ABSTRACT

Faecal sludge dewatering is often a necessary step in many treatment and reuse processes, and it can decrease costs of transporting large volumes of high water content sludge. Common dewatering methods such as settling-thickening tanks and drying beds are not feasible in space-constrained areas such as urban informal settlements, therefore innovative dewatering methods are needed. This study evaluated permeable membranes as a dewatering method for a transfer station operated by Sanergy in Nairobi, Kenya. The objective was to determine if membranes could provide a sustainable and economically-feasible dewatering method within the constraints of Nairobi’s informal settlements by evaluating multiple variables, such as flocculant dosage and initial total solids content, and their relation to faecal sludge dewatering. Experiments were conducted with several membrane types including commercial geotextiles and locally-produced plastic woven bags (gunny sacks). Increasing the flocculant dosage within an optimal range was seen to increase dewatering rates, but had minimal effect on the final dewatered solids content. Sludge with initial total solids contents below 3% was seen to require longer dewatering times to allow for drainage, while sludge above 3% required a minimal drainage period before evaporation began. A settling step proved paramount for sludge with high water content where the supernatant was then decanted prior to dewatering through permeable membranes; however, this may not be recommended in all cases depending on the treatment objectives. Reuse of geotextile membranes may lead to a reduction in dewatering performance, and single-use, locally-produced membranes are a more cost-effective, though operationally intensive, option.

摘要

粪便污泥脱水通常是许多处理和再利用过程中的必要步骤，它可以降低运输大量高含水污泥的成本。沉降浓缩池和干燥床等常见的脱水方法在城市非正规住区等空间受限的地区是不可行的，因此需要创新的脱水方法。本研究评估了渗透膜作为 Sanergy 在肯尼亚内罗毕运营的转运站的脱水方法。目的是通过评估多个变量（例如絮凝剂剂量和初始总固体含量，以及它们与粪便污泥脱水的关系）来确定膜是否可以在内罗毕非正规住区的限制内提供一种可持续且经济可行的脱水方法。对几种膜类型进行了实验，包括商业土工布和当地生产的塑料编织袋（麻袋）。在最佳范围内增加絮凝剂用量可以提高脱水速率，但对最终脱水固体含量的影响很小。初始总固体含量低于 3% 的污泥被认为需要更长的脱水时间才能排水，而高于 3% 的污泥在蒸发开始前需要最短的排水时间。对于含水量高的污泥，沉降步骤被证明是至关重要的，在通过渗透膜脱水之前，先将上清液倒出；但是，根据治疗目标，可能并非在所有情况下都建议这样做。土工膜的重复使用可能会导致脱水性能下降，并且一次性使用，