Insight into biochar properties and its cost analysis

Biochars (BCs) are widely produced and used for the remediation of environmental contaminants as bio-sorbents. In this review, statistical analysis of different BC physico–chemical properties was conducted. It was observed that woody materials are the most suitable for preparing BCs, among many other potential raw materials such as food wastes and agricultural materials. Currently BCs are produced through a variety of thermal treatment processes between 300 and 900 °C, among which slow pyrolysis is widely used due to its moderate operating conditions and optimization of BC yields. Hydrothermal carbonisation (HTC) is also an effective approach for BC production under certain conditions. As pyrolysis temperature is increased, the carbon content, ash content, surface area, and pore volume tend to be increased while the yield, hydrogen, oxygen, nitrogen content, and H/C and O/C molar ratios tend to decrease. The economic feasibility of BCs depends on a range of factors from raw material price to efficient production technologies. Thus, the overall cost equation of a pilot BC production plant together with the cost equation for BC regeneration has been proposed. The future research directions of BCs are also elaborated.     

Surface modified bacterial biosorbent with poly(allylamine hydrochloride): Development using response surface methodology and use for recovery of hexachloroplatinate(IV) from aqueous solution

In this study, poly(allylamine hydrochloride) (PAA/HCl) was cross-linked with fermentation bacterial waste (Escherichia coli) in order to introduce a large amount of amine groups as binding sites for potassium hexachloroplatinate(IV), as a model anionic pollutant. The sorption performance of PAA/HCl-modified E. coli was greatly affected by the dosages of PAA/HCl and crosslinker (epichlorohydrin, ECH), and by the pH of the modification reaction medium. These factors were optimized through the response surface methodology (RSM). A three-level factorial Box-Behnken design was performed, and a second-order polynomial model was successfully used to describe the effects of PAA/HCl, ECH and the pH on the Pt(IV) uptake (R² = 0.988). The optimal conditions that were obtained from the RSM were 0.49 g of PAA/HCl, 0.05 mL of ECH and pH 10.02, with 1.0 g of dried E. coli biomass. The biosorption isotherm and kinetics studies were carried out in order to evaluate the sorption potential of the PAA/HCl-modified E. coli that was prepared under the optimized conditions. The sorption performance of the developed bacterial biosorbent was 4.36 times greater than that of the raw E. coli. Desorption was carried out using 0.05 M acidified thiourea and the biosorbent was successfully regenerated and reused up to four cycles. Therefore, this simple and cost-effective method suggested here is a useful modification tool for the development of high performance biosorbents for the recovery of anionic precious metals.     

Biosorptive removal of Pband Cd onto novel biosorbent: Defatted Carica papaya seeds

Carica papaya seeds, an agricultural waste in Nigeria, were defatted to obtain defatted C. papaya seed biosorbent. The Fourier Transformed Infrared spectrum of defatted C. papaya seed biosorbent suggests the presence of CO, OH of carboxylic acid, lactonic and amide band functional groups. The adsorption of metal ion onto defatted C. papaya seed biosorbent led to small shifts in the IR bands. The adsorption capacity of defatted C. papaya seed biosorbent was evaluated to be 1666.67 mg/g for Pb²⁺ and 1000.00 mg/g for Cd²⁺. In binary metal ion solution, the defatted C. papaya seeds showed decreased adsorption capacity for either metal ion. The influence of different particle sizes was found to have negative impact on the adsorption capacity of C. papaya seed biosorbent in the removal of Pb²⁺ and Cd²⁺ from aqueous solution. The adsorption of both metal ions was observed to follow the Freudlich model better than the Langmuir model suggesting that the adsorption of both metal ions was on multisites on the defatted C. papaya seed biosorbent. The adsorption was found to be highly feasible, spontaneous and exothermic in nature. Optimization results suggests 5 m³ of 100 mg/L of Pb²⁺ and Cd²⁺ requires 43.3 and 49.2 kg of defatted C. papaya seeds to remove 95% of the metal ions from aqueous solution.     

