Biosorbent Particle Size Research Articles

Dried prickly pear cactus (Opuntia ficus indica) cladodes as a low-cost and eco-friendly biosorbent for dyes removal from aqueous solutions

The biosorption of Methylene Blue (MB), Eriochrome Black T (EBT) and Alizarin S (AS) from aqueous solutions by dried prickly pear cactus cladodes as a low-cost, natural and eco-friendly biosorbent was investigated. The study was carried out under various parameters, such as average biosorbent particle size, pH, biosorbent dosage, contact time, initial dye concentration and temperature. The experimental results show that, the percentage of biosorption increases with an increase in the biosorbent dosage, and the decrease of particle size. The biosorption was pH dependent with a high biosorption of cationic dye (MB) in basic range and a high biosorption of anionic dyes (EBT and AS) in acidic range. The equilibrium uptake was increased with an increase in the initial dye concentration in solution. Biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. The experimental isotherm data were analyzed using Langmuir, Freundlich, Redlich–Peterson, Temkin and Toth isotherm equations. The best fit was obtained by the Redlich–Peterson model and the Langmuir model with a Langmuir maximum monolayer biosorption capacity of 189.83mg/g for Methylene Blue, 200.22mg/g for Eriochrome Black T and 118.35mg/g for Alizarin S. The biosorption was exothermic in nature (ΔH°=−31.035kJ/mol for MB, −10.25kJ/mol for EBT and −11.69kJ/mol for AS). The reaction was accompanied by a decrease in entropy (ΔS°=−94.76J/Kmol for MB, −38.44J/Kmol for EBT and −41.93J/Kmol for AS). The Gibbs energy (ΔG°) increased when the temperature was increased from 25 to 60°C indicating a decrease in feasibility of biosorption at higher temperatures.

Acidic dye biosorption onto marine brown macroalgae: Isotherms, kinetic and thermodynamic studies

Acid Black 1 (AB1) is a diazo dye containing both NN and CC chromophores groups that has considerable health effects being irritating for skin, eye and respiratory system. It is essential to remove this dye from wastewater. In this study, the removal of AB1 with brown macroalgae Sargassum glaucescens and Stoechospermum marginatum was studied using a batch system. The effects of parameters such as initial pH (in the range 2–10), contact time (within 90min), biomass dosage (in the range 1–9g L−1), initial dye concentration (in the range 10–50mgL−1), particle size of biosorbent (0.53–500μm) and agitation speed (from 70 to 180rpm) on the adsorption capacity of AB1 were investigated. The equilibrium data indicated that the Freundlich model provided the best correlation of the experimental data for both biosorbents at least in the concentration range investigated in this study. The biosorption kinetic data were successfully described with pseudo-second order model (PSORE) for two biosorbents. Thermodynamic parameters showed adsorption of dye was feasible and endothermic at all temperatures (283–313K) for both biosorbents. A decrease in particle size of biosorbents increased acidic dye removal capacity. The agitation speed influences AB1 sorption capacity and optimum agitation speed observed at 130rpm among different agitation speed (i.e. 70–180rpm). FT-IR analysis demonstrated the involvement of different functional groups, mainly hydroxyl, carboxyl and amine groups. These results confirm that these algae have a good potential for removal of AB1 from aqueous solution at low dye concentration.

Biosorption of three acid dyes by the brown macroalga Stoechospermum marginatum: Isotherm, kinetic and thermodynamic studies

The brown macroalga Stoechospermum marginatum was tested for its ability to remove the acid dyes Acid Blue 25 (AB25), Acid Orange 7 (AO7) and Acid Black 1 (AB1) from aqueous solution. Biosorption was investigated under different conditions of pH, biomass and initial dye concentrations, temperature, contact time and biosorbent particle size. The results at equilibrium were successfully described by the Freundlich model, and the estimated sorption capacities were 22.2, 6.73 and 6.57mg/g for AB25, AO7 and AB1, respectively. Among the pseudo-first-order, pseudo-second-order and intraparticle diffusion models, which were applied to kinetically describe the biosorption, the second one showed the best fit of the experimental data (R2=0.99). The thermodynamic parameters of the process (ΔG°, ΔH° and ΔS°) were estimated from tests carried out at different temperatures (283, 298 and 313K). For all dyes, the standard changes of the Gibbs free energy were negative (−5.22<ΔG°<−3.68kJ/mol for AB25; −2.49<ΔG°<−1.72kJ/mol for AO7; −1.94<ΔG°<−0.94kJ/mol for AB1) and those of the enthalpy positive (ΔH°=10.8, 5.52 and 8.46kJ/mol for AB25, AO7 and AB1, respectively), hence pointing out that biosorption was a spontaneous and endothermic process. A decrease in particle size of S. marginatum biomass increased AB25 and AB1 removal efficiencies per unit weight of sorbent. FT-IR analysis demonstrated the involvement of different functional groups, mainly hydroxyl and amine groups. This study highlights the potential of the selected macroalga as an effective biosorbent for the removal of dyes from wastewaters.

