Pilot-scale foam and cast-coated nanocellulose filters for water treatment

Abstract

AbstractA large variety of substances, for instance heavy metal ions from different sources including mining, industry, and agricultural activities, pollute fresh water sources. Bio-based adsorbents, such as cellulose nanofibers (CNF), have recently been introduced in the process of treating water to remove hazardous pollutants primarily owing to their natural abundance, non-toxicity, and renewability. Surface modification of CNF, e.g. by catalytically oxidising the primary C6-OH groups of CNF selectively into carboxylic (COO−) groups with TEMPO, yields materials that are effective in adsorbing positively charged heavy metal ions, e.g. Cu ions. However, to utilise CNF in continuous processes beyond static, batch-wise adsorption, in particular on (pre-)industrial scale, they need to be immobilised on filter substrates in thin layers and an efficient manner. In this work, we report bio-adsorbent-based filters prepared by coating TEMPO-CNF on viscose filters using two different pilot-scale coating approaches, foam and cast coating. The performance of TEMPO-CNF filters was evaluated in terms of their water permeance as well as adsorption of metal ions including Cu(II) and Ca(II). By foam coating thin layers could be fabricated in a time efficient way facilitating high adsorption capacities (52 mg g−1), whilst by cast coating higher amounts of TEMPO-CNF could be deposited allowing for adsorbing higher absolute amounts (280 mg m−2) of heavy metal ions. Graphical abstract