In this study, we investigated the efficiency of dissolved methane collection by degasification from the effluent of a bench-scale upflow anaerobic sludge blanket (UASB) reactor treating synthetic wastewater. A hollow-fiber degassing membrane module was used for degasification. This module was connected to the liquid outlet of the UASB reactor. Accordingly, total CH 4 recovery efficiency increased from 71% to 97% at 15°C as a result of degasification. Moreover, degasification tended to cause an increase in particulate COD removal efficiency. The UASB reactor was operated at the same COD loading rate, but different wastewater feed rates and HRTs. Although average D-CH 4 concentration in the UASB reactor was almost unchanged (ca. 70 mg COD L -1 ) regardless of the HRT value, the CH 4 discharge rate from the UASB reactor increased because of an increase in the wastewater feed rate. Because the D-CH 4 concentration could be reduced down to 12 ± 1 mg COD L -1 by degasification at an HRT of 6.7 h, the 3 CH 4 recovery rate was 1.5 times higher under degasification than under normal operation.

Anaerobic treatment is an attractive option for the biological treatment of municipal wastewater. In this study, municipal wastewater was anaerobically treated with a bench-scale upflow anaerobic sludge blanket (UASB) reactor at temperatures from 6-31°C for 18 months to investigate total chemical oxygen demand (COD) removal efficiency, archaeal community structure, and dissolved methane (D-CH 4 ) recovery efficiency. The COD removal efficiency was more than 50% in summer and below 40% in winter with no evolution of biogas. Analysis of the archaeal community structures of the granular sludge from the UASB using 16S rRNA gene-cloning indicated that after microorganisms had adapted to low temperatures, the archaeal community had a lower diversity and the relative abundance of acetoclastic methanogens decreased together with an increase in hydrogenotrophic methanogens. D-CH 4 , which was detected in the UASB effluent throughout the operation, could be collected with a degassing membrane. The ratio of the collection to recovery rates was 60% in summer and 100% in winter. For anaerobic treatment of municipal wastewater at lower temperatures, hydrogenotrophic methanogens play an important role in COD removal and D-CH 4 can be collected to reduce greenhouse gas emissions and avoid wastage of energy resources.

Temperature is an important environmental variable that can strongly affect the performance of anaerobic reactors working at ambient temperatures. This study presents a mechanistic mathematical model which depends in an explicit way on the operating temperature. The cardinal temperature model function is proposed to describe the temperature dependence of the kinetic parameters and the experimental data from an UASB-degasification system was used to calibrate the model. The performance of the model is compared with the classic Arrhenius approach. The results showed that the 2 temperature-based model of the anaerobic digestion is able to reproduce a long-term reactor operation in terms of biogas production and the concentration of organic matter at fluctuating ambient temperature.

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The effectiveness of degasification using a degassing membrane to improve chemical oxygen demand (COD) removal efficiency was investigated using a bench-scale upflow anaerobic sludge blanket (UASB) reactor. Vacuum degasification was able to transfer dissolved gas in the bulk liquid of the UASB reactor inside the membrane. Such a process might provide thermodynamically favorable conditions for the degradation of organic compounds. The COD-removal efficiency improved from 83% during normal operation to 90% during the degassing operation.