Indonesian batik is a wax-resist dyeing technique of significant cultural and economic value; however, it also generates substantial environmental pollution, primarily in the form of wastewater contaminated with various heavy metals and dyes. This study investigated rice husks as a low-cost, effective, and sustainable adsorbent for treating batik effluent. Three potential adsorbents were tested, namely, rice husks, NaOH-treated rice husks, and FeCl3-treated rice husks. The results showed that further additives, such as pH control, FeCl2, and PAC (polyaluminum chloride), were added to improve the removal efficiency of heavy metals and dyes. The application of rice husk adsorbents with additive enhancement (i.e., FeCl2 (RHF2)) demonstrated high removal efficiencies of 97, 100, and 97% for methyl orange, reactive black, and methylene blue, respectively. Furthermore, the removal rates of heavy metals were 99, 99, 88, and 98% for Cd, Cr, Cu, and Zn, respectively. This method can also reduce the strong alkaline pH of batik effluent from 10.0 to 6.5. The high removal efficiency observed can be attributed to interactions between hydroxyl groups on the rice husks and Fe2+ ions from FeCl2, which facilitated the formation of Fe(OH)2 complexes, which promoted the aggregation of dyes and heavy metals via coprecipitation and generated additional active adsorption sites. Microtox analysis demonstrated that RHF2 effectively reduced the toxicity of the batik effluent for enhanced environmental safety. These results support the use of rice husks as a scalable and sustainable solution for treating batik effluent.
Sarkawi et al. (Tue,) studied this question.