Pee power urinal – microbial fuel cell technology field trials in the context of sanitation

TL;DR: In this article, the first trial was conducted on Frenchay Campus (UWE, Bristol) from February-May 2015 and demonstrated the feasibility of modular microbial fuel cells for lighting, with University staff and students as the users; the next phase of this trial is ongoing.

Abstract: This paper reports on the pee power urinal field trials, which are using microbial fuel cells for internal lighting. The first trial was conducted on Frenchay Campus (UWE, Bristol) from February–May 2015 and demonstrated the feasibility of modular MFCs for lighting, with University staff and students as the users; the next phase of this trial is ongoing. The second trial was carried out during the Glastonbury Music Festival at Worthy Farm, Pilton in June 2015, and demonstrated the capability of the MFCs to reliably generate power for internal lighting, from a large festival audience (∼1000 users per day). The power output recorded for individual MFCs is 1–2 mW, and the power output of one 36-MFC-module, was commensurate of this level of power. Similarly, the real-time electrical output of both the pee power urinals was proportional to the number of MFCs used, subject to temperature and flow rate: the campus urinal consisted of 288 MFCs, generating 75 mW (mean), 160 mW (max) with 400 mW when the lights were connected directly (no supercapacitors); the Glastonbury urinal consisted of 432 MFCs, generating 300 mW (mean), 400 mW (max) with 800 mW when the lights were connected directly (no supercapacitors). The COD removal was >95% for the campus urinal and on average 30% for the Glastonbury urinal. The variance in both power and urine treatment was due to environmental conditions such as temperature and number of users. This is the first time that urinal field trials have demonstrated the feasibility of MFCs for both electricity generation and direct urine treatment. In the context of sanitation and public health, an independent power source utilising waste is essential in terms of both developing and developed world.

Summary

Analysis

• Power performance was monitored with a multi-channel Agilent 34972A, LXI Data Acquisition Unit (Farnell, UK) and were then processed using the Microsoft Excel and GraphPad Prism software packages.
• Parameters such as pH and conductivity were measured with a Hanna 8424 pH meter (Hanna, UK) and 470 Jenway conductivity meter (Camlab, UK) respectively.
• COD was analysed using the potassium dichromate oxidation method (COD HR test vials, Camlab, UK) with an MD 200 photometer (Lovibond, UK) where 0.2 mL samples were taken before and during MFC treatment and filter-sterilised prior to analysis.
• Total Nitrogen (TN) was measured using MD 500 colorimeter (Lovibond, UK) and Vario Tube Test (0.5-25 mg/L) on diluted samples.
• The concentration of anions in the anolyte (inlet, outlet) and catholyte samples was determined by ion chromatography using a 930 Compact IC Flex (Metrohm, UK).

Results and Discussion

• Initial MFC module testing A single box assembled with 36 MFCs was initially tested under laboratory conditions.
• Inset graph is a magnification of the marked area, where the load was changed to 2.3Ω for approximately 24 hours.
• 1 activated sludge and urine mix, MFC modules were installed in the urinal and fed with neat fresh urine, also known as After inoculation with 1.
• The highest total nitrogen reduction was >50% for the anolyte and the lowest was <20%, which was the same for the synthesised catholyte (Fig. 5d ).

Glastonbury Trial

• The data presented in Figure 6a shows the stack power performance over the period of 8 days.
• The long decrease in capacitor voltage between the 27th-28th June is when the lights were intentionally left ON for 24 hours.
• Power output is significantly higher than the power levels recorded for the campus Pee Power Oxfam trial, which might be due to the increased number of modules (from 8 to 12), very high flow rate at the festival and elevated temperature due to the direct sunlight exposure.
• The very high flow rate and reduced HRT, did however affect the COD reduction capability of the system as a whole, recording a maximum of ca. 70%, a minimum of 15% and mean for the majority of the time of 25%.
• MFC electrochemical treatment is actively changing the chemistry of the treated substrate favouring pH and ion separation (see Supporting information), which leads to the recovery of slow-release fertiliser and electricity from urine (Zang et al., 2012) .

