Photocatalysis and phosphorus drive organic production in algal-bacterial co-cultures treating oil sands process affected water.

Photocatalysis has been previously identified as an effective pre-treatment for biodegrading naphthenic acid fraction compounds (NAFCs) in oil sands process-affected water (OSPW), achieving mineralization rates unattainable by standalone methods. However, previous studies focused on bacteria cultures for biological treatment, overlooking the potential of algae-bacteria co-growth and its possible effects on enhancing mineralization. Thus, this study replicated those experiments under conditions that promote algal growth. Synthetic OSPW underwent photocatalytic pre-treatment for varying durations, followed by biological treatment in illuminated microcosms. Biostimulation, through phosphate addition, was also tested to determine its effect on accelerating mineralization. Photocatalytic pre-treatments of 24 h or longer created oligotrophic conditions, triggering the production of algal-derived organics, which released nutrients into the water and reduced mineralization rates during the biological treatment phase. Moreover, nutrient addition generally exacerbated these effects by promoting photosynthetic biomass growth. Nutrient-fixing and symbiotic microbes were identified, contributing to prolonged organic production phases. These phases of persistent organic generation could pose a risk of eutrophication, highlighting the need to mitigate light exposure during post-biological treatments. Under controlled light exposure, BPCs with biological treatments offer a scalable, energy-efficient solution for addressing complex industrial wastewater challenges, advancing the sustainable management of OSPW and similar hard-to-treat water sources.