Combined AOP/GAC/AOP systems for secondary effluent polishing: Optimization, toxicity and disinfection

This study reports the use of advanced oxidation processes (AOPs), specifically O-3, O-3/H2O2 and UV/H2O2, in combination with granular activated carbon (GAC) to polish secondary effluents. For this purpose, three configurations were tested: O-3-GAC-O-3, O-3/H2O2-GAC-O-3/H2O2 and UV/H2O2-GAC-UV/H2O2. The efficiency evaluation was based on the ability of the systems to remove ammaticity (UV254), organic matter (chemical oxygen demand - COD), Escherichia coli and total coliforms content as well as toxicity (Artemia salina and Allium cepa). The methods were optimized using central composite design to investigate the influence of O-3 and H2O2 concentration in the efficiency of the system and the optimal conditions were subsequently applied to treat urban secondary effluents. High organic matter removal rates were obtained by all the tested configurations, of which O-3-GAC-O-3 proved to be the most efficient. The systems were also efficient to disinfect the samples, promoting nearby 5-log reduction of E. coli and total coliforms. Acute toxicity, cytotoxicity, and genotoxicity were observed in samples subjected to the UV/H2O2-GAC-UV/H2O2 method. When used alone, GAC removed around 80% of organic matter, nevertheless failed to disinfect the samples, which furthermore exhibited acute toxicity and genotoxicity toward A. cepa. Samples subjected to direct photolysis proved more toxic than untreated samples while uncombined H2O2, O-3, GAC, and UV, as well as O-3/H2O2 and UV/H2O2 failed to degrade organic matter or to mitigate the toxicity of the samples.

Automated summary

This study investigated the use of advanced oxidation processes (AOPs) combined with granular activated carbon (GAC) to treat secondary effluents. The results showed that the O-3-GAC-O-3 configuration was the most efficient in removing organic matter, while all systems were effective in disinfecting the samples. However, samples treated with the UV/H2O2-GAC-UV/H2O2 method exhibited acute toxicity, cytotoxicity, and genotoxicity.