Conclusions

• The provision of safe water, adequate sanitation and hygiene, is critically important for promoting individual and community-level health in the Developing World.
• MFC based technologies prove to be a sustainable solution even in remote locations, improving sanitation and hygiene, and opening the way to elemental recycling.
• The Authors would like to thank Dr Andy Bastable from Oxfam for the useful discussions and financial support, as well as Dunster House Ltd for donating both the urinal structures and further supporting the trials -in particular Mr Carl Dolby.
• The Authors would like to thank Mrs Clare Backman for organising the field trials and Dr Benjamin Taylor for assisting in the Glastonbury trial.

Figures

Figure 4. (a) Individual MFC module voltage performance of the 8 Oxfam stack boxes and (b) 242 voltage output of the connected capacitor. The decreases in the voltage data curves are from 243 when volunteers were visiting the urinal, and hence activating the lights to switch ON. The 244 magnitude and length of decrease is an indication of the length of time the lights were ON. 245 Figure 4B (inset) shows a calibration curve for the power consumed by the LED lighting at a 246 given voltage. As can be seen the MFC stack gave a maximum power of approximately 0.4W 247 for 75hrs. 248 249 250

Full text

Pee Power Urinal – Microbial Fuel Cell Technology Field
1
Trials In The Context Of Sanitation
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3
Ioannis Andrea Ieropoulos
1,2*
, Andrew Stinchcombe
1
, Iwona Gajda
1
,
Samuel Forbes
1
, Irene
4
Merino-Jimenez
1
, Grzegorz Pasternak
1
, Daniel Sanchez-Herranz
1
and John Greenman
1,2
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6
1
Bristol BioEnergy Centre, BRL, University of the West of England, Bristol, Frenchay Campus,
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BS16 1QY, UK.
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2
Biological, Biomedical and Analytical Sciences, University of the West of England, Bristol,
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Frenchay Campus, BS16 1QY, UK.
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Abstract
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This paper reports on the Pee Power urinal field trials, which are using Microbial Fuel Cells
14
for internal lighting. The first trial was conducted on Frenchay Campus (UWE, Bristol) from
15
February-May 2015 and demonstrated the feasibility of modular MFCs for lighting, with
16
University staff and students as the users; the next phase of this trial is ongoing. The second
17
trial was carried out during the Glastonbury Music Festival at Worthy Farm, Pilton in June
18
2015, and demonstrated the capability of the MFCs to reliably generate power for internal
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lighting, from a large festival audience (~1000 users/day). The power output recorded for
20
individual MFCs is 1-2mW, and the power output of one 36-MFC-module, was commensurate
21
of this level of power. Similarly, the real-time electrical output of both the Pee Power urinals
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was proportional to the number of MFCs used, subject to temperature and flow rate: the
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campus urinal consisted of 288 MFCs, generating 75mW (mean), 160mW (max) with
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400mW when the lights were connected directly (no supercapacitors); the Glastonbury
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urinal consisted of 432 MFCs, generating 300mW (mean), 400mW (max) with 800mW when
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the lights were connected directly (no supercapacitors). The COD removal was >95% for the
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campus urinal and on average 30% for the Glastonbury urinal. The variance in both power
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and urine treatment was due to environmental conditions such as temperature and number
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of users. This is the first time that urinal field trials have demonstrated the feasibility of
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MFCs for both electricity generation and direct urine treatment. In the context of sanitation
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and public health, an independent power source utilising waste is essential in terms of both
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Developing and Developed World.
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Keywords: microbial fuel cells; modular design; pee power urinal; sanitation; ceramic
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materials; fluidic isolation
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Introduction
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Microbial fuel cells (MFCs) have been receiving increased attention from the scientific
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community, even though the technology has been viewed with scepticism, at different levels
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of society. MFCs generate electrical energy directly from the break-down of organic matter
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via the metabolism of inhabitant microbes, with the rates of reaction being dictated by the
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microbial metabolic state (Ledezma et al., 2012). Electrical output is therefore
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thermodynamically limited by the carbon-energy metabolism of the constituent cells of the
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biofilm community (mono- or mixed-culture) colonising the electrode (Ieropoulos et al.,
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2007; Jong et al., 2006; Kim et al., 2000). Microbial reactions are inherently lower than
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chemical or even purely enzymatic reactions, and therefore the magnitude of the absolute
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power output at any given time, is typically orders of magnitude lower than those generated
