Enhanced biodiesel industry wastewater treatment via a hybrid MBBR combined with advanced oxidation processes: analysis of active microbiota and toxicity removal.

In the present study, a multistage route is proposed for the treatment of biodiesel industry wastewater (BWW) containing around 1000 mg L of total organic carbon (TOC), 3500 mg L of chemical oxygen demand (COD), and 1325 mg L of oil and grease. Initially, BWW aerobic biodegradability was assessed via Zhan-Wellens biodegradability test to confirm the appropriate treatment route. Then, a hybrid moving bed bioreactor (MBBR) system was chosen as the first treatment stage. The hybrid MBBR achieved 69 and 68% removal of COD and TOC removals, respectively, and provided great conditions for biomass growth. The bacterial community present in the hybrid MBBR was investigated by PCR-DGGE and potential biodegraders were identified such as: members of Desulfuromonadales, Nocardioidaceae and Pseudomonadaceae. Since biodegradation in the hybrid MBBR alone was unable to meet quality requirements, advanced oxidation processes, such as Fenton and photo-Fenton, were optimized for application as additional treatment stages. Physicochemical properties and acute toxicity of BWW were analyzed after the multistage routes: hybrid MBBR + Fenton, hybrid MBBR + photo-Fenton and hybrid MBBR + UV-C/HO. Hybrid MBBR + Fenton or photo-Fenton showed overall COD removal efficiencies greater than 95% and removed acute toxicity, thus being appropriate integrated routes for the treatment of real BWW. Graphical abstract ᅟ.