Granular activated carbon (GAC) fixed bed adsorption combined with ultrafiltration for shale gas wastewater internal reuse.

Membrane processes are widely applied in shale gas flowback and produced water (SGFPW) reuse. However, particulate matters and organic matters aggravate membrane fouling, which is one of the major restrictions on SGFPW reuse. The present study proposed fixed bed adsorption using granular activated carbon (GAC) combined with ultrafiltration (UF) for the first time to investigate the treatment performance and membrane fouling mechanism. The adsorption of GAC for SGFPW was best described by the Temkin isotherm model and the pseudo-second-order kinetic model. GAC fixed bed pretreatment with different empty bed contact times (EBCT) (30, 60 and 90 min) showed the significant removal rate for dissolved organic carbon (DOC) and turbidity, which was 34.7%-42.4% and 98.1%-98.9%, respectively. According to characterization of UF membrane fouling layer, particulate matters and organic matters caused major part of membrane fouling. After being treated by GAC fixed bed, total fouling index (TFI) and hydraulic irreversible fouling index (HIFI) respectively decreased by more than 32.5% and 18.3% respectively, showing the mitigation effect of GAC fixed bed on membrane fouling. According to the XDLVO theory, GAC fixed bed also mitigated membrane fouling by reducing the hydrophobic interactions between the foulants and the UF membrane. The integrated GAC fixed bed-UF process produced high-quality effluents that met the water quality standards of SGFPW internal reuse, which was an effective technology of the SGFPW reuse.

Tracing microplastics in rural drinking water in Chongqing, China: Their presence and pathways from source to tap.

Despite the significant attention given to microplastics in urban areas, our understanding of microplastics in rural drinking water systems is still limited. To address this knowledge gap, we investigated the presence and pathways of microplastics in rural drinking water system, including reservoir, water treatment plant (WTP), and tap water of end-users. The results showed that the treatment processes in the WTP, including coagulation-sedimentation, sand-granular active carbon filtration, and ultrafiltration, completely removed microplastics from the influent. However, the microplastic abundance increased during pipe transport from WTP to residents' homes, resulting in the presence of 1.4 particles/L of microplastics in tap water. This microplastic increase was also observed during the transportation from the reservoir to the WTP, suggesting that the plastic pipe network is a key source of microplastics in the drinking water system. The main types of polymers were PET, PP, and PE, and plastic breakdown, atmospheric deposition, and surface runoff were considered as their potential sources. Furthermore, this study estimated that rural residents could ingest up to 1034 microplastics annually by drinking 2 L of tap water every day. Overall, these findings provide essential data and preliminary insights into the fate of microplastics in rural drinking water systems.