Performance evaluation of an ex situ permeable reactive bio-barrier in phenol-contaminated water containment and remediation under a laminar flow regime

Petroleum hydrocarbons (PHCs) including phenolic compounds cause major environmental impacts just the once released into soils or groundwater. Among the core technologies, permeable reactive barriers (PRBs) have been so far exploited to contain and control such contaminants within the subsurface layers of the soil. Against this background, the present study investigated flow-biofilm interactions in a laboratory-scale permeable reactive bio-barrier (PRBB). To this end, an experimental setup was firstly built by embedding pressure measurement ports, at 10 cm intervals, onto a cylindrical column with a diameter of 57 mm and a height of 50 cm, and then filled with a porous medium, made up of sand with an average diameter of 1.78 mm. The bacterium, Pseudomonas putida (P. putida), was also utilized to generate the biofilm. Afterward, phenol-containing water was passed through the column at a rate of 2 L/h under a hydrodynamic laminar flow regime. Experimental evidence showed that the biofilm formed by bacterial growth could shrink the bio-barrier (BB) porosity from 0.35 to 0.07, instigating a drop by 590 and 840 times in the hydraulic pressure across the column at phenol concentrations, 200 and 400 mg/L, respectively. The desired biofilm additionally managed to remove 40 and 30% of phenol at concentrations of 200 and 400 mg/L, in that order. Exploring the variations in hydraulic conductivity in different layers plus the microscopic images further demonstrated that the biofilm created at phenol concentration of 200 mg/L seemed to be much stronger and even more stable, compared to the one at 400 mg/L. This was traceable to the better adaptation of P. putida to lower concentrations of phenol as the carbon source. Furthermore, the study results established that the given PRBB could help decompose only a small portion of phenol, but outperformed in terms of containing and controlling this contaminant through reducing hydraulic conductivity.

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