Answering the Call of Nature

Dyllon Randall explains how bio-bricks can be grown from human urine

MY research team at the University of Cape Town recently announced that we had successfully “grown” bio-bricks – an alternative to traditional building materials - from human urine.¹ There has been a phenomenal response, and the article went viral, with it being picked up by 142 news outlets in 23 countries and a potential media reach of 248m in the first five days of the article being published. The broader urine-related research we are conducting was also awarded the 2018 IChemE Warner Prize.

The journey started back in 2016 while I was working on the “re-invent the toilet challenge” at Eawag in Switzerland, specifically on urine treatment. The team had developed a novel process to keep urea in solution by increasing the pH of fresh urine.² We achieved this by adding calcium hydroxide to fresh urine, which coincidently also produced calcium phosphate, an inorganic fertiliser. This process of keeping urea in solution was termed stabilisation. The urea in urine is naturally converted to carbonate ions and ammonia by enzymatic urea hydrolysis, and stabilising urine prevents this from happening by inhibiting urease-producing bacteria (urease is a catalyst for this reaction).

Proof of concept

I learnt about a natural process called microbial induced calcium carbonate precipitation (MICP), which was successfully used to grow bio-bricks from synthetic urea (not urine) by a US-based startup called BioMASON a few years back and I was always curious to know if the urea present in urine could be used instead, thus offering a potentially more sustainable process. In February 2017 I returned to South Africa to take up a Senior Lecturer position in Civil Engineering at the University of Cape Town. I applied for funding from South Africa’s Water Research Commission to see if we could indeed use urine to grow bio-bricks. We obtained the funding, and within four months a visiting Master’s student from ETH Zürich, Jules Henze, showed that we could grow bio-columns using synthetic urine at elevated pH values.³

We chose to grow bio-columns at first as proof of concept because it is easier to test the compressive strength of a column compared to a brick. The column shape is also easier to handle experimentally and researchers had successfully grown this shape before. Jules’ first attempts to making bio-columns were not successful – we never got a perfectly formed column. We hypothesised that the reason for this was in the methodology. We fed the bacteria together with the urea-rich solution through the column and thought that this resulted in preferential flow, thus only parts of the column were colonised with bacteria and hence only certain parts were solidified over time. As a result, we changed the method and first colonised the loose sand material with bacteria before adding this mixture to the column mould. This change in method worked and with only two weeks to go before Jules’ final thesis hand in, he successfully grew a perfectly-formed bio-column.