Source separation and anaerobic co-digestion of blackwater and food waste for biogas production and nutrient recovery

Abstract

Anaerobic co-digestion of source-separated blackwater (BW) and food and kitchen waste (FW) offers decentralized circular economy solutions by enabling local production of biogas and nutrient-rich byproducts. In this study, a 2 m3 pilot-scale continuously stirred tank reactor (CSTR) operated under mesophilic conditions was utilized for co-digestion of BW and FW. The process obtained a CH4 yield of 0.7 ± 0.2 m3/kg influent-volatile solid (VS), reaching a maximum yield of 1.1 ± 0.1 m3/kg influent-VS, with an average organic loading rate of 0.6 ± 0.1 kg-VS/m3/d and HRT of 25 days. The CH4 production rate averaged 0.4 ± 0.1 m3/m3/d, peaking at 0.6 ± 0.1 m3/m3/d. Treatment of digestate through flocculation followed by sedimentation recovered over 90% of ammonium nitrogen and potassium, and 80–85% of total phosphorus in the liquid fraction. This nutrient-rich liquid was used to cultivate Chlorella vulgaris, achieving a biomass concentration of 1.2 ± 0.1 g/L and 85 ± 3% and 78 ± 5% ammonium nitrogen and phosphorus removal efficiency, respectively. These findings not only highlight the feasibility of anaerobic co-digestion of source-separated BW and FW in local biogas production but also demonstrate the potential of microalgae cultivation as a sustainable approach to converting digestate into nutrient-rich algae biomass. HIGHLIGHTS Anaerobic co-digestion of blackwater and food waste in a 2 m3 CSTR.; The maximum CH4 production rate was 0.6 ± 0.1 m3 per m3 reactor volume per day.; CH4 productivity was 50 ± 1% higher on the pilot-scale than in laboratory-scale BMPs.; Flocculation followed by sedimentation preserved >90% of macronutrients in digestate.; Chlorella vulgaris treatment reduced total and dissolved COD by 50 ± 10%.;

Keywords

• anaerobic co-digestion
• blackwater
• food waste
• microalgae
• nutrient recovery
• source separation