[Microbial Diversity Analysis of WWTPs Based on Hybrid-MBBR Process in a Low Temperature Season in the Yangtze River Delta].

The aim of this study was to characterize the changes of the microbial community in WWTPs based on hybrid-MBBR process in the Yangtze River Delta in a low temperature season, and to obtain the regularity of the microbial distribution. High-throughput sequencing of Illumina miSeq was conducted to analyze the microbial community structure of activated sludge and suspended carrier biofilm in the aerobic area of five WWTPs. The results showed that the number of microbial species in the suspended carrier biofilm was lower than that of the activated sludge in the same plant, and the species distribution was more uneven. The addition of a suspended carrier can improve the microbial diversity of the system, while the influent and operation mode have a certain selectivity to the microbial community composition of the system. The bacteria with high relative abundance in each plant primarily included Nitrospira, Mycobacterium, Defluvicoccus, Hyphomacrobium, and Macrocharacters,etc. The addition of suspended carriers significantly enhanced the enrichment of Nitrospira. The amount of nitrifying bacteria in the suspended carrier accounted for 86.12%-95.36% of that of the whole system. A certain relative abundance of denitrifying bacteria was detected in the suspended carrier in the aerobic area of each plant. Combined with the results of the measurement of water quality along the process and the lab-scale experiment, it was confirmed that significant SND occurred on the suspended carrier biofilm in the aerobic area, which enhanced the TN removal of the system.

[Start-up and Performance Optimization of a CANON Pilot Reactor].

A completely autotrophic nitrogen removal over nitrite (CANON) reactor was established by seeding ordinary activated sludge with reject water as the influent at (30±3)℃ from a sewage treatment plant in Qingdao. To solve bacterial loss and optimize reactor performance, a suspension of biological carriers was added to the CANON reactor. The result showed that the reactor was successfully started 130 days later. The total nitrogen removal load was up to 0.03 kg·(m3·d)-1, and the average variation ratio of nitrate and ammonia (RNaA) was 0.09, which was close to theoretical value 0.11. The CANON active sludge reactor ran for 300 days. During the stable operation period, the total nitrogen removal rate was stable at 0.20 kg·(m3·d)-1. Red granular sludge was mixed with the effluent of the system, and the particle size of granular sludge was between 1 and 3 mm. The suspension carriers were added to the CANON reactor with a filling rate of 30%. The fillers added to the moving bed biofilm reactor (MBBR) were mature fillers in the nitrifying reactor of the laboratory. The accumulation rate of nitrification was greater than 95%, and the ammonia-oxidized surface load reached 2.0 g·(m2·d)-1. After 30 days of operation and culturing, the system was successfully converted to a pure membrane system, and the biofilm on the surface of the carrier turned pale red. The total nitrogen removal load was up to 0.17 kg·(m3·d)-1. The average RNaA was 0.14, which was slightly higher than the theoretical value of 0.11. This suggested that the CANON sludge adapted to the environment in the MBBR and began to enter a stable stage. The CANON-MBBR ran for 200 days. During the stable operation period, the total nitrogen removal rate was stable at 1.15 kg·(m3·d)-1. The biofilm was bright brick red with a thickness of 150-250 µm. MLSS and MLVSS on the carriers were approximately 10200 mg·m-2 and 9000 mg·m-2, respectively, and the total biomass in the system was approximately 1.5 kg. Through high-throughput sequencing, AOB and AnAOB were found to be the dominant bacteria species on the suspension carrier, with a relative abundance of 26.24% and 30.08%, respectively, and nitrate oxidizing bacteria were successfully suppressed. The above results showed that CANON-MBBR with high-density polyethylene filler as the suspension carrier had good nitrogen-removal efficiency and was conducive to the stable operation of the autotrophic nitrogen removal process.