Effects of Slip Length and Inertia on the Permeability of Fracture with Slippery Boundary Condition.

Although the slippery boundary condition (BC) has been validated to enhance fracture permeability (k), the coupling effects of heterogeneous slippery BC and inertia on k remain less understood. We used computational fluid dynamics to investigate the competing roles of slippery BC and inertial forces in controlling k evolution with increasing pressure gradient by designing six cases with different slip length scenarios for a two-dimensional natural fracture. Our results suggest that pronounced inertial effects were directly related to and demonstrated by the growth of recirculation zone (RZ); this caused flow regimes transitioning from Darcy to non-Darcy and significantly reduced k, with an identical tailing slope for six cases, regardless of the variability in slip lengths. Moreover, the slippery BC dominantly determine the magnitude of k with orders depending on the slip length. Lastly, our study reveals that the specific k evolution path for the case with a varying slip length was significantly different from other cases with a homogeneous one, thus encouraging more efforts in determining the slip length for natural fractures via experiments.

Biodegradation of carbon tetrachloride from groundwater in an upflow solid-phase biofilm system.

In the present study, an upflow solid-phase denitrification biofilm reactor (US-DBR) was applied for simultaneous carbon tetrachloride (CT) and nitrate removal from groundwater by using poly(butylene succinate) (PBS) as carbon source and biocarrier. After 80 days continuous operation, the nitrate and CT removal efficiencies in the biofilm reactor were high of 98% and 94.3%, respectively. After PBS-biofilm formation, protein (PN) content in loosely bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS) significantly increased 2.6 and 4.0 times higher in the presence of CT than those of absence of CT, while PS increased 1.9 and 2.0 times higher. According to excitation-emission matrix (EEM), CT exposure contributed to the increased fluorescent intensities of the aromatic PN-like and tryptophan PN-like substances. Along with the height of US-DBR, the denitrification activity was inhibited by the CT exposure, and most of CT was significant transformed accompanied by nitrate removal. Two components of soluble microbial products (SMP) were identified, including humic-like substances for component 1 and PN-like substances for component 2, respectively. It was found from high-throughput 16S rRNA gene sequencing analysis that significant differences were observed at genus level by taxonomic assignments to CT exposure. Thiobacillus, Thauera, Candidatus_Competibacter and Hydrogenophaga were the main genus in the presence of CT at the proportion of 6.77%, 5.47%, 3.59% and 3.17%, respectively.