Use of Ozonization for the Treatment of Dye Wastewaters Containing Rhodamine B in the Agate Industry

The industrial processing of precious stones is a source of revenue for several Brazilian towns, especially in the state of Rio Grande do Sul. Given the growing number of small-sized companies that process precious stones, wastewater production is inevitable and is a cause for concern inasmuch as preservation of nature is considered. The present study investigates the detoxification of the wastewater produced by the process of rhodamine B dyeing using oxidation processes. Ozonization (O₃), ultraviolet irradiation (UV), and O₃/UV methods were assessed. Some of the parameters used to measure the efficiency of the analyzed treatments included COD, ecotoxicity (Daphnia magna), cytotoxicity, and genotoxicity assays (Allium cepa assays). Results show predominance of negative and local environmental impacts, which are reversible in more than 70% of cases. The major proposed reversibility measures were the change in the process layout and dye wastewater segregation. Among the analyzed methods, ozonization proved to be more efficient in decolorization, with 60 min of treatment, pH = 9 and dosage of 5.705 mg O₃/mg of rhodamine B. A pseudo first-order reaction, with a kinetic constant of 7.5 × 10⁻² min⁻¹, was observed. The cytotoxic and genotoxic effects were assessed for both raw and treated wastewaters. Despite complete decolorization, cytotoxicity and genotoxicity assays revealed an EC₅₀ of 28.6, in addition to chromosome aberrations in 40% of dividing cells for the treated wastewater.