Abstract
The combination of partial nitritation (PN) and anaerobic ammonium oxidation (anammox) has been proposed as an ideal process for nitrogen removal from source-separated urine, while the high organic matters in urine cause instability of single-stage PN-anammox process. This study aims to remove the organic matters and partially nitrify the nitrogen in urine, producing an ammonium/nitrite solution suitable for anammox. The organic matters in stored urine were used as the electron donors to achieve 40% total nitrogen removal in nitritation-denitrification process in a sequencing batch reactor (SBR). Granular aggregates were observed and high mixed liquor suspended solids (9.5 g/L) were maintained in the SBR. Around 70–75% ammonium was oxidized to nitrite under the volumetric loading rates of 3.23 kg chemical oxygen demand (COD)/(m3 d) and 1.86 kg N/(m3 d), respectively. The SBR produced an ammonium/nitrite solution free of biodegradable organic matters, with a NO2−–N:NH4+–N of 1.24 ± 0.13. Fluorescence in situ hybridization images showed that Nitrosomonas-like ammonium-oxidizing bacteria, accounting for 7.2% of total bacteria, located in the outer layer (25 μm), while heterotrophs distributed homogeneously throughout the granular aggregates. High concentrations of free ammonia and nitrous acids in the reactor severely inhibited the growth of nitrite-oxidizing bacteria, resulting in their absence in the granular sludge. The microbial diversity analysis indicated Proteobacteria was the predominant phylum, in which Pseudomonas was the most abundant genus.
Highlights
Source separation and treatment of human urine have attracted extensive interest in urban water management since urine constitutes at least 50% of total phosphorus (P) load and 80% of total nitrogen (N) load in municipal wastewater, but represents less than 1% of total volume (Hanæus et al 1997; Maurer et al 2006)
As described in Additional file 1, urine and reverse osmosis (RO) brine were mixed at a volumetric ratio of 1:1 in a precipitation reactor, the effluent from which was fed to a laboratory-scale sequencing batch reactor (SBR) for both organic matter removal and partial nitritation (PN)
Treatment performance In the present study, the feed to SBR was the effluent from a precipitation reactor, in which undiluted sourceseparated urine and RO brine were mixed at a volumetric ration of 1:1
Summary
Source separation and treatment of human urine have attracted extensive interest in urban water management since urine constitutes at least 50% of total phosphorus (P) load and 80% of total nitrogen (N) load in municipal wastewater, but represents less than 1% of total volume (Hanæus et al 1997; Maurer et al 2006). Owing to the high content of nutrients in source-separated. The combination of partial nitritation (PN) and anaerobic ammonium oxidation (anammox) has recently been regarded as a promising and energy efficient approach to remove the nitrogen compounds in high strength wastewaters (Kartal et al 2010). In the PN process, half NH4+ is oxidized into nitrite (NO2−) by autotrophic ammonium-oxidizing bacteria (AOB) under the aerobic environment. In the subsequent anammox process, the remaining NH4+ is oxidized by NO2− to di-nitrogen gas (N2) under the anaerobic conditions. In comparison to the conventional nitrification and denitrification, the combined PN-anammox process could save 63% oxygen requirement, and eliminate the addition of external
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