Start-up And Performance Of Nitrogen Removal Of CANON Reactor

Lack of organic carbon sources is always considered to be a key problem for it will influence the nitrogen removal efficiency and cost when conventional biological nitrogen removal process was used to treat ammonium-rich wastewater. While CANON (Completely Autotrophic Nitrogen removal Over Nitrite) process, hardly needs organic carbon in nitrogen removal. In addition, it also has a lot of advantages, such as it saves aeration gas, reduces sludge production and reduces greenhouse gas emissions, therefore it was considered to be a sustainable process for nitrogen removal. However, a lot of difficulties still exist in CANON process, such as the long time start-up stage and the unstable short-cut nitrification. In order to solve these problems above, four sets of Reactors were used to study the start-up and performance of CANON Reactor. All of four reactors used synthetic ammonia-rich wastewater without organic carbon as influent (NH4+-N was about 400mg?L-1). Among them, ReactorⅠwas started by inoculating common activated sludge, While ReactorⅡ, ReactorsⅢandⅣwere started by inoculating sludge from ReactorⅠwhen it was started successfully and performed stable.During the start-up stage of ReactorⅠ,which used a kind of sponge as carrier, temperature was controlled at 35℃±1℃, pH was controlled at 7.39～8.01, ReactorⅠexperienced partial nitration stage and Anammox stage on the condition of keeping aeration, the CANON process was finally started successfully at the 210th day, the total nitrogen removal load was up to 1.22kg/(m3?d), and corresponding total nitrogen removal efficiency was 80%. After the start-up, ReactorⅠcan maintained long-term stability, and the maximum total nitrogen removal load was 2.32 kg/(m3?d), corresponding nitrogen removal efficiency was 80%. During the start-up of ReactorⅠ, it was founded that the symbol for the successful start-up of CANON process and stable short-cut nitrification in CANON process was that there is an apparent nitrogen loss, values ofΔNO3--N/ΔTN keep relatively stable, and maintained at about 0.127.During the start-up stage of ReactorⅡ, which used modified polyethylene as carrier, temperature was controlled at room temperature, under anaerobic conditions first, though ReactorⅡexperienced 300 days to start Anammox stage, effect of nitrogen removal was still not significant, and total nitrogen removal load was only 0.12 kg/(m3?d). When the temperature was increased to 30℃for about 30 days, effect of nitrogen removal was improved to 0.23 kg/(m3?d). When anaerobic condition was changed to aerobic condition for about 30 days, the total nitrogen removal load was up to 1.01kg/(m3?d), and corresponding removal efficiency was up to 77.61%, which mean the completion of ReactorⅡ's start-up.During the start-up stage of ReactorⅢ, which use anther kind of sponge as carrier, the temperature was controlled at 20~30℃. The CANON process was directly started under aerobic conditions. About 50 days later, the start-up of ReactorⅢwas completed. The total nitrogen removal load was up to 1.56 kg/(m3?d), and corresponding removal rate was 73.67%. It was also found that the presence some dissolved oxygen not only does not inhibit Anammox bacteria, but also will speed up the start-up of CANON process.During the start-up stage of ReactorⅣ, which used a kind of volcanic rock as carrier, temperature was controlled at 20~30℃. Under anaerobic conditions, the Anammox stage was first started at the 137th days, and total nitrogen removal load was up to 0.87kg/(m3?d). When the anaerobic condition was changed to aerobic condition, the start-up of CANON process can be completed in 20 days. The total nitrogen removal load was up to 1.53kg/(m3?d), and corresponding nitrogen removal efficiency was 67.03%. With the continued operation of the ReactorⅣ, the maximum TN removal load can be up to 2.0 kg/(m3?d), and corresponding nitrogen removal efficiency was about 70% at 20℃. However, when the influent ammonium load was reduced, the maximum total nitrogen removal efficiency can be up to 85.50%, and corresponding total nitrogen removal load was 1.17kg/(m3?d). Effect of temperature impact on CANON process was studied by using a sequencing batch biofilm Reactor (SBBR) with sponge as carrier. Under stable operation at 30℃~35℃, the total nitrogen removal efficiency of SBBR can be up to 88.3%, and corresponding total nitrogen removal load was 0.52kg/(m3·d). Both the breakpoint of pH curve and DO curve can be used to indicate the termination of CANON reaction. When the temperature was at 26℃～35℃, the SBBR has a good nitrogen removal effect. However,when the temperature was below 20℃, the nitrogen removal effect was not so good, and nitrite accumulated, which means Anammox bacteria was more sensitive compared to AOB under low temperature impact. However, by the long-term operation of ReactorⅢbelow 30℃, it was found that Anammox bacteria can gradually adapted to lower temperature. By competition of Anammox bacteria and NOB on nitrite, coupled with inhibition on NOB by free ammonia, the temperature range of Applica ting short-cut nitrification can be extended to 20℃~35℃.The effect of aeration rate variations was also studied. A concept of limiting aeration rate was put forward. When aeration rate was less than limiting aeration rate, the total nitrogen removal efficiency increased with aeration rate. When aeration rate was more than limiting aeration rate, the nitrogen effect was no longer increased or even got worse. If sponge was used as carrier, the effect of total nitrogen removal can keep stable,while modified polyethylene was used as carrier, the effect of total nitrogen removal will deteriorate.Effect of different water quality on CANON process was also studied. It was found that the increasing concentration of both ammonium and nitrite was favor to total nitrogen removal until the concentration of ammonium and nitrite reach 50mg?L-1. On the condition of ammonium concentration was about 400 mg?L-1, when COD concentration was less than 100mg?L-1, COD hardly had effect on CANON process. But if COD concentration was more than 100mg?L-1 for a long time, it will caused the deterioration of CANON process.The stability of CANON process was studied during long term operation. It was found that reactorⅠcan keep stable for more than a year. ReactorⅡhas a poor stability, and the aeration will cause the loss of sludge easily. ReactorⅢand reactorⅣcan keep stable at 20℃above. Compared four sets of CANON Reactors, two kinds of sponge carrier and volcanic rock were considered to be the suitable carriers for CANON process. However, modified polyethylene carrier was not considered to be suitable.Finally, the characteristic of Anammox bacteria was summarized as follows: the ratio of consumed ammonium, nitrite, and produced nitrate was 1: 1.36: 0.22. Anammox bacteria have the highest activity at 30℃. Nitrite inhibit Anammox bacteria at the concentration range of 200~280mg?L-1. At least 90 mg?L-1 of phosphate concentration will not inhibit Anammox bacteria. High concentration of dissolved oxygen can inhibit the activity of Anammox bacteria, but its activity can be recovered as long as the dissolved oxygen concentration was reduced.