Chlorine disinfection has been reported to be ineffective in controlling RO membrane biofouling in some projects. Feed water temperature is a crucial factor in the formation of RO membrane biofouling. It has a positive impact on the wide application of the RO process to ascertain whether chlorine disinfection can alleviate the membrane biofouling at low temperatures. In this study, the effects of chlorination on the RO membrane biofouling at low feed water temperature (10 °C) were investigated by a lab-scale RO apparatus. The final normalized flux was 0.33 and 0.29 with and without chlorination, respectively. According to the normalized flux decline curve, chlorination could not alleviate the RO membrane fouling at low temperature. Based on the intermediate blocking model, chlorination increased the membrane fouling potential of the feed water. At low temperature, the biofilm on the membrane with chlorination was thinner and denser than that without chlorination. In addition, the membrane with chlorination contained more foulants and dissolved organic matter than that without chlorination. Chlorination failed to continuously prevent bacteria accumulation on RO membrane at low temperature, but screened out bacteria that were potentially more suitable for the low-temperature membrane environment.

  • Effects of chlorination on RO membrane biofouling at low temperature were studied.

  • Chlorine disinfection could not alleviate the RO membrane fouling at low temperature.

  • The biofilm with chlorination was thinner but had more foulants at low temperature.

  • Chlorine disinfection failed to prevent bacterial accumulation at low temperature.

  • Chlorination changed the microbial community structure at low temperature.

Graphical Abstract

Graphical Abstract
Graphical Abstract

In recent decades, to meet increasing demands for high-quality reclaimed water, reverse osmosis (RO) processes have become widely applied in water-scarce countries due to their features of small footprint, automatic operation and high-quality permeate (Radcliffe & Page 2020; Tseng et al. 2021; Zhao et al. 2021). Nevertheless, RO membrane fouling has always been a major obstacle for the large-scale application of RO systems. Membrane fouling deteriorates permeate and shortens membrane lifetime, which leads to membrane failure and higher operational costs (Shenvi et al. 2015; Jiang et al. 2017; Kehrein et al. 2021). Among the types of RO membrane fouling, biofouling, which represents the ‘Achilles’ heel’ of the RO process, is severe and more difficult to prevent due to bacterial regrowth (Flemming et al. 1997; Khedr 2000).

In order to alleviate biofouling of the RO membrane, multiple approaches have been investigated and proposed, including membrane surface modification, antiscalant and biocide application, feed water pretreatments and chemical cleaning (Nguyen et al. 2012; Yu et al. 2017; Yu et al. 2021). Among numerous approaches to alleviate biofouling, chlorination of feed water is a commonly used and economical technique to inhibit biofilm formation in RO systems (Zhang et al. 2015). However, chlorine disinfection could not inactivate all the bacteria completely. Studies have shown that chlorine disinfection could not always effectively control RO membrane fouling in some projects or lab-scale studies at room temperature (Winters 1997; Obaid & Ben Hamida 1998; Khan et al. 2015; Wang et al. 2019; Luo et al. 2021a). Furthermore, metagenomics analysis revealed that chlorine-resistant bacteria (CRB) could build stable biofilm to resist chlorine and cause RO membrane biofouling (Wang et al. 2021).

Feed water temperature is another important factor affecting biofilm formation on the RO membrane (Farhat et al. 2016). Temperature is well known as a key factor in governing microbial growth (Ratkowsky et al. 1982). Water temperature could modify hydrophobicity and microbial cell surface charge, which in turn affects bacterial cell attachment (Pompermayer & Gaylarde 2000). Water temperature could also affect the characteristics of extracellular polymeric substances (EPS) produced by bacteria (Lewis et al. 1989). Morimatsu et al. (2012) showed that low temperature could increase the viscosity of EPS matrix. Apparently, the water temperature could also affect the microbial community structure (Lindstrom et al. 2005). Wang et al. (2021) showed that chlorine disinfection affected RO membrane biofouling by changing microbial community and EPS characteristics on the membrane. The research findings from Farhat et al. (2016) showed that the membrane apparatus with low-temperature feed water was less susceptible to biofouling than that with high-temperature feed water. However, the biofilm at low temperature was thicker than that at high temperature, which meant that the biofouling formed at low temperature might be more difficult to clean (Farhat et al. 2016). It is worth noting that except for a few low-latitude countries, most countries must deal with low-temperature operation of RO systems. Therefore, it is necessary to investigate the alleviation of RO membrane biofouling at low temperature. Nevertheless, the effect of chlorine disinfection on membrane biofouling at low feed water temperature has not been reported in the literature, which still needs systematic investigation.

