A Biofilm Treatment Approach for Produced Water from Hydraulic Fracturing Using Engineered Microbial Mats

Abstract:

Hydraulic fracturing results in large volumes of wastewater, called “produced water”. Treatment of produced water is challenged by its high salt, organic compound, and radionuclide concentrations. Current disposal approaches include deep well injection and physical-chemical treatment for surface disposal; however, deep well injection has been recently linked to induced seismicity and physical-chemical treatments suffer from fouling and high cost. The reuse of the produced water has emerged as a desirable management option; however, this requires pretreatment to generate a water of usable quality and limit microbial activity. Biological treatment is an underexplored area in produced water management and has the potential to remove organics and reduce overall costs for physiochemical treatment or reuse. Suspended growth biological treatment techniques are known to be limited by salinity motivating a more robust biofilm approach: ‘microbial mats’.

In this study, we used engineered microbial mats as a biofilm treatment for the produced water. Evaluation of the biodegradation performance of microbial mats in synthetic and real produced waters showed microbial activity at up to 100,000 mg/L TDS concentration (three times the salt concentration of the ocean). Organic removal rates reached to 1.45 mg COD/gram_wet-day at 91,351 mg/L TDS in real produced water samples and initial evaluation demonstrated the potential for field-scale application. Metagenomic analyses of microbial mats demonstrated an adaptive shift in the microbial community treating different samples, suggesting the wide applicability of this treatment approach for produced waters with varying chemical composition. On-going studies focus on the evaluation of the removal of the organics and the contaminants of high concern in produced water using microbial mats as well as the effect of the biofilm growth conditions on the biodegradation in changing salt concentrations.