Removal of oxytetracycline and ofloxacin in wastewater by microalgae-bacteria symbiosis for bioenergy production

The development of microalgae-bacteria symbiosis for treating wastewater is flourishing owing to its high biomass productivity and exceptional ability to purify contaminants. A nature-selected microalgae-bacteria symbiosis, mainly consisting of Dictyosphaerium and Pseudomonas, was used to treat oxytetracycline (OTC), ofloxacin (OFLX), and antibiotic-containing swine wastewater. Increased antibiotic concentration gradually reduced biomass productivity and intricately changed symbiosis composition, while 1 mg/L OTC accelerated the growth of symbiosis. The symbiosis biomass productivity reached 3.4–3.5 g/L (5.7–15.3 % protein, 18.4–39.3 % carbohydrate, and 2.1–3.9 % chlorophyll) when cultured in antibiotic-containing swine wastewater. The symbiosis displayed an excellent capacity to remove 76.3–83.4 % chemical oxygen demand, 53.5–62.4 % total ammonia nitrogen, 97.5–100.0 % total phosphorus, 96.3–100.0 % OTC, and 32.8–60.1 % OFLX in swine wastewater. The microbial community analysis revealed that the existence of OTC/OFLX increased the richness and evenness of microalgae but reduced bacteria species in microalgae-bacteria, and the toxicity of OFLX to bacteria was stronger than that of OTC.