Sorption of malachite green from aqueous solution by potato peel: Kinetics and equilibrium modeling using non-linear analysis method

Potato peel (PP) was used as a biosorbent to remove malachite green (MG) from aqueous solution under various operating conditions. The effect of the experimental parameters such as initial dye concentration, biosorbent dose, initial pH, stirring speed, temperature, ionic strength and biosorbent particle size was investigated through a number of batch sorption experiments. The sorption kinetic uptake for MG by PP at various initial dye concentrations was analyzed by non-linear method using pseudo-first, pseudo-second and pseudo-nth order models. It was found that the pseudo-nth order kinetic model was the best applicable model to describe the sorption kinetic data and the order n of sorption reaction was calculated in the range from 0.71 to 2.71. Three sorption isotherms namely the Langmuir, Freundlich and Redlich–Peterson isotherms in their non-linear forms were applied to the biosorption equilibrium data. Both the Langmuir and Redlich–Peterson models were found to fit the sorption isotherm data well, but the Redlich–Peterson model was better. Thermodynamic parameters show that the sorption process of MG is endothermic and more effective process at high temperatures. The results revealed that PP is very effective for the biosorption of MG from aqueous solutions.

Kinetic and thermodynamic modeling for the removal of Direct Red-31 and Direct Orange-26 dyes from aqueous solutions by rice husk

The present study deals with the utilization of an inexpensive agro-industrial waste rice husk for the removal of Direct Red-31 and Direct Orange-26 from aqueous solutions in a batch mode. Experiments were carried out as function of pH, biosorbent dose, particle size of biosorbent, initial dyes concentration, contact time and temperature. The equilibrium biosorption data were analyzed by Langmuir, Freundlich, Temkin, Doubinin–Radushevich (D–R) and Harkins–Jura isotherm models. The results indicated that the Langmuir model provided the best correlation of the experimental data for both dyes. The biosorption kinetic data were modeled using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetic equations. It was observed that the pseudo-second-order kinetic equation could explain the biosorption kinetics of dyes on rice husk. Thermodynamic parameters such as enthalpy change (ΔH°), entropy change (ΔS°) and free energy change (ΔG°) were also investigated. Free energy change showed that biosorption of Direct Red-31 and Direct Orange-26 was spontaneous at all studied temperatures (30–70 °C). Surface adsorption of both the dyes at specific binding sites was confirmed through and Fourier Transform infrared spectroscopic (FT-IR) analysis. The changes in surface morphology of rice husk before and after adsorption was investigated through scanning electron microscopy (SEM). It was implied that rice husk may be suitable as an adsorbent for removal of direct dyes from aqueous solutions.

10.2478/s11814-009-0325-1

The present investigation explored the use of Citrus reticulata waste biomass (CWB) for the removal of Pb(II) and Co(II) from the aqueous solutions. The Pb(II) and Co(II) biosorption was found to be dependent on pH of the solution, biosorbent dose, biosorbent particle size, temperature, shaking speed, contact time and initial concentration of metal ions. A metal uptake capacity of 41.16 and 52.64 mg/g was observed at pH 5 and 7 for Pb(II) and Co(II), respectively. The biosorption data followed the Freundlich model for both metals. The overall biosorption process was best described by pseudo-second order kinetics. The effect of several pretreatments on the biosorption efficiency of CWB was also investigated. The results demonstrated that pretreatments influenced the biosorption capacity of the biomass for the both metals significantly. Maximum biosorption capacity of 83.77 and 95.55 mg/g was observed for Pb(II) and Co(II) with sodium hydroxide treated and simply heated biomass, respectively. FTIR spectrum indicated the presence of -OH, -NH, -COOH groups in the biomass. The surface structure of CWB was analyzed by JEOL JMT 300 scanning electron microscope (SEM), and the existence of metal ions on the surface of biosorbent was determined by energy dispersive X-ray (EDX) spectroscopy.

