Would you eat oyster mushrooms grown on used disposable diapers?

Guess what?

You may get your chance sooner than you think.

An article in the April 20, 2011 issue of The Economist describes a new approach to bioremediation.

Disposable diapers, despite their name, are notoriously difficult to dispose of, with studies of landfills suggesting they may take centuries to decompose.

From the article: "As [Alethia Vázquez-Morillas and colleagues from the Autonomous Metropolitan University in Mexico City] describe in Waste Management, cultivating the right type of mushroom on soiled nappies can break down 90% of the material they are made of within two months. Within four, they are degraded completely. What is more, she says, despite their unsavoury diet the fungi in question, Pleurotus ostreatus (better known as oyster mushrooms [top]), are safe to eat. To prove the point she has, indeed, eaten them.

"The culinary use of oyster mushrooms was one reason why she picked them for the experiment. The species is frequently used in stir-fries and is often added to soups. The other reason was that Pleurotus ostreatus is widely used in what is known as mycoremediation — the deployment of fungi to clean up waste. It is, for example, already grown on agricultural materials such as wheat and barley straw, and industrial waste like coffee grounds and the leftovers from making tequila. Dr Vázquez-Morillas and her colleagues were trying to extend the oyster mushroom’s own culinary range.

"The reason nappies are difficult to break down has nothing to do with their use. Even a clean nappy would hang around for a long time in a dump. The main ingredient of a nappy is cellulose, an annoyingly persistent material. Pleurotus, however, grows on dead or dying trees in the wild and is thus well provided with enzymes that break cellulose down. And, since Mexicans alone throw away 5 billion nappies every year, there is plenty of material from this source for them to get their mycelia into.

"The idea that the result might be sold and eaten may be controversial but it is not absurd. The nappies the researchers used were contaminated only with urine, not faeces. A healthy person’s urine is sterile and Dr Vázquez-Morillas also treated the nappies with steam, to make sure. Such treatment would kill the nasty bugs in faeces, too, though, so mushrooms grown on treated nappies should, in theory, be safe to eat.

"In practice, overcoming the yuck factor might be an insuperable barrier to marketing nappy-grown fungi, and the cost of the steam treatment could make the exercise futile. Mycoremediation of this sort does not, however, depend for its success on selling the results. Merely getting rid of what would otherwise hang around indefinitely is worthwhile. And of the fungi themselves, Dr Vázquez-Morillas observes, "they are cleaner than most of the vegetables you can find in the market, at least in Mexico."

Below, the abstract of the published paper.

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Disposable diapers degradation by the fungus Pleurotus ostreatus

This research assesses the feasibility of degrading used disposable diapers, an important component (5–15% in weight) of urban solid waste in Mexico, by the activity of the fungus Pleurotus ostreatus, also known as oyster mushroom. Disposable diapers contain polyethylene, polypropylene and a super absorbent polymer. Nevertheless, its main component is cellulose, which degrades slowly. P. ostreatus has been utilized extensively to degrade cellulosic materials of agroindustrial sources, using in situ techniques. The practice has been extended to the commercial farming of the mushroom. This degradation capacity was assayed to reduce mass and volume of used disposable diapers. Pilot laboratory assays were performed to estimate the usefulness of the following variables on conditioning of used diapers before they act as substrate for P. ostreatus: (1) permanence vs removal of plastic cover; (2) shredding vs grinding; (3) addition of grape wastes to improve structure, nitrogen and trace elements content. Wheat straw was used as a positive control. After 68 days, decrease of the mass of diapers and productivity of fungus was measured. Weight and volume of degradable materials was reduced up to 90%. Cellulose content was diminished in 50% and lignine content in 47%. The highest efficiency for degradation of cellulosic materials corresponded to the substrates that showed highest biological efficiency, which varied from 0% to 34%. Harvested mushrooms had good appearance and protein content and were free of human disease pathogens. This research indicates that growing P. ostreatus on disposable diapers could be a good alternative for two current problems: reduction of urban solid waste and availability of high protein food sources.

Highlights

► Used disposable diapers can be degraded by the fungus Pleurotus ostreatus.

► The process reduces volume and weight, producing a high protein byproduct with no pathogens.

► Efficiency is improved by shredding or grinding the diapers, as well as by addition of a substrate.