Permeable membrane dewatering of faecal sludge from pit latrines at a transfer station in Nairobi, Kenya.

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.

Unpacking intersecting complexities for WASH in challenging contexts: A review.

Ensuring access to water, sanitation, and hygiene (WASH) for all requires a thorough understanding of the many contextual complexities that influence access to these services. Complexities spanning environmental, economic, political, and social dimensions, amongst others, can intersect and compound to hinder sustainable access to WASH for certain demographics or entire communities. This is of particular importance for challenging contexts where conventional WASH approaches are ineffective. Targeted approaches are required for these contexts to ensure that communities are not left behind in pursuit of the Sustainable Development Goals. Review of WASH literature identified seven broad types of challenging contexts: challenging environments, transient or environmentally-dependant communities, climate vulnerable communities, remote communities, poor urban communities, refugee camps, and emergency contexts. This review explores the intersecting complexities affecting access to WASH in these challenging contexts and how failure to understand the interconnectedness of these complexities has resulted in WASH solutions that are unaffordable, not inclusive, or unsustainable. To our knowledge, this review is the first of its kind. We emphasise the need to unpack intersecting complexities affecting WASH in challenging contexts, and we believe that incorporating such an approach early in WASH programs can ensure that intersecting complexities are accounted for in the design of WASH solutions. Ultimately, this novel lens may provide critical guidance for WASH programs in challenging contexts, ensuring that WASH solutions are contextually appropriate.