Parameter Screening of PVDF/PVP Multi-Channel Capillary Membranes.

The increasing research in the field of polymeric multi-channel membranes has shown that their mechanical stability is beneficial for a wide range of applications. The more complex interplay of formation process parameters compared to a single-channel geometry makes an investigation using Design of Experiments (DoE) appealing. In this study, seven-channel capillary membranes were fabricated in a steam⁻dry⁻wet spinning process, while varying the composition of the polymer solution and the process temperatures in a three-level fractional factorial linear screening design. The polymers polyvinylidene flouride (PVDF) was the chemically resistant main polymer and polyvinylpyrrolidone (PVP) was added as hydrophilic co-polymer. Scanning electron microscopy and atomic force microscopy were applied to study the membrane morphology. Fabrication process conditions were established to yield PVDF/PVP multi-channel membranes, which reached from high flux (permeability P = 321.4 L / m 2 / h /bar, dextran 500 kDa retention R = 18.3%) to high retention (P = 66.8 L / m 2 / h /bar, R = 80.0%). The concentration of the main polymer PVDF and the molecular weight of the co-polymer PVP showed linear relations with both P and R. The permeability could be increased using sodium hypochlorite post-treatment, although retention was slightly compromised. The obtained membranes may be suitable for micro- or ultra-filtration and, at the same time, demonstrate the merits and limitations of DoE for multi-channel membrane screening.

Risk assessment to groundwater of pit latrine rural sanitation policy in developing country settings.

Parallel global rise in pit-latrine sanitation and groundwater-supply provision is of concern due to the frequent spatial proximity of these activities. Study of such an area in Malawi has allowed understanding of risks posed to groundwater from the recent implementation of a typical developing-country pit-latrine sanitation policy to be gained. This has assisted the development of a risk-assessment framework approach pragmatic to regulatory-practitioner management of this issue. The framework involves water-supply and pit-latrine mapping, monitoring of key groundwater contamination indicators and surveys of possible environmental site-condition factors and culminates in an integrated statistical evaluation of these datasets to identify the significant factors controlling risks posed. Our approach usefully establishes groundwater-quality baseline conditions of a potentially emergent issue for the study area. Such baselines are foundational to future trend discernment and contaminant natural attenuation verification critical to policies globally. Attribution of borehole contamination to pit-latrine loading should involve, as illustrated, the use of the range of contamination (chemical, microbiological) tracers available recognising none are ideal and several radial and capture-zone metrics that together may provide a weight of evidence. Elevated, albeit low-concentration, nitrate correlated with some radial metrics and was tentatively suggestive of emerging latrine influences. Longer term monitoring is, however, necessary to verify that the commonly observed latrine-borehole separation distances (29-58m), alongside statutory guidelines, do not constitute significant risk. Borehole contamination was limited and correlation with various environmental-site condition factors also limited. This was potentially ascribed to effectiveness of attenuation to date, monitoring of an emergent problem yet to manifest, or else contamination from other sources. High borehole usage and protective wall absence correlated with observed microbiological contamination incidence, but could relate to increased human/animal activity close to these poorly protected boreholes. Additional to factors assessed, a groundwater-vulnerability factor is recommended that critically relies upon improved proactive securing of underpinning data during borehole/latrine installations. On-going concerns are wide ranging, including poorly constrained pit-latrine input, difficulties in assessing in-situ plume natural attenuation and possible disposal of used motor oils to latrines.

Poly(piperazine-amide)/PES Composite Multi-Channel Capillary Membranes for Low-Pressure Nanofiltration.

The mechanical stability of conventional single-channel capillary fibres can be improved in a multi-channel geometry, which has previously found application in ultrafiltration. In this work, multi-channel polyethersulfone (PES) capillary membranes comprising seven feed channels were successfully fabricated in an enhanced steam⁻dry⁻wet spinning process and coated on the inner surface with a thin polyamide (PA) layer via interfacial polymerization (IP). The coating procedure consisted of impregnating the support multi-channel capillary membranes (MCM) with an aqueous piperazine solution, flushing with nitrogen gas to remove excess droplets, and pumping an organic trimesoylchloride solution through the channels. Insights into the interfacial polymerization process were gained through the investigation of various parameters, including monomer ratio, contact time, and drying time. Membranes were characterised via scanning electron microscopy (SEM), atomic force microscopy (AFM), and filtration experiments. The optimisation of both the PES support membrane and IP process parameters allowed for the fabrication of composite MCM with an MgSO4 rejection of 91.4% and a solute flux of 68.8 L m-2 h-1 at an applied pressure of 3 bar. The fabricated composite MCM demonstrates that a favourable multi-channel arrangement can be upgraded with a PA layer for application in low-pressure nanofiltration.