Review on the Effectiveness of using Bio-Char as an Adsorbent for the Removal of Water Pollutants

In the last few decades, biochar has been effectively used in water remediation and for improving soil fertility. Due to an aggravated desire for zero pollution and green technology, biochar application is gaining interest in wastewater treatment. Adsorption has been regarded as a clean and less costly technology to decontaminate water laden with harmful materials including heavy metals, dyes, pesticides, herbicides etc. Therefore, a review of the effectiveness of biochar derived from different feedstocks used as adsorbents is given in this paper. These include biochar from agricultural and forest residues, industrial by-products and waste, municipal solid waste materials, waste tyres and paper. In addition, this study reveals the effect of surface functional groups, surface charges, surface area, elemental composition and other parameters such as pyrolysis temperature, adsorbent and adsorbate concentrations, solution pH and others on the removal efficiencies. To achieve this, studies have been compiled using biochar derived from agricultural and forest residues. It was found that biochar feedstocks and pyrolysis temperature determine most of the biochar characteristics and their behaviour during removal of contaminants. Among these characteristics are the oxygenated surface functional groups which were found to aid in the removal of positively charged contaminant due to their negative charge hence electrostatic attraction. Furthermore, other reaction mechanisms involved during adsorption include surface complexation, ion exchange, chelation etc. Kinetic models were used to predict these mechanisms while kinetic isotherms predicted whether monolayer or multilayer adsorption occurred. This study has revealed that conversion of biomass to biochar offers an excellent alternative to waste management, wastewater treatment and green technology therefore intensive research on this topic should be of priority.