Microalgae-bacteria bioremediation of antibiotics and nutrients in wastewater

The widespread use and incomplete metabolism of antibiotics in human and veterinary medicine have led to their persistent presence in aquatic environments, posing significant ecological and public health risks. This study investigated the potential of using microalgae-bacteria consortia for the bioremediation of antibiotics commonly found in wastewater: amoxicillin (AMX), cephalexin (CEX), oxytetracycline (OTC), penicillin V (Pen V), sulphamethoxazole (SMX), Azithromycin (AZM), clarithromycin (CLR), ciprofloxacin (CIP), metronidazole (MTZ), and trimethoprim (TMP). The green microalga Chlorella sorokiniana was investigated alone and in combination with natural bacterial population via the in situ cultivation method (iChip). The study evaluated algal growth, nutrient removal, antibiotic degradation and associated mechanisms, and the dynamics of the microbial community. Results showed that the mixed antibiotics did not inhibit algal growth and nutrient removal in the absence of bacteria. The C. sorokiniana-bacteria consortium exhibited enhanced algal biomass production and superior removal efficiency for nutrients and antibiotics. Complete phosphate removal was achieved, while nitrate and chemical oxygen demand (COD) were significantly reduced in consortium condition with antibiotics. The highest antibiotic removal rates were observed for AMX, CEX, OTC, and Pen V. Biodegradation was identified as the primary removal mechanism, supported by photodegradation and bioadsorption. Metabolite profiling analysis confirmed the formation of various transformation products (TPs) from MTZ, SMX, and TMP, revealing complex degradation pathways. Microbial analysis indicated significant shifts in bacterial communities depending on the conditions tested, with an increased abundance of Cyanobacteria and Proteobacteria under consortium conditions with and without antibiotics. This research demonstrated the feasibility of microalgae-bacteria consortia for treating antibiotic-contaminated wastewater, removing nutrients, and increasing microalgae biomass production. The findings suggest that this system could be an environmentally friendly and effective solution for mitigating pharmaceutical pollution in aquatic ecosystems.