Use of Acid Mine Drainage in Recycling of Marcellus Shale Flowback Water: Solids Removal and Potential Fouling of Polymeric Microfiltration Membranes

摘要

Flowback water generated by hydraulic fracturing during shale gas reservoir stimulation can be reused for subsequent fracturing process. Acid mine drainage (AMD) is a potential water source that could alleviate low flowback water recovery by serving as a makeup water. AMD located near gas wells can be mixed with flowback water (Mixture 1 and 2), resulting in precipitation of barium sulfate. The feasibility of microfiltration to separate solids from two sets of mixtures of AMD and flowback water was evaluated using a bench-scale set-up. Hydrophilic polyvinylidene fluoride (PVDF) membranes with a pore size of 0.22 m were used in the experiments. udSevere membrane fouling occurred early during Mixture 1 filtration, while no significant fouling occurred for Mixture 2. Particle size distribution analysis and fouling mechanism identification of the two mixtures were performed to understand the cause of membrane fouling. udThe dominant fouling mechanisms in the early stages of Mixture 1 filtration were standard blocking (pore constriction) and complete blocking (pore blocking) caused by particles in the flowback water with size in the range of membrane pore diameter. On the contrary, no significant standard blocking or complete blocking was found during the filtration of Mixture 2, which was due to the fact that most particles in Flowback water B or Mixture 2 were larger than the membrane pore diameter. udAdditional filtration experiments were conducted using two barium sulfate solutions containing an order of magnitude difference in precipitate concentration. Identical permeate flux behavior were observed in both experiments. Therefore, precipitated had limited impact on membrane fouling. udAs an alternative to membrane filtration, coagulation with aluminium chloride and ferric chloride followed by sedimentation was investigated for turbidity and total organic carbon (TOC) removal. Ferric chloride dosage of 30mg/L at pH=6 for Mixture 1 and 20mg/L at pH=6 for Mixture 2 were found to be optimal coagulation parameters that could achieve similar turbidity and TOC removal (around 90%) as membrane filtration. udThis study has shown that membrane filtration has the potential to replace conventional coagulation – flocculation – sedimentation process for flowback water treatment for solids removal, but its efficiency depends on the flowback water quality.ud