On the Possibility to Reuse Superabsorbent Gels from Baby Diapers for Water Retention in Agriculture—Effect of Gel Washing and Sterilization

Global water scarcity and increasing amount of polymer waste pose two major environmental challenges that require urgent attention. One approach to addressing both these issues consists of the reuse of superabsorbent polymer (SAP) gels derived from baby diaper waste for water retention in agriculture. The present study aims to compare the water retention properties of three types of diaper SAP gels soaked with artificial urine with agrogel Aquasorb on two different soil substrates: sand and light loam. The soil hydrological constants were estimated using water retention curves obtained by equilibrium centrifugation of soil/gel mixtures containing 0.5 vol% gel. It was observed that the diaper gels soaked with artificial urine have almost the same degree of swelling and provide the same range of water available to plants as agricultural gel Aquasorb treated with the same urine—the effect of all the studied gels being more pronounced in a sand substrate. Washing from urine followed by sterilization enhances the gel swelling and water range available for plants, making these characteristics higher than those of agrogel. The water-retention properties of the sand/gel mixtures were maintained during several wetting/drying cycles. Moreover, the sterilized diaper gels similar to Aquasorb can restructure the sand substrate, reducing the pore volume, which makes them have potential to improve the erosion resistance of soil. The addition of GooN diaper gel to loamy soil improved the seedling growth of mustard (Brassica juncea L.) in a similar way to the agricultural gel Aquasorb and did not cause phytotoxic effects. Furthermore, the impact of diaper gels on seed germination was even greater than that of Aquasorb. Given these properties, diaper gels hold high potential for improving soil water retention and plant water availability, making them a promising alternative to traditional agricultural SAP products like Aquasorb.