biomass concentrations. In general, this wastewater presents a good biodegradability, especially in experiments with relatively low chemical oxygen demand (COD) (0.4 and 0.6?g O₂ L^?1) allowing a COD removal of 85?C90?%. The best results were obtained in the reactor initially loaded with 2?g?L^?1 of biomass and 0.4 or 0.6?g O₂ L^?1 of COD. These experiments also showed high COD removal rates: 4.25 and 3.88?g COD g^?1 volatile suspended solids (VSS) h^?1, respectively. The sedimentation rate, evaluated for different initial values of biomass (1, 2, and 3?g?L^?1), always presented higher values in the experiments with 2 and 3?g?L^?1 of biomass, regardless of the initial COD value used. After comparing different kinetic models (Monod, Contois, and Haldane), it was observed that the Haldane inhibition model satisfactorily describes the COD biodegradation. AQUASIM software allowed calculating the kinetic constant ranges: K _s, 1.59?C6.99?g COD L^?1; ?? _max, 25?C40?g COD g^?1 VSS day^?1; and K _i values, 0.07?C0.11. These kinetic constants corresponds to maximum rates (??*) between 1.48 and 4.25?g COD g^?1 VSS day^?1 for substrate concentrations (S*) from 0.38 to 0.88?g COD L^?1.