Anaerobic Co-Digestion of Coffee Processing Wastewater and Microalgal Biomass After Protein Extraction

The co-digestion of Scenedesmus obliquus—the raw (RB), the mechanically disrupted (DB) and the residual microalgal biomass after protein extraction (PEB)—with coffee processing wastewater (CPW) was assessed. Mono-digestion of microalgae biomass yielded 18.2, 70.6 and 39.6 mLCH₄ gVS⁻¹ for RB, DB and PEB, respectively. However, alkaline conditions used to increase protein extraction also promoted an enrichment of biogas (90% methane). The co-digestion presented maximum production of 269.6 mLCH₄ gVS⁻¹ (DB: CPW 75: 25), attributed to the higher anaerobic biodegradability of the CPW (343.3 mLCH₄ gVS⁻¹) and the pH of substrates. In the kinetic study, the Cone model presented a good fit. Mono-digestion of PEB and CPW exhibited higher values for k (1st order coefficient), while co-digestion improve k values for RB and DB. Results suggest that co-digestion contributed to the anaerobic digestion stability in terms of alkalinity, increased microalgae biodegradability and, particularly with PEB, enables an integrated waste management.