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from conventional chemical fuel cells (Kirubakaran et al., 2009; Mekhilef et al., 2012). Be that
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as it may, electricity generated in a MFC comes directly from waste or wastewater material,
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which in the break-down/utilisation process is rendered cleaner and potentially suitable for
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direct discharge to the environment (Habermann and Pommer, 1991; Ledezma et al., 2013;
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Winfield et al., 2012). This is a competitive advantage that largely compensates for the lower
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levels of power.
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Over the years, a wide range of organic substrates has been shown to work as fuels in MFCs.
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Without being exhaustive, these are: types of food waste such as rotten fruit and prawn
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shells (Ieropoulos and Melhuish, 2005); various types of wastewater from the paper
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industry, agriculture, dairy farms, municipal treatment plants, oil industry, wine distilleries
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and breweries, and tanning industry (Pant et al., 2010); more recently, biodegradable
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materials (Winfield et al., 2015, 2013b) as well as human urine and septic tank content, have
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also been shown to work very well as fuels for electricity generation (Ieropoulos et al., 2013,
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2012; Kuntke et al., 2012; Yazdi et al. 2015). The application of low cost ceramic membranes
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allowed to decrease the cost of structural material, which is separating the anode and the
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cathode, to as low as 4.14 GBP/m
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(Pasternak et al., 2015). Utilising human waste directly
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and decreasing the cost of MFCs by the use of ceramic membranes has allowed the
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technology to be exploited in the context of sanitation, especially in countries of the
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Developing World, which lack the basic infrastructure for clean water and sewerage
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(UNESCO, 2009). More than 2.5 billion people lack access to an improved sanitation facility
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while 1 billion practice open defecation (World Health Organisation, 2014). Inadequate
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drinking water, sanitation and hygiene (WASH) are important risk factors where diarrhoeal
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disease burden relies on access to water and sanitation facilities rather than water quality.
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The importance of improving water and sanitation is the key for the prevention of diarrhoeal
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diseases (Prüss-Ustün et al., 2014). In addition to the philanthropic dimension that the MFC
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approach has, sanitation in the Developing World offers the ground for step-wise scale up
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field trials, to evaluate the technology in the real world environment and thus assess its
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feasibility.
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The efficient utilization of urine through MFCs incorporated in stacks/modules would no
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longer require conventional energy intensive treatment by the wastewater companies and
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also result in better balanced fertiliser (Ieropoulos et al., 2013). Efficient energy harvesting
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electronics for direct MFC usage, is also a major challenge for scale up and implementation
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(Wang et al., 2015). So far, there have been a few MFC field trials, like for example: a ceramic
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cascade temporarily installed in a municipal wastewater treatment plant (Winfield et al
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2012), a multi electrode MFC system for contaminant removal (Heidrich et al., 2014) as well
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as for winery wastewater treatment (Cusick et al., 2011), wireless sensors (Donovan et al.,
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2008) and more recently, floating MFCs at the Nosedo, Milan wastewater treatment plant
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(Martinucci et al., 2015).
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The present study is based on previously reported novel ceramic designs developed as single
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MFCs, showing high power performance with catholyte production and an ability to operate
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practical applications, including direct LED lighting (Gajda et al., 2015a) and recharging a
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mobile phone via a single MFC unit (Gajda et al., 2015c). The design gives the advantage of
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simplicity and functionality by utilising multiple MFCs submerged in the same feedstock
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tank. The multiplication of units in parallel would form a module, which could then be
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connected in series or parallel with other modules, to scale-up into a flexible and robust