In this study, the main objective was to investigate the effects of chlorine disinfection on the biofouling of the RO membrane at low feed water temperature (10 °C) for wastewater reclamation. The permeate flux with and without chlorination during the operation process was recorded using a lab-scale cross-flow RO apparatus. After the operation, the foulants on the membrane were analyzed comprehensively using microscopic and DNA sequencing-based techniques to elucidate the effects of chlorination at low temperature.

Feed water characterization

The feed water of the lab-scale RO apparatus was collected from the effluent of a municipal wastewater treatment plant in Qingdao, China. The treatment plant adopted the moving-bed biofilm reactor as the secondary treatment, with coagulation and filtration as tertiary treatments. The water samples were filtered by filter paper and stored at 4 °C. The general water quality parameters are shown in Table 1.

Table 1

Feed water characteristics

CharacteristicsConcentration
pH 7.0–8.0 
Conductivity (μS/cm) 3,560 ± 20 
DOC (mg/L) 8.88 ± 0.18 
-N (mg/L) 1.06 ± 0.12 
UV254 (cm−10.123 ± 0.002 
Hardness (mg/L CaCO3443.50 ± 31.50 
Cl (mg/L) 900.17 
F (mg/L) 0.27 
(mg/L) 188.45 
(mg/L) 7.57 
CharacteristicsConcentration
pH 7.0–8.0 
Conductivity (μS/cm) 3,560 ± 20 
DOC (mg/L) 8.88 ± 0.18 
-N (mg/L) 1.06 ± 0.12 
UV254 (cm−10.123 ± 0.002 
Hardness (mg/L CaCO3443.50 ± 31.50 
Cl (mg/L) 900.17 
F (mg/L) 0.27 
(mg/L) 188.45 
(mg/L) 7.57 

Experimental setup

To investigate the effects of chlorination on the RO membrane fouling at low temperature, one set of experiments was run for 27 days at 10 °C of feed water temperature. The water samples disinfected by 0 (without chlorination) and 5 mg-Cl2/L chlorine were set as the feed water. NaClO solution (2.30 g/L) was added to the sample to simulate chlorine dosage 5 mg-Cl2/L. After 30 min of the lightproof reaction, the excess of Na2S2O3 solution (2%) was added for dechlorination. For the water sample without chlorination, an equal volume of NaClO and Na2S2O3 solutions was mixed and then added into the water sample to achieve the same ionic strength as compared with that in the water sample with 5 mg-Cl2/L chlorine. After disinfection, the residual bacteria were counted by the heterotrophic plate count (HPC) method (Yu et al. 2018). Chlorine disinfection of the water samples was performed daily during the 27-day continuous operation of the experiment.

A lab-scale cross-flow RO apparatus with two RO membrane cells was used for the chlorine disinfection simulation process (Figure 1). The aromatic polyamide composite RO membrane (LC HR-4040, DOW, USA) was cut into round coupons (S = 8.04 × 10−4 m2) and used as the simulating membrane. The operational pressure was fixed at 1.2 MPa and the flow rate of the feed water was 1.0 mL/min. The permeate flux data were collected based on the method adopted from Wang et al. (2019). The RO permeate mass data were monitored by an electronic balance (WT60001X, WANT, China) and recorded by a computer. The feed water temperature was controlled by a refrigerating/heating water bath (DC-0515, shunmayq) at approximately 10 °C. The temperature data were monitored by a temperature sensor and recorded by a computer. The permeate flux (J) was calculated by the following equation:
formula
(1)
where J is the permeate flux (L/(m2·h)) at time t; Δm is the mass difference of the permeate at 3,600 s before and after that time point (kg); ρ is the feed water density (103 kg/m3); A is the RO membrane coupon area (8.04 × 10−4 m2); Δt is the time difference (3,600 s) and T is the temperature at that time point (°C). The flux was normalized based on the initial flux (J0) in the first 3,600 s of operation. The normalized flux of the permeate was calculated as J/J0. The normalized flux decline curves were fitted using the intermediate blocking model (Ochando-Pulido & Martínez-Ferez 2017). The model is shown in the following equation (Equation (2)).
formula
(2)
Figure 1

Lab-scale cross-flow RO apparatus with and without chlorination.