Removal of Methylene Blue and Eriochrome Black T from aqueous solutions by biosorption on Scolymus hispanicus L.: Kinetics, equilibrium and thermodynamics

The biosorption of Methylene Blue (MB) and Eriochrome Black T (EBT) from aqueous solutions was investigated using low-cost, natural and eco-friendly biosorbent, Scolymus hispanicus L., as an ideal alternative to the current expensive methods of removing dyes from wastewater. The biosorption studies were carried out under various parameters, such as average biosorbent particle size, pH, biosorbent dosage, contact time, initial dye concentration and temperature. The experimental results show that the percentage of biosorption increases with an increase in the biosorbent dosage and the decrease of particle size. The maximum biosorption occurred at the pH value of 6.8 for Methylene Blue and 3 for Eriochrome Black T. The equilibrium uptake was increased with an increase in the initial dye concentration in solution. Biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. The experimental isotherms data were analyzed using Langmuir, Freundlich, Toth and Tempkin isotherm equations. The best fit was obtained by the Toth model with high correlation coefficients ( r 2 > 0.99). The Langmuir model also yielded a good fit to experimental data ( r 2 around 0.98–0.99) with a maximum monolayer adsorption capacity of 263.92 mg/g for Methylene Blue and 165.77 mg/g for Eriochrome Black T. The adsorption of the dyes was exothermic in nature (Δ H° = −19.79 kJ/mol for MB and −8.03 kJ/mol for EBT). The reaction was accompanied by a decrease in entropy (Δ S° = −54.01 J/K mol for MB and −23.88 J/K mol for EBT). The Gibbs energy (Δ G°) increased from −4.04 to −1.82 kJ/mol and from −1.32 to −0.41 kJ/mol respectively for MB and EBT when the temperature was increased from 20 to 60 °C.

Use of low cost crop biological wastes for the removal of Nitrobenzene from water

Low cost and locally available maize stems and rice stems as potential biosorbents were tested for their effectiveness in removing nitrobenzene (NB) from aqueous solution. The sorption capacities of the biosorbents were evaluated using isotherm tests and other factors such as solution pH and ionic strength, biosorbent loading and particle size, contact time and initial NB concentration were also investigated. The sorption equilibration time of NB at 25 °C was about 72 h, and the optimal NB removal efficiency was achieved with biosorbent particle size of 80–100 mesh, further decrease in biosorbent particle size contributed to little changes in NB removal efficiency. When the biosorbent dosage was 10 g L − 1 , the NB removal efficiency approached to the optimization. Both biosorbents performed similarly and NB was completely removed when treated at pH > 7. So the optimized biosorbent loading was 10 g L − 1 with optimum particle size of 80–100 mesh. High pH conditions (pH > 7) were found to improve NB removal, while increasing the ionic strength in solution was found to decrease NB removal efficiency. Maize and rice stems were shown to be capable in removing NB from solution and have demonstrated their potential use as biosorbents.

Biosorption characteristics of Cadmium(II) onto Scolymus hispanicus L. as low-cost natural biosorbent

This work reports the results of the study of Cadmium (II) removal from aqueous solution by the natural, plentiful and low-cost biosorbent Scolymus hispanicus L. using batch biosorption technique. The biosorption studies were carried out as a function of average biosorbent particle size, pH, biosorbent dosage, contact time, initial metal concentration and temperature. The percentage of biosorption increases with an increase in the biosorbent dosage and the decrease of particle size. The equilibrium metal uptake was increased with an increase in the initial concentration. The maximum biosorption occurred at pH 6.5. Biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. Equilibrium data were well interpreted by Langmuir model with maximum biosorption capacity of 54.05 mg g − 1. The biosorption is not temperature dependent. The FT-IR spectroscopic analysis of unloaded and Cadmium(II)-loaded Scolymus hispanicus L. confirmed that the functional groups on the biosorbent surface were involved in biosorption.

