Effect of carrier particle size on enrichment and shift in nitrifier community behaviors for treating increased strength wastewater

Abstract

In activated sludge systems, adding carriers can improve nitrifier enrichment. Different attachment area induced by different particle sizes of carriers may result in different nitrifier community. This research investigated the effect of different particle sizes of coal ash on nitrifier enrichment treating increased strength wastewater. Results indicated efficient nitrifying coal ash was obtained with smaller coal ash. The ammonia removal rates reached over 98%, which outclassed that in negative control (63.28%), and no nitrite accumulated in these systems under high nitrogen concentration of 1123.35 mg N/L. The high-throughput sequencing assays indicated carriers changed the microbial community structure significantly, thus facilitated the nitrification capacity. Increase abundance of nitrifier has a negative correlation with particle size of carriers. Nitrosomonas became the biggest beneficiary, which maximum composed 50.29% in fillers system and only 13.69% in negative control, whereas the number of Nitrobacter (less than 3.04%) became much lower than ammonia-oxidizing bacteria (AOB). However, the shift of microbial structures, large number of Dokdonella for instance, may guarantee the complete nitrification in systems with smaller carriers. Batch experiments showed a high dissolved oxygen (DO) concentration (4 mg/L) and slightly alkaline condition (pH 8.0) had a positive effect on nitrifying coal ash. PRACTITIONER POINTS: The increase size of nitrifier has a negative correlation with particle size of coal ash. The smaller coal ash reduces the adverse effect of high nitrogen on nitrification. The ammonia removal rate reached 99.82% with influent of 1123.35 mg ${\text{NH}}_4^{+}\text{- N}$ /L in the smallest carriers system.

Keywords: complete nitrification; efficient nitrifying coal ash; high nitrogen loading; microbial community structure; nitrifier enrichment.