Comparative Analysis of Sugarcane Vinasse Anaerobic Treatment: Ultra-Filtration Anaerobic Membrane and UASB Reactors with a Focus on Operational Strategies and Microbiological Evaluation

Vinasse is a by-product of sugarcane processing and represents a source of nutrients such as calcium, magnesium, and potassium. For that reason, its main destination is the fertigation. However, vinasse has high concentrations of solids and organic matter, low pH, and a high sulfate content, all of which can detrimentally impact soil productivity and contribute to various environmental concerns. Therefore, vinasse treatment before its use in fertigation is desirable. Anaerobic digestion is an alternative for reducing the pollutants and, simultaneously, recovering of bioenergy during the treatment of vinasse. The main reactors used in the anaerobic treatment of the vinasse are high-rate anaerobic reactors, most of them relying on sludge granulation for a successful treatment. The presence of recalcitrant compounds, high concentration of solids, low pH, high salinity, and high temperature, can affect granule formation, and cause sludge wash out. For this reason, anaerobic membrane bioreactors (AnMBR), which do not require granulation, may be considered for vinasse treatment. In this study, an AnMBR with an attached external ultrafiltration membrane is proposed for vinasse treatment. The AnMBR showed potential for vinasse treatment operating with increasing volumetric organic load of up to 6 kg COD.m-3.d-1, producing a final effluent free of solids. At such organic load rate UASB reached 75 +- 7% of organic matter removal efficiency, while AnMBR generated an effluent without solids and reached 88 +- 2 % of organic matter removal efficiency, carried out by microorganisms such as Clostridia, Bacteroidia, Mesotaga, Syner-01, Dehalococcoidia and (mainly) Bacteroidia-DMER64, in association with hydrogenotrophic Methanolinea and sulfate reducing bacteria.