Biochar production from microalgae: a new sustainable approach to wastewater treatment based on a circular economy

The generation of wastewater due to human activities are the main responsible for environmental problems. These problems are caused by the large amount of organic and inorganic pollutants related to the presence of pesticides, metals, pathogens, drugs and dyes. The photosynthetic treatment of effluents emerges as a sustainable and low-cost alternative for developing wastewater treatment systems based on a circular economy. Chemical compounds present in wastewater can be recovered and reused as a source of nutrients in microalgae cultivation to produce value-added bioproducts. The microalgal biomass produced in the cultivation with effluents has the potential to produce biochar. Biochar is carbon-rich charcoal that can be obtained by converting microalgae biomass through thermal decomposition of organic raw material under limited oxygen supply conditions. Pyrolysis, torrefaction, and hydrothermal carbonization are processes used for biochar synthesis. The application of microalgal biochar as an adsorbent material to remove several compounds present in effluents is an effective and fast treatment. This effectiveness is usually related to the unique physicochemical characteristics of the biochar, such as the presence of functional groups, ion exchange capacity, thermal stability, and high surface area, volume, and pore area. In addition, biochar can be reused in the adsorption process or applied in agriculture for soil correction. In this context, this review article describes the production, characterization, and use of microalgae biochar through a sustainable approach to wastewater treatment, emphasizing its potential in the circular economy. In addition, the article approaches the potential of microalgal biochar as an adsorbent material and its reuse after the adsorption of contaminants, as well as highlights the challenges and future perspectives on this topic.

Automated summary

The generation of wastewater from human activities is the main cause of environmental problems, containing a large amount of organic and inorganic pollutants such as pesticides, metals, pathogens, drugs, and dyes. Photosynthetic treatment of effluents is a sustainable and low-cost alternative for wastewater treatment, allowing the recovery and reuse of chemical compounds present in wastewater as a source of nutrients for microalgae cultivation. The cultivation of microalgae with effluents can produce biochar, a carbon-rich charcoal that can be used as an effective adsorbent material for removing pollutants from effluents. Biochar synthesis can be achieved through processes such as pyrolysis, torrefaction, and hydrothermal carbonization. This review article focuses on the production, characterization, and use of microalgae biochar in wastewater treatment, highlighting its potential in the circular economy and discussing the challenges and future perspectives.