Thursday, 6 October 2016

Modelling water and energy recovery

The last in the current series of three papers from our Energy team.   This one describes the potential water and energy recovery from the Nano Membrane Toilet and how the recovery of these two resources can be balanced.   An exciting conclusion is that the toilet should have a net power output equivalent to a USB port peak power, enough for charging a mobile phone.

Hanak, D., Kolios, A., Fidalgo, B., McAdam, E., Parker, A., Williams, L., Tyrrel, S., Cartmell, E., (2016) Conceptual energy and water recovery system for self-sustainednano-membrane toilet, Energy Conversion and Management 126, 352-361

With about 2.4 billion people worldwide without access to improved sanitation facilities, there is a strong incentive for development of novel sanitation systems to improve the quality of life and reduce mortality. The Nano Membrane Toilet is expected to provide a unique household-scale system that would produce electricity and recover water from human excrement and urine. This study was undertaken to evaluate the performance of the conceptual energy and water recovery system for the Nano Membrane Toilet designed for a household of ten people and to assess its self-sustainability. A process model of the entire system, including the thermochemical conversion island, a Stirling engine and a water recovery system was developed in Aspen Plus®. The energy and water recovery system for the Nano Membrane Toilet was characterised with the specific net power output of 23.1 Wh/kgsettledsolids and water recovery rate of 13.4 dm3/day in the nominal operating mode. Additionally, if no supernatant was processed, the specific net power output was increased to 69.2 Wh/kgsettledsolids. Such household-scale system would deliver the net power output (1.9–5.8 W). This was found to be enough to charge mobile phones or power clock radios, or provide light for the household using low-voltage LED bulbs.

Wednesday, 21 September 2016

Latest prototypes on display at New Scientist Live

We have developed a new prototype based on our latest system configuration.  This will be on display to the public at New Scientist Live in the Excel Centre from 22-25 Sept.   We are on stand 841!

Update, here are some photos from the event:

Thursday, 18 August 2016

Experiments to combust human faeces

The next paper in the series from our energy team describes a series of experiments to combust human faeces, which is informing the design of the gasifer.   The paper is free to download from the journal "Fuel".

Onabanjo, 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. (2016) Cartmell, E., An experimental investigation of the combustion performance of human faeces, Fuel 184, 780–791

Poor sanitation is one of the major hindrances to the global sustainable development goals. The Reinvent the Toilet Challenge of the Bill and Melinda Gates Foundation is set to develop affordable, next-generation sanitary systems that can ensure safe treatment and wide accessibility without compromise on sustainable use of natural resources and the environment. Energy recovery from human excreta is likely to be a cornerstone of future sustainable sanitary systems. Faeces combustion was investigated using a bench-scale downdraft combustor test rig, alongside with wood biomass and simulant faeces. Parameters such as air flow rate, fuel pellet size, bed height, and fuel ignition mode were varied to establish the combustion operating range of the test rig and the optimum conditions for converting the faecal biomass to energy. The experimental results show that the dry human faeces had a higher energy content (∼25 MJ/kg) than wood biomass. At equivalence ratio between 0.86 and 1.12, the combustion temperature and fuel burn rate ranged from 431 to 558 °C and 1.53 to 2.30 g/min respectively. Preliminary results for the simulant faeces show that a minimum combustion bed temperature of 600 ± 10 °C can handle faeces up to 60 wt.% moisture at optimum air-to-fuel ratio. Further investigation is required to establish the appropriate trade-off limits for drying and energy recovery, considering different stool types, moisture content and drying characteristics. This is important for the design and further development of a self-sustained energy conversion and recovery systems for the NMT and similar sanitary solutions.

Thursday, 9 June 2016

Modelling the energy recovery from human waste via gasification

The Nano Membrane Toilet will use gasification to convert the faeces to ash (rendering all pathogens harmless), but also providing an energy source for the toilet processes.   The Cranfield team have been working to understand the science behind the gasification of faeces to inform the final design of the gasifier.   The first piece of this work is now published in the journal "Energy Conversion and Management" - open access of course!

