Capillary Nanofiltration under Anoxic Conditions as Post-Treatment after Bank Filtration

Abstract

Bank filtration schemes for the production of drinking water are increasingly affected by constituents such as sulphate and organic micropollutants (OMP) in the source water. Within the European project AquaNES, the combination of bank filtration followed by capillary nanofiltration (capNF) is being demonstrated as a potential solution for these challenges at pilot scale. As the bank filtration process reliably reduces total organic carbon and dissolved organic carbon (DOC), biopolymers, algae and particles, membrane fouling is reduced resulting in long term operational stability of capNF systems. Iron and manganese fouling could be reduced with the possibility of anoxic operation of capNF. With the newly developed membrane module HF-TNF a good retention of sulphate (67–71%), selected micropollutants (e.g., EDTA: 84–92%) and hardness (41–55%) was achieved together with further removal of DOC (82–87%). Fouling and scaling could be handled with a good cleaning concept with acid and caustic. With the combination of bank filtration and capNF a possibility for treatment of anoxic well water without further pre-treatment was demonstrated and retention of selected current water pollutants was shown.

Advances and Applications of Hollow Fiber Nanofiltration Membranes: A Review

“…This is especially an issue for spiral-wound modules, which are prone to (bio)fouling and have limited cleaning possibilities [12]. HF NF membranes have been named as a promising alternative [20,43], since they offer the advantage to combine the beneficial cleaning conditions of HF UF membranes with the separation efficiency of spiral-wound modules.…”

“…In 2018, Jährig et al upgraded the commercially available HFW 1000 membrane (Pentair X-Flow) with specific extra coatings to increase the retention capabilities and investigated the performance for sulfate removal in a pilot-scale set-up on well water with elevated sulphate concentration [43]. Pilot operation at a flux of 22.5 L•m −2 h −1 and a recovery of 75% resulted in sulfate removal of 67%.…”

Effect of TiO2 Nanoparticles on Capillary-Driven Flow in Water Nanofilters Based on Chitosan Cellulose and Polyvinylidene Fluoride Nanocomposites: A Theoretical Study

“…The flow of water on both sides, superior and inferior, of the membrane is governed by gravity (from top to bottom). However, the flow of water throughout the NF membrane is driven by action of capillary pressure which depends on the wettability [ 17 , 35 ].…”

“…However, when the force of adhesion is greater than the cohesion force of water molecules and it forms a concave meniscus with contact angle less than 90° ( Figure 2 b), water molecules tend to penetrate spontaneously into nanopores [ 38 ]. This latter situation is defined as the capillary-driven flow known as spontaneous imbibition [ 17 , 18 , 19 , 35 ].…”

“…The flow of water on both sides, superior and inferior, of the membrane is governed by gravity (from top to bottom). However, the flow of water throughout the NF membrane is driven by action of capillary pressure which depends on the wettability [17,35]. In fact, at normal conditions of temperature and pressure, the spontaneous flow of the water across porous structure is determined by an interplay of surface and gravity In fact, at normal conditions of temperature and pressure, the spontaneous flow of the water across porous structure is determined by an interplay of surface and gravity forces.…”