Research Of SONIR(Self-driven Oscillation Nitrogen Removal)Process

Ammonia nitrogen pollution is one of the major factors that cause the eutrophication of water bodies. For this reason, it has become a hot issue in the field of environmental engineering. A series of efficient bio-technologies have been developed for the nitrogen removal from ammonia-containing wastewaters, among which, the PN-ANAMMOX processes possess the advantages of shorter flowsheet, smaller land requirement and lower cost. It has an attractive application prospect. However, the partial nitrification (PN) process and anaerobic ammonium oxidation (ANAMMOX) process, the two units of PN-ANAMMOX process, have different functional microorganisms and operating conditions. And it also has some problems such as substrate inhibition, substrate competition and alkalinity consumption. So it is necessary to develop a new integrated reactor and optimize process parameters to solve the problems above.SONIR (Self-driven Oscillation Nitrogen Removal) reactor is based on half nitritation and ANAMMOX. It successfully compartmentalizes the aerobic and anaerobic zone so that the functional bacteria can location in their suitable habtats. By independently releasing offgas from aerobic area, the SONIR reactor gets out of the embarrassment of coincident movement of air flow and liquid flow that exists in the traditional air-lift bioreactor. The SONIR reactor holds the advantage of completely mixed flow and plug flow in the vertical direction. So the habitats are optimized since the nitrite can be consumed once produced from nitritation. As a result, alkalinity consumption is significantly cut down, the acidification and the toxicity of nitrite can satisfactorily be avoided and the NH4+-N/NO2--N ratio can easily be regulated.In this paper, the SONIR process, a new PN-ANAMMOX process, has been systematically investigated. The major results are as follows:1) The half nitritation unit and ANAMMOX unit both had high efficiency and stability, so it was feasible for the two units to make up the SONIR process. The maximal volumetric ANL (Ammonia Nitrogen Load), ARR (Ammonia Removal Rate) and NiAR (Nitrite Accumulation Rate) of the half nitritation unit were 7.0 kg N·m-3·d-1,3.79 kg N·m-3·d-1 and 3.22 kg N·m-3·d-1, respectively, with average nitrite accumulation efficiency of (91.83±2.98)%. Its volumetric capacity was up to the top level reported in literature (NL=5.9 kg N·m-3·d-1,ARR=3.1 kg N·m-3·d-1). The maximal volumetric NL (Nitrogen Load) and NRR (Nitrogen Removal Rate) of the ANAMMOX unit were 11.00 kg N·m-2·d-1 and 8.68 kg N·m-3·d-1, respectively. Its volumetric capacity was up to the top level reported in literature (NL=9.5 kg N·m-3·d-1). The half nitritation unit and ANAMMOX unit were able to resist fluctuation of volumetric load in the range of 2.71 kg N·m-3·d-1 to 7.00 kg N·m-3·d-1 and 3.99 kg N·m-3·d-1 to 11.00 kg N·m-3·d-1, respectively. It was found that the substrate ratio (NH4+-N:NO2--N ratio) significantly affect the performance of ANAMMOX unit, but it did not affect the conversion of limited substrate. The greater the substrate ratio deviated from the theoretical value (NH4+-N:NO2--N=1:1.32), the greater the effect on the volumetric capacity was. At NH4+-N/NO2--N ratio of 1:3, the ANAMMOX process got the minimum NRR (3.59 kg N·m-3·d-1) due to the biological toxicity of nitrite. Its NRR decreased by 58.64% compared to the maximal NRR. So it was better to make nitrite be the limited substrate and NH4+-N/NO2--N ratio approximate 1 in order to reduce the effect of nitrite toxicity on the performance of SONIR process.2) The SONIR process was of high-efficiency. Its ANL and NRR reached 7.86 kg N·m-3·d-1 and 2.91 kg N·m-3·d-1, respectively. When influent NH4+-N concentration was 563.73±7.81 mg·L-1, HRT (Hydraulic Retention Time) was 4.0h, gas-water ratio was 120, the oxygen supplying rate was 216.0 kg O2·m-3·d-1 and the volumetric load was 3.38±0.04 kg N·m-3·d-1, the maximal NRR and the maximal NRE(Nitrogen Removal Efficiency) of the SONIR reactor were 2.68kg N·m-3·d-1 and 78.11%, respectively. Its volumetric capacity was up to the top level of the same type process.3) The SONIR process had a significant advantage over traditional biological nitrogen removal process on the economical efficiency. It was a completely autotrophic nitrogen removal process without additional carbon resources, and its main material consumption were oxygen and alkalinity. The oxygen utilization coefficient of SONIR process was (3.01±0.14)%, it needed a further optimization. The Alk/N ratio of SONIR process was 4.11±0.14 g CaCO3/g NH4+-N, which can save alkalinity consumption by 48.11% compared to two-stage PN-ANAMMOX process.4) The optimal operation parameters of SONIR process were as follows:the influent NH4+-N concentration was in the range of 289.00 mg·L-1 to 565.00 mg·L-1, the HRT was in the range of 4h to 6h, the volumetric load was in the range of 2.0 kg N·m-3·d-1 to 4.0 kg N·m-3·d-3, the oxygen supplying rate was in the range of 187.2 kg O2·m-3·d-1 to 216.0 kg O2·m-1 and the corresponding gas-water ratio was from 104 to 120.5) The dominant functional bacteria genera of SONIR process are Nitrosmonas, Kuenenia and Brocadia. AOB and AnAOB showed two different distribution patterns. In one distribution pattern, AOB mainly located in the exterior layer of granular sludge, and AnAOB mainly located in the inside layer of granular sludge. In the other distribution pattern, AOB and AnAOB located in the granular sludge in a mixed way.