Impact of low temperature on nitrification of laboratory scale freshwater and saline sequencing batch reactors

Abstract

Introduction Nitrification is vital for nitrogen removal by nitrification-denitrification in wastewater treatment. In this study, the nitrification ability of freshwater and saline sewage reactors against low temperature shocks was studied. SAUR (specific ammonia uptake rate), SNUR (specific nitrite uptake rate) and SOUR (specific oxygen uptake rate) were tested to quantify the effects of low temperature shocks. The microbial community was also characterized by PCR and cloning-sequencing methods. Methods Concentrations of NH4+, NO2-, NO3- and VSS (volatile suspended solid) were recorded. SOUR, SNUR and SAUR were all tested before and after the temperature shocks. The genomic DNA was extracted and amplified by PCR using primer set of EUB8F and Univ1392. The clone library was constructed and the inserts were sequences using the primer M13R. Results For both reactors, the performance during the 1st temperature shock was quite different to other two shocks. For the freshwater one, it performed toughly in the 1st shock with no decrease in SOUR, and relatively less tough in the latter two shocks, with about 40% drop in SAUR and SNUR (SA&NUR). Different to the freshwater reactor, the saline reactor performed relatively tough in the latter two shocks with about 40% decrease in SA&NUR, and fragile in the first shock with more than 70% reduction in SA&NUR. The sequencing results indicated Actinobacteria and Proteobacteria were the two main phyla in the freshwater reactor, accounting for 69% and 21%, respectively. Especially, Tetrasphaera genus, a group of phosphate accumulating organisms (PAO), accounted for 20% in the Actinobacteria. Micropruina genus, the glycogen-accumulating bacteria, was also found in the reactor. But Nitrosomonas and other ammonia-oxidizing bacteria were not detected in the sample by the cloning approach, probably due to its low percent and the small size of the clone library. Conclusions In the 1st shock, the freshwater reactor seemed to be tougher than the saline one. But in the following two shocks, the saline reactor performed slightly tougher than the freshwater one, and this is not consistent with the experience of the sewage plants, which needs further study. The results indicated Actinobacteria was the main phylum in the freshwater reactor. The role of Tetrasphaera deserves further study.