Abstract:
To study the result of organic loading rates, pH in acid reactor, and recycle ratio for the performance of two-phase UASB in treating wastewater from ethanol distillery process. CSTR acidification tank (1.7 L) was connected to 10 L-UASB tank in series, while the flow rate was kept constant at 3.5 L/d throughout all experiments. The retention time of acidification tank and UASB tank was 0.5 d and 2.8 d, respectively. The studying organic loading rates were 3.8, 7.0, 10.0, 11.7, and 13.0 kgCOD/cubic m-d. The studying pH in acid reactor were 5.97, 5.53, and 5.15 and recycle ratio were 0, 1, 2, and 3, using organic loading rate of 5.0 kgCOD/cubic m-d. Results showed that two-phase UASB worked efficiently at organic loading rate of 3.8-10.0 kgCOD/cubic m-d, soluble COD removal efficiencies were 57.8 ± 0.3%. Approximate methane yield were 0.24 - 0.31 L/gCOD removed. Approximate specific substrate removal rates were 0.066-0.129 gCOD removed-d/gMLSS. At organic loading rates of 11.7 and 13.0 kgCOD/cubic m-d, two-phase UASB efficiency decreased and failed although pH and VFA/ALK were in suitable level. This might happen from other reasons such as toxicity, very high COD and different wastewater due to factory operating system. Decreasing pH in acid reactor from 6 to 5 reduced alkalinity addition by 50% and did not significantly affect on two-phase UASB. Increasing recycle ratio significantly reduced alkalinity addition and recycle ratio of 3 did not need any alkalinity addition during 10 days of two-phase UASB operation.