Research On Nitrogen Removal Performance And Microbial Characteristics Of Partial Nitrification And Anammox For Low Strength Wastewater Treatment

Compared with the conventional biological nitrogen removal processes, partial nitrification(PN) coupled with anaerobic ammonium oxidizing(ANAMMOX) process was thought to be a novel biological nitrogen removal biotechnology. It could save aeration energy consumption, as well as need no organic carbon consumption and no secondary pollution, lower biomass production, increase volume loading. However, most of PN-ANAMMOX process focused on treating warm and concentrated waste streams, such as digested sludge supernatant(DSS) and landfill leachate. Less PN-ANAMMOX process has been built for wastewater treatment, which is of low ammonia concentration at ambient temperature. In order to advance theories on PN-ANAMMOX process, to accelerate the full-scale application of PN-ANAMMOX process in municipal wastewater treatment plant(WWTP), based on two lab-scale PN reactors and a lab-scale ANAMMOX reactor, this study mainly investigated these contents as follows: start-up strategy and influence factors of PN process; nitrogen removal performance and corresponding microbial c haracteristics of ANAMMOX process at different operating temperatures; influence factors of ANAMMOX process at ambient temperature; feasibility for treating domestic sewage using PN-ANAMMOX process.A variety of reactor forms can be used to start up partial nitrification, this study carried out partial nitrifying experiments based on a continuous stirred tank reactor(CSTR) and a moving bed biofilm reactor(MBBR), which were used for comparing the effects of partial nitrification treating low strength nitrogen wastewater at ambient temperature. Results suggested that CSTR could obtain more stable partial nitrification than MBBR. This was because that sludge in CSTR was completely mixed, activity of nitrite-oxidizing bacteria(NOB) in the reactor could be roundly inhibited by high free ammonia(FA) and low dissolved oxygen(DO). Moreover, some NOB which may be adapt to high FA could be washed off by discharging sludge of CSTR. However, those NOB which was adapt to high FA could attach other microorganisms to form a biofilm on the surface of the carrier in MBBR, NOB were difficult to be washed off separately. Na OH was added into CSTR replacing part of Na HCO3, which could reduce about 60% of the cost of alkalinity and obtain good partial nitrification effect simultaneously. Compared with the single addition of Na HCO3, Na OH could inhibit the activity of NOB intensively. Even high DO or high p H value presented for a short time in CSTR, the efficiency of partial nitrification was able to recover quickly.In order to apply anammox process in municipal WWTP, this study investigated start-up strategy of anammox process at 33±1oC and nitrogen removal performance of anammox process at 20±2oC and 15±1oC and 10±1oC treating low strength nitrogen wastewater. The anammox reactor was successfully started up in 100 days at 33±1oC, and the total nitrogen(TN) removal efficiency was 88.3±6.5% as the influent ammonia and nitrite concentrations were both 73 mg/L. At 20±2oC, when hydraulic retention time(HRT) was 1.5 h, the influent ammonia and nitrite concentrations were 29 mg/L and 41 mg/L, respectively, a nitrogen removal rate(NRR) of the reactor of 1.0 g/(L·d) was obtained, the effluent(NH4++NO2-) concentration was 0.08±0.08 mg/L and the effluent TN concentration was 5.3-12.1 mg/L. As the temperature was decreased to 15±1oC and 10±1oC, the reactor still showed a high nitrogen removal efficiencies, which were 82.5% and 73.0%, respectively.The study also investigated influence factors of ANAMMOX reactor at 20±2oC. Results showed that, when influent alkalinity value was below 350 mg/L, change of alkalinity value had a large influence on the activity of anammox bacteria. But keeping the ratio of influent alkalinity to ammonia(A/a) above 1.2, a nitrogen removal efficiency of the reactor of 80% could be obtained. Because the sludge in the reactor had been adapted to influent DO concentration of 0.6-1.5 mg/L for a long time, the reactor could keep a high nitrogen removal efficiency as influent DO concentration below 3.0 mg/L.In this study, microbial characteristics of ANAMMOX reactor had been researched at different operating temperatures. Although the influent substrate contained no organic carbon, there was still a large number of different species of bacteria identified in the reactor. Anammox bacteria(Candidatus Brocadia and Candidatus Jettenia), denitrifying bacteria, nitrifying bacteria could coexist in the reactor, while the genera of AOB and NOB were single. Some other kinds of bacteria such as Dokdonella and Gallionella existed in ANAMMOX reactor, which promoted the stability of biological membrane. The activity of anammox bacteria was decreased at 15±1oC, Denitratisoma played an important role in the nitrogen removal process, led the reactor a high nitrogen removal efficiency even at 15±1oC or 10±1oC.Based on the above findings, domestic wastewater was treated using a High rate bio-filter, whose effluent containing low COD and relatively high ammonia. Then, the effluent flowed into PN and ANAMMOX reactor successively. Results showed that COD in the effluent of High rate bio-filter had little effect on the efficiency of partial nitrification of PN reactor, DO in the effluent of PN reactor had no effect on the nitrogen removal efficiency of ANAMMOX reactor. PN reactor reactor continued to provide a suitable matrix for subsequent ANAMMOX reactor. C, N from domestic sewage could be removed in this system economically and efficiently.