Microalgae as potential agents for biochar production: Future of industrial wastewater treatment

Diverse industries like breweries, textiles, paper & pulp, mining, chemical & nuclear, and food processing generate huge amounts of wastewater which can be toxic. This wastewater, rich in both organic compounds and inorganic salts, suspended solids, heavy metal ions and other pollutants should be properly treated before discharging into the environment. Recent studies demonstrated the efficiency of microalgae-based treatment. Microalgae are efficient in this regard since they produce photogenerated oxygen oxidizing the pollutants and toxin degrading enzymes, readily consume organics, and uptake/adsorb other pollutants. The current bottlenecks for microalgal bioremediation are high costs and low energy efficiency. The resulting biomass can be utilized for producing various forms of bioenergy via assorted traditional as well as modern techniques such as hydrothermal carbonization, pyrolysis, and torrefaction. One of the valuable outputs of these processes is biochar which is rich in nutrients and is capable of ion exchange. Therefore, it finds potential application in agriculture e.g., for revamping soil fertility and in wastewater treatment as adsorbent removing organic and inorganic pollutants. Here, we review novel processes designed for microalgae-based wastewater treatment with an emphasis on biochar production and utilization. Special attention is paid to the characterization of the physicochemical properties of biochar to maximize its targeted applications.