BACKGROUND: Untreated high-strength salinity wastewaters pose a serious threat to the environment. Anaerobic treatment is an effective process with double advantages of waste stabilization and energy production. However, high organic compound and sodium toxicity in high-salinity wastewaters adversely affect the performance of anaerobic treatment. In this study, anaerobic hybrid (AH) and upflow anaerobic sludge blanket (UASB) reactors were investigated for their efficiencies to alleviate the negative effects of high-salinity wastewater.RESULTS: Double increases in the NaCl concentration drastically deteriorated the performances of both reactors. The activities of acetoclastic methanogens (ACM) and hydrogenotrophic methanogens (HTM) in both reactors decreased to 22-28% and 36-40% compared to the previous period, respectively. However, the methanogen population (Methanosarcinales and Methanobacteriales) was not affected negatively. The AH reactor exhibited excellent performance during the recovery and restart periods, which only required 7 days to complete the recovery period. Furthermore, during the restart period, the AH reactor showed high chemical oxygen demand (COD) removal efficiency, methane (CH 4 ) production and yield as ≈90%, 2600 mL day −1 and 0.30 m 3 CH 4 kg −1 COD removed , respectively. The rate of biomass washout from the AH reactor also was lower compared to the UASB reactor. The concentration of attached biomass in the packed zone of the AH reactor gradually increased indicating the growth of an active microbial biofilm. CONCLUSION: The excellent performance of the AH reactor was presumably a result of its packed zone configuration which provided the supporting media to entrap smaller microbial aggregates, reduce biomass washout and support the growth of active biofilm.

BACKGROUND: In the unfavorable conditions of anaerobic digestion systems, the attached or immobilized microbial communities used as biofilm are more resistant to being washed out than the suspended biomass. The biofilm formation was determined by the carrier characteristics, considering their physicochemical properties and high availability. This study presented an approach for improving the use of polyurethane (PU) foam as a biofilm carrier for methanogenic consortium. RESULTS:The effect of powdered activated carbon (PAC) on the reactor performance and biofilm formation was apparent during days 0-30. The average chemical oxygen demand (COD) removal, methane (CH 4 ) composition, and CH 4 yield of PACsupplemented reactor (R2) in this period were 71.40%, 82.0%, and 0.3 L CH 4 g −1 COD removed, respectively; these values were higher than those of the control reactor (R1). In addition, a greater amount of biomass was observed on the PU foam of R2 (1.47 g VSS), indicating a higher biofilm formation. Scanning electron microscopy (SEM) analysis revealed that microbial biofilm on the PAC-supplemented PU was also denser than that on the control PU. In addition, fluorescence in situ hybridization (FISH) detected layers of Methanosarcinales and Smithella sp.CONCLUSION: This study demonstrated that PAC supplementation had synergistic effects during initial biofilm formation of the methanogenic consortium by accelerating microbial attachment, preserving biofilm structure, and enhancing methanogenic activity.

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