Can Dirty Diapers Clean the Air?

They coined the word “counterintuitive” to describe ideas like this one: take soiled disposable diapers and transform them into diesel fuel while helping to keep the air clean and reclaim some of the hydrocarbons that went into their manufacture.

The “diapers-to-diesel” idea is about to get off the drawing board and into a new plant in Montreal, where the inspiration — and the science behind it — were born. AMEC — an international engineering and project management company that’s ranked “number one” on the Dow Jones Sustainability Index — is working with a client on a process to transform used diapers into diesel that is chemically similar to the fuel produced by refineries.

As the fledgling process matures, it will be able to handle most other hydrocarbon-based solid wastes; while it won’t exactly turn garbage into gold, it will do the next best thing: turn financial and environmental liabilities into clean air and cold cash.

The advantages of this process for the environment are two-fold. First, most jurisdictions send soiled disposable diapers, along with other solid wastes, to landfills. In time, as they decompose, the diapers release methane gas into the atmosphere, contributing to the creation of greenhouse gases (GHG). Diapers-to-diesel will divert vast volumes of diapers away from landfill and the methane-generation process.

Second, the process of transforming diapers into diesel fuel is a clean one, dispersing no pollutants into the atmosphere. In addition, the diesel so produced will help to reduce demand for fuel produced the conventional way (i.e., by oil refineries).

The system

At the heart of the process are Quebec’s hospitals, which among them generate about 120,000 tonnes of soiled disposable diapers each year. At present, they pay to have the whole soggy mess carted away, and they pay tipping fees for the privilege of leaving them at the landfill. The new plant has signed with the hospitals to dispose of (for free, initially) 30,000 tonnes a year of this waste. Instead of paying hauling and tipping fees, hospitals will actually save money on their current disposal costs. And landfills will be spared of the dirty diapers they used to have to bury.

The diapers, contents and all, will be trucked to the plant, which features specially designed reactors that are at the heart of the “diapers-to-diesel” process. Conventional furnaces use air and open flames for their burns, spewing a lot of ash and gases into the atmosphere. But the furnaces in this process burn at high temperature without air in a process designed by AMEC. Think of coals in a barbecue; even without the flames, they produce an intense, smoldering heat. Now, put the same process in a specially insulated furnace, one that emits no pollutant, and turn up the heat to industrial levels. (See the “Waste Business” article on gasification, page 14.)

The result is a very different reaction: at high temperature and in the absence of air, the plastic is thermally decomposed, slowly, and returns to its near-original form of hydrocarbon. The material thus produced is similar to the diesel from a conventional refinery, but without any emissions into the atmosphere.

The initial calculations call for every 30,000 tonnes of diapers to yield 11,000 tonnes of diesel fuel. AMEC’s partner reckons it can turn a profit after expenses (that include plant construction and operation, and, of course, acquisition of “raw” materials from hospitals).

While the thermal decomposition process is still being refined, the implications for the future are exciting; subsequent phases of the plant will handle greater volumes of hospital diaper waste, diverting more of the remaining 90,000 tonnes away from landfills.

There’s no reason why the process can’t also be extended to other hydrocarbon-based materials; think of discarded car tires, and the plastics reclaimed from scrapped cars, which currently accumulate and pose significant risks to human health and the environment. As with these and countless other kinds of solid wastes, the supply is endless, and cheap.

It all started out as hydrocarbons and it can all become hydrocarbons again.

Luciano Piciacchia is Vice President of AMEC in Laval, Quebec. Contact Luciano at luciano.piciachia@amec.com