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Abstract

Malaysia's glove manufacturing industry generates wastewater containing hazardous chemicals, including zinc. This study aims to use rice husks as environmentally acceptable zinc reduction additives. Zinc (14.1 mg/L), COD (2092 mg/L), BOD (520 mg/L), TSS (2130 mg/L), and pH (1.6–7.2) were all found in wastewater characterization. Factorial analysis established the key zinc-contributing agents: nitrile, antifoam, and backwash. Antifoam has long been considered the main source (F-value: 88.23, P-value: 0.003). A predictive model for zinc concentration optimization was obtained. Raw rice husk (RRH) and rice husk ash (RHA) were produced by cleaning, thermal treatment (105°C), and pre-alkaline treatment. RHA had a stronger ability to adsorb zinc, with 10 mg/L or even greater reductions achieved. The optimal amounts for both were found to be 4 mg for RRH and 6 mg for RHA, which led to the best performance in lowering zinc concentration while maintaining good water quality. This comparison analysis of natural filtration (rice husk, limestone) and chemical pre-treatment (using caustic soda) showed that the latter was better at both cost and ease. The actual implementation was carried out in one glove factory's pilot-scale wastewater treatment plant, where data confirmed increased efficiency of zinc removal brought about by RHA. The findings of this study demonstrate Raw Rice Husk and Rice Husk Ash as suitable remedies for removing heavy metals, supporting cost-efficient, ecological performance in wastewater handling.

Keywords: wastewater, zinc, rice husk, rice husk ash