Pee-Power Urinal

The Microbial Fuel Cell (MFC) is an energy converter, which turns organic matter directly into electricity, via the metabolism of live microorganisms. The bacteria break down organic molecules and generate electricity – that could run on the organic molecules found in urine, such as uric acid, creatinine and small peptides. The electricity output from MFCs is relatively small and these low levels of energy are stored and accumulated into capacitors or super-capacitors, for short charge/discharge cycles.

Smaller cells have higher energy densities and are more efficient, so the technology relies on miniaturization and multiplication, building stacks of cells. The latest models of MFC use ceramic cylinders.

There is a continuous stream of urine passing through a series of fuel cells, that keeps up the electricity production by constantly ‘feeding’ the bacteria. The electricity is collected by an energy harvesting board.

Ceramic cylinders were purchased from International Biological Laboratories (Haryana, India) and were made from porous ceramic (earthenware) material. The average dimensions were 10.2 cm (length), 3.5 cm (outer diameter), 2.5 cm (inner diameter), with an approximate volume of 49 mL. The closed ends of the cylinders were removed so that the 3D printed lids (air-gap adaptors – see below) could be introduced at both ends (see Fig. 1). The anode electrodes were made from 337.5 cm² of carbon fiber veil (PRF Composites, Dorset, UK) with two 10 cm long strips of 0.25 mm diameter stainless steel wire (SWC, UK) folded so as to form a spiral brush. The cathode was prepared by painting two coats of a microporous layer (MPL) on the outer surface of the ceramic cylinder. More details to be found here.

Users can contact the manufacturer on their website.

In theory, infinite lifetime

It was tested 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 is a larger urinal that has been tested during the Glastonbury Music Festival at Worthy Farm, Pilton in June 2015. It demonstrated the capability of the MFCs to reliably generate power for internal lighting, from a large festival audience (∼1000 users per day).

Field results of the system (2016, UK’s music festival) under uncontrolled usage indicate an optimal retention time for power production between 2.5 h and ~9 h. When measured (HRT of ~11h40), the COD decreased by 48% and the total nitrogen content by 13%. Compared to the previous Pee-Power field-trial (2015, laboratory) the present system achieved a 37% higher COD removal with half the HRT. The 2016 setup produced ~30% more energy in a third of the total volumetric footprint (max 600 mW). This performance corresponds to ~7-fold technological improvement.

More details about vetted performance to be found here.

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