RSM-Based Optimization Approach for an Integrated Bioremediation–Electrokinetic System for Remediation of Petroleum Hydrocarbon-Contaminated Soils

Soil contamination by petroleum hydrocarbons is one of the global environmental challenges. This study presents an integrated bio-electrokinetic framework that enhances petroleum remediation in contaminated soils by combining bioremediation with an optimized electrokinetic system for improved TPH degradation. Therefore, a phytoremediation approach was developed using bermudagrass for soils contaminated with 1.5%, 3%, and 4.5% crude oil under different moisture conditions (field capacity, FC, 0.8FC, and 0.6FC), electric current of 0, 1.5, and 3 V cm -1 , and either 3%wt Pseudomonas fluorescens or a 3%wt combined application of dried Chlorella biomass and Pseudomonas fluorescens . The high R² values of the models indicated the satisfactory performance of Response Surface Methodology (RSM) in optimizing the effectiveness of the remediation system. The incorporation of desiccated Chlorella biomass alongside Pseudomonas fluorescens constitutes the core innovation of the proposed integrated bioremediation strategy, overcoming the logistical challenges associated with live algal cultures while enhancing microbial activity, facilitating passive biosorption and bioavailability of petroleum hydrocarbons, and improving soil water retention. The integrated bioelectric remediation approach showed superior TPH removal from soil (up to 65.60%, 75.63%, and 80.58% in soils with 4.5, 3, and 1.5%wt oil contamination, respectively) along with a significant increase in TPH accumulation in bermudagrass biomass, plant dry weight, and its resilience compared with those of their standalone approaches. To achieve the highest possible removal efficiency, the following optimal values were predicted: an electrical current of 3 V cm -1 , a biological treatment consisting of a 3%wt combined application of dried Chlorella biomass and Pseudomonas fluorescens , and moisture conditions of 80%, 100%, and 100% field capacity (FC) for 1.5%, 3%, and 4.5% contamination levels, respectively. Notably, continuous post-harvest plant regrowth and vitality highlighted the long-term restorative potential of the applied remediation approach and its capability to facilitate the uptake and processing of contaminants. In other words, this study proposes a practical, data-based, environmentally friendly, and scalable approach for the efficient remediation of petroleum hydrocarbon-contaminated soils.