Mechanisms and Factors Influencing Adsorption of Microcystin-LR on Biochars

Abstract

The adsorption of microcystin-LR (MCLR) by biochar has never been well understood. For the first time, the unconventional adsorption of hydrophilic MCLR on wood-based biochars was comprehensively investigated as a function of biochar properties, environmental temperature, solution pH, coexisting dissolved organic matter (DOM), and polar organic competitors. High-temperature-prepared biochar from 700°C (BC-700) and low-temperature-prepared biochar from 300°C (BC-300) were characterized with significantly different surface areas but similar alkaline nature. Despite a very low surface area, BC-300 exhibited very high adsorption capacity, which implies the important contribution of surface groups to biochar. MCLR adsorption on biochars was pH dependent and was strongly reduced by macromolecular DOM. Polycarboxylic aliphatic acids and 2-(2-hydroxyethyl) guanidinium cation, which are similar to specific structural groups in MCLR, exhibited an evident competitive effect. The results indicated that both carboxylic and guanidino groups of MCLR serve significant functions in MCLR adsorption to biochar. The adsorption mechanisms may be primarily related to the columbic attractions and the hydrogen bonding interactions between MCLR and biochar surface. In particular, the irreversible adsorption enhancement of MCLR was observed on BC-700, which suggests that biochar amendment can aid in immobilizing MCLR from water to sediment, thereby prolonging MCLR environmental fate in biocharamended sediment.

The challenges of anaerobic digestion and the role of biochar in optimizing anaerobic digestion

“…The factors that influence the performance of adsorbent during adsorption have been extensively reported in literature. These parameters include the contact time, operating temperature, adsorbent and adsorbate dosage, particle size and pore distribution, surface chemistry and pH (Li et al, 2014;Hadi et al, 2015;Yargicoglu et al, 2015).…”

The Use of Biochar and Pyrolysed Materials to Improve Water Quality through Microcystin Sorption Separation

“…Π ± π EDA represents π ± π electron donor-acceptor interactions between protonated guanidine groups of MCs and π-electron rich graphene surfaces of biochar [28]. Π − π stacking is the main interaction between the benzene ring of MCs and aromatic units on biochar surfaces [74]. As mentioned previously, molecules of MCs have a more hydrophilic character with reactive carboxyl or guanidine functional groups.…”

“…The authors highlighted a number of natural and artificial materials with extensive internal porosity for application in water purification. Despite possessing a lipophilic side chain of ADDA residue, molecules of microcystins are quite hydrophilic because of two carboxylic groups on its aspartic/glutamic acid side and one guanidine group on its arginine acid side [74]. Kim et al [75] applied industrial waste biomass of Escherichia coli to develop biosorbents for MC-LR immobilization.…”

“…The study of biochar application in the removal of various organic structures has illustrated the potential of this pyrogenic material in separation processes. The biochar boom in environmental technologies and agronomy raised the question of potential risk evaluation for MCs interaction with this pyrogenic carbonaceous material present in sediment/water environments [74]. While at the same time, Zhang et al [29], Li et al [27], and Liu et al [28] revealed the efficiency of modified charcoal and biochar utilization as potential sorbents of MC-LR from aqueous solutions.…”

“…As mentioned previously, molecules of MCs have a more hydrophilic character with reactive carboxyl or guanidine functional groups. Therefore, the dominant mechanism of MCs sorption can be often attributed to hydrophobic interactions [74]. Liu et al [28] reported that the hydrophobic leucine unit in a MC-LR molecule tends to be attracted to hydrophobic surfaces of giant reed-derived biochar via a hydrophobic interaction.…”