[Achieving Partial Nitritation in a Continuous-flow Aerobic Granular Sludge Reactor at Different Temperatures Through Ratio Control].

Mature aerobic granular sludge (AGS) was inoculated in a continuous-flow reactor to treat low ammonia sewage, and the feasibility of achieving partial nitritation in a continuous-flow aerobic sludge system and the demand for R value (the ratio of dissolved oxygen and ammonia nitrogen) when partial nitritation is achieved at different temperatures (30, 20, and 10℃) were investigated. The control strategy was designed to maintain a constant ratio between dissolved oxygen (DO) and ammonia nitrogen (NH4+-N). The results revealed that stable nitritation in a continuous-flow aerobic sludge reactor could be achieved via ratio control, and the value of R were 0.50 (±0.05), 0.35 (±0.03), and 0.20 (±0.02) at the temperatures 30, 20, and 10℃, respectively, from which it can be concluded that stronger oxygen-limiting conditions were required when the temperature was lower. The experiment of fluorescence in situ hybridization (FISH) revealed that ammonia oxidizing bacteria (AOB) have a certain concentration, and the relative number of nitrite oxidizing bacteria (NOB) gradually reduced through the ratio control strategy. Based on the ratio control strategy and the characteristics of wastewater quality, full nitritation of high ammonia wastewater may be allowed; however, for low ammonia wastewater, only partial nitritation is recommended.

[Effect of Two-Stage Aeration on Nitrogen Removal Performance of Aerobic Granular Sludge].

Four mini experiments were conducted at different conditions. The heterotrophic microorganisms on the aerobic granular sludge surface consumed organic compounds at the initial stage of aeration. The denitrification rate and the efficiency of NO2--N and NO3--N removal were relatively low. Therefore, under the normal temperature conditions (20-23℃), aerobic granular sludge sequencing batch reactor (SBR) was operated in the two-stage aeration mode(first in low aeration then in high aeration mode). The low aeration time were carried out at 1, 2 and 3 hours stages respectively, and the characteristics of the granular sludge and its effects on microorganisms were analyzed by scanning electron microscopy (SEM) and fluorescence in situ hybridization (FISH) technique. The results show that the increase in the aerobic granular sludge (AGS) particle size improved the denitrification capacity; the denitrification rate of NO2--N was the highest at low aeration mode with 2 h and reached 9.66 mg·(g·h)-1. The accumulation rate of nitrite increased to 77.84% and the total nitrogen removal rate to 70%. The bacterial count inside the granular sludge increased and they were mainly cocci, bacillus, and ellipsoidal bacteria. Moreover, the proportion of ammonia-oxidizing bacteria in total bacterial count increased from 13.70% to 15.40%. Therefore, the two-stage aeration process achieved shortened simultaneous nitrification and denitrification processes and showed a good denitrification performance.

Achieving nitritation in a continuous moving bed biofilm reactor at different temperatures through ratio control.

A ratio control strategy was implemented in a continuous moving bed biofilm reactor (MBBR) to investigate the response to different temperatures. The control strategy was designed to maintain a constant ratio between dissolved oxygen (DO) and total ammonia nitrogen (TAN) concentrations. The results revealed that a stable nitritation in a biofilm reactor could be achieved via ratio control, which compensated the negative influence of low temperatures by stronger oxygen-limiting conditions. Even with a temperature as low as 6°C, stable nitritation could be achieved when the controlling ratio did not exceed 0.17. Oxygen-limiting conditions in the biofilm reactor were determined by the DO/TAN concentrations ratio, instead of the mere DO concentration. This ratio control strategy allowed the achievement of stable nitritation without complete wash-out of NOB from the reactor. Through the ratio control strategy full nitritation of sidestream wastewater was allowed; however, for mainstream wastewater, only partial nitritation was recommended.