Sequential Activation of Geothermal Silica Enhances Immobilization of Indigenous Bacterial Consortia for Wax‐Rich Batik Wastewater Bioremediation

ABSTRACT

Batik wastewater contains high concentrations of recalcitrant hydrophobic wax, reactive dyes, and heavy metals. Conventional biological treatments are limited because single strains often cannot degrade wax effectively, whereas free bacterial consortia (FBC) are susceptible to washout. This study evaluated indigenous wax‐degrading bacterial consortia immobilized on sequentially activated geothermal waste silica and optimized the carrier properties to enhance wax and organic load removal from real batik wastewater. Geothermal silica was tailored through a four‐step activation sequence including water washing, hydrochloric acid activation, thermal activation, and surface functionalization to improve its physicochemical suitability as an immobilization carrier. The performance of immobilized bacterial consortia (IBC) was compared with FBC using standard indicators (oil and grease, COD, and BOD). The activated silica achieved an immobilization efficiency of 64.04%. In real batik wastewater, IBC delivered 99.32% oil and grease removal with simultaneous reductions of 56.01% in BOD and 58.20% in COD, outperforming FBC (98.96% oil and grease removal; 26.29% BOD and 47.73% COD reduction). These results demonstrate that sequentially activated geothermal silica is a low‐cost, effective carrier for immobilizing indigenous consortia, enabling more stable and enhanced removal of wax and organic load in batik wastewater.