Separation of Volatile Fatty Acids from Model Anaerobic Effluents Using Various Membrane Technologies

Abstract

Effluents of anaerobic processes still contain valuable components, among which volatile fatty acids (VFAs) can be regarded and should be recovered and/or used further in applications such as microbial electrochemical technology to generate energy/energy carriers. To accomplish the separation of VFAs from waste liquors, various membrane-based solutions applying different transport mechanisms and traits are available, including pressure-driven nanofiltration (NF) and reverse osmosis (RO) which are capable to clarify, fractionate and concentrate salts and organics. Besides, emerging techniques using a membrane such as forward osmosis (FO) and supported liquid membrane (SILM) technology can be taken into consideration for VFA separation. In this work, we evaluate these four various downstream methods (NF, RO, FO and SILM) to determine the best one, comparatively, for enriching VFAs from pH-varied model solutions composed of acetic, butyric and propionic acids in different concentrations. The assessment of the separation experiments was supported by statistical examination to draw more solid conclusions. Accordingly, it turned out that all methods can separate VFAs from the model solution. The highest average retention was achieved by RO (84% at the applied transmembrane pressure of 6 bar), while NF provided the highest permeance (6.5 L/m2hbar) and a high selectivity between different VFAs.

Advances and Applications of Hollow Fiber Nanofiltration Membranes: A Review

“…There are many other examples of acids that are valuable enough to be recovered. Recent research showed that PEM HF NF membranes (dNF40 NX Filtration) can also be used for the separation of volatile fatty acids (VFA) from anaerobic effluents [180]. The recovered VFAs can be used not only in the chemical industry for the synthesis of, among other things, ketones, esters and alcohols, but also in the textile industry.…”

Impact of the Recovery on Concentrating Acetic Acid with Low-Pressure Reverse-Osmosis Membranes

“…At higher pressure, the retention of acetate is slightly higher and remains practically constant (88%) throughout the range of CF (Figure 5). A lower retention (75%) was obtained by Bóna et al with LPRO membrane at the same pH, although at lower pressure of 6 bar [17]. Choi et al also observed lower acetic retentions at pH 5.5; however, looser NF membranes were used in their study [10].…”

“…The pH was 5.4 ± 0.1, and the electrical conductivity was 17 ± 0.5 mS/cm. It was decided to use only acetic acid because previous works showed that its retention is equal or smaller than that of other relevant VFAs such as propionate, butyrate, and lactate [17,25]. At this pH, acetate accounts for 80% of total acetic acid, according to the Henderson-Hasselbalch equation.…”

“…For instance, acetic acid is retained 11.5% and 7.8% more, when it is mixed with butyric and propionic acid, respectively [16]. Bóna et al performed a statistical analysis on several runs of filtration of mixtures containing acetic, propionic, and butyric acid using NF and LPRO membranes [17]. As expected, NF showed higher permeability (4.2 L/(m 2 h bar)) and lower retentions (on average 50%, 64%, and 74% for acetic, propionic, and butyric acid, respectively) compared to LPRO (2.5 L/(m 2 h bar), 80% retention for acetic, and 84% for propionic and butyric acid) and was more susceptible to changes in the pH.…”

State-of-the-Art Organic- and Inorganic-Based Hollow Fiber Membranes in Liquid and Gas Applications: Looking Back and Beyond

“…Hollow fiber NF membranes have been widely used in various applications such as wastewater treatment [ 231 , 232 ], food and beverage industry [ 233 , 234 ], chemical and petrochemical industry [ 235 , 236 , 237 , 238 , 239 ], and biorefinery [ 240 , 241 ]. Dynamic deposition technology was introduced to develop robust membranes under real-time performance monitoring.…”