Search

Publisher Copyright: © 2022 The Authors Adsorption is a well known effective technology for water treatment. Although limited capacities of adsorbents and regeneration issues are two common challenges. This study proposed and tested innovative approaches for improving adsorption/desorption of biochar made from macadamia nutshell (MBC). These approaches are capacitive deionization (CDI) and degaussing (full process detailed in methods), for the respective enhancement of adsorption and desorption of MBC. Nitrate was used as a model contaminant. It was found that CDI could extend the saturation time of MBC by increasing the bed specific throughput by 10 fold. Modeling of the breakthrough curves showed that the modified dose-response model fits well the experimental data. The regeneration of MBC with degaussing and deionized water backwash was compared with conventional tap and deionized water backwash. Degaussing increased the maximum nitrate recovery for deionized water from 50% to 73%. In comparison, the maximum nitrate recovery with tap water was 23%. The degaussing improvement of nitrate desorption holds for only the first 60 min. The obtained charge efficiency for MBC-CDI was slightly higher than literature values for the same applied voltage (78,6%). The degaussing system was also proven to be efficient with energy consumption of 43,7 J/mmol of NO3−. The possible mechanism behind degaussing improvement of nitrate desorption is the removal of the static charges on nitrate ion hydration. The regenerated MBC with degaussing and deionized water was tested with CDI for nitrate adsorption and compared to fresh MBC. The regenerated MBC-CDI exhibited better nitrate adsorption than fresh MBC for two cycles.

The removal of inorganic arsenic (As) species from water using bone char pyrolyzed at 900 °C was investigated. Results revealed that the Sips model resulted in the best As(III) experimental data fit, while As(V) data were best represented by the Langmuir model. The adsorption rate and mechanisms of both As species were investigated using kinetic and diffusional models, respectively. At low As(III) and As(V) concentrations of 0.5 and 2.5 mg/L, the removal was due to intra-particle interactions and pore diffusion following Pseudo-first-order kinetics. However, at higher concentrations of 5 and 10 mg/L, the pore diffusion mechanism was ineffective, and the adsorption was best described by Pseudo-second-order and Elovich models. The goodness of the fit of linearized and nonlinear forms of all models against experimental data was thoroughly tested using error function analysis. Nonlinear regressions produced lower error values, so they were utilized to calculate the parameters of the models. The changes in bone char surface chemistry were examined using FTIR and Energy-dispersive X-ray spectroscopy (EDS). Arsenic oxide and complexes with metals were the confirmed immobilized forms of As on the bone-char surface. To the authors’ knowledge, this study is the first attempt at As(III) adsorption analysis using bone char.

This study examined arsenite [As(III)], arsenate [As(V)] and fluoride (F−) removal potential of bone char produced from sheep (Ovis aries) bone waste. Pyrolysis conditions tested were in the 500 °C–900 °C range, for a holding time of 1 or 2 h, with or without N2 gas purging. Previous bone char studies mainly focused on either low or high temperature range with limited information provided on As(III) removal. This study aims to address these gaps and provide insights into the effect of pyrolysis conditions on bone char sorption capacity. A range of advanced chemical analyses were employed to track the change in bone char properties. As pyrolysis temperature and holding time increased, the resulting pH, surface charge, surface roughness, crystallinity, pore size and CEC all increased, accompanied by a decrease in the acidic functional groups and surface area. Pyrolysis temperature was a key parameter, showing improvement in the removal of both As(III) and As(V) as pyrolysis temperature was increased, while As(V) removal was higher than As(III) removal overall. F− removal displayed an inverse relationship with increasing pyrolysis temperature. Bone char prepared at 500 °C released significantly more dissolved organic carbon (DOC) then those prepared at a higher temperature. The bone protein is believed to be a major factor. The predominant removal mechanisms for As were surface complexation, precipitation and interaction with nitrogenous functional groups. Whereas F− removal was mainly influenced by interaction with oxygen functional groups and electrostatic interaction. This study recommends that the bone char pyrolysis temperature used for As and F− removal are 900 °C and 650 °C, respectively.

Arsenic (As) is an emerging contaminant on a global scale posing threat to environmental and human health. The relatively brief history of the applications of biochar and bone char has mapped the endeavors to remove As from water to a considerable extent. This critical review attempts to provide a comprehensive overview for the first time on the potential of bio- and bone-char in the immobilization of inorganic As in water. It seeks to offer a rational assessment of what is existing and what needs to be done in future research as an implication for As toxicity of human health risks through acute and chronic exposure to As contaminated water. Bio- and bone-char are recognized as promising alternatives to activated carbon due to their lower production and activation cost. The surface modification via chemical methods has been adopted to improve the adsorption capacity for anionic As species. Surface complexation, ion exchange, precipitation and electrostatic interactions are the main mechanisms involved in the adsorption of As onto the char surface. However, arsenic-bio-bone char interactions along with their chemical bonding for the removal of As in aqueous solution is still a subject of debate. Hence, the proposed mechanisms need to be scrutinized further using advanced analytical techniques such as synchrotron-based X-ray. Moving this technology from laboratory phase to field scale applications is an urgent necessity in order to establish a sustainable As mitigation in drinking water on a global scale. Keywords: Inorganic arsenic, Engineered biochar, Bone char, Surface modification, Sorption capacity, Immobilization