Hybrid O₃/UV/Fe process using rebar flakes waste for removal of congo red dye in wastewater

In Indonesia, textile is one of the labour-intensive industries that makes an important contribution to the national economy sectors. This industry tends to develop rapidly to meet domestic and export needs. This phenomenon increases wastewater generation from the textile industry. Textile wastewater contains dyes that are designed to be durable to resist sunlight and washing process. These properties pose a challenge to the treatment of dye wastewater. The complex structure of dye molecules is generally difficult to degrade by conventional biological processes, while the physical-chemical precipitation process will generate hazardous sludge. Therefore, alternative treatment processes for dye removal are urgently required. In this work, ozonation (O3), ozone and ultraviolet (O3/UV), and catalytic ozone coupling with ultraviolet (O3/UV/Fe) processes were tested for decolourisation of synthetic Congo red dye wastewater. Laboratory assays were carried out under various operating conditions: pH (3-7); ozonation mode (continuous, sequential); and catalyst dose (0.5-2 g/L). Ozonation in sequential mode and the utilisation of rebar flake waste from building construction project as iron catalyst presents a degree of novelty in this work. Congo red decolourisation up to 97% was achieved in less than one-hour of reaction by the continuous O3 process. Mineralisation in terms of COD reduction (50%) can be increased by either performing ozonation in sequential mode (79%) and coupling with UV irradiation (86%). Nevertheless, the effect of the iron catalyst was found to be negligible.