Biosorption of Zn (II) onto the Surface of Non-living Biomasses: A Comparative Study of Adsorbent Particle Size and Removal Capacity of Three Different Biomasses

Present research has delineated the biosorption potential of three different nonliving biomasses namely eucalyptus bark saw dust, mango bark saw dust, and pineapple fruit peel with respect to Zn (II) ion removal from liquid phase through batch experiments. The efficacy of Zn (II) ion biosorption onto surface of biosorbents was judged and correlated with biosorbent particle size, surface chemistry, and surface texture. Maximum metal ion uptake capacity, percentage removal, and minimum equilibrium concentration as 1.688 mg/g, 84.4%, and 1.56 mg/l, respectively, was obtained using eucalyptus bark saw dust mediated biosorption followed by mango bark saw dust as 1.028 mg/g, 51.4%, and 4.867 mg/l and pineapple fruit peel as 0.45 mg/g, 22.9%, and 7.71 mg/l, respectively, at a particle size of 0.5 mm. Additionally, present investigation also proved that biosorption efficiency and metal ion interaction with adsorbent surface also depends upon presence of functional groups involved in metal ion adsorption and surface porosity.

Removal of lead and cobalt using lignocellulosic fiber derived from Citrus reticulata waste biomass

The present investigation explored the use of Citrus reticulata waste biomass (CWB) for the removal of Pb(II) and Co(II) from the aqueous solutions. The Pb(II) and Co(II) biosorption was found to be dependent on pH of the solution, biosorbent dose, biosorbent particle size, temperature, shaking speed, contact time and initial concentration of metal ions. A metal uptake capacity of 41.16 and 52.64 mg/g was observed at pH 5 and 7 for Pb(II) and Co(II), respectively. The biosorption data followed the Freundlich model for both metals. The overall biosorption process was best described by pseudo-second order kinetics. The effect of several pretreatments on the biosorption efficiency of CWB was also investigated. The results demonstrated that pretreatments influenced the biosorption capacity of the biomass for the both metals significantly. Maximum biosorption capacity of 83.77 and 95.55 mg/g was observed for Pb(II) and Co(II) with sodium hydroxide treated and simply heated biomass, respectively. FTIR spectrum indicated the presence of -OH, -NH, -COOH groups in the biomass. The surface structure of CWB was analyzed by JEOL JMT 300 scanning electron microscope (SEM), and the existence of metal ions on the surface of biosorbent was determined by energy dispersive X-ray (EDX) spectroscopy.

Removal of Cu(II) and Zn(II) Using Lignocellulosic Fiber Derived from Citrus reticulata (Kinnow) Waste Biomass

The biosorption of Cu(II) and Zn(II) using dried untreated and pretreated Citrus reticulata waste biomass were evaluated. The Cu(II) and Zn(II) sorption were found to be dependent on the solution pH, the biosorbent dose, the biosorbent particle size, the shaking speed, the temperature, the initial metal ions (800 mg/L), and the contact time. Twenty-eight physical and chemical pretreatments of Citrus reticulata waste biomass were evaluated for the sorption of Cu(II) and Zn(II) from aqueous solutions. The results indicated that biomass pretreated with sulphuric acid and EDTA had maximum Cu(II) and Zn(II) uptake capacity of 87.14 mg/g and 86.4 mg/g respectively. Moreover, the Langmuir isotherm model fitted well than the Freundlich model with R 2 > 0.95 for both metal ions. The sorption of Cu(II) and Zn(II) occurred rapidly in the first 120 min and the equilibrium was reached in 240 min. FTIR and SEM studies were also carried out to investigate functional groups present in the biomass and the surface morphological changes of biomass.

Biosorption of Cu(II) ions from aqueous effluents by blackgram bran (BGB)

Biosorption of Cu(II) ions onto blackgram bran (BGB) waste biomass in a well stirred batch system was investigated and optimum conditions were determined. The maximum Cu(II) uptake capacity of BGB was 107.65 mg L −1 at pH 5, biosorbent dose 0.025 g/100 mL, biosorbent particle size <0.250 mm at an initial metal concentration of 50 mg L −1 achieved after equilibrium time of 480 min. The equilibrium data fitted very well to Langmuir isotherm model as compared to the isothermal model of Freundlich. The pseudo 1st and 2nd order kinetic models were used to describe the kinetic data. The experimental data fitted well to 2nd order kinetic model. Due to its outstanding Cu(II) ions uptake capacity, BGB biomass proved to be an excellent material of bioorigin for accumulating Cu(II) ions from aqueous solutions.

