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), NH 4 +-N and NO x-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 NH 4 +-N from the nitrification reactor with proper pH control using excess alkalinity and a recycle ratio of 3. The average removal efficiency of NO x-N in the anoxic reactor was above 80% with the poor effluent quality (25 mg/l). This high concentration of NO x-N in the effluent of the anoxic reactor was removed by the sulfur-packed biofilter with the stable effluent concentrations between 0.4 and 4 mg/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.

Swine wastewater contains high amounts of organic matter and nutrients (nitrogen and phosphorus). The biological nitrogen removal can be achieved by nitrification and denitrification processes. Nitrification-denitrification can be performed via nitrite which is called as the short-cut process. This Short-cut process saves up to 25% of oxygen and 40% of external carbon during nitrification and denitrification. In this study, the batch tests were conducted to assess the different parameters for the nitrite sulfur utilizing denitrification, such as alkalinity, temperature, initial nitrite concentration, and dissolved oxygen. The experimental results showed that the nitrite removal efficiency of the reactor was found to be over 95% under the optimum condition (30℃ and sufficient alkalinity). Autotrophic nitrate denitrification was inhibited at low alkalinity condition showing only 10% removal efficiency, while nitrite denitrification was achieved over 95%. The nitrite removal rates were found similar at both 20℃ and 30℃. In addition, nitrite removal efficiencies were inhibited by increasing oxygen concentration, but sulfate concentration increased due to sulfur oxidation under an aerobic condition. Sulfate production and alkalinity consumption were decreased with nitrite compared those with nitrate.