Nano Membrane Toilet

IntroductionThe Nano Membrane Toilet will be able to treat human waste on-site without external energy or water. It is designed for single-household use (equivalent to 10 people) and will accept urine and faeces as a mixture. It is still under development and this paper provides an update on progress.System configurationThe Nano Membrane Toilet uses a unique rotating mechanism to transport the mixture into a holding tank without using any water whilst simultaneously blocking odour and the user’s view of the waste. The solids then settle to the bottom of the tank, while the liquids float on the top. The solids are transported out of the tank by mechanical screw (Mercer at al 2016, Mercer et al 2017, a paper at this conference) into a gasifier or combustor which will convert them into ash and energy. The energy will be used to power essential toilet processes, and any residual energy used for charging mobile phones or other low voltage items. The liquids pass over a weir in the holding chamber and into the membranes bundle. The unique nanostructured membrane wall facilitates water transport in the vapour state rather than as a liquid which yields high rejection of pathogens and some odorous volatile compounds. The clean water will be collected for reuse at the household level in washing or irrigation applications. An overview of this configuration can be found in Figure 1. Developing the business model will be a key focus in the coming months of the project. One possibility is that the Nano Membrane Toilet will be rented by the households and maintenance will be undertaken with a trained operative responsible for the franchised area.Developing the membrane and gasifier modulesEnsuring the membrane works as efficiently as possible to separate clean water from pathogens and other liquid contaminants is vital. Experimental work has defined the tubeside mass transfer coefficient derived in hollow fibre membrane contactors of different characteristic length scales (equivalent diameter and fibre length) under the slow flow conditions that are expected in the toilet (Wang et al 2016). This provides vital information to the membrane module design. To power the membranes, energy needs to be recovered from the faeces combustion. Modelling showed that the maximum recoverable exergy potential from average adult moist human faeces can be up to 15 MJ/kg (Onabanjo 2016a). Experimental work has also showed that dry human faeces had a higher energy content than wood biomass which is promising for the development of the combustor. Simulant faeces can be successfully combusted even if the moisture levels are as high as 60% by weight (Onabanjo 2016b). Energy modelling suggests that the Nano Membrane Toilet will be a net exporter of energy and power, and can be optimised for either water or energy recovery. If optimised for energy recovery its output could be equivalent to a USB port (Hanak et al 2016). Further development of these modules forming the “back end” is planned over the coming period and will be necessary before full system integration can take place.Human User TestsThe flush, screw, tank and weir modules were combined into a “Front End” prototype for human testing in summer 2016. This successfully demonstrated the concept and highlighted areas for improvement. More extensive user trials of the Front End will be carried out in the UK and Africa in early 2017.ReferencesHanak, D., Kolios, A., Fidalgo, B., McAdam, E., Parker, A., Williams, L., Tyrrel, S., Cartmell, E., (2016) Conceptual energy and water recovery system for self-sustained nano-membrane toilet , Energy Conversion and Management 126, 352-361Mercer, E., Cruddas, P., Williams, L., Kolios, A., Parker, A.H., Tyrrel, S.F., Cartmell, E., Pidou, M., McAdam,E. (2016) Selection of screw characteristics and operational boundary conditions to facilitate post-flush urine and faeces separation within single household sanitation systems, Environmental Science: Water Research & Technology, in pressOnabanjo, T., Patchigolla, K., Wagland, S.T., Fidalgo, B., Kolios, A., McAdam, E., Parker, A., Williams, L., Tyrrel, A., Cartmell, E. (2016a) Energy recovery from human faeces via gasification: A thermodynamic equilibrium modelling approach, Energy Conversion and Management 118, 364-376Onabanjo, T., Kolios, A.J., Patchigolla, K., Wagland, S., Fidalgo, B. Jurado, N., Hanak, D.P., Manovic, V., Parker, A., McAdam, E., Williams, L., Tyrrel, S. (2016b) Cartmell, E., An experimental investigation of the combustion performance of human faeces, Fuel 184, 780–791Wang, C.Y., Cartmell, E., Kolios, A., McAdam, E., Parker, A.H., Tyrrel, S.F., Williams, L. (2016) Tube-side mass transfer for hollow fibre membrane contactors operated in the low Graetz range, Membrane Science, in press