# Biochar for Wastewater Treatment--Conversion Technologies and Applications
## 4 Biochar as an Efficient Adsorbent for Organic and Inorganic Pollutants  
### Organic Pollutants  
Biochar derived from different biomass have been intensively and effectively used as sorbents for organic contaminants in water and wastewater. The greatest concern of organic contaminants in aqueous solutions has been focused on phenols and dyes (Table 2). For instance, pyrolysis biochar derived from macroalgae have been effectively used to remove textile dyes (malachite green, crystal violet and Congo red), which are hardly degraded due to their stability to light and oxidizing agents, and resistance to aerobic digestion [20]. Other biochars derived from switchgrass at higher than normal pyrolysis temperatures were used to effectively remove methylene blue, orange G, and Congo red [21]. The results indicated that methylene blue (cationic dye) was highly adsorbed than orange G and Congo red (anionic dye), this was reported due to the small molecular weight of methylene blue and its favorable electrostatic property and strong \(\pi\)-\(\pi\) interaction with biochar surface. Adsorption was also high for biochars prepared at 900 \({}^{\circ}\)C than those prepared at 600 \({}^{\circ}\)C due to the significantly enhanced surface area at the highest pyrolysis temperature. Biochar have also been reported as an effective adsorbent for phenols in wastewater [97; 98]. The study of [PERSON] et al. [97] investigated the potential of biochar derived from chicken manure to remove toxic phenol and 2_A_-dinitrophenol from aqueous solution. The obtained biochar exhibited higher adsorption capacities; 106.2 m\({}^{2}\)/g for phenol and 148.1 mg/g for 2,4-dinitrophenol and a high stability up to five cycles. According to the authors, the interaction mechanisms such as hydrogen bonding, electrostatic interaction and \(\pi\)-\(\pi\) bonding are possibly interfering during the adsorption of phenols on biochar under various conditions [97]. In the study performed by [PERSON] and [PERSON] [99], polymer/ biomass-derived biochar was used for the removal of ionizable halogenated phenols from aqueous solution. Solution pH was an important factor in controlling the hydrophobicity and deprotonation of compounds, which was confirmed by correlation analysis of the maximum sorption capacity.  
The effectiveness of straw-based biochar as compared to that of commercial activated carbon to remove dyes (reactive brilliant blue and rhodamine B) was evaluated by [PERSON] et al. [100]. Both carbon materials showed high affinity to adsorb reactive brilliant blue and rhodamine B at pH values of 3.0 and 6.5 with slight difference in favor of biochar to adsorb rhodamine B due to the enhancement of the \(\pi\)-\(\pi\) interactions by the surface functional groups of the biochar. In another study performed by [PERSON] et al. [101], authors compared the adsorptive performance of biochars from paper mill sludge with commercial activated carbon to remove fish anaesthetics from water in recirculating aquaculture systems. Despite the higher adsorption capacity of the commercial activated carbon (289-631 mg/g) as compared to the biochars (53-109 mg/g), the authors concluded that paper mill sludge-based adsorbents could be considered as a cost-effective alternative for the adsorption of fish anaesthetics considering that the cost associated to the precursor (paper mill sludge) of these adsorbents is null and the production process did not use chemicals and allows the recovery of energy from wastes, which makes the whole process as an environmentally friendly process.