Effective dampening of temperature effects in an anammox reactor treating real mainstream wastewater

The aim of the present study was to evaluate the capability of an up-flow anammox sludge bed reactor (13 L) of dampening a 10 degrees C temperature drop at mainstream conditions while operating at constant nitrogen loading rates (0.11 +/- 0.01 g N L-1 d(-1)). The up-flow anammox sludge bed reactor was fed with an aerobically pre-treated mainstream wastewater. The reactor temperature was controlled as to mimic a (realistic) summer-to-winter transition from 20 to 10 degrees C plus a three months period at 10 degrees C. During the 350 days of operation, the average nitrogen removal rate remained high (0.10 +/- 0.01 g N L-1 d(-1)), indicating that the 10 degrees C drop did not affect the overall efficiency of the reactor. This can be explained as anammox activity differed among the different sludge bed sections. At 20 degrees C, anammox activity was mainly located at the bottom of the sludge bed. At 10 degrees C, the anammox activity decrease of the bottom sludge bed was compensated by an activity increase within the upper sludge bed sections. The contribution of heterotrophic denitrifying activity to the total nitrogen removal rate was assessed to be 3-to-5 times lower than that of anammox, even at 10 degrees C. Microbial community of 16S rRNA gene-targeted sequencing analyses resulted in the identification of an uncharacterized Planctomycetes in high numbers. This study demonstrated that the low temperatures should not be an obstacle for the feasibility of anammox bacteria in the main water line of an urban wastewater treatment plant.

Automated summary

This study demonstrated that the up-flow anammox sludge bed reactor was able to maintain a high nitrogen removal rate even with a 10-degree temperature drop at mainstream conditions. The difference in anammox activity among different sludge bed sections allowed for efficient nitrogen removal even at lower temperatures. The microbial community analysis identified high numbers of uncharacterized Planctomycetes, indicating potential for anammox bacteria feasibility in urban wastewater treatment plants under low temperature conditions.