Figure 1

Lab-scale cross-flow RO apparatus with and without chlorination.

Close modal

where J/J0 is the normalized flux at time t. Jpss is the final normalized flux at the equilibrium phase where the flux would not decline. k is the membrane surface ‘blocked’ per unit of total volume permeated through the membrane, which could represent the fouling potential of the water sample (m−1).

Analytical methods

Water quality analysis

The water temperature was monitored in real time by a temperature recorder (Jucsan, China) and uploaded to a computer. Conductivity and pH were measured by a multi-parameter controller (LEICI, China). UV absorbance at 254 nm (UV254) was measured by a Uvmini-1240 spectrophotometer (Shimadzu, Japan). Dissolved organic carbon (DOC) was measured by a Multi N/C 2100 analyzer (Analytik Jena, Germany). The total hardness was determined by EDTA titration. The anion concentration was determined by a Dionex ICS-5000 ion chromatograph (Thermo Fisher, USA).

Membrane foulant analysis

At the end of the running of the RO apparatus, the membrane coupons were taken out from the RO cell and cut into small pieces of a certain area for further analysis. Photographs of the fouled membranes were taken with a digital camera. Scanning electron microscope (SEM, QUANTA FEG250) analysis was used to investigate the microscopic details of the membrane images. The surface roughness of the membranes was measured by AFM (Agilent 5400) with a scan area of 50 μm × 50 μm. The roughness parameters (Ra) were calculated using the Nano-Navi Station analysis platform.

The biofilm accumulated on the membrane was analyzed by a confocal laser scanning microscope (CLSM, OLYMPUS FV1000). Fouled membrane samples were stained by four types of fluorescent dyes. Total cells, dyed cells, proteins, and polysaccharides were labeled by SYTO9 (Molecular Probes, ex 480/em 500 nm, shown as green), propidium iodide (PI, Molecular Probes, ex 490/em 635 nm, shown as red), SYPRO® Orange Protein Gel Stain (Thermo Fisher, ex/em 470/570, shown as blue), and tetramethylrhodamine conjugates of concanavalin A (TRITC-ConA, Thermo Fisher, ex/em 555/580, shown as yellow), respectively. The staining step was adopted from the method described by Yuan et al. (2015).

The total amount of foulant on the membrane was characterized by turbidity. The foulant on the membrane was scraped and suspended in ultrapure water, then measured by turbidity using an ultravioletvisible spectrophotometer (DR6000, HACH). The dissolved organic matter in the foulant were characterized by the DOC concentration using NaOH solution (pH 12) as a solvent, following the method as described by Wang et al. (2019).

Microbial density and community analysis

The microbial density in the foulants was characterized by the HPC method. A piece of the fouled membrane was cut with the area measured. The bacteria on the coupon were suspended by 0.9% NaCl solution and then cultured in R2A agar plates at 25 °C for 7 days. For microbial community analysis, a piece of the fouled membrane was cut, and the total genomic DNA was extracted using an E.Z.N.A.® Water DNA Kit (Omega Bio-tek, USA) following the manufacturer's protocol. The V4 hypervariable region of the bacterial 16S rRNA gene was amplified and then sequenced using an Illumina Miseq platform (PE300, Illumina, USA) (Caporaso et al. 2012). The microbial community analysis, including operational taxonomic unit (OTU) classification and alpha and beta diversity analyses, was performed as described in the previous study based on the SILVA Taxonomy database (GTDB 2022) (Yu et al. 2017; Parks et al. 2018). All analyzed sequences were submitted to the NCBI SRA database under an accession number PRJNA806491.

Operational performance of the RO apparatus

Different concentrations (0 and 5 mg-Cl2/L) of chlorine were added to the water samples for disinfection. After chlorination, the residual bacterial concentrations in the water samples are shown in Table 2. The results showed that some bacteria still survived after disinfection with 5 mg-Cl2/L chlorine in 30 min, which was consistent with the previous study (Wang et al. 2019).

