Sequential combination of photocatalysis and microalgae technology for promoting the degradation and detoxification of typical antibiotics

Antibiotic contamination has become the primary environmental concern due to its potential to induce the emergence and spread of antibiotic resistance genes (ARGs). To obtain the efficient antibiotic removal approach, the combination of photocatalysis and microalgae technology for the efficient removal and reducing environmental risk of three typical antibiotics (norfloxacin, oxytetracycline and sulfamethoxazole) was demonstrated in this study. The g-C3N4 material, with advantages of low cost, simple synthesizing, nontoxic, and wider spectral absorption, was selected and synthesized by an easy thermal polymerization process of urea. Characterization results showed that the prepared material exhibited a typical structure of g-C3N4 and irregular nanosheet structure with the large BET surface area and mesoporous structure. The irradiation wavelength and solution pH showed great influences on the photocatalytic degradation of norfloxacin over g-C3N4 nanosheets. •O2-, h+, and •OH generated by the photocatalysis of g-C3N4 nanosheets were confirmed based on energy band results and electron spin resonance detection, while •O2- was the main contributor to the antibiotics degradation in accordance with scavenging experiments. Many NOR photocatalytic products were identified and degradation pathway was proposed. Due to the formation of many unmineralized products, the acute toxicity of NOR photocatalytic reaction solution was increased. And then, the introduction of microalgae promoted the degradation of some photocatalytic degradation products of NOR, but only Chlorella pyrenoidosa treatment resulted in the decrease of toxicity of NOR reaction solution. This study provides useful information on the application of the combination of photocatalysis and microalgae technology for removal of antibiotics.