Nowadays, the use of reclaimed water from wastewater treatment plants (WWTPs) for agricultural irrigation is a long-established practice in many countries to improve yields and production. Despite the advantages, concerns have been raised about their impact on the environment and human health. Due to the limited treatment processes of WWTPs, effluents typically contain multiple contaminants of emerging concern (CECs), including antibiotics, chemicals that have persistent, bioaccumulating, and toxic properties, and promote the spread of antibiotic resistance genes (ARGs). Once plants, fruits, vegetables, and surrounding soils are exposed to antibiotics on irrigated lands, which represents a potential pathway of transmission and accumulation of antibiotics and ARGs in ecosystems and food webs. Therefore, adequate treatment of wastewater is necessary to ensure water reuse and agroecosystem safety. Considering the benefits of aerobic granular sludge (AGS) over the conventional WWTP-activated sludge, and the promising sustainability rank of microalgae, here at lab scale, the removal and fate of 07 mixed antibiotics by microalgae-AGS, and AGS in sequential batch reactors were investigated at different antibiotic concentrations (0, 50, 200 and 500 µg L⁻¹) for 120 days. Within a 30-day operation, the microalgal-AGS consortia could be successfully developed, and the two biomasses showed excellent stability and good removal of carbon oxygen demand (COD) and nutrients under none and 50 µg L⁻¹ mixed antibiotics. Increased antibiotic concentration affected system performance with different removal patterns observed at different antibiotic doses. Overall, the consortium microalgae-AGS treatment showed higher efficiency than AGS treatment across different stages, with mean antibiotic removal ranges of 31-98% and 5-99% respectively. Although identical antibiotic transformation products (TPs) were identified from both biomasses, different TPs unique to each treatment were also confirmed. Toxicity prediction using ECOSAR showed that most TPs from microalgae-AGS treatment were of lower toxicity compared to their parent antibiotics. In addition, based on the Microtox^® bioassay, the microalgae-AGS effluent appears to be less toxic to Aliivibrio fischeri than the AGS effluent, indicating lower risks. Our study proposed an environmentally friendly technique for antibiotic wastewater bioremediation to minimize the risks associated with the use of reclaimed water in agrosystems.

Qian Sun

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