Table 2

The results of chlorine disinfection of the water samples

Bacteria concentration (CFU/mL)
Inactivation ratio (log)
Before disinfectionAfter disinfection
(2.2 ± 0.35) × 104 70 ± 20 2.5 ± 0.2 
Bacteria concentration (CFU/mL)
Inactivation ratio (log)
Before disinfectionAfter disinfection
(2.2 ± 0.35) × 104 70 ± 20 2.5 ± 0.2 

After dechlorination, water samples were used as the feed water of the RO apparatus. The normalized flux decline curves of water samples with and without chlorination are shown in Figure 2. During 27 days of operation, the normalized flux declines with and without chlorination were similar. The decline with 5 mg-Cl2/L chlorination was slightly faster than that without chlorination, indicating severe fouling formed on the RO membrane with 5 mg-Cl2/L chlorination. The final normalized flux was 0.33 and 0.29 without and with chlorination, respectively. This result indicated that chlorination could not alleviate the RO membrane fouling at low temperature, which was consistent with the previous study at ambient temperature (25 °C) (Wang et al. 2019).
Figure 2

Normalized flux decline curves of water samples with and without chlorination.

Figure 2

Normalized flux decline curves of water samples with and without chlorination.

Close modal

The flux decline curves with and without chlorination were fitted using Equation (2) via the intermediate blocking model. The final normalized flux Jpss of water samples with and without chlorination was 0.0291 and 0.0295, respectively. The fouling potential parameter k of water samples with and without chlorination was 0.135 and 0.109 m−1, respectively (Table 3). These results indicated that chlorine disinfection would increase the RO membrane fouling potential of the water sample at low feed water temperature (10 °C), which was consistent with the previous study at ambient temperature (25 °C) (Wang et al. 2019).

Table 3

Fitting results of normalized flux declines via the intermediate blocking model

k (m−1)JpssAdjusted R2
0 mg-Cl2/L 0.0109 0.0295 0.998 
5 mg-Cl2/L 0.0135 0.0291 0.992 
k (m−1)JpssAdjusted R2
0 mg-Cl2/L 0.0109 0.0295 0.998 
5 mg-Cl2/L 0.0135 0.0291 0.992 

The conductivity of the RO permeate of water samples was monitored during the 27-day operation. The conductivity rejection of the water samples with and without chlorination was above 97%, indicating the intactness of the RO membranes. The conductivity rejection of the water sample with chlorination was slightly lower than that without chlorination, which indicated that the permeate quality of the water sample with chlorination was worse than that without chlorination (Figure 3).
Figure 3

The conductivity rejection of the water samples with and without chlorination.

Figure 3

The conductivity rejection of the water samples with and without chlorination.

Close modal

Membrane morphological properties

The fouled membranes were taken out from the RO cells and investigated by visual observation (Figure 4). The color of the foulants on the RO membranes with and without chlorination was light brown. According to the micrographs, bacteria were visible in the foulants on the membrane. The profile of bacteria on the membrane surface with chlorination was more blurred than that without chlorination, which indicated that more EPS were secreted by the bacteria on the membrane with chlorination. The roughness of fouled membranes is listed in Table 4. The Ra values of fouled RO membranes with and without chlorination were 50 and 290 nm, respectively. The difference in the roughness of fouled RO membranes reflected the effect of chlorination on the biofilm formation on the RO membrane surface at low temperature.
Table 4

Roughness of fouled RO membranes

SamplesRa (nm)
Clean membrane 90 
0 mg-Cl2/L membrane 290 
5 mg-Cl2/L membrane 50 
SamplesRa (nm)
Clean membrane 90 
0 mg-Cl2/L membrane 290 
5 mg-Cl2/L membrane 50 
Figure 4

Macroscopic/microscopic appearance of fouled RO membranes without chlorination (a) and with chlorination (b) via a digital camera and the SEM.

Figure 4

Macroscopic/microscopic appearance of fouled RO membranes without chlorination (a) and with chlorination (b) via a digital camera and the SEM.

Close modal

Foulants on the RO membranes

The densities of total foulants, dissolved organic matter and bacteria on RO membranes were characterized by turbidity, the DOC concentration and the HPC method, respectively. As shown in Table 5, the total foulant on the RO membrane with chlorination was 40.77 ± 0.82 FTU/cm2, which was much higher than that without chlorination (29.87 ± 0.60 FTU/cm2). Similar to the density of total foulants, the density of dissolved organic matter and bacteria on the RO membrane with chlorination was much higher than that without chlorination (Table 5). These results indicated that chlorine disinfection of the feed water would accelerate the accumulation of foulants on the RO membrane surface at low temperature, which was consistent with the previous study at ambient temperature (Wang et al. 2019).

