Smelly farms may succumb to subtle science

FARMYARDS smell. There is no getting away from that. They smell because of the excrement produced by the animals which live there. And however carefully this excrement is dealt with—whether by modern versions of the time-honoured process of muck-spreading that inject it below the surface of the fields it is fertilising; or by anaerobic digestion, in which it is used to make methane that can, in turn, be employed to generate electricity—it is still the case that the buildings housing the animals themselves stink.

Besides being unhealthy for farmworkers (not to mention the neighbours, if the farmyard is near a village), such smells are bad for business. Research has found that improving the air quality of the places where pigs and other livestock are housed makes for healthier and more productive animals. The question is, how to do that cheaply? Jacek Koziel of Iowa State University reckons he has the answer: titanium dioxide and disco lights.

In the late 1960s researchers at the University of Tokyo discovered that, when given a helping hand by ultraviolet light, titanium dioxide encourages the breakdown of all sorts of organic compounds. It does so by causing oxygen and water vapour in contact with its surface to react and form molecules called free radicals. These substances oxidise and destroy organic compounds, turning them into small molecules such as carbon dioxide and water. Since the odour of excrement is composed largely of organic compounds, and titanium dioxide is cheap, Dr Koziel wondered whether it might be employed to de-pong byres, sties, stables, sheds and other animal dwelling places.

In their initial experiments, he and his team created a standardised manure-like stench from a mixture of dimethyl disulphide, dimethyl trisulphide, diethyl disulphide, butyric acid, para-cresol and guaiacol. This is a combination that is not for the faint of nose. They then coated the interior surface of a glass container with a commercial preparation of titanium dioxide, known as PURETi Clean, which contains zillions of tiny crystals of the chemical. These greatly increase the surface area of titanium dioxide available for reactions to occur on. That done, the researchers pumped their smelly gas into the container and activated the coating using a “black light”—a low-powered source of ultraviolet similar to that employed in dance clubs to encourage customers’ clothes to fluoresce.

Dr Koziel varied temperature, humidity and ventilation levels in the container to mimic conditions in both summer and winter. In summer-like simulations the drop in odorant level was 27-62%. In winter conditions it was up to 100%. Tests during actual summer, on a pig farm in Iowa, in which Dr Koziel and his colleagues drew real farm air through a black-lit, titanium-oxide-coated tunnel, cut overall levels of noxious chemicals by 16% and reduced one of the worst-smelling constituents of pig pong, para-cresol, by 22%. That may not sound huge, but the difference was detectable by human noses. Moreover, the apparatus the team used for this trial was only 2½ metres long and 30cm in diameter. Scale things up to create a bigger surface area and better conversion rates might reasonably be expected.

Painting a large area, such as the interior of a barn, with titanium dioxide would cost about the same, around $3 a square metre, as a conventional paint job. Black lighting is inexpensive, too. Conventional fluorescent black lights cost about $20. Ultraviolet light-emitting diodes, a recent innovation, are cheaper still. And, if mounted on portable fittings, they might even form an extra source of revenue for an enterprising farmer as the lighting set for barn dances.