Feasibility of microbial-induced calcite precipitation in soils polluted by hydrocarbons

Abstract

Microbial-Induced Calcite Precipitation (MICP) is an effective bioremediation method for heavy metals, which often co-exist with organic pollutants in soils. Organic pollutants such as hydrocarbons inhibit soil urea hydrolysis critical in MICP whilst its feasibility in such enviroments is poorly understood. This study presents an investigation on the potential of biostimulation and bioaugmentation of MICP in soils polluted by polycyclic aromatic hydrocarbons (PAH) and their effect on ureolyisis at cell and enzyme level. Biostimulation of urea hydrolysis by soil autochthonous ureolytic bacteria was not detected over 62 days. Flow cytometry revealed Sproposarcina pasteurii at initial OD₆₀₀ = 0.01 was able to grow in soil water extracts of increasing hydrocarbon concentration (TOC = 0.035–35 mg L⁻¹), showing no negative effects on cell membrane stability. Urease activity assays in soil water extracts inoculated with S. pasteurii (OD₆₀₀ = 0.01 and 1) and soybean Glycine Max urease enzyme (1 and 100 g L⁻¹) indicated hydrocarbons negative effect on cell and enzyme urease activity was dependant on hydrocarbon and cell/enzyme concentrations, indicating the mechanism of inhibition was competitive. Glycine Max urease activity was unaffected at 100 g L⁻¹ but at 1 g L⁻¹ decreased with increasing hydrocarbon concentration up to 61%, whilst S. pasteurii urease activity (OD₆₀₀ = 1) readily decreased at the lowest hydrocarbon concentration (TOC = 0.35 mg L⁻¹) to an overall reduction of 31% at the highest TOC concentration. Bioaugmentation of S. pasteurii (OD₆₀₀ = 1) inoculated in the soil matrix successfully hydrolysed urea within 24 h. These results evidence for the first time the ability of model MICP bacteria S. pasteurii to grow and maintain relevant metabolic ureolytic activity in soils significantly polluted by PAH.