Experimental treatment of oil-contaminated soil structure using vermiculture

Soil contamination with petroleum hydrocarbons represents one of the most critical environmental challenges in oil-producing regions of Kazakhstan, where approximately 59% of total oil-related soil pollution is concentrated in the Atyrau Region, with the total area of contaminated land exceeding 194,000 ha. This study investigated the potential of vermiculture-based bioremediation using Californian red worms (Eisenia fetida) and native wild earthworms (Lumbricus terrestris) for the restoration of petroleum-contaminated soils under controlled laboratory conditions. Experiments were conducted over a 90-day period using artificially contaminated soil samples with total petroleum hydrocarbons (TPH) concentrations of 0.5%, 1.0%, and 2.0%, supplemented with organic amendments. Physicochemical parameters – including pH, organic matter content, TPH levels, and microbiological activity – were monitored at regular intervals throughout the experimental period. Biometric assessments recorded changes in worm survival rate, biomass, and population dynamics. Key macronutrients (nitrogen, phosphorus, potassium), carbon-to-nitrogen (C : N), and temperature variations were determined using standardized laboratory methods. The central mechanism of remediation relied on the synergistic interaction between earthworm gut-associated microbiota and indigenous hydrocarbon-oxidizing soil bacteria, which collectively facilitated biochemical cleavage of hydrocarbon chains. The results demonstrated that vermiculture application facilitated TPH degradation of 60–80%, with the highest remediation efficiency observed in treatments involving Eisenia fetida, which maintained an optimal C : N ratio and the greatest microbiological activity throughout the experiment. Zooremediation significantly enhanced soil microbiological activity, improved physicochemical soil properties, and increased the concentration of plant-available nutrients in the treated substrate. The findings suggest that vermiculture constitutes an environmentally sound, cost-effective, and scalable bioremediation technology with strong potential for large-scale application in petroleum-impacted regions of Kazakhstan.