NITROGEN REMOVAL FROM ANAEROBICALLY DIGESTED SWINE WASTEWATER THROUGH COMBINED AMMONIA STRIPPING AND MEMBRANE BIOREACTOR PROCESSES.

Anaerobically digested swine wastewater has high concentrations of total ammoniacal nitrogen (TAN) (approximately 1,000 mg N L-1) and a low chemical oxygen demand (COD) to total nitrogen (TN) (COD/TN) ratio of <3.0, making it difficult to achieve a high TN removal rate using traditional biological nitrogen removal processes. The purpose of this study was to investigate the effectiveness of combining ammonia stripping (AS) and membrane bioreactor (MBR) processes to remove nitrogen from anaerobically digested swine wastewater. The coupling parameters that would lead to a high TN removal rate and cost effectiveness were also explored. Ammonia stripping was conducted at two pH levels of 10.0-10.5 (High-pH) and 9.0-9.5 (Low-pH). The MBR had the configuration of anoxic biofilm and aerobic MBR, and it was operated at two influent COD/TN ratios of 6.0-8.0 and 5.0-6.0 coupled with two TAN sludge loading rates in the oxic zone of 0.04-0.05 and 0.12-0.16 kg N kg-1 mixed liquid suspended solid (MLSS) d-1. Total nitrogen removal rate for the High-pH and Low-pH AS was 83% and 65%, respectively. In the MBR at a dissolved oxygen (DO) level of 6.12 -0.69 mg L-1, increasing the TAN sludge loading rate from 0.04 to 0.16 kg N kg-1 MLSS d-1 led to an increase in free ammonia from 0 to 4-9 mg L-1 and an increase in nitrite accumulation rate (NAR) from 0% to 71%. At a TAN sludge loading rate in the oxic zone of 0.12 kg N kg-1 MLSS d-1 and NAR of 53%, the TN removal rate reached 82% in the MBR through shortcut nitrification and denitrification (SND). The influent biochemical oxygen demand (BOD5) to TN (BOD5/TN) ratio was 1.41, COD/TN was 5.41, and the oxidation-reduction potential (ORP) of the denitrification zone was as low as -300 to -400 mV. Among the experimental conditions examined, the combined Low-pH AS+SND process provided the highest TN removal rate of 94% with the least cost and HRT. [ABSTRACT FROM AUTHOR]