Enhancement of biogas production and COD removal of caramel process condensate by anaerobic-aerobic treatment and a pilot-scale application

The caramel production process generates substantial volumes of caramel process condensate (CPC) with high chemical oxygen demand (COD) levels (20,000-30,000 mg/L) and low pH (2-3). This study evaluated biogas production and COD removal using anaerobic-aerobic treatment under varying pH (7-4) and salinity (0-50 g/L). Laboratory experiments achieved over 90 % COD removal and a daily biogas production rate (DBPR) of 0.64 m3/ (kg center dot COD) at an organic loading rate (OLR) of 5 kg COD/(m3 center dot d), influent COD concentration of 10,000 mg/L, hydraulic retention time (HRT) of 2 days, and influent pH of 4. Salt tolerance tests showed that at an OLR of 2.5 kg COD/(m3 center dot d) and NaCl concentration below 10 g/L, COD removal efficiency remained 90 %, with a DBPR of 0.92 m3/(kg center dot COD). At 34 g/L NaCl, COD removal decreased to 80 % and DBPR to 0.63 m3/(kg center dot COD). Pilot experiments confirmed that, under conditions of an OLR of 1.8 kg COD/(m3 center dot d), influent COD of 10,000 mg/L, a HRT of 6 days, and a pH range of 6.8 to 4.8, the COD removal efficiency was 90 %, the DBPR was 0.63 m3/ (kg center dot COD), and methane production(MP) reached 0.31 m3 CH4/(kg COD). The anaerobic-aerobic combined treatment achieves over 90 % COD removal, offering an efficient and cost-effective solution for the resource utilization of CPC.