Use of Ponkan mandarin peels as biosorbent for toxic metals uptake from aqueous solutions

Waste Ponkan mandarin (Citrus reticulata) peel was used as biosorbent to extract Ni(II), Co(II) and Cu(II) from aqueous solutions at room temperature. To achieve the best adsorption conditions the influence of pH and contact time were investigated. The isotherms of adsorption were fitted to the Langmuir equation. Based on the capacity of adsorption of the natural biosorbent to interact with the metallic ions, the following results were obtained 1.92, 1.37 and 1.31 mmol g(-1) for Ni(II), Co(II) and Cu(II), respectively, reflecting a maximum adsorption order of Ni(II)>Co(II)>Cu(II). The quick adsorption process reached the equilibrium before 5, 10 and 15 min for Ni(II), Co(II) and Cu(II), respectively, with maximum adsorptions at pH 4.8. In order to evaluate the Ponkan mandarin peel a biosorbent in dynamic system, a glass column was fulfilled with 1.00 g of this natural adsorbent, and it was fed with 5.00 x 10(-4)mol l(-1) of Ni(II) or Co(II) or Cu(II) at pH 4.8 and 3.5 ml min(-1). The lower breakpoints (BP(1)) were attained at concentrations of effluent of the column attained the maximum limit allowed of these elements in waters (>0.1 mg l(-1)) which were: 110, 100 and 130 bed volumes (V(effluent)/V(adsorbent)), for Ni(II), Co(II) and Cu(II), respectively. The higher breakpoints (BP(2)) were attained when the complete saturation of the natural adsorbent occurred, and the values obtained were: 740, 540 and 520 bed volumes for Ni(II), Co(II) and Cu(II), respectively.     

Continuous-flow metal biosorption in a regenerable Sargassum column

Metal biosorption behavior of raw seaweed S. filipendula in ten consecutive sorption-desorption cycles has been investigated in a packed-bed flow-through column during a continuous removal of copper from a 35mg/L aqueous solution at pH 5. The elutant used was a 1% (w/v) CaCl2/HCl-solution at pH 3. The sorption and desorption was carried out for an average of 85 and 15h, respectively, representing more than 41 days of continuous use of the biosorbent. The weight loss of biomass after this time was 21.6%. The Cu-biosorption capacity of the biomass, based on the initial dry weight, remained relatively constant at approximately 38 mg Cu/g. Loss of sorption performance was indicated by a shortening breakthrough time and a broadening mass-transfer zone. The column service time, considered up to 1 mg Cu/L in the effluent, decreased continuously from 25.4 h for the first to 12.7 h for the last cycle. The critical bed length, representing the mass-transfer zone, increased almost linearly from 28 to 34cm. "Life-factors" for S. filipendula were found to be 0.0008h(-1) for the breakthrough time and 0.008cm/h for the critical bed length, using an exponential decay and linear fitting functions, respectively. Regeneration with CaCl2/HCl at pH 3 provided elution efficiencies up to 100%. Maximum concentration factors were determined to be in the range 16-44, a decreasing tendency was observed with an increasing exposure time.     

Biosorption of cadmium (II) and lead (II) from aqueous solutions using mushrooms: A comparative study

Sorption capacity of oyster mushroom (Pleurotus platypus), button mushroom (Agaricus bisporus) and milky mushroom (Calocybe indica) were evaluated on biosorption of heavy metals, viz. cadmium (II) and lead (II) from aqueous solutions. The optimum sorption conditions were studied for each metal separately. The desired pH of the aqueous solution was found to be 6.0 for the removal of cadmium (II) and 5.0 for removal of lead (II) for all the mushrooms. The percent removal of both the metals was found to increase with the increase in biosorbent dosage and contact time. The fitness of the biosorption data for Langmuir and Freundlich adsorption models was investigated. It was found that biosorption of cadmium (II) and lead (II) ions onto the biomass of the three mushrooms were better suitable to Langmuir than Freundlich adsorption model. P. platypus showed the highest metal uptake potential for cadmium (q_max 34.96 mg/g) whereas A. bisporus exhibited maximum potential for lead (q_max 33.78 mg/g). Milky mushroom showed the lowest metal uptake capacity for both the metals. The present data confirms that mushrooms may be used as efficient biosorbent for the removal of cadmium (II) and lead (II) ions from aqueous solution.     

Statistical evaluation of dye desorption – mixed two- and three-level design and kinetic modeling

Abstract

Biosorption has been shown in the literature to be effective in the removal of dye from aqueous solution. To be fully useful, a desorption process is necessary, which has a direct impact on the process costs. The aim of this work was to evaluate the desorption of the azo dye Acid Yellow 23 adsorbed in a biosorbent obtained from Bombyx mori cocoons. Temperature and pH media were evaluated through a mixed two- and three-level design, using NaOH as desorbing agent. Kinetic desorption was also obtained at the optimized condition. The statistical evaluation of the experimental design showed that the pH has almost two times more influence on the dye desorption than the temperature, with only the linear parameters being statistically significant. Among four kinetic desorption models adjusted to the experimental data, the proposed n-order model was statistically determined as the best representation of the experimental data.     

