For many years, the industry has struggled to find effective solutions for the disposal of used diaper waste. Currently, diaper waste is either incinerated for energy recovery, a popular method in Europe, or converted into RDF (Refuse-Derived Fuel) for heat generation in industrial processes. The disposal of biodegradable baby diaper waste often involves landfilling in anaerobic waste disposal sites. Surprisingly, this method is not more environmentally friendly than incineration, especially when landfill sites lack methane gas recovery systems or when diapers with materials suitable for recycling cannot dry completely in sunlight, requiring pre-treatment with centrifuges and dryers.
Moreover, initiatives like Knowaste and TerraCycle are attempting new diaper recycling technologies, but their economic sustainability remains questionable, with insufficient case studies proving global replicability. Despite some technologies being in use for decades, investors still harbor doubts about their business models.
In reality, despite increasing consumer concerns about the environment, the majority of used diapers are still being landfilled. Consumer dissatisfaction with the industry's current environmentally-friendly solutions for reducing diaper impact on the environment is evident. Incineration, which produces carbon dioxide, a greenhouse gas, is viewed negatively by consumers. Some companies are working on developing new technologies to effectively handle greenhouse gases generated from incineration, but these methods are yet to become ideal solutions in the short term.
Two and a half years ago, two companies started revealing information about their projects for recycling used diaper waste and introduced their solutions on social media platforms. They are currently presenting technical reports to potential clients globally and publishing papers at international diaper industry conferences. The prototype factory implementing a used diaper waste recycling solution is located in Treviso, Italy, operated by P&G-Fater. The process involves separating raw materials using rotating high-pressure vessels and sieves. Unicharm proposes using diaper waste biomass to produce hydrogen, and ozone bleaching is employed to recover pulp. Other companies, including Kimberly-Clark collaborating with Envirocorp in New Zealand, and Essity partnering with Renewi in Europe, are also making efforts in diaper recycling. All these projects are attempting to prove that they can provide the best, most economical, or ecologically valuable used diaper waste solution and aspire to become leaders in this field.
However, a particular contradiction that few people mention still exists. Traditional recycling of diapers requires separating all plastic components, such as polyethylene and polypropylene, into pellets for use in other industries, like plastic injection molding. To work most effectively, the equipment needs high-purity recycled plastic materials, as impurities can damage the quality of recycled materials or necessitate additional separation processes.
It's not as simple as it seems. In today's market, a growing number of consumers prefer natural materials over synthetic ones for their baby's skin, resulting in the use of plant-based alternatives. These consumers want diapers with natural components, like starch-based films, PLA (Polylactic Acid), adhesive fibers made from bamboo, pine, or eucalyptus, and biodegradable SAP (Superabsorbent Polymer). Adding hydrophobic cotton to nonwoven materials used for the surface or bottom layers doesn't pose a major issue in recycling, as cotton can be extracted and blended with cellulose as a single product. However, mixing natural film materials or plant-based plastics with synthetic materials may complicate material composition and make the recycling process more challenging. The question arises: how can we organize the diaper waste collection process to prevent different types of diapers from mixing?
A well-known solution for processing plant-based diaper waste is composting. However, this process cannot be implemented by consumers in their home gardens, as most plant-based materials, such as PLA or other plant-based plastics used in diapers, require a minimum of 60°C to begin decomposing for composting, which exceeds the capabilities of small-scale composting facilities. Additionally, air needs to be pumped in to avoid methane gas generation, which is many times more harmful to the environment than carbon dioxide. The proper way to handle composting of diapers is to use industrial composting facilities, managed as aerobic composting solutions. In this process, plant-based diapers are mixed with other biodegradable materials and composted in an industrial plant with constant air circulation and temperatures above 60°C. After the composting cycle ends, filters are used to remove any uncomposted secondary components, such as elastic materials, hot melt adhesives, and other materials, which may be smaller in volume compared to the resulting compost. For diapers using biodegradable SAP materials or potassium-based synthetic polyacrylic acids (similar to the original SAP sold in the mid-1980s), the SAP can be recovered and used in the final composting. For Na-SAP, consideration needs to be given to whether the proportion is low enough to avoid an increase in soil salinity. Using K-SAP instead of Na-SAP can prevent excessive salinity, which may harm plants using composted soil. Finding a biodegradable SAP (such as those currently being developed by companies like Thethis or Ecovia) or a good synthetic K-SAP alternative (compatible with agriculture) is less complicated than the overall recycling solution for diapers. However, any recycling process requiring a high-pressure sterilizer to work in batches is not as efficient as continuous operation.
For plant-based diaper materials, we face the same problem as with synthetic fibers. If diapers are made entirely of synthetic components but are mixed with plant-based materials after recycling for composting, they will never compost and may even contaminate the composting process. At least the bottom layer of diapers needs to be compostable to enable decomposition and expose the organic components inside the diaper during composting.
In conclusion, the exploration of recyclable solutions for diapers needs to simultaneously develop these two conflicting paths to provide consumers with more choices, whether they prefer recyclable synthetic materials or natural plant-based materials. Both options require a proper waste disposal solution. Another key issue is that they share the same bottleneck: the need for an efficient collection process to recycle synthetic materials from diaper waste or correspondingly industrial composting.
