Investigation of membrane processes for the removal of volatile fatty acids

Abstract

The accumulation of volatile fatty acids such as acetic acid can cause reactor pH problems and the inhibition of microorganisms utilised in anaerobic digestion processes. A cross-flow membrane process using Teflon and ion-exchange membranes was investigated as a means of separating acetic acid from pure acetic acid solution and rumen fluid. Acetic acid transfer across the Teflon membrane was dependent on the free acid concentration (CH3COOH) in the acid solution. Concurrent transfer of water was minimal due to the hydrophobic nature of the membrane. The strong base anionic exchange membrane facilitated the separation of acetic acid from both pure solutions and rumen fluid with flux again being dependent on the free acid gradient across the membrane. Flux rates were lower than other studies of diffusion dialysis, however, this may be partly attributed to improper preparation of the membrane. The currently achieved rates of transfer using these membranes are very low and are therefore not yet suitable for full-scale use in anaerobic digestion. Additional research is needed to achieve higher trans-membrane transport rates at reasonable costs.

Porous diffusion dialysis membranes for rapid acid recovery

“…Diffusion dialysis as an attractive separation technology has been widely applied to recover inorganic or organic acid from waste solutions due to the unique advantages of diffusion dialysis especially the environmental benignity and low energy consumption [5][6][7][8]. Diffusion dialysis separation process utilizing anion exchange membrane (AEM) is driven by concentration gradient, in which the solutes spontaneously pass through AEM from high to low concentration side [9].…”

Innovative BPPO Anion Exchange Membranes Formulation Using Diffusion Dialysis-Enhanced Acid Regeneration System

“…where C 0 f and C t f are feed concentrations at time 0 and t, respectively, and C t d is the dialysate. Dialysis coefficient U H and U Fe can be measured by utilizing the above relationships (4) and (5). The separation factor (S) is the ratio of dialysis coefficients (U) of the two species present in the solution.…”

“…This waste has become a crucial candidate for generating water pollution, thus resulting in huge economical losses [ 4 ]. Therefore, several works were carried out to discover such a type of technology that can remove these acids and wastes from wastewater such as neutralization, fluidized beds, and precipitation [ 3 , 5 ]. Several techniques in the field of membrane technologies were utilized for acidic and alkaline recovery, including several individual processes such as electrodialysis, nanofiltration, or the most preferred process called diffusion dialysis [ 6 , 7 , 8 , 9 , 10 ].…”

“…The diffusion dialysis (DD) system due to its superiority compared to other methods is installed for acid extraction since it is a green process that requires no power dissipation and has simple progression and equipment [ 5 ]. Initiated by Graham (1861), the notion of dialysis demonstrates a concentration driven spontaneous process using a semi-permeable membrane to split large and small molecules from each other [ 11 ].…”

Tuning the diffusion dialysis performance by surface cross-linking of PPO anion exchange membranes—simultaneous recovery of sulfuric acid and nickel from electrolysis spent liquor of relatively low acid concentration

“…This technology has been exploited to recover inorganic or organic acid from waste solutions being generated in steel, metal-refining, ion exchange resin regeneration waste and electroplating industries [2][3][4][5][6][7][8][9][10]. In this operation, the anion exchange membrane is the linchpin.…”