Copper desorption from Gelidium algal biomass

Desorption of divalent copper from marine algae Gelidium sesquipedale, an algal waste (from agar extraction industry) and a composite material (the algal waste immobilized in polyacrylonitrile) was studied in a batch system. Copper ions were first adsorbed until saturation and then desorbed by HNO(3) and Na(2)EDTA solutions. Elution efficiency using HNO(3) increases as pH decreases. At pH=1, for a solid to liquid ratio S/L=4gl(-1), elution efficiency was 97%, 95% and 88%, the stoichiometric coefficient for the ionic exchange, 0.70+/-0.02, 0.73+/-0.05 and 0.76+/-0.06 and the selectivity coefficient, 0.93+/-0.07, 1.0+/-0.3 and 1.1+/-0.3, respectively, for algae Gelidium, algal waste and composite material. Complexation of copper ions by EDTA occurs in a molar proportion of 1:1 and the elution efficiency increases with EDTA concentration. For concentrations of 1.4, 0.88 and 0.57 mmoll(-1), the elution efficiency for S/L=4gl(-1), was 91%, 86% and 78%, respectively, for algae Gelidium, algal waste and composite material. The S/L ratio, in the range 1-20gl(-1), has little influence on copper recovery by using 0.1M HNO(3). Desorption kinetics was very fast for all biosorbents. Kinetic data using HNO(3) as eluant were well described by the mass transfer model, considering the average metal concentration in the solid phase and the equilibrium relationship given by the mass action law. The homogeneous diffusion coefficient varied between 1.0 x 10(-7)cm(2)s(-1) for algae Gelidium and 3.0 x 10(-7)cm(2)s(-1) for the composite material.     

Removal of heavy metals from aqueous solution by nonliving Ulva seaweed as biosorbent

The growth of dense green seaweed mats of Ulva spp. is an increasing problem in estuaries and coasts worldwide. The enormous amount of Ulva biomass thus becomes a troublesome waste disposal problem. On the other hand, it has been revealed that nonliving seaweed biomass, particularly brown seaweeds, has a high capacity for assimilating heavy metals. In this study, the possibility of using Ulva seaweed biomass as a biosorbent for the removal of heavy metals was examined. After processing, the biomass material was very easy to separate from the aqueous solution using a mesh. The sorption capacity of Cd on Ulva biomass increased upon pretreatment with alkali solution. The outstanding function of the biosorbent was demonstrated at around pH 8. On the basis of the Langmuir isotherms of Cd, Zn and Cu using the alkali-pretreated biomass, the parameters q(m) and b were determined to be within the narrow range of 60-90 mg/g and 0.03-0.04 L/mg, respectively, for each metal. Given the q(m) and b values, Ulva seaweed is a good biosorbent material for removing heavy metals. In an experiment using artificial wastewater containing Cd, Zn, Cu, Cr and Ni, it was possible to remove each metal simultaneously using Ulva biomass. Adsorption by Ulva biomass is effective for the removal of heavy metals from wastewater.     

Methylene blue biosorption from aqueous solutions by yellow passion fruit waste

The yellow passion fruit (Passiflora edulis Sims. f. flavicarpa Degener) (YPFW) a powdered solid waste, was tested as biosorbent for the removal of a cationic dye, methylene blue (MB), from aqueous solutions. Adsorption of MB onto this low-cost natural adsorbent was studied by batch adsorption at 25 °C. The effects of shaking time, biosorbent dosage and pH on adsorption capacity were studied. In alkaline pH region the adsorption of MB was favorable. The contact time required to obtain the maximum adsorption was 48 h at 25 °C. Four kinetic models were tested, being the adsorption kinetics better fitted to pseudo-first order and ion exchange kinetic models. The ion exchange and pseudo-first order constant rates were 0.05594 and 0.05455 h⁻¹, respectively. The equilibrium data were fitted to Langmuir, Freundlich, Sips and Redlich–Peterson isotherm models. Taking into account the analysis of the normal distribution of the residuals (difference of q_measured − q_model), the data were best fitted to Sips isotherm model. The maximum amount of MB adsorbed on YPFW biosorbent was 44.70 mg g⁻¹.