Application of CANON process for nitrogen removal from anaerobically pretreated husbandry wastewater

In this study, the removal of nitrogen from anaerobically pretreated husbandry wastewater using a continuous stirred tank reactor of a completely autotrophic nitrogen removal over nitrite (CANON) process coupled with a simple aeration setup was investigated. The reactor was operated with anaerobically pretreated husbandry wastewater at hydraulic retention times (HRTs) of 16, 8, and 6 h with stepwise increased in average nitrogen loading rates (NLRs) of 0.47, 0.95, and 1.16 kg N m(-3) d(-1). The highest and stable nitrogen removal was obtained at HRT of 8 h (NLR of 0.95 kg N m(-3) d(-1)). The key operating conditions were intermittent aeration for maintaining low dissolved oxygen concentrations (0.1-0.2 mgl(-1)) and alkalinity adjustment for obtaining pH values of 7.6-7.8. The effluent quality met Vietnamese husbandry wastewater standard for total nitrogen (< 150 mgl(-1) N). High chemical oxygen demand (COD) concentration (> 400 mgl(-1)) in the feed wastewater reduced ammonia oxidizing bacteria (AOB) activity. At shorter HRT (6 h), the washout of fine bioflocs containing aerobic heterotrophs and AOB occurred, while the reddish anammox granules still remained in the reactor.