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Wastewater treatment activities in the chemical industry have generated abundant gypsum waste, classified as scheduled waste (SW205) under the Environmental Quality Regulations 2005. The waste needs to be disposed into a secure landfill due to the high heavy metals content which is becoming a threat to the environment. Hence, an alternative disposal method was evaluated by recycling the waste into fired clay brick. The brick samples were incorporated with different percentages of gypsum waste (0% as control, 10, 20, 30, 40 and 50%) and were fired at 1050 °C using 1 °C per minute heating rate. Shrinkage, dry density, initial rate of suction (IRS) and compressive strength tests were conducted to determine the physical and mechanical properties of the brick, while the synthetic precipitation leaching procedure (SPLP) was performed to scrutinize the leachability of heavy metals from the crushed brick samples. The results showed that the properties would decrease through the incorporation of gypsum waste and indicated the best result at 10% of waste utilization with 47.5% of shrinkage, 1.37% of dry density, 22.87% of IRS and 28.3% of compressive strength. In addition, the leachability test highlighted that the concentrations of Fe and Al was significantly reduced up to 100% from 4884 to 3.13 ppm (Fe) and from 16,134 to 0.81 ppm (Al), respectively. The heavy metals content in the bricks were oxidized during the firing process, which signified the successful remediation of heavy metals in the samples. Based on the permissible incorporation of gypsum waste into fired clay brick, this study promised a more green disposing method for gypsum waste, and insight as a potential towards achieving a sustainable end product.

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There is about 2.01 billion metric tons of municipal solid waste (MSW) produced annually and organic waste constitutes of a major portion from total waste generation worldwide. This current circumstance not only create extra burden on the landfill, but also causing some environmental issues such as greenhouse gases emission, odor emission and leachate production. Therefore, a sustainable and pro-environmental of organic waste disposal solution is acknowledged by composting practice. However, organic waste consists of some significant properties include high in salt, oil, nitrogen and moisture content. All of these properties contributing difficulties on the efficiency of organic waste composting process. In previous studies, researchers had studied various bulking agents such as biochar, sawdust, lime and others in order to optimize the efficacy of composting process. Nevertheless, utilization of zeolite as bulking agent in composting process is getting famous in the recent years due to its unique physiochemical characteristics. Hence, this article attempts to review the potential of zeolites in optimizing the composting process for better understanding of the mechanism as well provides valuable insights for sustainable organic waste management practice.