Environmental pollution caused by produced water from petroleum extraction remains one of the most persistent and complex global challenges. This industrial byproduct typically contains a diverse mixture of hydrocarbons including aliphatic and polycyclic aromatic hydrocarbons (PAHs) alongside toxic heavy metals and high salinity, making its remediation technically demanding and economically burdensome. Traditional physicochemical methods, while effective in specific scenarios, are energy-intensive and often generate secondary pollutants, limiting their sustainability and large-scale applicability [1], [2].

Bioremediation has emerged as a promising eco-friendly alternative, leveraging the metabolic capabilities of hydrocarbon-degrading microorganisms to transform toxic pollutants into benign end products. Notably, bacterial strains such as Pseudomonas, Rhodococcus, and Alcanivorax have shown varying degrees of success in degrading petroleum hydrocarbons in aqueous environments [3], [4]. Among these, Alcanivorax borkumensis has drawn increasing interest due to its obligate hydrocarbonoclastic nature, genomic specialization in alkane catabolism, and capacity to produce surface-active biosurfactants that facilitate hydrocarbon emulsification and uptake [5], [6]. It possesses multiple alkane hydroxylases, including AlkB1, AlkB2, and P450 systems, enabling the degradation of a wide range of aliphatic hydrocarbons [7], [8]. These traits make A. borkumensis an ideal candidate for targeted bioremediation in marine and produced water environments. However, its practical application is often hindered by limitations such as slow degradation rates for complex hydrocarbons, limited access to hydrophobic pollutants, and variable survival under industrial effluent conditions [9].

In parallel, recent advances in nanotechnology have introduced a new class of photocatalytic materials capable of degrading recalcitrant organic compounds under light irradiation. Zinc oxide (ZnO) nanoparticles are widely studied in this context due to their high oxidative potential and low toxicity. However, their utility is restricted by a wide band gap (∼3.2 eV), low stability, and rapid recombination of photogenerated charge carriers [10], [11]. To overcome these limitations, researchers have introduced dopants such as lanthanum (La³⁺) into the ZnO matrix to enhance its photocatalytic activity under visible light and improve charge separation [12], [13]. Additionally, the incorporation of carbon-based nanostructures particularly graphene quantum dots (GQDs) has shown promise in stabilizing the nanocomposite, enhancing its surface area and facilitating electron mobility [14], [15]. GQDs also confer improved dispersion, light-harvesting ability, and surface functionality, which can benefit microbial interaction in hybrid systems [16].

Despite the independent promise of bioremediation and photocatalysis, very few studies have explored their combination in a unified treatment platform for produced water. Recent research has begun to investigate nano–bio hybrid systems, in which microbial degradation is supported by nanomaterials that either act as scaffolds, surfactants, or catalysts [17]. For instance, chitosan-functionalized lignin nanoparticles were shown to enhance bacterial adhesion and metabolic activity, but such systems lacked oxidative or photocatalytic functions [18]. Conversely, ZnO-based nanocomposites demonstrated high photocatalytic degradation of dyes but were not integrated with biological components, and their compatibility with sensitive bacterial species remained untested [19]. Recent findings indicate that nano–bio composites may enhance microbial colonization and pollutant bioavailability through surface roughness and charge effects [20], but long-term stability and biocompatibility still require further verification. Furthermore, electrochemical studies have shown that GQDs enhance charge separation and photostability when incorporated with ZnO-based nanomaterials, supporting sustained catalytic activity even under visible-light conditions [21]. Spectroscopic analyses such as FTIR and Raman have further confirmed strong interfacial bonding between GQDs and metal oxide matrices, which contributes to efficient electron mobility and pollutant adsorption [22], [23]. These properties suggest that GQD–ZnO systems could provide a favorable microenvironment for microbial attachment and synergistic degradation [24].

This knowledge gap provides a critical opportunity for innovation. The current study proposes a novel hybrid system that synergistically couples A. borkumensis with a nitrogen-doped GQDs/ZnO/La₂O₃ nanocomposite to remediate petroleum-contaminated produced water. The rationale for this system is grounded in several strategic design elements. First, A. borkumensis offers robust biodegradation of long-chain alkanes and natural biosurfactant production, which can emulsify hydrophobic hydrocarbons. Second, the ZnO/La₂O₃ nanocomposite provides photocatalytic degradation pathways for recalcitrant organics and enhances system robustness under varying physicochemical conditions. Third, the inclusion of GQDs increases biocompatibility, supports bacterial colonization, and facilitates electron transfer bridging the microbial and catalytic domains [25].

Accordingly, this study aims to isolate and characterize A. borkumensis from oilfield production equipment, synthesize a GQD-modified ZnO/La₂O₃ nanocomposite via hydrothermal and co-precipitation techniques, and integrate both into a hybrid platform. This system is evaluated for its ability to remove total petroleum hydrocarbons (TPHs), PAHs, and total organic carbon (TOC) from produced water, under varied environmental parameters. Through a combination of microbiological, physicochemical, and spectroscopic assessments, the study provides a detailed understanding of the degradation mechanisms, synergistic interactions, and potential for practical application.

Ultimately, this research introduces a new, environmentally compatible solution that merges biological specialization with catalytic innovation. It addresses a critical gap in the field of sustainable wastewater treatment and offers a scalable model for bio-nano systems tailored to petroleum remediation.