污泥蚯蚓堆肥过程中胞外聚合物的结构变化

为揭示污泥胞外聚合物(EPS)特征与蚯蚓堆肥产物腐熟的关系,以无蚯蚓为对照组,探究蚯蚓堆肥对污泥EPS结构变化的影响。结果表明,蚯蚓堆肥显著加快了蚯蚓堆肥产物有机质的矿化速率,其电导率和硝酸盐氮含量比对照组产物分别显著提升了0.64和0.22倍(P<0.05)。蚯蚓堆肥产物EPS层中的蛋白质和多糖的总含量比对照组产物分别降低了32.77%和31.54%。三维荧光结果表明,蚯蚓堆肥过程中蛋白质的荧光强度下降速率比对照组更高,其腐殖质在堆肥后期一直处于较高水平。污泥蚯蚓堆肥产物的紧密结合层(TB-EPS)和松散结合层(LB-EPS)中的色氨酸含量比对照组分别减少7.69%和13.62%,而LB-EPS和粘液层(SEPS)中腐殖酸含量比对照组分别增加了25.1%和7.82%。蚯蚓堆肥期间的硝酸盐氮含量和电导率均同SEPS、LB-EPS结构中的DOC、蛋白质和多糖含量呈显著正相关(P<0.05),其总DOC含量与EPS各层中的DOC及多糖含量呈显著相关性(P<0.05)。实验过程中对照组仅有机质和DOC含量同EPS各层多糖含量呈显著相关(P<0.05)。研究表明,蚯蚓堆肥能够破坏污泥EPS结构以促进有机物的分解,加快污泥的腐殖化和稳定化进程,且污泥EPS结构的变化可作为反映污泥蚯蚓堆肥产物腐熟程度的关键指标。

Changes in the structure of extracellular polymeric substances during sludge vermicomposting

Extracellular polymer substance (EPS) is an important factor affecting the stabilization of excess sludge. To reveal the relationship between EPS characteristics of sludge and its decomposition of vermicomposting, this study investigated the effect of vermicomposting on structural changes of sludge EPS, by comparing with the control treatment without earthworms. The results showed that the electric conductivity and nitrate nitrogen content of vermicompost significantly increased by 0.64 and 0.22 fold, respectively, compared with control treatment (P<0.05), suggesting that vermicomposting can significantly accelerate the mineralization rate of organic matter in sludge. In addition, total protein, and polysaccharide contents of EPS in each layer of vermicomposting decreased by 32.77% and 31.54% compared with control treatment, respectively. Fluorescence intensity of protein reduced more rapid in vermicompost than control, while humus of vermicompost remained at a higher level in later stages. Compared to control, the tryptophan contents in tightly-bound EPS (TB-EPS) and loosely-bound EPS (LB-EPS) in vermicompost decreased by 7.69% and 13.62%, respectively, while the humic acid content in LB-EPS and soluble EPS (SEPS) increased by 25.1% and 7.82%, respectively. The nitrate nitrogen content and electric conductivity during vermicomposting were significantly and positively correlated with DOC, protein, and polysaccharide contents in the structure of SEPS and LB-EPS (P<0.05), and their total DOC contents was significantly correlated with DOC and polysaccharide contents in each layer of EPS (P<0.05). However, only organic matter and DOC contents were significantly correlated with the polysaccharide contents of EPS layers in control during the experiment (P<0.05). The study indicated that earthworms could destroy the EPS structure of sludge to promote the decomposition of organic matter, thus accelerating the humification and stabilization process of vermicomposting, and the change of EPS structure of sludge could be a key indicator to assess the degree of sludge vermicomposting.