Photolysis of glutaraldehyde in brine: A showcase study for removal of a common biocide in oil and gas produced water.

Glutaraldehyde (GA) has been used extensively as a biocide in hydraulic fracturing fluid leading to its presence in oil and gas produced water. In this study, photolysis was used to degrade GA from brine solutions simulating produced water. Photolysis of GA was performed under ultraviolet (UV) irradiation. GA can be photolyzed by UV at all studied conditions with the efficiency ranging from 52 to 85% within one hour irradiation. Photolysis of GA followed pseudo-first order kinetics. A photolysis rate constant of GA at 0.1 mM in 200 g/L of salt at pH 7 was 0.0269 min-1 with a quantum yield of 0.0549 under 224 W illumination. The degradation rate of GA increased with increasing incident light intensity and decreasing pH. Increasing initial GA concentration resulted in decreasing degradation rate of GA. The degradation of GA was affected by salt concentration. At lower salt concentrations, notable retardation of GA photodegradation rate was observed while at higher salt concentrations GA photodegradation was improved compared to those without salt. OH was more dominant in sample without salt than sample with salt suggesting different photolytic mechanisms, indirect and direct photolysis, respectively. Oligomers were identified as the main photoproducts of GA photolysis.