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Nanofiltration of treated digested agricultural wastewater for recovery of carboxylic acids

Zacharof, Myrto-Panagiota, Mandale, Stephen J., Williams, Paul M., Lovitt, Robert W.
Journal of cleaner production 2016 v.112 pp. 4749-4761
acetates, acetic acid, butyric acid, effluents, microfiltration, nanofiltration, pH, sodium bicarbonate, sodium chloride, wastewater, Japan, United States
Synthetic solutions of varying concentrations of carboxylic acids, namely acetic and butyric acids (50 mM, 100 mM) and treated digested agricultural wastewater with a carboxylic acids concentration of 21.08 mM of acetic acid and 15.81 mM of butyric acid were processed with a range of nanofiltration membranes and enrichment schemes to concentrate carboxylic acids. The study was conducted with the scope of platform chemicals recovery from complex effluents, investigating the feasibility of nanofiltration as a method of choice. Membrane filtration is easily scalable into various arrangements, allowing versatility in operation and enrichment treatments, which other recovery practices such as liquid extraction do not allow. Among the five nanofiltration membranes used (NF270 (Dow Chemicals, USA), HL, DL, DK (Osmonics, USA), LF10 (Nitto Denko, Japan)) the DK, DL and NF270 were identified as the best candidates for carboxylic acids separation and concentration from these complex effluents, both in terms of retention and permeate flux. These membranes achieved retention ratios, up to 75% giving retentates up to 53.94 mM acetate and 28.38 mM butyrate for the agricultural wastewater. Effluents were modified by the addition of alkali and salts (sodium chloride and sodium bicarbonate), and it was found that highest productivity, retention and flux was achieved at pH 7 but at higher pH there was a significant reduction in flux.