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CURATOR
A pinboard by
Shardul Wadekar

PhD Student, University of Pittsburgh

PINBOARD SUMMARY

Recovery of products suitable for industrial reuse from adandoned mine drainage using nanofiltration

Wastewater treatment and desalination is one of the most important aspects in environmental and chemical engineering and the use of membranes is helping to exploit this field to the greatest horizons. My research is specifically related to nanofiltration (NF) membranes: understanding their separation characteristics and quantifying their separation mechanisms as well as applying these membranes for the recovery of different types of waste waters. For the IDA world congress, I will be focussing my presentation on the recovery of abandoned mine drainage (AMD) using NF membranes. Because of the problems with sludge formation and inability to meet water reuse standards with traditional limestone neutralization, NF was evaluated for treatment of AMD. This study contributes to the process of selecting NF membranes based on laboratory-scale studies that is validated in pilot-scale system with real AMD under relevant process conditions to recover: (1) treated water stream (NF permeate) that can serve as a substitute for fresh water in industrial applications, and (2) concentrated sulfate stream (NF reject) that is well-suited to control divalent cations in the produced water from unconventional gas extraction by sulfate precipitation and enable its reuse for hydraulic fracturing of subsequent wells. Eight commercially available NF membranes were tested with synthetic and real AMD in laboratory-scale dead-end and cross-flow membrane filtration modules. NF90 membrane was selected for pilot-scale study that consisted of aeration and sedimentation for iron control, bag filtration and ultrafiltration for particulate control and NF. The system was operated for 208 hours using real AMD at 10 bar and 3.5 GPM feed flow rate and consistently achieved more than 98% removal of TDS at 57% water recovery with a nominal pressure drop of 1.7 bar. Pressure drop monitoring and water permeability tests post pilot-scale study along with chemical equilibrium calculations indicated that no fouling/scaling of the membranes occurred. Thus, along with providing insights about NF membranes for treatment of AMD, this study provides valuable information for the recovery of products from AMD for industrial reuse.

3 ITEMS PINNED

Fouling in Direct Contact Membrane Distillation of Produced Water from Unconventional Gas Extraction

Abstract: Hydraulic fracturing used for natural gas extraction from unconventional onshore resources generates large quantities of produced water that needs to be managed efficiently and economically to ensure sustainable development of this industry. Membrane distillation can serve as a cost effective method to treat produced water due to its low energy requirements, especially if waste heat is utilized for its operation. This study evaluated the performance of commercially available hydrophobic microfiltration membranes in a direct contact membrane distillation system for treating very high salinity (i.e., up to 300,000 mg/L total dissolved solids) produced water. Polypropylene and polytetrafluoroethylene membranes yielded the highest permeate flux with membrane distillation coefficient of 5.6 l/m2/hr/kPa (LMH/kPa). All membranes showed excellent rejection of dissolved ions, including naturally occurring radioactive material (NORM), which is a significant environmental concern with this high salinity wastewater. Analysis of membranes after extended testing with actual produced waters revealed unevenly distributed inorganic deposits with significant iron content. A key finding of this study is that the iron oxide fouling layer had negligible effect on membrane performance over extended period of time despite its thickness of up to 12 μm. The results of this study highlight the potential for employing membrane distillation to treat high salinity wastewaters from unconventional gas extraction.

Pub.: 27 Nov '16, Pinned: 30 Jun '17

Laboratory and Pilot-Scale Nanofiltration Treatment of Abandoned Mine Drainage for the Recovery of Products Suitable for Industrial Reuse

Abstract: Because of the problems with sludge formation and inability to meet water reuse standards with traditional limestone neutralization, nanofiltration (NF) has been evaluated for treatment of abandoned mine drainage (AMD). This study contributes to the process of selecting NF membranes based on laboratory-scale studies that is validated in pilot-scale system with real AMD under relevant process conditions to recover: (1) treated water stream (NF permeate) that can serve as a substitute for fresh water in industrial applications and (2) concentrated sulfate stream (NF reject) that is well-suited to control divalent cations in the produced water from unconventional gas extraction by sulfate precipitation and enable its reuse for hydraulic fracturing of subsequent wells. Eight commercially available NF membranes were tested with synthetic and real AMD in laboratory-scale dead-end and cross-flow membrane filtration modules. NF90 membrane was selected for pilot-scale study that consisted of aeration and sedimentation for iron control, bag filtration and ultrafiltration for particulate control and NF. The system was operated for 208 h using real AMD at 10 bar and 3.5 GPM feed flow rate and consistently achieved more than 98% removal of TDS at 57% water recovery with a nominal pressure drop of 1.7 bar. Pressure drop monitoring and water permeability tests post pilot-scale study along with chemical equilibrium calculations indicated that no fouling/scaling of the membranes occurred.

Pub.: 02 Jun '17, Pinned: 30 Jun '17

Influence of active layer on separation potentials of nanofiltration membranes for inorganic ions.

Abstract: Active layers of two fully aromatic and two semi-aromatic nanofiltration membranes were studied along with surface charge at different electrolyte composition and effective pore size to elucidate their influence on separation mechanisms for inorganic ions by steric, charge and dielectric exclusion. The membrane potential method used for pore size measurement is underlined as the most appropriate measurement technique for this application owing to its dependence on the diffusional potentials of inorganic ions. Crossflow rejection experiments with dilute feed composition indicate that both fully aromatic membranes achieved similar rejection despite the differences in surface charge, which suggests that rejection by these membranes is exclusively dependent on size exclusion and the contribution of charge exclusion is weak. Rejection experiments with higher ionic strength and different composition of the feed solution confirmed this hypothesis. On the other hand, increase in the ionic strength of feed solution when the charge exclusion effects are negligible due to charge screening strongly influenced ion rejection by semi-aromatic membranes. The experimental results confirmed that charge exclusion contributes significantly to the performance of semi-aromatic membranes in addition to size exclusion. The contribution of dielectric exclusion to overall ion rejection would be more significant for fully aromatic membranes.

Pub.: 18 Apr '17, Pinned: 30 Jun '17