HRT对ABR处理低浓度废水的效果和颗粒污泥特征的影响

采用效果检测、粒度分布与分形等方法，研究了ABR处理低浓度废水时水力停留时间(HRT)对其运行状况和颗粒污泥特征的影响.结果表明，随着HRT从24 h逐渐缩短到5 h，反应器保持了较高的有机物去除效果，运行稳定阶段的COD去除率多在90%以上，主要承担COD去除的格室由反应器的前2格逐渐过渡到中间3格室；反应器后面格室颗粒污泥的MLSS值随着HRT的缩短总体也呈增加趋势，MLVSS/MLSS值先降低后升高，前3个格室的MLVSS/MLSS值高于后2个格室的趋势越来越明显.分形维数和粒度的变化表明，HRT为24 h和18 h时，ABR中颗粒污泥呈现表面光滑、结构密实和粒径逐渐增大的特点；HRT为12 h和8 h时，形成大而中空、表面相对不规则的疏松颗粒污泥； HRT为5 h时，水力扰动破碎、筛分以及微生物修补作用的综合影响导致颗粒污泥粒径减小、表面光滑、结构密实.在同一HRT下，ABR不同格室中颗粒污泥D1和D2呈现出相反的变化趋势，显示了沿着ABR格室，颗粒污泥表面变得光滑时对应的结构比较密实的特征.

Impact of Hydraulic Retention Time (HRT) in ABR on Its Operation Performance and Granular Sludge Characteristics When Treating Low-strength Wastewater

The impact of hydraulic retention time(HRT) in an anaerobic baffled reactor (ABR) on its operation performance and granular sludge characteristics was investigated through both testing its operation and analyzing the particle size distribution(PSD) and fractal dimensions of these sludge granules when treating low-strength wastewater. As HRT was gradually reduced from 24 h to 5 h, ABR had good performance on the organics removal and could reach about 90% for the COD removal, the VFA contents in ABR effluent and their pH values showed opposite trends. Most COD in wastewater was removed in the first two compartments of ABR during the running period of HRT from 24 h to 12 h, after that, the middle three compartments in ABR performed the most removal work. The MLSS in latter compartments of ABR increased and the tendency of MLVSS/MLSS ratios in the former three compartments were higher than that in the latter two ones appeared more and more remarkable along with the decrease of HRT. At HRT 24 h and 18 h, the granules grew bigger than before start-up, whose one-dimensional fractal dimension (D1) decreased and two-dimensional fractal dimension (D2) increased, implying the smoother surface and more compact structure. As the HRT changed to 12 h and 8 h, the increasing D1 and decreasing D2 of granular sludge indicated its rougher surface and looser structure, and the bigger granules were formed with holes in their center. At HRT 5 h, smoother and more compact granules formed with smaller number median diameters of 0.72_0.82 mm than that at HRT 8 h. The looser granules were broken-up and some granules were discharged from ABR under the hydraulic disturbance and screening effect, at the same time, the growth of microorganism and their EPS (extracellular polymer substance) secretion could smooth the surface of the fragmentized granules. The fractal dimensions of granular sludge in the one-dimensional and two-dimensional topological spaces behaved inversely in each compartment of ABR at the same HRT, that is to say, the granular sludge along the ABR sequences became smoother on the surface meanwhile more compact structurally.