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stack. The study reported herewith, funded by the Bill & Melinda Gates Foundation and
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Oxfam, had the following aims: (i) evaluate the modular approach of stacking MFCs in a pilot
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scale trial for energy generation; (ii) integrate the technology with the toilets that Oxfam
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uses in refugee camps and disaster areas to demonstrate utility in terms of indoor lighting;
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(iii) scale-up of the urinal, at a systems level, for testing during the Glastonbury Music
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Festival 2015 and (iv) assess the efficacy of urine treatment.
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Methods
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MFC construction
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MFC units were constructed using closed at one end terracotta caves (Weston Mill Pottery,
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UK) as previously described (Gajda et al., 2015a). The dimensions of the ceramic cylinders
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used in this work were 150mm long, 48mm outside and 42mm inside diameter. Anode
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electrodes were made of 30g/m
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carbon veil fibre (PRF Composites, UK) of the dimensions:
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600 x 260mm and folded in half along its length. The carbon veil was then wrapped around
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the ceramic cylinder and tied with a 50mm diameter stainless steel wire to secure the anode
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in place and to provide a connection to the external circuit. Cathode electrodes were
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prepared using activated carbon and PTFE mixture as previously described and inserted
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inside the ceramic cylinder (Gajda et al., 2015a) as a single sheet of 130 x 140mm
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dimensions. Stainless steel crocodile clips were then used to connect the cathode to the
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electrical circuit.
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MFC module design & Inoculation
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Thirty six 36 MFCs were fitted into a plastic container of dimensions 70 (length) x 30 (width)
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x 16cm (depth). The anodes and cathodes were connected in a parallel electrical
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configuration using aluminium bus bars and stainless steel wire, nuts and washers. The
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container was inoculated with a mixture of activated sewage sludge (Cam Valley, Saltford,
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UK) and fresh urine and operated in batch mode for the preliminary test. The total liquid
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capacity was 25 litres. Urine was collected from healthy individuals with no known previous
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medical conditions, and pooled together before using as a feedstock. The pH would be oan
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average 6.4. No pH control was applied to the MFC stacks in both urinals.
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Pee Power Oxfam urinal- UWE campus
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Eight modules (288 MFCs in total) as described above were fluidically connected using
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plastic elbow connectors and pipes to create a series loop and air gaps between the boxes.
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This was to allow the 8 modules to be connected in a series electrical configuration. They
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were inserted under the men’s urinal unit installed at the Frenchay Campus, University of
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the West of England, as shown in Figure 1. The structure was built to accommodate two
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urinal bowls directly feeding the MFC modules fitted underneath the structure. The urinal on
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the University campus resembles toilets produced by Oxfam and used in refugee camps to
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make the trial as realistic as possible. Inside the cubicle, LED light modules were fitted to be
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energised by the MFC stack via a capacitor bank consisting of 4x3000F capacitors in a series
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parallel configuration (BCAP3000 p270, Maxwell Technologies). The lighting consisted of 4x
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4.5W modified LED modules (Dial MR16-3H-WH-A1 12V-50Hz 530mA 4.5W 14W20). The
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purpose of modification was to reduce the LED forward voltage from ~12V to ~3V and so
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better suit the requirements of the MFC system. With this modification, the 4 LED modules
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were consuming approximately 1.2W. The switching of the LED lights was controlled using a
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low power passive-infra-red (PIR) sensor and a low power microcontroller (Microchip
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PIC24F16KA102). This also allowed for a 3V backup power supply in the case of MFC system
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failure. The holding tank was fitted as the initial (inlet/buffer) tank at the beginning of the
