Growing potential for ‘humanure’

Katie in the early days with her wheat seedlings.

Last year, CAT and the University of Leeds began a new four-year partnership investigating the potential of composted human manure (known as ‘humanure’) to provide a sustainable alternative to chemical crop fertilisers.

Using resources from CAT and facilities at the University of Leeds Research Farm, Leeds PhD researcher Katie Allen is conducting field trials investigating the impact of using humanure as fertiliser for the three most commonly grown crops in the UK: wheat, barley and oilseed rape.

Thanks to the multiple compost toilets we have on site (see box), CAT is able to supply approximately 500kg of humanure every two years to help with the trials; 455kg of humanure already supplied has now been added to around 70m2 of test beds at the University of Leeds Research Farm.

Katie will examine a variety of outcomes, including yield, carbon content, nutrient load and soil microbiology. At the end of the growing process she will investigate root structure, density and earthworms in the soil, and she is also looking at the impacts of herbicide and fungicide treatments on the productivity of the wheat growth.

Katie emptying a compost toilet resting chamber at CAT.

Composting humanure at CAT

CAT’s Water and Waste Officer Fin Jordao

Some of the composting toilets at CAT appear to be regular low-flush toilets but are in fact backstage composters, using an ingenious centrifugal separator system called the aquatron. Others are urinediverting twin-vault composting toilets, which is still the recommended approach for complete treatment in the smallest space, with the lowest maintenance and maintaining the greatest hygiene. The aims are broadly the same: creating a contained leak-proof composting chamber that diverts the bulk of the liquid portion of excreta into a reed bed or soakaway, while maximising the volume available for the containment and decomposition of the solid portion. This makes it easier to maintain aerobic conditions, gives you more control over the composting process, minimises smells and keeps the experience of maintenance pleasant. Humanure at CAT is contained in a composting chamber for a year, then moved to a maturation chamber for another year, then finally added to the flower beds… and now to a field-scale trial in Leeds! If you have used our compost loos during a visit to CAT over the last two years, thank you for your contribution to the research!

As various sectors look to drastically cut their emissions and the UK Government has a target for halting and reversing nature’s decline by 2030, the scaled-up use of humanure could be one part of the solution to both the climate and biodiversity crises. By replacing chemical fertilisers and providing an alternative way of dealing with human waste, the use of humanure in agricultural applications has the potential to reduce fossil fuel use, lessen pollution of waterways, cut overall water use, and help limit the amount of valuable nutrients that are wasted by being flushed away.

Increasing the evidence-based understanding of humanure as an effective soil improver could lead to producing standards, clear guidance and even training for making and using this nutrient-rich resource. CS