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The study provides a review of various applications of biomass-derived biochars, waste-derived biochars, and modified biochars as adsorbent materials for removing dyestuff from process effluents. Processing significant amounts of dye effluent discharges into receiving waters can supply major benefits to countries which are affected by the water crisis and anticipated future stress in many areas in the world. When compared to most conventional adsorbents, biochars can provide an economically attractive solution. In comparison to many other textile effluent treatment processes, adsorption technology provides an economic, easily managed, and highly effective treatment option. Several tabulated data values are provided that summarize the main characteristics of various biochar adsorbents according to their ability to remove dyestuffs from wastewaters. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fractional Theoretical Capacity measure was proposed for isotherm model selection. [•] Using error analysis statistics alone may lead to wrong isotherm model selection. [•] The sorption system for all dyes was heterogeneous based on the Toth model. [•] Fractal dimension can be determined based on the theoretical sorption capacity. [•] The sorbent (GAC) surface was smooth according to the fractal dimension parameter. [Copyright &y& Elsevier]

A comparison of chi-square (X²) and Log-likelihood (G²) statistics of 19 adsorption isotherm models--seven two-parameter models (Langmuir, Freundlich, Dubinin-Radushkevich, Tem- kin, Jovanovic, Harkins-Jura and Halsey) and 12 three-parameter models (Koble-Corrigan, Langmuir-Freundlich, Toth, Redlich-Peterson, Radke-Prausnitz (three models), Fritz-Schlun- der, Jossens, Khan, UNILAN, Vieth-Sladek) have been applied to the experiment of two dyes (Acid Blue 113, Acid Black 1) sorption onto Granular PineCone derived Activated Carbon (GPAC) and three dyes (Acid Blue 80, Acid Red 114, Acid Yellow 117) sorption onto Granular Activated Carbon type Filtrasorb 400 (GAC F400). The study has focused on the assessment of the adequacy and goodness of the fitted models, using two well-known--X² and G²--statistics. The results showed that G² could be better than X² statistic when the number of model parameters is three. [ABSTRACT FROM AUTHOR]

The adsorption of a reactive dye, Ariazol Scarlet 2G (AS2G) (C.I.: Reactive Red 234), onto compost, from aqueous solutions, was studied in a batch system. The effects of initial dye concentration, initial pH and sorbent mass have been studied. Four two-parameter isotherm models--Langmuir, Freundlich, Temkin and Harkins Jura -- were used to fit the experimental data using a nonlinear trial-and-error method. The best fit of the adsorption isotherm data was obtained using the Langmuir model (X² = 1.97E-03). A comparison of kinetic models applied to the adsorption of AS2G on compost was evaluated using the pseudo-second order, Elovich and Lagergren first-order kinetic models. Results showed that the pseudo-second order kinetic model was found to agree well with the experimental data. An intra-particle diffusion model analysis showed multi-linearity with two steps and a non-zero intercept which indicated the intra-particle diffusion model is not a dominant rate controlling mechanism in the sorption of AS2G by compost. [ABSTRACT FROM AUTHOR]

Abstract: A number of chars from waste tyre rubber were prepared by carbonisation at 673–1173K. The effects of holding time, heating rate and particle size on the textural characteristics and elemental composition of the resultant chars were investigated. It was demonstrated that temperatures over 773K did not have a significant improvement on the total surface area but resulted in lower char yields following increased aromatisation. Modelling of dye adsorption isotherms showed that the Redlich–Peterson expression yields the best-fit between experimental and predicted data. Furthermore, for a larger sized dye like Acid Yellow 117 (MW=848g/mol), the amount adsorbed by the tyre char is not directly proportional to the total surface area when compared with a commercial carbon, revealing that factors other than total surface area are involved in the adsorption potential of the tyre chars. [Copyright &y& Elsevier]

Abstract: Two types of activated carbons from tyre char (with or without sulphuric acid treatment) were produced via carbon dioxide activation with BET surface areas in the range 59–1118m2/g. Other characterisation tests include micropore and mesopore surface areas and volumes, pH, and elemental compositions, particularly heteroatoms such as nitrogen and sulphur. They were correlated to the adsorption capacity which were in the range of 0.45–0.71mmol/g (untreated) and 0.62–0.84mmol/g (acid-treated) for Acid Blue 25. In the case of larger-sized molecules like Acid Yellow 117, capacities were in the range of 0.23–0.42mmol/g (untreated) and 0.29–0.40mmol/g (acid-treated). Some tyre carbons exhibit a more superior performance than a microporous, commercial activated carbon (Calgon® F400). By modelling the dye adsorption equilibrium data, the Redlich–Peterson isotherm is adopted as it has the lowest SSE. Based on the surface coverage analysis, a novel molecular orientation modelling of adsorbed dyes has been proposed and correlated with surface area and surface charge. For the acid dyes used in this study, molecules were likely to be adsorbed by the mesopore areas. [Copyright &y& Elsevier]

Abstract: Experiments have been carried out to prepare char from waste bamboo scaffolding for wastewater treatment. Carbonisation parameters such as temperature, holding time, heating rate and particle size were investigated. When the material was heated to 1173K for 2h, surface area and total pore volume (V total) were 327m2/g and 0.185cm3/g, respectively. Particle size and heating rate appear less influential to the yield and textural characteristics of the resultant chars. Bamboo char obtained in this study did not show very high adsorption capacities for two acid dyes (Acid Blue 25 and Acid Yellow 117) but exhibited significant uptake of Methylene Blue. The equilibrium data were modelled by three different isotherms, namely, Langmuir, Freundlich and Redlich–Peterson model. Comparing the predicted data using optimised parameters from each model based on the SSE error function, the Redlich–Peterson isotherm appears the ‘best’ model to correlate experimental data. [Copyright &y& Elsevier]

Abstract: The disposal of waste tyre represents a serious concern in environmental management. Owing to the high carbon content of waste tyre rubber, it is feasible to convert waste tyres to a value-added product, i.e. activated carbon, for environmental applications. This study focuses on the effect of different activation conditions (e.g. temperature, holding time and acid treatment) on the porosity of activated carbons produced from tyre rubber. Experimental studies showed that nitric acid treatment to tyre chars is able to remove certain mineral contents such as Ca, K and Na, which affect the reactivity of gas–solid reactions in the subsequent physical activation process (CO2 as activating agent). Those acid-treated carbons developed high surface areas (over 1000m2/g) that were comparable to commercial products. They also posses high mesopore volume up to 0.855cc/g which has been shown favourable to the adsorption of larger-sized dye molecules. The Redlich–Peterson equilibrium isotherm model yielded the best-fit to experimental data for all three dyes using the non-linear error functions. [Copyright &y& Elsevier]