The waste produced using absorbent hygiene products represent nowadays a large fraction of the common public solid waste. In the recent years, baby diapers waste have received a lot of attention due to the high volume produced and the difficult recycling processes. In our daily life disposable diapers are normally dismissed after single use and their usage is preferred over that of cloth diapers since they are more practical. But what about recycling them?
In the European Union, the annual market demand for disposable baby diapers exceeds 20 billion units, dramatically increasing the amount of dry weight waste (1.3 t/min). Despite the high value of their components, especially the super-absorbent polymer, the waste baby diapers have been mostly landfilled or incinerated. This is generating more than 3.5 million tons of diaper waste that requires around 500 years to be fully decomposed.
Generally, the disposable diapers consists of three main elements: plastics (polyethylene sheet, polypropylene fabrics etc.), cellulosic fibres and the superabsorbent polymer (SAP) made of granular sodium polyacrylate, a chemical compound capable of increasing the diaper´s absorption capacity by more than 100 times their mass. All of these can be considered as valuable reusable resources.
The problem of recycling baby diapers
So far, disposable diapers are mostly destined for landfill or incineration after the end of their life. Lately, some processes have been developed in order to mechanically recycle the different diapers components. However, this methodology has still some caveats regarding the complete separation of all the components, thus not allowing to retrieve highly pure materials. Furthermore, biological treatments by aerobic and anaerobic digestion were applied in order to obtain a reduced volume and a low moisture content. Nonetheless, the compost derived from the process is of low quality and difficult to commercialize.
Using Enzymes for Degradation
Enzymatic approaches ensure more specificity without damaging the valuable molecules. Therefore, enzymatic treatment of these substrates can be considered a powerful strategy for a complete economic circle solution. Due to the exciting results and the knowledge acquired with plastics and cellulose degradation, a new approach was developed to recycle diapers. A first cleaning step to remove the organic residues in diapers is widely known and can be considered as state of the art. The remaining mixture of cellulose fibres and plastic fibres forms the matrix that can be separated with the novel enzymatic procedure.
Cellulose fibres are broken down by enzymes to their basic compounds, glucose, and used in fermentative processes. This isolates the remaining plastic fibres, which can be wither re-granulated for reuse or be subjected to an enzymatic degradation process for recovery of valuable building blocks. Hence, the essential compounds deriving from the enzymatic separation of plastics can be used for production of polymers or as platform chemicals.
Ready for scale-up!
In conclusion, these enzymatic processes need to be developed and improved for industrial use. The focus is on the development and optimization of suitable enzymes with a view to commercial application. Enzymatic recycling of a fibre mixture has the advantages over chemical recycling that no toxic or hazardous chemicals need to be used and that the process is carried out at a maximum of 50°C. Unlike thermal recycling, no CO2 is produced. The recycling process is therefore a measure to slow down the effects of climate change.
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