Apple Juice, Manure and Whey Concentration with Forward Osmosis Using Electrospun Supported Thin-Film Composite Membranes

Abstract

Forward osmosis (FO), using the osmotic pressure difference over a membrane to remove water, can treat highly foul streams and can reach high concentration factors. In this work, electrospun TFC membranes with a very porous open support (porosity: 82.3%; mean flow pore size: 2.9 µm), a dense PA-separating layer (thickness: 0.63 µm) covalently attached to the support and, at 0.29 g/L, having a very low specific reverse salt flux (4 to 12 times lower than commercial membranes) are developed, and their FO performance for the concentration of apple juice, manure and whey is evaluated. Apple juice is a low-fouling feed. Manure concentration fouls the membrane, but this results in only a small decrease in overall water flux. Whey concentration results in instantaneous, very severe fouling and flux decline (especially at high DS concentrations) due to protein salting-out effects in the boundary layer of the membrane, causing a high drag force resulting in lower water flux. For all streams, concentration factors of approximately two can be obtained, which is realistic for industrial applications.

Keywords: apple juice; electrospun thin-film composite (TFC) membrane; forward osmosis; manure; whey.

Figure 7

Membrane performance using a 1.2 M NaCl solution DS and UPW as FS. (a) Specific reverse salt flux as a function of the osmotic pressure difference over the membrane between bulk DS and bulk FS. Average values calculated based on five separate runs. (b) Specific reverse salt flux of the electrospun membrane developed in this work compared to other frequently applied FO membranes CSM [18,31], HTI [32] and FTS [33]. All data measured with demineralized water against 1M NaCl as DS.

Figure 1

(a) Principle of FO using the osmotic pressure difference between two solutions to concentrate a dilute feed solution; (b) FO process.

Figure 2

(a) Dilutive ICP; (b) Concentrative ICP; (c) impact of ICP on clean-water flux through the membrane.

Figure 3

Reaction scheme of the formation of the thin polyamide (MPD + TMC) layer covalently attached to the porous electrospun PSU support.

Figure 4

Image of the experimental FO set up.

Figure 5

SEM images of the surface of (a) the uncoated electrospun PSU support; (b) the PA coated PSU support; and (c,d) the cross-section of the PA-coated PSU support.

Figure 6

Membrane performance using a 1.2 M NaCl solution DS and UPW as FS: water flux and reverse salt flux as a function of the osmotic pressure difference over the membrane between bulk DS and bulk FS. Average values calculated based on five separate runs.

Figure 8

(a) Water flux as a function of the concentration factor using apple juice as FS. The intermission in the curve is due to the refreshing of the DS to reset it to 3.6 M NaCl; (b) freshly squeezed apple juice (left bottle) and the concentrated feed at two stages in the FO-concentration process.

Figure 9

(a) Water flux as a function of the concentration factor using manure as FS. The intermission in the curve is due to the refreshing of the DS to reset it to 3.6 M NaCl; (b) Initial manure slurry; (c) Opened membrane cell after the manure concentration process.

Figure 10

(a) Water flux as a function of the concentration factor using whey as FS. The intermission in the curve is due to the refreshing of the DS to reset it to 3.6 M NaCl; (b) Initial cheese whey feed; (c) Opened membrane cell after the whey concentration process.

Figure 11

Water flux as a function of the FO operation time using apple juice, manure or whey as FS and using a (a) 1.2 M or (b) 3.6 M NaCl solution as DS. The intermissions in the curves with 3.6 M NaCl as DS are due to the refreshing of the DS to reset it to 3.6 M NaCl.

Figure 12

Water flux and concentration factor of industrial apple juice, manure or whey streams as FS and using (a) 1.2 M or (b) 3.6 M NaCl solution as DS. Average values represent two runs. Concentration time for experiments with 1.2 M NaCl as DS was 24 h, and for experiments with 3.6 M NaCl as DS: apple juice, 24 h; manure, 48 h; whey, 64 h.