Dynamic biosorption of Zn(II) and Cu(II) using pretreated Rosa gruss an teplitz (red rose) distillation sludge

Abstract This work presented conditions for Cu(II) and Zn(II) removal using native, physically and chemically pretreated Rosa gruss an teplitz (red rose) distillation sludge. Cu(II) and Zn(II) sorption was found dependent on solution pH, biosorbent dose, biosorbent particle size, shaking speed, temperature, initial concentration of metal ions being sorbed and contact time. Physical and chemical pretreatments of biomass resulted in an increase or decrease in metals uptake capacity. The effect of different pretreatments is discussed in detail. Highest Cu(II) and Zn(II) biosorption capacities were observed for PEI + gluteraldehyde (68.64 mg/g) and NaOH (43.4 mg/g) pretreated biomass, respectively. The native biomass showed Cu(II) biosorption capacity that was adequately described by Freundlich isotherm, whereas Zn(II) biosorption phenomenon was described by Langmuir isotherm. The suitability of a pseudo-first-order chemical reaction for sorption of Cu(II) and Zn(II) ions onto this biomass was apparent as this kinetic model described adequately the largest part of the process.

Removal of Zn +2 and Ni +2 by adsorption in a fixed bed of wheat straw

Zn +2 and Ni +2 in a solution were removed by biosorption in a fixed bed of wheat straw Triticum aestivum. The removal rate and the mass transfer coefficient for Zn +2 and Ni +2 were found to be proportional to the liquid superficial velocity to the power of 0.31 for the range of the particle Reynolds number from 18 to 445 (equivalent liquid rates of 0.00070–0.0175 m 3 m −2 s −1). This agrees well with reported literature for mass transfer in a packed bed of solid particles under a laminar flow regime. Effect of the solution pH, temperature and the particle size (0.5, 1.0, 1.5 and 2.0 in.) on biosorption of Zn +2 and Ni +2 was also investigated. Biosorption of both Zn +2 and Ni +2 increased significantly with the solution pH from 4.0 to 7.0. On the other hand, Zn +2 and Ni +2 removal appeared to be insensitive to liquid temperature from 25 to 30 °C. Nevertheless, a 25% increase in the percentage removal of metal ions was observed with further increase of liquid temperature from 30 to 35 °C. However, the biosorbent particle size did not seem to have a systematic effect on the biosorption of Zn +2 and Ni +2. In addition, biosorption of Zn +2 was not affected considerably by co-adsorption of the bimetal solution while biosorption of Ni +2 decreased about 14%.

Kinetic and Equilibrium Modeling for Cr(III) and Cr(VI) Removal from Aqueous Solutions by Citrus reticulata Waste Biomass

The pulp left after the extraction of juice from Citrus reticulate (kinnow), is a waste material, which was used as a potential sorbent for Cr(III) and Cr(VI) in the present study. The effect of experimental parameters such as pH, biosorbent dosage, biosorbent particle size, initial metal concentrations, temperature, shaking speed and sorption time on the Cr removal is apparent from the obtained results. The Freundlich isotherm and pseudo second order kinetic models fitted well to the data of Cr(III) and Cr(VI) biosorption by Citrus reticulata waste biomass. Effect of several pretreatments such as gases, natural coagulant and many other chemicals on Cr(III) and Cr(VI) sorption capacity of Citrus reticulata waste biomass was first time analyzed in the present study. The metal sorption capacity of Citrus reticulata waste biomass after a specific pretreatment was not only related to the nature of chemical but also strongly dependent on the oxidation state of the metal.

Biosorption of zinc from aqueous solution using Azadirachta indica bark: Equilibrium and kinetic studies

The removal of zinc ions from aqueous solutions on the biomass of Azadirachta indica bark has been studied by using batch adsorption technique. The biosorption studies were determined as a function of contact time, pH, initial metal ion concentration, average biosorbent size and biosorbent dosage. The equilibrium metal uptake was increased and percentage biosorption was decreased with an increase in the initial concentration and particle size of biosorbent. The maximum zinc biosorption occurred at pH 6 and percentage biosorption increases with increase in the biosorbent dosage. Experimental data obtained were tested with the adsorption models like Langmuir, Freundlich and Redlich–Peterson isotherms. Biosorption isothermal data were well interpreted by Langmuir model with maximum biosorption capacity of 33.49 mg/g of zinc ions on A. indica bark biomass and kinetic data were properly fitted with the pseudo-second-order kinetic model.

