Waste treatment and valorization have become crucial for sustainable development towards a circular economy. As an alternative, biochar production is a promising process to convert wastes into a valuable product that presents several potential applications to cope with environmental problems. Biochar in recent years has been the subject of many studies, which have leveraged the number of patents and the industrial interest in this process. Against this background, this overview aimed: (i) to identify the advances in biochar research; (ii) to assess the number of patents on biochar over the years; (iii) to look at the industrial production of biochar worldwide; (iv) to detect the potential for biochar production in Brazil regarding waste biomass availability; and (v) to discuss the potential of biochar in contributing to reach some Sustainable Development Goals (SDGs). The holistic analysis presented here suggests that progress has been made in research, patent development, and industrial implementation of biochar, and that its potential role in achieving certain SDGs is noteworthy. Therefore, this overview can be useful in guiding future research about biochar to improve the knowledge of the different branches in this field.

The management of municipal solid waste represents a significant challenge for the future of society. The technologies of composting and anaerobic digestion process organic waste, providing material, and energy recovery, respectively. This study evaluated the most suitable locations for installing treatment plants for the organic fraction of municipal solid waste in two Brazilian cities, João Pessoa and Florianópolis, considering environmental, social, and geographical criteria. Furthermore, the main legislation on organic waste management in these cities was discussed, highlighting advances in relation to national regulations. In Florianópolis, the suitable areas represent 0.5% of the total area, totaling 3.10 km². In João Pessoa, the final suitable area covers 16.76 km² or 8% of the territory. Environmental aspects and residential areas were identified as the most relevant restrictive criteria for selecting suitable sites. In terms of existing public policies, Florianópolis stands out in terms of organic waste management, with clearer and more effective rules, while João Pessoa still needs a more consistent and integrated policy.

The management of sludge from water and sewage treatment plants (WTP and STP, respectively) is still a challenge due to its high complexity and high costs. In that regard, this research proposes to evaluate the potential of using sewage sludge and water sludge as cover material for landfills. The methodology involved three steps: (i) characterization of WTP sludge, STP sludge, and clay soil used in landfill cover; (ii) alkaline stabilization (CaO or Ca(OH) ₂ ) to sanitize the sludge before making it a landfill cover product; and (iii) geotechnical evaluation the mixtures of WTP and/or STP sludges with CaO or Ca(OH) ₂ before and after blending with natural soil. The selected material was tested in a pilot landfill cell to verify its influence in leachate quality. The results showed that it is environmentally feasible to sanitize the sludge with low lime levels. Geotechnically, the WTP and STP sludge stabilized with 5%, 10%, and 15% CaO are not suitable, but when natural soil was blended, the geotechnical behavior was similar to a natural soil used as landfill cover. The study showed that using the sludge treated as landfill cover provides environmental benefits.