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

Abstract

Harmful algal blooms have increased globally with warming of aquatic environments and increased eutrophication. Proliferation of cyanobacteria (blue-green algae) and the subsequent flux of toxic extracellular microcystins present threats to public and ecosystem health and challenges for remediation and management. Although methods exist, there is currently a need for more environmentally friendly and economically and technologically feasible sorbents. Biochar has been proposed in this regard because of its high porosity, chemical stability, and notable sorption efficiency for removing of cyanotoxins. In light of worsening cyanobacterial blooms and recent research advances, this review provides a timely assessment of microcystin removal strategies focusing on the most pertinent chemical and physical sorbent properties responsible for effective removal of various pollutants from wastewater, liquid wastes, and aqueous solutions. The pyrolysis process is then evaluated for the first time as a method for sorbent production for microcystin removal, considering the suitability and sorption efficiencies of pyrolysed materials and biochar. Inefficiencies and high costs of conventional methods can be avoided through the use of pyrolysis. The significant potential of biochar for microcystin removal is determined by feedstock type, pyrolysis conditions, and the physiochemical properties produced. This review informs future research and development of pyrolysed materials for the treatment of microcystin contaminated aquatic environments.

Immobilization of Microcystin by the Hydrogel–Biochar Composite to Enhance Biodegradation during Drinking Water Treatment

“…This is likely due to the higher aromatic content in FSHA than in MC-LR that competes with MC-LR for the binding sites on BC via π–π interactions . Furthermore, FSHA (average molar mass 39.098 kDa) can also block BC mesopores to hinder the adsorption of MC-LR (∼1 kDa) by BC. ,, Therefore, the presence of FSHA negatively impacted the two major driving forces of MC-LR adsorption by BC (π–π interactions and mesopore filling) . Coating PDDA hydrogel on BC also reduced the mesopore volume (from 0.055 to 0.027 cm 3 /g as shown in Figure S2) but introduced new functional groups to the adsorbent, consequently altered the mechanisms of MC-LR adsorption from pore-filling to chemical attractions, and overcame the drawbacks of BC for MC-LR adsorption in the presence of FSHA.…”

Multi-Soil-Layering Technology: A New Approach to Remove Microcystis aeruginosa and Microcystins from Water

“…Techniques used for water filtration to remove harmful compounds, such as cyanobacteria and cyanotoxins, include activated carbon filtration, clay-like silica material, adsorption, biologically active sand filtration, and membrane filtration. In most cases, these techniques are preceded by coagulation-flocculation processes [89][90][91][92][93][94].…”

“…For instance, it was reported that there is strong proton adsorption in the case of the presence of several hydroxyl or phenolic groups under certain pH conditions [95,97,100]. Activated carbon may derive from different materials, namely wood, coal, coconut shells, or peat [75,92,[101][102][103]. Notwithstanding, Albuquerque et al [102] related the existence of MC-LR adsorption differences even among types of woods from which charcoal can be made; therefore, a wise choice of the sample of wood to be used has been made to maximize adsorption.…”

Nature-Based Solution to Eliminate Cyanotoxins in Water Using Biologically Enhanced Biochar

“…These techniques rely on the removal of whole cells and are not as effective against the free microcystins released upon cell lysis . Sand filtration is another commonly used water treatment technique, which can effectively remove up to 94% of microcystins under optimal conditions. , However, reductions in temperature to 0–10 °C have been found to greatly reduce efficiency, with only 43% microcystin removal reported. Sand filtration also relies on long water residing times of 2–6 months for optimal microcystin removal, which is not always feasible; therefore, rapid sand filtration methods with reduced residing times are often employed.…”

“…In conjunction with the aforementioned water treatment methods, additional disinfection processes such as chlorination, ozone, or activated carbon may be employed. Chlorination has been shown to remove up to 99% of microcystin in lab-scale studies, however, the formation of undesirable toxic byproducts is problematic. , Ozone treatment of drinking water can effectively remove microcystins; however, the process requires close monitoring as the amount of ozone required to achieve this varies depending on the water quality. , Combination of these methods with UV irradiation has been shown to improve their efficacy. , …”