Nitrogen Removal from Anaerobically Pretreated Swine Wastewater in an Intermittent Aeration Process

Intermittent aeration (IA) process was investigated for nitrogen removal from anaerobically pretreated swine wastewater (APTSW) that contained a high concentration of ammonium (average 265 mgNH4N/l) and a low sCOD (soluble chemical oxygen demand)/N ratio (average 1.4). Nitrogen removal from the APTSW was achieved through nitrification and denitrification in a single, semi-continuously fed reactor that was operated with alternation of aeration and non-aeration at room temperature (23鎺矯). To optimize the IA process, different Aeration:Non-Aeration (ANA) ratios and cycle lengths were used in the reactors as follows: Reactor A, 1 hour : 1 hour; Reactor B, 1 hour : 3 hours; Reactor C, 0.5 hour : 1.5 hours; Reactor D, 0.5 hour : 2 hour; Reactor E, 1 hour : 4 hours; Reactor F, 1 hour : 5 hours; and Reactor G, 1 hour : 6 hours. The hydraulic retention time (HRT) and mean cell residence time (MCRT) for the reactors were 3 and 20 days, respectively. Over 79 % ammonium was removed in all of the reactors. The reactor with the highest ANA ratio (Reactor A) achieved the highest NH3-N removal (99%), while the reactor with the longest non-aeration period (Reactor F) achieved the highest total nitrogen removal (83%). It was found that nitrogen removal was achieved through nitrate denitrification in Reactors A, B, C, and D, but it was via nitrite reduction in Reactors E and F. The high nitrogen removal efficiency indicated that the required organic carbon must have been obtained from the solubilization of solids contained in the influent or from microbial decay byproducts. The substantially higher denitrification rates observed in Reactors E and F were likely due to the decreased sCOD requirements for nitrogen removal via nitrite versus those required via nitrate.