T. Onabanjo, K. Patchigolla, S.T. Wagland, B. Fidalgo, A. Kolios, E. McAdam, A. Parker, L.Williams, S. Tyrrel, E. Cartmell, Energy recovery from human faeces via gasification: A thermodynamic equilibrium modelling approach, Energy Conversion and Management 118:364-376
Non-sewered sanitary systems (NSS) are emerging as one of the solutions to poor sanitation because of the limitations of the conventional flush toilet. These new sanitary systems are expected to safely treat faecal waste and operate without external connections to a sewer, water supply or energy source. The Nano Membrane Toilet (NMT) is a unique domestic-scale sanitary solution currently being developed to treat human waste on-site. This toilet will employ a small-scale gasifier to convert human faeces into products of high energy value. This study investigated the suitability of human faeces as a feedstock for gasification. It quantified the recoverable exergy potential from human faeces and explored the optimal routes for thermal conversion, using a thermodynamic equilibrium model. Fresh human faeces were found to have approximately 70–82 wt.% moisture and 3–6 wt.% ash. Product gas resulting from a typical dry human faeces (0 wt.% moisture) had LHV and exergy values of 17.2 MJ/kg and 24 MJ/kg respectively at optimum equivalence ratio of 0.31, values that are comparable to wood biomass. For suitable conversion of moist faecal samples, near combustion operating conditions are required, if an external energy source is not supplied. This is however at 5% loss in the exergy value of the gas, provided both thermal heat and energy of the gas are recovered. This study shows that the maximum recoverable exergy potential from an average adult moist human faeces can be up to 15 MJ/kg, when the gasifier is operated at optimum equivalence ratio of 0.57, excluding heat losses, distribution or other losses that result from operational activities.

Friday, 6 May 2016

Latest system configuration

After a period of intense technical development of the Nano Membrane Toilet we're pleased to be able to share our latest diagram of the system configuration:
We're also starting to publish some of the science behind the Nano Membrane Toilet in open access academic journals, watch this space!

Wednesday, 18 March 2015

Prizes and publicity!

We are pleased to announce the Nano Membrane Toilet has been selected as winner of the award for Excellence in the Field of Environmental Technology Research, by a panel chaired by HSH Prince Albert II of Monaco.   The award was presented to PhD student Jake Larsson, at CleanEquity Monaco 2015, the forum for emerging cleantech and resource efficiency companies, hosted by London based specialist investment bank Innovator Capital. 

Jake (centre) receives the award form the Prince (right)

 A photo of all the award winners was displayed in Times Square in New York

The award has lead to some increased media coverage of the Nano Membrane Toilet.   An interview that Jake gave explaining the processes within the toilet and its possible applications has been carried by newspapers all over the world, from Australia to Ireland and Malta, as well as on the BBC website (see full list here).   Alison gave a live interview on BBC Three Counties Radio (from 1.48.44) and it was mentioned on the ABC702 Breakfast Show in Australia.

However, another highlight has to be being satirized in the Sydney Morning Herald with this cartoon showing how the Nano Membrane Toilet will be able to charge mobile phones:

Tuesday, 17 March 2015

Perspectives from potential users

Earlier this year four members of the Nano Membrane Toilet team traveled to Ghana to hear from our potential users and get their input into the design of the toilet.

We were really pleased to work with Clean Team who made sure we got all the surveys done (103!) and pre-tested them for us.   We were keen to talk to their customers as they have already made the decision to invest in an aspirational sanitation product, so we thought they would have some useful ideas for us.   Clean Team work across six districts of the city of Kumasi which allowed us to observe the many differences in style of houses, income levels, religion and water supplies.  
Jake interviews one of the Clean Team customers

People seemed very open to most of the concepts around the toilet: the water would be useful for cleaning, as even where people had taps in the house metering was becoming commonplace so there’s a money saving from the reuse.   Very few people liked the idea of drinking it, although one woman did say that since we had come from a University in England we must be doing a good job and therefore if I said the water was safe to drink she would be happy with it!

The potential for charging mobile phones from a toilet lit up almost everyone’s eyes, partially just the concept but also because, despite everyone we spoke to having electricity in the house, the dreaded ‘doomsa-doomsa’ - power cuts - were so common that getting caught short of phone battery during the blackouts was a big headache for many people! 

Ross takes a respondent through the a hidden needs assessment

Many people were excited about the idea and would be willing to accept a new technology, and work to keep it clean, safe, and well maintained. Many asked how quickly they could see it or buy it but they'll have to wait until next year when we start our field trials!
Ross contemplates the consequences of poor sanitation

We'll publish our full report shortly, and will also present the details of the perspectives on water reuse at the forthcoming WEDC Conference in Loughborough (UK) in July 2015.