Integrated production of bacterial cellulose and biogas from agro-industrial wastewater: technical feasibility of implementing a biorefinery concept

Bacterial cellulose (BC) is an organic substance produced by bacteria that has shown immense potential as an efficient biopolymer. BC has high potential for diverse applications, but low productivity and high production costs prevent widespread use. Several studies have been conducted recently to develop low-cost fermentation media, encouraging the use of residues and industrial by-products as substrates. Agro-industrial wastewaters can be used as substrates for BC production, including glycerol, vinasse, and whey. Therefore, this study initially aimed to produce BC from these wastewaters. BC was produced by Gluconacetobacter hansenii grown statically at room temperature. The BC media were the same as the Hestrin and Schramm medium, with only the original carbon source (glucose) replaced with agro-industrial residues: glycerol, vinasse, or 50% vinasse + 50% whey. After 28 days of growth, the glycerol medium achieved the highest BC per surface cultivation area and productivity. The second objective of the paper was to treat the effluent from the best condition of BC production (BCE) in an anaerobic sequencing batch reactor (ASBR) to produce biogas. Anaerobic digestion of BCE was carried out in bioreactors containing granular biomass operated at 100 rpm, 30 °C, and 24- hour cycle length. At 2.0 g-COD/L, BCE treatment resulted in 77% COD removal efficiency and 2.79 mmol-CH₄/L. Experimental data using glycerol allowed the estimation of the maximum potential for BC production on an industrial scale, obtaining 63 tons-BC/month from 5,800 tons-glycerol/year generated by a Brazilian biodiesel industry. The ASBRs required for industrial biogas production from BCE treatment would be 2.8 × 10⁴ m³, and the methane produced could be burned to generate 3.2 × 10² kW.