On anammox activity at low temperature: effect of ladderane composition and process conditions.

The application of partial nitritation-anammox (PN/A) under mainstream conditions can enable substantial cost savings at wastewater treatment plants (WWTPs), but how process conditions and cell physiology affect anammox performance at psychrophilic temperatures below 15 °C remains poorly understood. We tested 14 anammox communities, including 8 from globally-installed PN/A processes, for (i) specific activity at 10-30 °C, (ii) composition of membrane lipids, and (iii) microbial community structure. We observed that membrane composition and cultivation temperature were closely related to the activity of anammox biomasses. The size of ladderane lipids and the content of bacteriohopanoids were key physiological components related to anammox performance at low temperatures. We also indicate that the adaptation of mesophilic cultures to psychrophilic regime necessitates months, but in some cases can take up to 5 years. Interestingly, biomass enriched in the marine genus "Candidatus Scalindua" displayed outstanding potential for nitrogen removal from cold streams. Collectively, our comprehensive study provides essential knowledge of cold adaptation mechanism, will enable more accurate modelling and suggests highly promising target anammox genera for inoculation and set-up of anammox reactors, in particular for mainstream WWTPs.

Cold shocks of Anammox biofilm stimulate nitrogen removal at low temperatures.

The adaptation of Anammox (ANaerobic AMMonium OXidation) to low temperatures (10-15°C) is crucial for sustaining energy-efficient nitrogen removal from the mainstream of municipal wastewater. But, current adaptation methods take months or even years. To speed up the adaption of Anammox to low temperatures, this study describes a new approach: exposing Anammox microorganisms to an abrupt temporary reduction of temperature, i.e., cold shock. Anammox biomass in a moving bed biofilm reactor was subjected to three consecutive cold shocks (reduction from 24 ± 2 to 5.0 ± 0.2°C), each taking eight hours. Before the cold shocks, Anammox activity determined in ex situ tests using the temperature range of 12.5-19.5°C was 0.005-0.015 kg-N kg-VSS-1 day-1 . Cold shocks increased the activity of Anammox at 10°C to 0.054 kg-N kg-VSS-1 day-1 after the third shock, which is similar to the highest activities obtained for cold-enriched or adapted Anammox reported in the literature (0.080 kg-N kg-VSS-1 day-1 ). Fluorescence in situ hybridization analysis showed that Ca. Brocadia fulgida was the dominant species. Thus, cold shocks are an intriguing new strategy for the adaptation of Anammox to low temperature. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:277-281, 2018.

Good servant, bad master: sulfide influence on partial nitritation of sewage.

When applying partial nitritation (PN) to anaerobically pre-treated sewage, ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) will be exposed to dissolved sulfide and methane. Both sulfide and methane may inhibit nitrification. To gain knowledge necessary for sustaining PN under these conditions, we exposed an AOB enrichment and a mixed nitrifying culture to dissolved sulfide and methane. In the mixed nitrifying culture, sulfide selectively inhibited NOB activity (KI,AOB1 = 150 mg-S L-1, KI,NOB = 10 mg-S L-1) which shows that sulfide may help establish PN. The AOB enrichment showed similar KI,AOB2 (130 mg-S L-1), but nitritation activity lagged longer than the time necessary to remove sulfide from the liquid. This demonstrates that feeding of sulfide into established PN should be avoided. Methane inhibition of AOB enrichment was assessed in batch assays with 10 mg-CH4 L-1. As compared to control without methane, AOB enrichment activity was identical. Up to 51% of methane was converted to methanol, thus reducing the greenhouse gas emissions.