Anaerobic digestion has been widely employed in waste treatment for its ability to capture methane gas released as a product during the digestion. Certain wastes, however, cannot be easily digested due to their low nutrient level insufficient for anaerobic digestion, thus co-digestion is a viable option. Numerous studies have shown that using co-substrates in anaerobic digestion systems improve methane yields as positive synergisms are established in the digestion medium, and the supply of missing nutrients are introduced by the co-substrates. Nevertheless, large-scale implementation of co-digestion technology is limited by inherent process limitations and operational concerns. This review summarizes the results from numerous laboratory, pilot, and full-scale anaerobic co-digestion (ACD) studies of wastewater sludge with the co-substrates of organic fraction of municipal solid waste, food waste, crude glycerol, agricultural waste, and fat, oil and grease. The critical factors that influence the ACD operation are also discussed. The ultimate aim of this review is to identify the best potential co-substrate for wastewater sludge anaerobic co-digestion and provide a recommendation for future reference. By adding co-substrates, a gain ranging from 13 to 176% in the methane yield was accomplished compared to the mono-digestions.

Semiconductor materials have been shown to have good photocatalytic behavior and can be utilized for the photodegradation of organic pollutants. In this work, three-dimensional flower-like SnS₂ (tin sulfide) was synthesized by a facile hydrothermal method. Core-shell structured SiO₂@α-Fe₂O₃ nanocomposites were then deposited on the top of the SnS₂ flowers. The as-synthesized nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis Spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis, and photoluminescence (PL) spectroscopy. The photocatalytic behavior of the SnS₂-SiO₂@α-Fe₂O₃ nanocomposites was investigated by observing the degradation of methylene blue (MB). The results show an effective enhancement of photocatalytic activity for the degradation of MB especially for the 15 wt % SiO₂@α-Fe₂O₃ nanocomposites on SnS₂ flowers.

Coconut shells, low-cost and renewable agro-wastes, were used as a starting material in the synthesis of hierarchical activated carbons via hydrothermal, KOH-activation, and carbonization techniques. The ratio of KOH to hydrochar was varied in a systemic manner to study how it influences the texture and electrochemical behavior of the capacitor. Coconut shell-based carbon coated on nickel foams presented a surface area of 1567 m² g⁻¹, with micropores as well as mesopores widely distributed. The sample showed superior electrochemical performance, attaining 449 F g⁻¹ at 1 A g⁻¹ in 6 M LiNO₃ aqueous solution. The solid-state symmetric supercapacitor device delivered a specific capacitance of 88 F g⁻¹ at 1 A g⁻¹ and a high energy density of 48.9 Whkg⁻¹ at a power density of 1 kW kg⁻¹. At a wide voltage window of 2.0 V, the sample was highly stable during the cycle test, showing a 92% capacitance retention at 2 A g⁻¹ after cycling for 5000 times. The superior performance is due to the sample possessing great BET surface area, a good distribution of pores, and the usage of a suitable electrolyte. This facilitates an electrical double layer that can be deployed for applications to store energy.

The rapid emergence of Industry 4.0 implies that our engineering graduates need to acquire new competences to adapt to the digital transformation. This paper evaluates the benefits of integrating 3D printing and Industry 4.0 into engineering undergraduate programs. Surveys were conducted to gather the feedbacks and views from academics and students. 75% and 86% of the participating students and lecturers, respectively, have heard about Industry 4.0. 63% of the students were exposed to modules with such elements. Tangible 3D-printed models enable visualization of fundamental theories and concepts. Enhanced 3D drawing skills and rapid 3D-printed prototypes can greatly help students study common processing equipment, manufacturing, maintenance, logistics, and operations. Some limitations were identified such as budgeting, lack of knowledge, and difficulty in changing from traditional pedagogy. This paper thus proposes a blended learning model for integrating Industry 4.0 into engineering teaching, which consists of traditional, online learning, and flipped classroom approaches. Implementation of the model can be started off with cross-multidisciplinary collaborations or expert-led training for the instructors, followed by traditional face-to-face teaching and online learning. Flipped classroom is one of the essential components of the model which encourages learning-by-making approaches such as ‘bring your own device’ and ‘do it yourself’. Integrating Industry 4.0 into engineering teaching can create a student-based learning environment, where students are gradually trained to become proactive and lifelong learners who are more conscious of the environment and economy.