Mainstream partial nitritation and anammox: long-term process stability and effluent quality at low temperatures

Abstract

The implementation of autotrophic anaerobic ammonium oxidation processes for the removal of nitrogen from municipal wastewater (known as “mainstream anammox”) bears the potential to bring wastewater treatment plants close to energy autarky. The aim of the present work was to assess the long-term stability of partial nitritation/anammox (PN/A) processes operating at low temperatures and their reliability in meeting nitrogen concentrations in the range of typical discharge limits below 2 mgNH4-N·normalL−1 and 10 mgNtot·L−1. Two main 12-L sequencing batch reactors were operated in parallel for PN/A on aerobically pre-treated municipal wastewater (21 ± 5 mgNH4-N·normalL−1 and residual 69 ± 19 mgCODtot·L−1) for more than one year, including over 5 months at 15 °C. The two systems consisted of a moving bed biofilm reactor (MBBR) and a hybrid MBBR (H-MBBR) with flocculent biomass. Operation at limiting oxygen concentrations (0.15–0.18 mgnormalO2·normalL−1) allowed stable suppression of the activity of nitrite-oxidizing bacteria at 15 °C with a production of nitrate over ammonium consumed as low as 16% in the MBBR. Promising nitrogen removal rates of 20–40 mgN·L−1·d−1 were maintained at hydraulic retention times of 14 h. Stable ammonium and total nitrogen removal efficiencies over 90% and 70% respectively were achieved. Both reactors reached average concentrations of total nitrogen below 10 mgN·L−1 in their effluents, even down to 6 mgN·L−1 for the MBBR, with an ammonium concentration of 2 mgN·L−1 (set as operational threshold to stop aeration). Furthermore, the two PN/A systems performed almost identically with respect to the biological removal of organic micropollutants and, importantly, to a similar extent as conventional treatments. A sudden temperature drop to 11 °C resulted in significant suppression of anammox activity, although this was rapidly recovered after the temperature was increased back to 15 °C. Analyses of 16S rRNA gene-targeted amplicon sequencing revealed that the anammox guild of the bacterial communities of the two systems was composed of the genus “Candidatus Brocadia”. The potential of PN/A systems to compete with conventional treatments for biological nutrients removal both in terms of removal rates and overall effluent quality was proven.

The role of inoculum and reactor configuration for microbial community composition and dynamics in mainstream partial nitritation anammox reactors

“…Similar results were obtained in a study by Laureni et al. (), who reported higher community dynamics in suspended biomass compared to biofilm carriers in PNA reactors operated at 15°C. Such community behavior seemed to be caused by the lack of structural preservation which was available in the MBBRs.…”

“…Other studies reported biofilm PNA systems with Ca . Brocadia as a preferred choice at low temperature (Gilbert, Agrawal, Schwartz, Horn, & Lackner, ; Lackner & Horn, ; Laureni et al., ). Fast start‐up and stable performance of mainstream PNA systems thus relies on the inoculum composition and the reactor configuration.…”

Cold shocks of Anammox biofilm stimulate nitrogen removal at low temperatures

“…The growth of Candidatus Brocadia in these conditions is not a surprise, because Candidatus Brocadia was the dominant Anammox genus in eight systems operated close to 10°C …”

“…This study applied cold shocks for 8 h, reduced the temperature from 24 ± 2 to 5°C and applied only three consecutive shocks over 45 days with incremental increases of Anammox activity at 10°C. Conversely, Laureni et al abruptly reduced the temperature in partial nitritation/Anammox (PN/A) from 15 to 11°C for a month. Back at 15°C, these researchers reported a recovery of Anammox activity in 1 week, showing survival of Anammox under these cold shock conditions that are environmentally relevant.…”

Anaerobic treatment of municipal wastewater in a UASB-Digester system : temperature effect on system performance, hydrolysis and methanogenesis

“…ANAMMOX and DAMO processes are already studied individually Laureni et al, 2016;Lotti et al, 2015). The volumetric nitrite consumption rate of the DAMO process was shown to be not sufficient yet, and applying a membrane was suggested to increase the biomass retention .…”