Sanergy Inc., Sameer Africa, Nairobi, Kenya.
Sandec: Department Sanitation, Water and Solid Waste for Development, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
Environ Technol. 2022 Jun;43(14):2218-2229. doi: 10.1080/09593330.2020.1870573. Epub 2021 Jan 11.
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.
粪便脱水通常是许多处理和再利用过程中的必要步骤，可以降低运输高含水量污泥的成本。在空间有限的地区，如城市非正规住区，常见的脱水方法，如沉降浓缩池和干燥床是不可行的，因此需要创新的脱水方法。本研究评估了渗透膜作为肯尼亚内罗毕 Sanergy 运营的转运站的脱水方法。目的是通过评估多种变量，如絮凝剂剂量和初始总固体含量及其与粪便污泥脱水的关系，确定膜是否可以在不影响内罗毕非正规住区的情况下提供可持续且经济可行的脱水方法。进行了多项膜类型的实验，包括商业土工织物和本地生产的塑料编织袋（麻袋）。在最佳范围内增加絮凝剂剂量被认为可以提高脱水率，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%的污泥需要更长的脱水时间才能排水，而初始总固体含量高于 3%的污泥在开始蒸发之前需要最短的排水时间。沉淀步骤对于高含水量的污泥至关重要，其中在通过渗透膜进行脱水之前，先将上清液倾析；然而，这可能不是所有情况下都推荐的，具体取决于处理目标。土工织物膜的再利用可能会导致脱水性能下降，而一次性、本地生产的膜是一种更具成本效益但操作密集的选择。
