Encapsulation techniques of sludge generated from wastewater treatment

Human civilization's progress, along with the linear economy approach, is leading us toward major environmental and economic challenges. Industrial waste, one of these challenges, has always been a topic of research and development. Encapsulation is a method that offers a promising implementation of waste and reutilizing it as a resource in a value-added product while immobilizing toxic components such as heavy metals. Focusing on sludge, the review studies its classification, composition, and challenges associated with conventional methods such as landfills, incineration, etc. The study delves into the types of encapsulation that are micro-, macro-, and nano-encapsulation and highlights their recent advancements emphasizing their effectiveness in immobilizing the heavy metals while improving the structural properties of the product. Although encapsulation is mostly studied in food and pharmaceutical industrial applications, its application in sludge management remains unexplored. The study focuses on the recent advancements in sludge encapsulation and identifies geopolymerization and alkali-activation methods as emerging technologies. The results highlight that 5–10 % of sludge can be used to make construction material without losing its mechanical properties while encapsulating heavy metals up to 99 %. Compared to the earlier work done, this review provides a framework to evaluate the role of encapsulation. Considering waste as a resource and reutilizing it into a product strengthens the application of the circular economy concept. Seeing it as a possible environmentally sustainable way, the review also draws attention to the potential and scope of encapsulation in waste management by identifying the current research gaps and trends.