Wastewater treatment in the cosmetic industry, which operates in batch mode, is a complex task due to the highly variable composition of the water to be treated. Among other parameters, n-heksan extractable material (HEM) and surfactants must comply with the specified limits. From theory, the advanced oxidation process (AOP) with a Fenton-like process is more suitable for surfactant degradation, while the coagulation/flocculation process (CFP) is more efficient for HEM removal. Determining the appropriate sequence of AOP treatment and CFP affects the quality of released water, the efficiency of each process step, and the consumption of required chemicals.
The objective of this research was to optimize the treatment sequence, the time required for each treatment, and the amount of sludge from wastewater treatment. For this purpose, AOP treatment and CFP laboratory tests were performed for different groups of samples and samples with high HEM and/or surfactant content. Based on the efficiency of the laboratory tests and the assessed wastewater composition (from mass and concentration balances), an optimization model was developed. The optimization model enables optimization of the wastewater treatment plant (WWTP) by feeding each of the streams to either i) AOP treatment, ii) CFP treatment, iii) AOP treatment followed by CFP treatment, iv) CFP pretreatment followed by AOP and CFP, v) bypass (i.e. the wastewater stream is not treated but mixed with treated streams). The optimal solution can be determined by minimizing the total annual cost of treatment or/and maximizing removal of pollutants. An additional analysis was performed considering the dilution of wastewater with freshwater after the treatment process. The results show that this last proposal is more economical but leads to questionable environmental impacts.