Integrated electrocoagulation, anaerobic-aerobic biofiltration and zeolite-activated carbon polishing of batik wastewater for on-site water reuse

Batik wastewater is deeply colored and carries a heavy organic and solids load, because the naphthol and indigosol dyes used in hand-drawn production resist conventional biological treatment.This study tested whether a three-stage train of iron-aluminum electrocoagulation, attached-growth biofiltration and zeolite-granular activated carbon polishing can turn such wastewater into water fit for reuse inside the workshop that produced it.Six electrode-current combinations were screened at 3 A and 5 A for 30 min, aerobic and sequential anaerobic-aerobic biofilters were compared over hydraulic retention times of 15-50 h, and the polishing column was run in continuous downflow at an empty-bed contact time of 4.59 h.Every condition was repeated in three independent runs.The raw wastewater contained 3918.4 mg/L chemical oxygen demand (COD), 1533.0 mg/L five-day biochemical oxygen demand (BOD₅), 1080 mg/L total suspended solids (TSS), 3715 mg/L total dissolved solids (TDS), 967 Pt-Co of color and 184 mg/L of oil and grease.Alternating iron and aluminum plates at 5 A gave the most balanced pretreatment, removing 56.1% of COD, 60.0% of BOD₅, 76.9% of TSS, 88.2% of total phosphorus and 84.0% of color, although TDS rose by 44.2% as the sacrificial plates dissolved.At a total retention time of 50 h the sequential biofilter outperformed the aerobic-only reactor for every parameter, lowering COD to 152.6 mg/L against 593.5 mg/L.The layered zeolite-activated carbon bed then delivered 3.7 mg/L COD, 0.10 mg/L BOD₅, 1.0 mg/L TSS, 155 mg/L TDS and 1 Pt-Co of color, with phosphorus, nitrogen species and oil and grease below their reporting limits.The final water satisfied every physicochemical criterion of the Indonesian river water quality standard and is fit for return to the non-potable stages of batik production, which points to a workable closed water loop for small producers.