The Potential of super absorbent polymers from diaper wastes to enhance water retention properties of the soil

Abstract

The management of disposable diapers is a major problem. Moreover, light-textured soils are characterized by low water holding capacity and excessive drainage, thus significant portion of irrigation water is lost below the root zone. A laboratory study was conducted to evaluate the potential of recycling disposable baby diapers to conserve soil moisture in light-textures soils. The water absorbency [water absorption capacity (WAC) and water absorption rate (WAR)] of the recovered Super absorbent polymers (SAPs), from diapers, was evaluated and described under different ionic solute strengths (0.0, 0.5, 1.0, 2.0, 3.0 and 4.0 dS m) at different time periods. Additionally, several swelling measurements of the SAPs were determined when added to sandy clay loam soil using different levels [0.0, 0.4, 0.6, 0.8 and 1.6% (w/w)] for five rewetting cycles (over a period of 6 months). As the swelling time increased, the WAC increased, while WAR decreased. However, both WAC and WAR were reduced as the solution salinity increased. The recovered SAPs exhibited WAC of 311.0 and 111.0 g g in solution of 0.0 and 3.0 dS m, respectively. Polynomials functions were used to calculate the equilibrium time and threshold solute concentration for the SAPs. The average equilibrium time was 4.5 minutes and the threshold solute concentration was 2.78 dS m. At SAPs concentration of 1.6%, the water retained by the soil increased by 2.6 folds. The specific amount of water retained (SWR) by SAPs in the SAPs-soil mixture was decreased with repeating wetting, thus, after 6 months, the average WHC of the soil was decreased by 14% compared to initial wetting. The recycling of baby diapers might have a great potential to conserve soil moisture in light soils using water of good quality. However, since the SAPs in diapers are Na based, further research is needed to explorer the impact of such treatment on soil chemical properties.