For over a century, enzyme immobilisation has been proven to be a superior strategy to improve catalytic activity and reusability and ensure easy separation, easy operation, and reduced cost. Enzyme immobilisation allows for an easier separation of the enzyme from the reaction mixture, thus simplifying downstream processing. This technology protects the enzyme from degradation or inactivation by harsh reaction conditions, making it more robust and suitable to be used in various applications. Recent strategies of immobilisation methods, such as adsorption, cross-linking, entrapment or encapsulation, and covalent bonding, were critically reviewed. These strategies have shown promising results in improving enzyme stability, activity, and reusability in various applications. A recent development in enzyme immobilisation in nanomaterials and agrowaste renewable carriers is underlined in the current review. Furthermore, the use of nanomaterials and agrowaste carriers in enzyme immobilisation has gained significant attention due to their unique properties, such as high surface area, high mass transfer, biocompatibility, and sustainability. These materials offer promising outcomes for developing more efficient and sustainable immobilised enzymes. This state-of-the-art strategy allows for better control over enzyme reactions and enhances their reusability, leading to more cost-effective and environmentally friendly processes. The use of renewable materials also helps to reduce waste generation and promote the utilisation of renewable resources, further contributing to the development of a circular economy.

Steel slag is one of the most common waste products from the steelmaking industry. Conventional methods of slag disposal can cause negative impacts on humans and the environment. In this paper, the process of steel and steel slag production, physical and chemical properties, and potential options of slag recycling were reviewed. Since steel is mainly produced through an electric arc furnace (EAF) in Malaysia, most of the recycling options reviewed in this paper focused on EAF slag and the strengths and weaknesses of each recycle option were outlined. Based on the reports from previous studies, it was found that only a portion of EAF slag is recycled into more straightforward, but lower added value applications such as aggregates for the construction industry and filter/absorber for wastewater treatments. On the other hand, higher added value recycling options for EAF slag that are more complicated such as incorporated as raw material for Portland cement and ceramic building materials remain at the laboratory testing stage. The main hurdle preventing EAF slag from being incorporated as a raw material for higher added value industrial applications is its inconsistent chemical composition. The chemical composition of EAF slag can vary based on the scrap metal used for steel production. For this, mineral separation techniques can be introduced to classify the EAF slag base on its physical and chemical compositions. We concluded that future research on recycling EAF slag should focus on separation techniques that diversify the recycling options for EAF slag, thereby increasing the waste product’s recycling rate.

Microbial fuel cell (MFC) technology has attracted a great amount of attention due to its potential for organic and inorganic waste treatment concomitant with power generation. It is thus seen as a clean energy alternative. Modifications and innovations have been conducted on standalone and hybrid/coupled MFC systems to improve the power output to meet the end goal, namely, commercialization and implementation into existing wastewater treatment plants. As the energy generated is inversely proportional to the size of the reactor, the stacking method has been proven to boost the power output from MFC. In recent years, stacked or scale-up MFCs have also been used as a power source to provide off-grid energy, as well as for in situ assessments. These scale-up studies, however, encountered various challenges, such as cell voltage reversal. This review paper explores recent scale-up studies, identifies trends and challenges, and provides a framework for current and future research.

In recent years, numerous studies have focused on the use of biochar as a biological material for environmental remediation due to its low-cost precursor (waste), low toxicity, and diversity of active sites, along with their facile tailoring techniques. Due to its versatility, biochar has been employed as an adsorbent, catalyst (for activating hydrogen peroxide, ozone, persulfate), and photocatalyst. This review aims to provide a comprehensive overview and compare the application of biochar in water remediation. First, the biochar active sites with their functions are presented. Secondly, an overview and summary of biochar performance in treating organic pollutants in different systems is depicted. Thereafter, an evaluation on performance, removal mechanism, active sites involvement, tolerance to different pH values, stability, and reusability, and an economic analysis of implementing biochar for organic pollutants decontamination in each application is presented. Finally, potential prospects to overcome the drawbacks of each application are provided.