Characteristics of nitrifier in sludge denitrifying phosphorus removal and recovery process

Nitrogen and phosphorus are known as two main factors contributing to eutrophication of water body. A novel two-sludge denitrifying phosphorus removal and phosphorus recovery process responsible for simultaneous nitrogen and phosphorus removal from wastewater was established in our previous studies. Many reports suggested that a better understanding of microbial communities in a wastewater treatment process could give an important guidance for stable operation as well as reconstruction. In addition, nitrification is the limiting procedure based on the theory of simultaneous nitrogen and phosphorus removal. For this, this paper analyzed the microbial characteristics in nitrification pond within a two-sludge denitrifying phosphorus removal and phosphorus recovery process by using fluorescence in situ hybridization (FISH), scanning electron micrograph (SEM) and the software of Image-Pro Plus (IPP). In this process, the abundance of ammonia-oxidizing bacteria (AOB) responsible for the transformation of ammonia nitrogen to nitrite was significantly higher than that of nitrite-oxidizing bacteria (NOB) capable of the conversion of nitrite to nitrate. According to the FISH analysis, the proportion of AOB to total bacteria was 46.2%, while NOB was 28.5%. Generally, the AOB was close to the external layer of sludge granule while the NOB was in the internal layer. From SEM, the nitrifiers in the nitrification pond were typically coccus or short rods and preferably grown the dense clusters. The aggregates formed by the AOB were bigger than those of NOB tending to combine with several cells. Based on the three dimensional graphs of microstructures of nitrification sludge analyzed by using IPP software, it was found that the structure was density in the external layer, while that was loose in the internal layer and much void or hollows were found as well, which might be due to the difference of the abundance of microorganisms and the concentrations of nutrients and oxygen between the external and the internal. In conclusion, compared with the conventional single-sludge wastewater treatment processes, two-sludge denitrifying phosphorus removal processes have a great advantage to enrich the nitrifiers. Therefore, these results obtained here could be effective for optimization of process parameters or construction of pilot plant and design of wastewater treatment process responsible for nitrogen and phosphorus removal as well.