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A modified lab-scale anoxic/oxic process was designed incorporating an upflow sulfur-packed biofilter for the treatment of anaerobically digested swine wastewater. In this study, chemical oxygen demand (COD), NH4+-N and NOx--N removal efficiencies were investigated. The experimental results showed that by increasing the internal recycle ratio from 1 to 3, the overall performance of the system improved. Organics removal efficiency was found to be fairly high and stable and the average total chemical oxygen demand (TCOD) removal efficiency ranged from 79 to 90%. This process removed up to 98% of the total NH4+-N from the nitrification reactor with proper pH control using excess alkalinity and a recycle ratio of 3. The average removal efficiency of NOx--N in the anoxic reactor was above 80% with the poor effluent quality (25 mg/l). This high concentration of NOx--N in the effluent of the anoxic reactor was removed by the sulfur-packed biofilter with the stable effluent concentrations between 0.4 and 4mg/l. This result indicates that the sulfur-packed biofilter would be used as an efficient option for denitrification by autotrophic denitrifiers during swine wastewater treatment.
Key words: Biological nitrogen removal, nitrification, denitrification, chemical oxygen demand (COD), intermittent aeration, sulfur-packed bed reactor, swine wastewater, anoxic-oxic process, internal recycle.