Estimating the potential for resource recovery from productive sanitation in urban areas.
To-date, sanitation has mainly been approached from a public and environmental health perspective and this implies that excreta and other organic waste streams are seen not only as a hazard to quickly get rid of but also as a very costly menace to manage. However, looking at sanitation management from a resource recovery perspective provides an avenue for solutions with multiple co-benefits. Revenues from sanitation end-use products can act as an incentive for improving sanitation infrastructure while also covering part or all of the investment and operation costs for the same. Until now, estimating the potential for resource recovery from sanitation systems and technologies has largely been done on a case by case basis according to project or geography with no standardized universal tools or methodologies being used across the world. This study is aimed at developing a generic model for the rapid estimation of the quantities of various resources that can be recovered from sanitary waste streams in urban areas.
Key waste streams from sanitation systems in low and middle income countries were identified and their major characterization parameters identified. The mathematical relationships between key waste stream characterization parameters and the potential amounts of resource products derived from treatment were determined and then used to develop the model in MS Excel. The model was then tested with waste stream flow rates and characterization data (for faecal sludge, sewage sludge and organic municipal solid waste) from the city of Kampala with two scenarios; the current collection amounts (390 m3 of faecal sludge, 66 tonnes of sewage sludge and 700 tonnes of organic solid waste) and the potential amounts with increased collection efficiency and coverage (900 m3 of faecal sludge, 282 tonnes of sewage sludge and 2199 tonnes of organic solid waste). The results were shared with Kampala city authorities to obtain feedback.
The results showed that there is significant potential in utilizing the daily amounts of the three waste streams collected in Kampala. With increased collection coverage and efficiency, they could altogether yield; up to 361,200 Nm3 of biogas per day which could meet the daily energy needs of 824,000 people that are currently met by firewood. Alternatively, the three sources could produce, 752 tonnes of solid combustion fuel per day which could meet the daily energy needs of 1,108,700 people that are currently met by firewood. As a third alternative, the three sources could produce 198 tonnes of Black Soldier Fly prepupae per day which could substitute for 134 tonnes of dry fish per day currently used as animal feed ingredient and up to 909 tonnes of compost fertilizer per day which is enough to substitute two tonnes of urea that is currently used by farmers. The model thus proved to be a simple way to provide decision support by making rapid estimations of the potential for resource recovery in urban areas, without the burden of having to do full scale feasibility studies. It is expected that this model could be a useful complement to the excreta flow diagrams (SFDs) developed within the Sustainable Sanitation Alliance (SuSanA) and hence give a holistic picture of the potential of a closed loop approach to excreta and waste management in cities.
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