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Comparative Study
. 2019 Jul 18;16(14):2568.
doi: 10.3390/ijerph16142568.

Chemical Cleaning of Ultrafiltration Membrane Fouled by Humic Substances: Comparison between Hydrogen Peroxide and Sodium Hypochlorite

Kai Li  1   2 , Shu Li  3   4 , Tinglin Huang  5   6 , Chongzhe Dong  3   4 , Jiawei Li  3   4 , Bo Zhao  3   4 , Shujia Zhang  3   4
Affiliations
Comparative Study

Chemical Cleaning of Ultrafiltration Membrane Fouled by Humic Substances: Comparison between Hydrogen Peroxide and Sodium Hypochlorite

Kai Li et al. Int J Environ Res Public Health. .

Abstract

Chemical cleaning is indispensable for the sustainable operation of ultrafiltration (UF) system in water and wastewater treatment. Sodium hypochlorite (NaClO) is an established cleaning agent for membranes subject to organic and microbial fouling, but concerns have been raised about the generation of toxic halogenated by-products during NaClO cleaning. Hydrogen peroxide (H2O2) is a potential "green" cleaning agent that can avoid the formation of halogenated by-products. In this work, cleaning efficacy of H2O2 and NaClO for UF membrane fouled by humic substances (HS) was evaluated under a wide pH range, and change of HS's properties due to reaction with cleaning agents was examined. The cleaning efficacy of H2O2 was lower than that of NaClO at pH 3-9, but it increased to a level (91.4%) comparable with that of NaClO at pH 11. The extents of changes in properties and fouling potential of HS due to reacting with cleaning agents were consistent with their cleaning efficacy. H2O2 treatment at pH 11 significantly increased negative charge of HS molecules, decomposed high-MW molecules, and reduced its fouling potential. Therefore, considering treatment/disposal of cleaning waste and cleaning efficacy, H2O2 cleaning under strong alkaline condition can be a good choice for HS-fouled membrane.

Keywords: chemical cleaning; humic substances (HS) fouling; hydrogen peroxide (H2O2); sodium hypochlorite (NaClO); ultrafiltration (UF) membrane.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Distribution of main species in H2O2 (a) and NaClO (b) solutions as a function of pH at 25 °C and for C(H2O2)T = C(NaClO)T = 500 mg/L.
Figure 2
Figure 2
Effects of pH on cleaning efficacy of H2O2 and NaClO for ultrafiltration (UF) membranes fouled by humic substances (HS). C(H2O2)T = C(NaClO)T = 500 mg/L, with pure water as control, and pH was adjusted by adding HCl or NaOH; cleaning time 6 h.
Figure 3
Figure 3
Fouling potential of HS before and after reacting with H2O2 and NaClO: (a) Flux decline, (b) unified membrane fouling index (UMFI). The ratio of oxidant to dissolved organic carbon (DOC): 13:1; reaction time: 6 h. (TFI: total fouling index, HIFI: hydraulically irreversible fouling index).
Figure 4
Figure 4
Zeta potential of HS before and after reacting with H2O2 and NaClO. The ratio of oxidant to DOC: 13:1; reaction time: 6 h.
Figure 5
Figure 5
Apparent molecular weight distributions of HS before and after reacting with H2O2 and NaClO: (a) pH 9, (b) pH 11. The ratio of oxidant to DOC: 13:1; reaction time: 6 h.
Figure 6
Figure 6
Differential log-transformed absorbance spectra (−DLnA) (a) and change in spectral parameter (−DSlope325–375) (b) of HS before and after reacting with H2O2 and NaClO. The ratio of oxidant to DOC: 13:1; reaction time: 6 h.
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