An integrated anaerobic-aerobic treatment system was proposed here to achieve low sludge production, and low energy consumption for Hong Kong sewage treatment. Before integrating the whole system, a laboratory study was conducted to investigate the feasibility of autotrophic denitrification that utilized dissolved sulfide produced during anaerobic treatment. An upflow anaerobic sludge bed (UASB) was used to treat sulfate-rich synthetic wastewater (TOC = 100 mg/L and sulfate = 500 mg/L) that simulated Hong Kong sewage in terms of carbon and sulfate concentration and its effluent containing dissolved sulfide was fed into an anoxic filter (AF), for autotrophic denitrification....[ Read more ]

An integrated anaerobic-aerobic treatment system was proposed here to achieve low sludge production, and low energy consumption for Hong Kong sewage treatment. Before integrating the whole system, a laboratory study was conducted to investigate the feasibility of autotrophic denitrification that utilized dissolved sulfide produced during anaerobic treatment. An upflow anaerobic sludge bed (UASB) was used to treat sulfate-rich synthetic wastewater (TOC = 100 mg/L and sulfate = 500 mg/L) that simulated Hong Kong sewage in terms of carbon and sulfate concentration and its effluent containing dissolved sulfide was fed into an anoxic filter (AF), for autotrophic denitrification.

The results of this study demonstrated that dissolved sulfides produced through the sulfidogenic pathway in the UASB were effectively utilized for autotrophic denitrification. Excellent and stable organic and nitrate removal could be attained in the UASB reactor and anoxic filter, respectively. Feeding the system with synthetic wastewater having COD of 300 mg/L and a sulfate concentration of 500 mg/L, 60 - 90 mg S/L of dissolved sulfides produced anaerobically were sufficient for completely removing 30 - 50 mg N/L nitrate, which is commonly found in the nitrified effluent. This study also confirmed that the process performed equally well with both nitrate and nitrite in the feed, but the amount of dissolved sulfide required to remove 1 g of nitrate was almost double the amount required to remove the same amount of nitrite. The performance of the autotrophic denitrification was sensitive to the feed sulfide concentration. The nitrate removal efficiency reached 90% at the S/N ratio of about 1.6 and complete nitrate removal was observed when the S/N ratios greater than 2.0.

The net sludge production was approximately 0.22 - 0.31 g VSS/g NO₃^--N in the anoxic reactor and 0.15 - 0.18 g VSS/g COD in the anaerobic reactor. The overall sludge yield was below 0.18 g VSS / g COD, which is only about 32% sludge production of a conventional activated sludge process. Based on the findings of this study, it is evidently applicable to develop an integrated anaerobic-aerobic treatment system incorporating autotrophic denitrification for complete treatment of saline sewage with low sludge production and low energy consumption

Keywords

Anaerobic treatment; autotrophic denitrification; integrated treatment; sulfate reduction; Hong Kong saline sewage