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Anaerobic biofilm reactors have limitations in treating wastewaters with low organic substrate concentrations (COD value below 1000 mg/L) because the substrate cannot reach the microorganisms present in the interior part of the biogranules. Hence, the performance of these reactors is mainly influenced by the size of the biogranules present within the reactor. An anaerobic hybrid reactor with a tapered configuration has been developed where the self-immobilized biogranules are kept under completely fluidized condition. The tapered configuration can retain smaller sized biogranules more effectively than a cylindrical configuration for the same hydraulic loading rate. A synthetic effluent containing glucose as the sole carbon source was used to study the performance of this reactor. The reactor could handle an organic loading rate up to 19.1 kgCOD/(m3 x d) with a hydraulic retention time (HRT) of 0.63 h, removing around 90% of inlet COD. Even though the strength of the wastewater is low, the resultant organic loading rate is also high because of the high hydraulic loading rate (low HRT). The specific substrate utilization rate study showed that the concentration of methanogenic bacteria within the biogranules increased along the reactor height, whereas the concentration of acidogens decreased. The morphology and hydrodynamic characteristics of the biogranules obtained from the reactor at different heights were also studied. The biogranules obtained from the upper port of the reactor had a lower diameter, lower terminal settling velocity and more cavities than those from the lower port. Biogranules up to the size of 5.2 mm were observed.

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This study details the development of mixed anaerobic culture capable of degrading high concentrations of chlorophenols, 4-chlorophenol (MCP), 2,4-dichlorophenol (DCP) and pentachlorophenol (PCP) were used for that purpose. The role of glucose concentration and the relative potential of mixed culture for acclimatization of different chlorophenols under anaerobic conditions were studied. Methane production, pH and their reduction in concentrations of glucose and chlorophenols were measured at regular intervals. It was observed that after 350 days of acclimatization, anaerobic cultures degraded up to 200 ppm MCP, 200 ppm DCP and 250 ppm PCP. It was also found that the biogenic substrate such as glucose increased the rate of chlorophenols acclimatization and degradation.