Biodegradability of Gel-Forming Superabsorbents for Soil Conditioning: Kinetic Assessment Based on CO2 Emissions

Abstract

Quantification of the biodegradability of soil water superabsorbents is necessary for a reasonable prediction of their stability and functioning. A new methodological approach to assessing the biodegradability of these polymer materials has been implemented on the basis of PASCO (USA) instrumentation for continuous registration of kinetic CO2 emission curves in laboratory incubation experiments with various hydrogels, including the well-known trade brands Aquasorb, Zeba, and innovative Russian Aquapastus composites with an acrylic polymer matrix. Original kinetic models were proposed to describe different types of respiratory curves and calculate half-life indicators of the studied superabsorbents. Comparative analysis of the new approach with the assessment by biological oxygen demand revealed for the first time the significance of CO2 dissolution in the liquid phase of gel structures during their incubation. Experiments have shown a tenfold reduction in half-life up to 0.1–0.3 years for a priori non-biodegradable synthetic superabsorbents under the influence of compost extract. The incorporation of silver ions into Aquapastus innovative composites at a dose of 0.1% or 10 ppm in swollen gel structures effectively increases their stability, prolonging the half-life to 10 years and more, or almost twice the Western stability standard for polymer ameliorants.