The nano membrane toilet: separation processes.

It is estimated that 61 % and 29 % of the global population lack safely managed sanitation and clean water services respectively. The water Sustainable Development Goals (SDG 6) actioned by the UN, aim to provide global access to sanitation and clean water by 2030. However, in low income countries (LICs) conventional centralised wastewater treatment plants are economically unfeasible and for affordable decentralised alternatives, only 22 % of the waste is safely managed, leading to contamination of water resources. The Reinvent the Toilet Challenge (RTTC) initiated by the Bill & Melinda Gates Foundation (BGMF) proposes to innovate off-grid, self- sustaining systems, which are able to safely manage human waste and provide opportunity for resource recovery, at ≤US$0.05 user⁻¹ d⁻¹. In response, the Nano Membrane Toilet (NMT) developed at Cranfield University propositions a household scale sanitation system which combusts human faeces and provides an off-grid opportunity for advanced treatment technologies to treat the liquid fraction, comprising faecally contaminated urine (FCU). This thesis investigated a series of potential separation processes which integrate with the combustor, for FCU treatment. It was demonstrated that solids liquid separation can be facilitated post flush with a screw auger, which allowed for effective faecal solids recovery for the combustor. Thermally driven membrane processes, which operate from heat energy, evidenced that high water quality where reuse standards could be achieved (with operational optimisation) in a single stage. In addition, they proved robust to faecal contamination and manipulated odour profiles to change negative perception. The most adaptable process, membrane distillation (MD), provided a salinity gradient consisting of a concentrated retentate and deionised permeate where salinity gradient energy was converted to electrical energy through reverse electrodialysis (RED), sufficient to power an auxiliary low voltage fluidic device (0.25 W) for 4.9 hours. Importantly, the integrated separation processes within this thesis, evidenced high quality water and energy recovery, which are the foundations of an SDG 6 solution.