Copper biosorption from aqueous solutions by sour orange residue

In this study, copper uptake by sour orange residue (SOR) was investigated. Equilibrium isotherms and kinetics were obtained and the effects of solution pH, temperature, and particle size were studied in batch experiments. Equilibrium was well described by Langmuir and Freundlich isotherms and kinetics was found to be best-fit pseudo-second order equations. Maximum uptake was observed at pH 5. With an increase in temperature from 20 to 50 °C, copper removal decreased about 20%. Additional chemical treatment of the biosorbent by NaOH, increased the biosorption capacity. It was found that increase in biosorbent particle size had no significant effects on the final equilibrium concentration, but decreased biosorption rate.

Removal of Zn(II) ions from aqueous solution using Moringa oleifera Lam. (horseradish tree) biomass

The removal of Zn(II) ions from aqueous solution using pure and chemically pretreated biomass of Moringa oleifera was investigated at 30 ± 1 °C in this study. The experimental results explored that the maximum pH (pH max) for efficient sorption of Zn(II) was 7 ± 0.1 at which evaluated biosorbent dosage and biosorbent particle size, were 0.5 g/L, <0.255 mm, respectively. The cellular Zn(II) concentration increased with the concentrations of Zn(II) in solution. Pretreatment of M. oleifera biomass affected the sorption process and the uptake capacity (mg/g) of biomass for Zn(II) uptake was in following order: NaOH (45.76) > H 2SO 4 (45.00) > CTAB (42.80) > Ca(OH) 2 (42.60) > Triton X-100 (42.06) > H 3PO 4 (41.22) > Al(OH) 3 (41.06) > SDS (40.41) > HCl (37.00) > non-treated biomass (36.07). There was significant increase in uptake capacity of M. oleifera biomass, which suggested that affinity between metal and sorbent can be increased after some sort of pretreatment. Both Langmuir and Freundlich isotherm model fitted well to data of Zn(II) biosorption as represented by high value of their correlation coefficient (i.e. R 2 ≈ 1). Kinetic studies revealed that Zn(II) uptake was fast with 90% or more of uptake occurring with in 40 min of contact time and the equilibrium was reached in 50 min of contact time. The sorption rates were better described by a second order expression than by a more commonly applied Lagergren equation. Finally it was concluded that pretreatment of M. oleifera biomass can achieve superior Zn(II) uptake capacity in comparison to non-pretreated biomass.

Zinc (II) ion recovery by biosorption onto powdered waste sludge (PWS): effects of operating conditions

AbstractPowdered waste sludge (PWS) obtained from a paint industry wastewater treatment plant and pretreated with 1% H2O2 was used for biosorption of Zn(II) ions from aqueous solution. The effects of operating conditions, pH, temperature, agitation speed, PWS particle size, Zn ion and PWS concentrations on the extent of Zn ion biosorption were investigated in batch experiments. The optimum pH resulting in maximum Zn ion biosorption was found to be pH = 5, since Zn ions precipitated in the form of Zn(OH)2 at pH levels above 5. The rate and extent of Zn ion biosorption increased with temperature between 25 and 50 °C, although biosorption was not strongly sensitive to temperature variations since the activation energy was low at 4.5 kcal mol−1. Biosorbent particle size had a significant effect on Zn ion biosorption, yielding high percentage Zn removals at small particle sizes (Dp &lt; 100 µm) or large surface areas of PWS. Agitation speed also considerably affected the extent of Zn ion removal, and should be above 150 rpm in order to obtain a high rate. The extent of Zn ion biosorption was also affected by the initial Zn ion and PWS concentrations. At constant biosorbent (PWS) concentration, percentage Zn ion removal decreased, but the biosorbed Zn concentration increased with increasing initial Zn ion concentrations. However, at constant initial Zn concentrations, percentage Zn removal increased, but the biosorbed Zn ion concentration decreased with increasing adsorbent (PWS) concentration. With a maximum Zn ion biosorption capacity of 168 mg g−1 powdered waste sludge was proven to be an effective biosorbent compared to other biosorbents. Copyright © 2006 Society of Chemical Industry