Sheng Guo-Ping, Yu Han-Qing, Li Xiao-Yan
School of Chemistry, University of Science & Technology of China, Hefei, Anhui, 230026 China.
Biotechnol Bioeng. 2006 Apr 20;93(6):1095-102. doi: 10.1002/bit.20819.
The roles of extracellular polymer substances (EPS) in the shear stability of aerobic and anaerobic flocs were investigated. Both pH and EDTA concentration had a significant effect on the floc stability. The sludge flocs became much weaker as the solution pH increase to above 10. Addition of 1 mM EDTA or more could cause considerable cell erosion and deflocculation of the anaerobic flocs, whereas more than 3 mM EDTA was needed to show its adverse effect on the stability of aerobic flocs. A fraction of the EPS, around 10 mg/g SS for the aerobic flocs and 15 mg/g SS for the anaerobic flocs, could be extracted by fluid shear when the dispersed mass concentration approached the equilibrium. This suggests that most of the dispersed particles were glued by a small amount of readily-extractable EPS fraction. In addition to the abundance of this EPS fraction, its proteins/carbohydrates ratio, about 0.22:1 for the aerobic flocs and 2.66:1 for the anaerobic flocs, also appeared to be an important factor governing the microbial floc stability. A lower content of the readily-extractable EPS fraction and a lower ratio of proteins/carbohydrates were responsible for the greater stability of microbial flocs. The total content of the EPS, however, did not show a direct correlation with the floc stability. A hypothesis about biological flocs with two distinct structural regions was proposed. The outer part contained dispersible cells loosely entangled by the readily-extractable EPS fraction. This part was layered and would become completely dispersed at an infinite shear intensity. On the other hand, the inner part contains biomass in a stable structure tightly glued by EPS, which could not be dispersed by shear except under unfavorable conditions.
研究了胞外聚合物（EPS）在好氧和厌氧絮体剪切稳定性中的作用。pH值和EDTA浓度对絮体稳定性均有显著影响。当溶液pH值升高到10以上时，污泥絮体变得更加脆弱。添加1 mM或更多的EDTA会导致厌氧絮体出现相当程度的细胞侵蚀和絮体解体，而需要超过3 mM的EDTA才会对好氧絮体的稳定性产生不利影响。当分散质量浓度接近平衡时，一部分EPS（好氧絮体约为10 mg/g SS，厌氧絮体约为15 mg/g SS）可通过流体剪切作用被提取出来。这表明大多数分散颗粒是由少量易于提取的EPS部分黏合在一起的。除了这种EPS部分的丰度外，其蛋白质/碳水化合物比率（好氧絮体约为0.22:1，厌氧絮体约为2.66:1）似乎也是控制微生物絮体稳定性的一个重要因素。易于提取的EPS部分含量较低以及蛋白质/碳水化合物比率较低导致了微生物絮体具有更高的稳定性。然而，EPS的总含量与絮体稳定性并未呈现直接相关性。提出了一个关于具有两个不同结构区域的生物絮体的假设。外部包含由易于提取的EPS部分松散缠结的可分散细胞。这部分是分层的，在无限剪切强度下会完全分散。另一方面，内部包含由EPS紧密黏合的稳定结构中的生物质，除了在不利条件下，其不会因剪切而分散。
