Natural polysaccharide polymer network for sustained nutrient release to stimulate the activity of aromatic hydrocarbon-degrading indigenous microflora present in groundwater

Abstract

Aromatic hydrocarbons (AHs) are known to contaminate groundwater with low indigenous microorganism populations and limited nutrient substrates for degradation reactions, resulting in weak natural remediation abilities of groundwater ecosystems. In this study, we aimed to utilize the principles of AH degradation by microorganisms to identify effective nutrients and optimize nutrient substrate allocation through actual surveys of AH-contaminated sites and microcosm experiments. Building on this, using biostimulation and controlled-release technology, we developed a natural polysaccharide-based encapsulated targeted bionutrient (SA-H-CS) that is characterized by easy uptake, good stability, controllable slow-release migration, and longevity to stimulate indigenous microflora in groundwater to efficiently degrade AHs. Results showed that SA-H-CS is a simple overall dispersion system, and nutrient components diffuse readily through the polymer network. The crosslinking of SA and CS resulted in a more compact structure of the synthesized SA-H-CS, effectively encapsulating the nutrient components and extending their active duration to >20 days. SA-H-CS improved the degradation efficiency of AHs and prompted microorganisms to maintain a high degradation rate (i.e., above 80 %) even in the presence of high concentrations of AHs, particularly naphthalene and O-xylene. Under SA-H-CS stimulation, microorganisms grew rapidly, and the diversity and total number of species of microflora increased significantly, with a notable increase in the proportion of Actinobacteria in the microbial community primarily due to the increased abundance of Arthrobacter, Rhodococcus, and Microbacterium, which are capable of degrading AHs. Concurrently, there was a notable enhancement in the metabolic function of the indigenous microbial communities responsible for AH degradation. SA-H-CS injection facilitated the delivery of nutrient components into the underground environment, improved the conversion ability of inorganic electron donors/receptors in the indigenous microbial community system, and strengthened the co-metabolism mechanism among microorganisms, achieving the goal of efficient AH degradation.