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stack, providing feedstock for the MFC modules. There was also a collection tank fitted at the
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outlet of the MFC stack. The operational time was 3 months starting in 05/03/15 – 31/05/15
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and the analytical data presented herein were collected over the period of 5 weeks to assess
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power and nutrient removal. Urine was donated voluntarily by the campus student and staff
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population.
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Figure 1. (a) Pee Power field trial funded by Oxfam at the UWE campus in February –May
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2015; (b) 3D representation of the MFC stack with the inlet and outlet tanks underneath the
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urinal.
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Pee Power field trial – Glastonbury
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A field trial was performed at the Glastonbury Music Festival, England, between 22/06/15 –
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30/06/15. A specially adapted urinal (Dunster House, UK) was installed in the “Sacred
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Space” (aka “Stone Circle”) field. The urinal structure was fitted with 3 troughs which
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collected the urine from festival-goers and was used to 'feed' the MFC modules. Next to the
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urinal, an educational information point was used to interact with the public explaining the
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ideas and the technology behind the project. The men’s urinal was installed as shown in
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Figure 2 where 12 MFC modules (8 from the Oxfam Pee Power urinal + 4 new ones) were
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installed giving in total 432 MFCs in the stack and 300 litres of working volume. Similar to
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the previous trial, supercapacitors (10x3000F in a series parallel configuration giving
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7500F) were used as an energy store. The same LEDs as the ones used in the Oxfam system,
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but a higher number of 6, were used, due to the larger urinal facility. The total power
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consumption of the 6 LED modules was 1.8W. Due to the high number of users (between
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825-1000 per day) the estimated flow rate was approximately 330 l/day and the hydraulic
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retention time was 0.9 days.
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Figure 2. (a) Pee Power field trial in Glastonbury Music Festival, June 2015; (b) Urinal
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assembly and MFC stack arranged in 12 modules.
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Analysis
182
Power performance was monitored with a multi-channel Agilent 34972A, LXI Data
183
Acquisition Unit (Farnell, UK) and were then processed using the Microsoft Excel and
184
GraphPad Prism software packages. Parameters such as pH and conductivity were measured
185
with a Hanna 8424 pH meter (Hanna, UK) and 470 Jenway conductivity meter (Camlab, UK)
186
respectively. Dry weight was determined by drying 1 mL of catholyte over 72 h in ambient
187
temperature and weighing the dry mass.
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COD was analysed using the potassium dichromate oxidation method (COD HR test vials,
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Camlab, UK) with an MD 200 photometer (Lovibond, UK) where 0.2 mL samples were taken
191
before and during MFC treatment and filter-sterilised prior to analysis. Total Nitrogen (TN)
192
was measured using MD 500 colorimeter (Lovibond, UK) and Vario Tube Test (0.5-25 mg/L)
193
on diluted samples. The concentration of anions in the anolyte (inlet, outlet) and catholyte
194
samples was determined by ion chromatography using a 930 Compact IC Flex (Metrohm,
195
UK). The samples were diluted with ultrapure water before they were collected by the 858
196
professional sample processor and introduced into the ion chromatograph.
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Results and Discussion
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Initial MFC module testing
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A single box assembled with 36 MFCs was initially tested under laboratory conditions. After
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inoculation the MFC module was connected to a fixed resistor load and it was supplemented
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with fresh and/or old urine daily. The resistor load was adjusted between 2.3 and 3.3 Ω with
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stable performance achieved under a 3.3 Ω load. The module reached steady state
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performance at 40 mW, however, when the resistor was adjusted to 2.3 and with some
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modification and improvement of the cathode current collector, the peak power reached 62
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mW (Figure 3), which is consistent with the individual ceramic MFC performance of up to
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2.58 mW under controlled conditions. Multiple individual MFC units were also previously
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tested in series and parallel configurations. These preliminary experiments constituted the
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first tests of multiple MFC units in the same anodic feedstock, which simplified the
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realisation of an MFC collective.
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