Start-up and Performance Optimization of a CANON Pilot Reactor

Abstract

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.