Solid Waste & Recycling


Diaper Recycling (April 01, 2003)

Last November, the small town of Santa Clarita, California boldly did what no other town has done before -- it began recycling its diapers. Just to be clear, this means dirty diapers, disposable bed l...

Last November, the small town of Santa Clarita, California boldly did what no other town has done before — it began recycling its diapers. Just to be clear, this means dirty diapers, disposable bed liners, and feminine hygiene products, technically known as absorbent hygiene products (AHPs).

Billions of diapers

About two per cent of parents living in North America use reusable cotton diapers for their babies. Everyone else takes the more convenient route with the single-use, disposable diaper. In fact, the U.S. EPA estimates that about 18 billion disposal diapers are generated annually in America. That’s about one tonne of disposable diapers per baby before toilet training. In addition, the amount of AHP is on the rise, as our population gets older and consumption of adult incontinence products increases. Given these facts, it’s not surprising that AHP recycling is beginning to take off.

In the beginning

About 14 years ago Marlene Conway, a mother from Ontario began to research possible solutions for this growing waste problem. The first pilot facility, Knowaste, opened in Mississauga, Ontario, and processed about 3,628 to 4,535 tonnes of AHPs. At the time, the tip fee was competitive with the cost of local landfills (about $150 per tonne). But it didn’t take long for Ontario’s waste to start flowing south to cheaper disposal options in the U.S., forcing Knowaste to shut its Ontario operation.

Throughout most of the 1990s, Knowaste refined the recycling technology and began looking for opportunities in Europe and Asia where disposal costs were more cost competitive.

Recycling AHPs

In 1999, Knowaste opened a large-scale state-of-the-art facility in Arnhem, Holland. The facility processes 63,500 tonnes of used AHPs per year (with a capacity of up to 90,700 tonnes). AHP wastes from senior facilities, daycare centers, and other commercial establishments are collected from parts of Western Europe.

In November 2002, a small-scale version of the technology — Knowaste Diaper Processor (KDP) — began recycling dirty diapers from 500 householders involved in a test pilot in Santa Clarita, California. If successful, the program will expand to the entire community of 143,000 households. Santa Clarita collects about one tonne of AHPs per week. Residents place materials in plastic bags in 64-gallon bins usually placed outside of the home or in the garage (the city provided bags and bins). Santa Clarita staff report that the program is very popular with residents and collection is going smoothly.

This small-scale KDP seems to be gaining ground in smaller community diversion programs. With a footprint of 1,500 square feet and 18-foot height clearance, the KDP can be placed directly in a municipal material recycling facility (MRF).

The unit has a maximum capacity of 4,535 tonnes of AHP waste per year (about one tonne per hour), and can result in up to 907 to 1,088 tonnes of fibre and 453 to 544 tonnes of plastic output for end-use markets.

The technology

The patented Knowaste recycling process separates the components of AHPs. By weight, these are: 24 per cent paper fibre, 10 per cent plastic (60 per cent low density polyethylene and 40 per cent polypropylene), five per cent super absorbent polymer (SAP, which provides the water retention function), six per cent sludge and 55 per cent moisture.

The material is shredded into small pieces and sent to a pulper that initiates separation of the components and chlorine treatment for sanitization. The plastic is removed by finger conveyors, pressed and pelletized for sale to the market.

The pulp stream goes through a series of coarse screens, and is treated with aluminum sulfate (inorganic salt) to deactivate the SAP, which makes it possible to separate out the fibre. The deactivated SAP, along with residual small plastics, are separated from the fibre through a cleaning process. The deactivated SAP can be collected and reactivated for reuse.

Fibres are then put through a fine mechanical washing, cleaning and screening process. The high quality clean fibre is then pressed, baled and sold into the market. Currently, value added products from secondary AHP fibre in Holland are: shoe soles, oil filters and car fluff.

The water extracted in the washing and thickening steps is sent to internal treatment using a dissolved air clarifier and recycled in the system as dilution water. In Arnhem, sludge from the clarifier, as well as the fine screening and cleaning rejects, are thickened and sent for composting. In Santa Clarita, the sludge is sent to the municipal sewer system (a requirement of the permit).

