Characterization of Irreversible Fouling after Ultrafiltration of Thermomechanical Pulp Mill Process Water

Figures & data

TABLE 1 Characteristics of the process water from the thermomechanical pulp mill and the permeate after MF of the process water

	Process water	MF permeate
Total solids (g/L)	6.7	5.4
Ash (g/L)	1.0	0.9
Hemicelluloses (g/L)	2.0	1.3
– Arabinan (g/L)	0.1	0.1
– Galactan (g/L)	0.3	0.1
– Glucan (g/L)	0.4	0.3
– Mannan (g/L)	1.2	0.8
Lignin (g/L)	0.8	0.8
Turbidity (NTU)	604	16

FIGURE 1 Influence of pressure on flux during UF of process water (•) and MF permeate (o).

FIGURE 2 Flux during withdrawal of permeate in the experiments with process water (•) and MF permeate (o).

FIGURE 3 Average pure water flux recovery of the duplicate experiments, where the bars show the maximum and minimum values, after rinsing the fouled membranes with deionized water, cleaning with the alkaline cleaning agent Ultrasil 10 (U10), and cleaning with the acidic cleaning agent Ultrasil 73 (U73).

FIGURE 4 SEM images of cleaned membranes: a) pristine reference membrane, b) membrane exposed to process water and c) membrane exposed to MF permeate. Note the different scale in b).

FIGURE 5 SEM-EDS spectrum for the a) pristine reference membrane, b) membrane exposed to process water and c) membrane exposed to MF permeate.

FIGURE 6 ATR-FTIR spectra of a) pristine reference membrane, b) membrane exposed to process water and c) membrane exposed to MF permeate.

TABLE 2 ATR–FTIR peak assignments

Wavenumber (cm^−1)	Assignment	Reference
834, 873	C–H bending, rocking of PSU	^[^25^]
1014, 1080	Skeletal aliphatic C–C/aromatic C–H of PSU and polysaccharides	^[^25^,^26^]
1106, 1169	C–C/aromatic hydrogen bending/rocking of PSU	^[^26^]
1151	C–SO2–C symmetric stretching of PSU	^[^25–27^]
1242	C–O–C symmetric stretching of PSU	^[^25–27^]
1295	Asymmetric stretching S˭O of PSU	^[^25–27^]
1488	CH3–C–CH3 stretching of PSU	^[^26^]
1503, 1586	C˭C stretching in the aromatic rings of PSU	^[^26^]
2967	Aromatic C–H stretching of PSU and polysaccharides	^[^27^]
3000–3400	O–H stretching of polysaccharides	^[^25^]

TABLE 3 Sugars detected after acid hydrolysis of membranes exposed to process water and MF permeate

Amount of polysaccharides (mg/m^2)	Process water	MF permeate
Total adsorbed polysaccharides	508	37
– Arabinan	12	—
– Galactan	25	—
– Glucan	346	22
– Xylan	14	—
– Mannan	111	15

– Below the quantification limit (<10 mg/m²).

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