(255f) The composition of fracturing chemicals plays a key role in membrane fouling by flowback and produced waters from hydraulic fracturing

Sustainable wastewater management is critical to minimize the environmental impacts of high-volume hydraulic fracturing (HVHF). Membrane treatment provides a more sustainable option than current practices (e.g., reuse or direct disposal), but severe membrane fouling by this complex stream limits application. The key fouling components in HVHF wastewater have not yet been clearly identified and characterized. We first investigated actual wastewaters collected from different wells in the Marcellus Shale Play, and observed severe fouling of a commercial polyvinylidene fluoride microfiltration membrane by all raw waters with a large range of fouling indices ranging from 29-1300 m-1. Surprisingly, no correlation was observed between fouling indices with the level of total organic carbon or suspended solids, suggesting the lack of a consistent fouling mechanism and a large variation in water quality that is hard to resolve with current analytical tools. By deploying a synthetic slickwater fracturing fluid, formed by reacting with shale under deep subsurface conditions (e.g., 80℃, 83 bar, 24 h), we generated a range of synthetic wastewaters using varying compositions of slickwater fracturing chemical additives. These resulted in membrane fouling with fouling indices of 0.1 to 2000 m−1, which is similar in range to actual wastewaters. More importantly, we identified that high molecular weight (MW) polyacrylamide (107 Da, used as a friction reducer) was the predominant foulant during microfiltration, compared to all other organic additives (e.g, surfactants). Polyacrylamide was also found to be degraded chemically and mechanically as a function of shale mineralogy, fracturing conditions, and fluid compositions. Ultimately, we present correlations between the measured fouling index and the peak MW and concentration of the high MW components in the synthetic wastewater. These results highlight the importance of polymer and its degradation products in fouling of subsequent membrane systems, providing insights that can help in the development of effective treatment processes for hydraulic fracturing wastewater.