Data for: Particle size as a driver of dewatering performance and its relationship to stabilization in fecal sludge

Poor and unpredictable dewatering performance of fecal sludge is a major barrier to sanitation provision in urban areas not served by sewers. Fecal sludge comprises everything that accumulates in onsite containments, and its characteristics are distinct from wastewater sludges and from feces. There is little fundamental understanding of what causes poor dewatering in fecal sludge. For the first time, we demonstrate that particle size distribution is a driver of dewatering performance in fecal sludge, and is associated with level of stabilization. Higher concentrations of small particles (<10 µm) and smaller median aggregate size (D50) corresponded to poor dewatering performance (measured by capillary suction time (CST) and supernatant turbidity) in field samples from Kenya and Uganda and in controlled laboratory anaerobic storage experiments. More stabilized fecal sludge (higher C/N, lower VSS/TSS) had better dewatering performance, corresponding to lower concentrations of small particles. Samples with the largest aggregates (D50 > 90 µm) had higher abundance of Gammaproteobacteria Pseudomonas, and samples with the smallest aggregates (D50 ≤ 50 µm) were characterized by higher abundance of Bacteroidetes Vadin HA17 and Rikenellaceae. Contrary to common perceptions, stabilization, particle size distribution, and dewatering performance were not dependent on time intervals between emptying of onsite containments or on time in controlled anaerobic storage experiments. Our results suggest that the stabilization process in onsite containments, and hence the dewaterability of sludge arriving at treatment facilities, is not dependent on time in containment but is more likely associated with specific microbial populations and the in-situ environmental conditions which promote or discourage their growth.

粪污泥脱水性能不佳且难以预测，是无下水道服务的城市地区卫生设施供给的主要阻碍因素。粪污泥指的是现场储污设施中积存的所有物质，其特性与废水污泥及粪便均存在显著差异。目前学界对粪污泥脱水性能不佳的成因尚缺乏基础认知。本研究首次证明，粒径分布是影响粪污泥脱水性能的关键因素，且与污泥稳定化程度相关。在肯尼亚、乌干达的现场样本以及受控实验室厌氧储存实验中，粒径小于10 µm的细颗粒浓度越高、团聚体中值粒径（D50）越小，粪污泥的脱水性能就越差——该性能通过毛细管吸水时间（capillary suction time, CST）与上清液浊度进行表征。稳定化程度更高的粪污泥（碳氮比C/N更高、挥发性悬浮固体与总悬浮固体比值VSS/TSS更低）具备更优的脱水性能，同时其细颗粒浓度也更低。团聚体粒径最大的样本（D50＞90 µm）中，γ-变形菌纲（Gammaproteobacteria）假单胞菌属（Pseudomonas）的丰度更高；而团聚体粒径最小的样本（D50≤50 µm）则以拟杆菌门（Bacteroidetes）Vadin HA17菌属与理研菌科（Rikenellaceae）的高丰度为特征。与普遍认知相悖的是，污泥稳定化程度、粒径分布与脱水性能均不依赖于现场储污设施的清空间隔时长，也不受受控厌氧储存实验中储存时间的影响。本研究结果表明，现场储污设施内的污泥稳定化过程——进而影响输送至处理设施的污泥脱水性能——并不取决于污泥在储污设施内的停留时长，而更可能与特定微生物类群及其促生/抑生的原位环境条件密切相关。