Heavy metal contamination in drinking water is a growing concern due to its severe health effects on humans. Among the many metals, lead (Pb), which is a toxic and harmful element, has the most widespread global distribution. Pb pollution is a major problem of water pollution in developing countries and nations. The most common sources of lead in drinking water are lead pipes, faucets, and plumbing fixtures. Adsorption is the most efficient method for metal removal, and activated carbon has been used widely in many applications as an effective adsorbent, but its high production costs have created the necessity for a low-cost alternative adsorbent. Biochar can be a cost-effective substitute for activated carbon in lead adsorption because of its porous structure, irregular surface, high surface-to-volume ratio, and presence of oxygenated functional groups. Extensive research has explored the remarkable potential of biochar in adsorbing Pb from water and wastewater through batch and column studies. Despite its efficacy in Pb removal, several challenges hinder the real application of biochar as an adsorbent. These challenges include variability in the adsorption capacity due to the diverse range of biomass feedstocks, production processes, pH dependence, potential desorption, or a leaching of Pb from the biochar back into the solution; the regeneration and reutilization of spent biochar; and a lack of studies on scalability issues for its application as an adsorbent. This manuscript aims to review the last ten years of research, highlighting the opportunities and engineering challenges associated with using biochar for Pb removal from water. Biochar production and activation methods, kinetics, adsorption isotherms, mechanisms, regeneration, and adsorption capacities with process conditions are discussed. The objective is to provide a comprehensive resource that can guide future researchers and practitioners in addressing engineering challenges.

Tobacco plants can be developed as an energy crop for biofuels production. Tobacco represents a well-established non-food crop with an over 400-year tradition of cultivation in the United States. It is the most popular non-food crop in the world, grown in more than 120 other countries. Energy tobacco as a platform biomass for biofuels, combined with a water-based green-process technology to produce fermentable sugars from tobacco plants or tobacco stalks, was the aim of this study. The composition analysis showed that non-structural sugars in modified or unmodified tobacco leaves are comparable to those of energy crops (switch grass, miscanthus), whereas lignin content in tobacco leaves is significantly lower. Moreover, the elemental analysis of tobacco leaves showed that the carbon content is in the range of 37–39 wt% on a dry basis, and oil content was about 5 wt%. Upon hydrolysis, more than 75 wt% of structural or non-structural sugars in tobacco biomass was available as glucose. The results showed that tobacco cellulose could be effectively converted to hydrolytic products (glucose, cellobiose and oligosaccharides) within a few seconds under hydrothermal liquefaction (HTL) conditions. There are some parameters that are crucial for a successful HTL reaction, such as residence time, temperature, pressure and the particle size of the biomass.