Nitrogen removal as nitrous oxide for energy recovery: Increased process stability and high nitrous yields at short hydraulic residence times. (15th April 2020)

• Record Type: Journal Article
• Authors: Wang, Zhiyue; Woo, Sung-Geun; Yao, Yinuo; Cheng, Hai-Hsuan; Wu, Yi-Ju; Criddle, Craig S.
• Is Part Of: Water research. Volume 173(2020)
• Publication Date: 2020-04-15
• Subjects: Anaerobic digester centrate -- Denitritation -- Nitrous oxide -- Polyhydroxyalkanoate -- Short-cut nitrogen removal -- Wastewater; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2020.115575
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: The Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO) is a two-stage process for nitrogen removal and resource recovery: in the first, ammonia is oxidized to nitrite in an aerobic bioreactor; in the second, oxidation of polyhydroxyalkanoate (PHA) drives reduction of nitrite to nitrous oxide (N2 O) which is stripped for use as a biogas oxidant. Because ammonia oxidation is well-studied, tests of CANDO to date have focused on N2 O production in anaerobic/anoxic sequencing batch reactors. In these reactors, nitrogen is provided as nitrite; PHA is produced from acetate or other dissolved COD, and PHA oxidation is coupled to N2 O production from nitrite. In a pilot-scale study, N2 O recovery was affected by COD/N ratio, total cycle time, and relative time periods for PHA synthesis and N2 O production. In follow-up bench-scale studies, different reactor cycle times were used to investigate these operational parameters. Increasing COD/N ratio improved nitrite removal and increased biosolids concentration. Shortening the anaerobic phase prevented fermentation of PHA and improved its utilization. Efficient PHA synthesis and utilization in the anaerobic phase correlated with high N2 O production in the anoxic phase. Shortening the anoxic phase prevented reduction of N2 O to N2 . By shortening both phases, total cycle time was reduced from 24 to 12 h. This optimized operation enabled increased biomass concentrations, increased N2 O yields (from 71 to 87%), increased N loading rates (from 0.1 to 0.25 kg N/m 3 -d), and shorter hydraulic residence times (from 10 to 2 days). Long-term changes in operational performance for the different bioreactor systems tested were generally similar despite significant differences in microbial community structure. Long-term operation at short anaerobic phases selected for a glycogen-accumulating community dominated by a Defluviicoccus -related strain. Graphical abstract: Image 1 Highlights: Nitrite removal as nitrous oxide was evaluated under field conditions. Extended anaerobic/anoxic phases adversely affected nitrous oxide production. Follow-on bench-scale studies resolved challenges observed at pilot-scale. Optimized performance achieved with a 2-day hydraulic residence time.