Impact of adding agricultural waste on fuel potential of faecal sludge : A case study of Naivasha, Kenya

Today developing countries across the globe fringes to access basic sanitation, and billions of people rely on on-site sanitation systems to meet their basic sanitation needs. The faecal sludge generated from these on-site sanitation technologies is not managed safely due to compromised infrastructure, lack of proper collection and transportation technologies, and limited treatment facilities. Consequently, it end-up in the environment, posing a hazard to the environment and human health. Thus, finding innovative solutions for adequate faecal sludge management, proposing viable business models focusing on resource recovery in alignment with United Nations Sustainable Development Goal 6. One such country is Kenya. The country is highly influenced by compromised infrastructure, illegal disposal of faecal sludge in the environment and no treatment and, thus, a broken sanitation value chain. Besides unsustainable faecal sludge management, more than 89% of Kenyan households are getting severely affected by the type of traditional cooking fuel (fuelwood and wood charcoal), which reasons millions of premature deaths. In addition, this over-exploitation has also led to deforestation, thus creating a dire need to switch to alternative cooking fuels that are affordable and sustainable. Therefore, aim of this research was to study the impact and viability of co-managing two waste streams, crop-residue (corncob) and faecal sludge as potential household cooking fuel. In this regard, the case-study area selected was Naivasha sub-county in Kenya. Thus, twentyfour raw faecal sludge samples were collected from top and middle sections of twelve randomly on-site containment systems like pit latrines, ventilated improved pit latrines and urine diverting dehydrating toilets across Naivasha. The raw samples were then extensively characterized for their volatile solids, fixed solids, calorific value in terms of higher heating value, inorganic elemental composition and organic elemental composition (C, H, N, S, O) for samples characterized under raw and mixed categories. It was discovered that faecal sludge collected, in general, possessed higher energy content of more than 17.5 MJ/kg DS compared to prior studies measured calorific value generally below 15MJ/kg DS. It was further established that the term associated with faecal sludge being highly variable is due to the activities associated with the operation of OSS and variability in its inorganic composition (like metals, inclusion of soil etc.) rather than its organic composition. Furthermore, the co-management of crop-residue is a viable option when faecal sludge possess low energy content (HHV