The KDP batch processor combines the functions of shredding, pulping, SAP deactivation, sanitization and separation in one step. Similar to a washing machine, water is continuously pumped into and extracted from the unit, a process that continuously removes the fibre, plastic, deactivated SAP and waste. Water is clarified in a dissolved air flotation (DAF) tank and recycled in the facility as dilution. Waste diverted from the screen and cleaner, along with the sludge extracted by the DAF, is sent to the municipal sewer system. All discharged water is treated internally to reduce suspended solids.


The cost of a KDP machine is US$750,000 or CDN$1.1-million with a two-year warranty. While operation costs will vary depending on factors like energy, labour and water costs, Knowaste estimates direct operating costs including maintenance will run at about $100 per tonne, not including material revenues.

If a KDP machine is set up within a MRF, bagged material can be collected curbside or via depot and sorted with other recyclables, incurring incremental collection costs. Depending on the costs of alternatives, diaper recycling can be not only environmentally preferable to disposal, but economically advantageous as well.

Shifting the costs: EPR

By applying a standard extended producer responsibility (EPR) model approach to a diaper-recycling program one can estimate the cost to the producer and/or its customer. With about 6,064 diapers per tonne, the cost to recycle diapers (not including capital or collection costs) would be only about a penny per diaper for the consumer.

Yet the diaper industry promotes composting as the ideal solution to divert single-use diapers. With EPR policy growing globally the diaper industry is looking for the cheapest solution. And what can be cheaper for industry and its customers than taxpayer-funded, municipal composting?


The industry claims that diapers can be effectively composted in municipal solid waste composting plants. In fact, industry has conducted pilot studies in communities that claim to have had “very positive results.” One large diaper company put a message on its packaging stating, “This product is compostable in municipal composting units. Support recycling and composting in your community.” The problem with this is that very few centralized municipal composting facilities are prepared to handle the material.

Difficulties associated with AHP composting can be numerous. The first is the issue of health and safety of facility workers’ exposure to fecal matter or other human waste. Second, there’s plastic contamination in the finished compost, which will require removal and additional costs.

Third, diapers are usually tightly bundled-up by parents before they are thrown away. This necessitates use of a front-end shredder at the compost facility. Shredding material at the front-end means shredding contaminates, which are usually pulled out from the finished compost (like batteries, metal products, etc.) Once shredded, extracting the contaminants from the back-end is impossible, resulting in a less than grade compost quality. And finally, end-markets for finished compost are fairly undeveloped all over the world, which may result in another waste problem.

However, if sustained end-markets exist and a properly designed facility with the necessary health and safety measures are in place, then composting is an opti

on for diverting small volumes of materials. In fact, Canada’s largest city, Toronto, is in the process of rolling-out a wet waste program, which will accept diapers, incontinent pads, sanitary products for composting. Because the program is still in its infancy, results cannot be reported at this time.

Environmental savings

According to Knowaste Recycling, the up-stream environmental savings of recycling AHPs are significant. They estimate that for every ton of AHP waste recycled, 400 kg of wood, 145 cubic meters of natural gas and 8,700 cubic meters of water is saved.

Roy Brown, president and CEO of the company says, “What makes diaper recycling the best diversion option is that it maintains the integrity of the valuable raw materials contained in AHPs.”

“Considering the world’s appetite for one-way products, we simply can’t afford to throw away any high quality fibre or plastic resin — there are only so many trees left,” says Mr. Brown.

But in the end, some would argue that the most environmentally preferable way to mitigate the impacts of disposal diapers is not to use them at all. Cotton diaper services exist in most large urban cities and the environmental savings are huge. Reusable diapers use about half as much water, three times less energy, twenty times less raw materials, generates sixty times less waste and costs taxpayers nothing.

Clarissa Morawski is principal of CM Consulting, based in Toronto, Ontario. E-mail Clarissa at

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