Ju Lu-Kwang, Huang Lin, Trivedi Hiren
Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, Ohio 44325-3906, USA.
Water Environ Res. 2007 Aug;79(8):912-20. doi: 10.2175/106143007x175942.
Simultaneous nitrification and denitrification (SND or SNdN) may occur at low dissolved oxygen concentrations. In this study, bench-scale (approximately 6 L) bioreactors treating a continuous feed of synthetic wastewater were used to evaluate the effects of solids retention time and low dissolved oxygen concentration, under cyclic aeration, on the removal of organics, nitrogen, and phosphorus. The cyclic aeration was carried out with repeated cycles of 1 hour at a higher dissolved oxygen concentration (HDO) and 30 minutes at a lower (or zero) dissolved oxygen concentration (LDO). Compared with aeration at constant dissolved oxygen concentrations, the cyclic aeration, when operated with proper combinations of HDO and LDO, produced better-settling sludge and more complete nitrogen and phosphorus removal. For nitrogen removal, the advantage resulted from the more readily available nitrate and nitrite (generated by nitrification during the HDO period) for denitrification (during the LDO period). For phosphorus removal, the advantage of cyclic aeration came from the development of a higher population of polyphosphate-accumulating organisms, as indicated by the higher phosphorus contents in the sludge solids of the cyclically aerated systems. Nitrite shunt was also observed to occur in the LDO systems. Higher ratios of nitrite to nitrate were found in the systems of lower HDO (and, to less dependency, higher LDO), suggesting that the nitrite shunt took place mainly because of the disrupted nitrification at lower HDO. The study results indicated that the HDO used should be kept reasonably high (approximately 0.8 mg/L) or the HDO period prolonged, to promote adequate nitrification, and the LDO kept low (< or =0.2 mg/L), to achieve more complete denitrification and higher phosphorus removal. The above findings in the laboratory systems find strong support from the results obtained in full-scale plant implementation. Two plant case studies using the cyclic low-dissolved-oxygen aeration for creating and maintaining SND are also presented.
同步硝化反硝化（SND 或 SNdN）可能在低溶解氧浓度下发生。在本研究中，使用处理合成废水连续进料的实验室规模（约6升）生物反应器，评估在循环曝气条件下，固体停留时间和低溶解氧浓度对有机物、氮和磷去除的影响。循环曝气以在较高溶解氧浓度（HDO）下1小时和在较低（或零）溶解氧浓度（LDO）下30分钟的重复周期进行。与在恒定溶解氧浓度下曝气相比，当以适当的HDO和LDO组合运行时，循环曝气产生了沉降性更好的污泥以及更完全的氮和磷去除效果。对于氮去除，优势源于更易于获得的硝酸盐和亚硝酸盐（在HDO期间由硝化作用产生）用于反硝化（在LDO期间）。对于磷去除，循环曝气的优势来自于聚磷菌数量的增加，循环曝气系统的污泥固体中较高的磷含量表明了这一点。在LDO系统中也观察到了亚硝酸盐旁路现象。在较低HDO（以及在较小程度上，较高LDO）的系统中发现亚硝酸盐与硝酸盐的比例更高，这表明亚硝酸盐旁路主要是由于在较低HDO下硝化作用受到干扰而发生的。研究结果表明，应将使用的HDO保持在合理的高水平（约0.8毫克/升）或延长HDO时间，以促进充分的硝化作用，并将LDO保持在低水平（≤0.2毫克/升），以实现更完全的反硝化和更高的磷去除。实验室系统中的上述发现得到了全尺寸工厂实施结果的有力支持。还介绍了两个使用循环低溶解氧曝气来实现和维持SND的工厂案例研究。
