A Two-Stage Bacterial and Phyco-Mycoremediation Approach for Produced Water Treatment: Optimization via Taguchi Experimental Design Methodology and FAME Analysis

Produced water (PW) from oil and gas operations is a complex wastewater that requires efficient, sustainable treatment. This study develops a two-stage process integrating bacterial pretreatment with phyco-mycoremediation to enhance pollutant removal and resource recovery. Rhodococcus opacus improves hydrocarbon biodegradability in the first stage, enabling enhanced downstream treatment by a Chlorella vulgaris - Aspergillus oryzae consortium (phyco-mycoremediation). Furthermore, process parameters for phyco-mycoremediation were optimized using a Taguchi L9 orthogonal array. Under optimized conditions, biomass production increased to 1.37 ± 0.02 g/L compared to 1.16 ± 0.08 g/L in unoptimized conditions. COD and oil and grease (O&G) removal reached 79.58 ± 2.55% and 98.25 ± 0.91%, respectively, exceeding those in nonoptimized conditions. The integrated system achieved overall removals of 85.88 ± 1.77% (COD) and 99.34 ± 0.34% (O&G), with strong agreement between predicted and experimental results. Enhanced performance is attributed to improved substrate bioavailability and synergistic microbial interactions, which were confirmed by GC–MS analysis. The resulting fuel properties showed balanced FAME composition, good ignition quality, adequate oxidative stability, and favorable cold-flow properties, demonstrating suitability for biodiesel production and applications. Overall, the integrated bacterial pretreatment and phyco-mycoremediation strategy provides a robust, resource-efficient, and scalable framework for treating complex PW streams.