Biomass based biochar production approaches and its applications in wastewater treatment, machine learning and microbial sensors

Influence of different stalks on the metallization degree of FeCl3-derived magnetic biochar through pyrolysis behavior and compositional differences

To investigate the effect of stalk type on the metallization degrees in FeCl3-derived magnetic biochar (MBC), MBC was synthesized via an impregnation-pyrolysis method using six different stalks. The Fe0 content in MBC significantly influenced its magnetic properties and ostensibly governed its catalytic capabilities. Analysis of the interaction between stalks and FeCl3 revealed that the variation in metallization degrees, resulting from FeCl2 decomposition (6.1%) and stalk-mediated reduction (20.7%), was directly responsible for the observed differences in MBC metallization. The presence of oxygen-containing functional groups and fixed carbon appeared to promote metallization in MBC induced by reduction. A series of statistical analyses indicated that the cellulose, lignin, and hemicellulose content of the stalks were key factors contributing to differences in MBC metallization degrees. Further exploration revealed that hemicellulose and cellulose were more effective than lignin in enhancing metallization through FeCl2 decomposition and reduction. Constructing stalk models demonstrated that the variance in the content of these three biomass components across the six stalk types could lead to differences in the metallization degree attributable to reduction and FeCl2 decomposition, thereby affecting the overall metallization degree of MBC. A prediction model for MBC metallization degree was developed based on these findings. Moreover, the elevated Si content in some stalks facilitated the formation of Fe2(SiO4), which subsequently impeded the reduction process. This study provides a theoretical foundation for the informed selection of stalk feedstocks in the production of FeCl3-derived MBC.

High surface area biochar for the removal of naphthenic acids from environmental water and industrial wastewater

This study reports the production of biochar adsorbents from two major crop residues (i.e., rice and wheat straw) to remove naphthenic acids from water. The alkali treatment approach was used for biochar activation that resulted in a tremendous increase in their surface area, i.e., up to 2252 and 2314 m2/g, respectively, for rice and wheat straw biochars. Benzoic acid was used as a model compound to optimize critical adsorption parameters. Its maximum monolayer adsorption capacity of 459.55 and 357.64 mg/g was achieved for activated rice and wheat straw biochars. The adsorption of benzoic acid was exothermic (∆H° =  - 7.06 and - 3.89 kJ/mol) and identified possibly as physisorption (Gibbs free energy ranges 3.5-4.0 kJ/mol). The kinetic study suggested that adsorption follows pseudo-second-order kinetics with qe2 for rice straw and wheat straw-derived adsorbents at 200 and 194 mg/g, respectively. As adsorbent, the recyclability of activated biochars was noticed with no significant loss in their efficiency for up to ten successive regeneration cycles. The adsorption results were validated using a commercial naphthenic acid mixture-spiked river water and paper/pulp industrial effluent. The activated rice and wheat straw biochars exhibited excellent adsorption efficiency of 130.3 and 74.6 mg/g, respectively. The naphthenic acid adsorption on biochar surface was due to various interactions, i.e., weak van der Waal's, pore filling, π-π stacking, and ionic interactions. This study offers a cost-effective and eco-friendly approach to valorizing agricultural residues for pollutant removal from industrial wastewater, including petroleum refineries.

Potential strategies for phytoremediation of heavy metals from wastewater with circular bioeconomy approach

Water pollution is an inextricable problem that stems from natural and human-related factors. Unfortunately, with rapid industrialization, the problem has escalated to alarming levels. The pollutants that contribute to water pollution include heavy metals (HMs), chemicals, pesticides, pharmaceuticals, and other industrial byproducts. Numerous methods are used for treating HMs in wastewater, like ion exchange, membrane filtration, chemical precipitation, adsorption, and electrochemical treatment. But the remediation through the plant, i.e., phytoremediation is the most sustainable approach to remove the contaminants from wastewater. Aquatic plants illustrate the capacity to absorb excess pollutants including organic and inorganic compounds, HMs, and pharmaceutical residues present in agricultural, residential, and industrial discharges. The extensive exploitation of these hyperaccumulator plants can be attributed to their abundance, invasive mechanisms, potential for bioaccumulation, and biomass production. Post-phytoremediation, plant biomass can be toxic to both water bodies and soil. Therefore, the circular bioeconomy approach can be applied to reuse and repurpose the toxic plant biomass into different circular bioeconomy byproducts such as biochar, biogas, bioethanol, and biodiesel is essential. In this regard, the current review highlights the potential strategies for the phytoremediation of HMs in wastewater and various strategies to efficiently reuse metal-enriched biomass material and produce commercially valuable products. The implementation of circular bioeconomy practices can help overcome significant obstacles and build a new platform for an eco-friendlier lifestyle.