Table 5

The density of total foulants, dissolved organic matter and bacteria on RO membranes

Characteristics0 mg-Cl2/L5 mg-Cl2/L
Turbidity (FTU/cm229.87 ± 0.60 40.77 ± 0.82 
DOC (mg/cm22.36 ± 0.07 4.29 ± 0.06 
HPC (CFU/cm26.23 × 105 ± 1.85 × 105 1.23 × 106 ± 2.55 × 105 
Characteristics0 mg-Cl2/L5 mg-Cl2/L
Turbidity (FTU/cm229.87 ± 0.60 40.77 ± 0.82 
DOC (mg/cm22.36 ± 0.07 4.29 ± 0.06 
HPC (CFU/cm26.23 × 105 ± 1.85 × 105 1.23 × 106 ± 2.55 × 105 

The biofilms accumulated on the membranes were analyzed by CLSM (Figure 5). The biofilm thickness on the membrane without chlorination was about 20 μm, which was approximately twice as thick as that with chlorination. However, the research findings at ambient temperature (25 °C) from Wang et al. (2019) showed that the thickness of the foulants on the RO membrane increased with the chlorine dosage significantly, which was inconsistent with this study. This inconsistency indicated that the biofilm thickness on the RO membrane might be not only related to the chlorine disinfection but also to the feed water temperature. Studies showed that water temperature had a significant effect on EPS formation and low temperature results in an increase in the EPS viscosity (Lewis et al. 1989; Morimatsu et al. 2012). However, the mechanism of the interaction among various factors such as chlorination and temperature needs to be further studied. Although the biofilm without chlorination was thicker, it was looser than that with chlorination (Figure 5). This result was consistent with the density of total foulants and dissolved organic matter on the fouled membranes (Table 5), indicating that although the biofilm without chlorination was thicker, the total foulants were less than those with chlorination. More interestingly, large numbers of dead bacterial cells were found on the membrane without chlorination, but not on the membrane with chlorination (Figure 5). This was consistent with the result of HPC on the fouled membranes (Table 5). This might be because CRB could form dense biofilm to resist the low temperature environment. Besides, in terms of EPS components, there were obvious loose protein components on the membrane without chlorination but had dense polysaccharide components on the membrane with chlorination. This might be related to the EPS characteristics of CRB, which needs to be further studied. In addition, research had showed that chlorination led to extracellular polysaccharide production by the microorganisms to protect themselves from the chlorine, which caused more severe RO membrane fouling (Winters 1997; Chen et al. 2022).
Figure 5

Cross profiles of CLSM images of the biofilm on the fouled membranes. (a) Bacterial cells (total cells shown as green, dyed cells shown as red) on the membrane with chlorination, (b) proteins (shown as blue) and polysaccharides (shown as yellow) on the membrane with chlorination, (c) bacteria cells on the membrane without chlorination, and (d) proteins and polysaccharides on the membrane without chlorination. Please refer to the online version of this paper to see this figure in colour: http://dx.doi.org/10.2166/wrd.2022.156.

Figure 5

Cross profiles of CLSM images of the biofilm on the fouled membranes. (a) Bacterial cells (total cells shown as green, dyed cells shown as red) on the membrane with chlorination, (b) proteins (shown as blue) and polysaccharides (shown as yellow) on the membrane with chlorination, (c) bacteria cells on the membrane without chlorination, and (d) proteins and polysaccharides on the membrane without chlorination. Please refer to the online version of this paper to see this figure in colour: http://dx.doi.org/10.2166/wrd.2022.156.

Close modal

Microbial communities in the foulants on RO membranes

The alpha diversity of fouled membranes and water samples was analyzed and is shown in Table 6. According to the Shannon and Simpson indices, not surprisingly, microbial community diversity in RO feed water decreased significantly after chlorination. Furthermore, the results in Table 6 showed that, under the unchlorinated condition, compared with the feed water, the low temperature resulted in the decrease of microbial community diversity on the RO membrane surface. Meanwhile, under the chlorinated condition, with the operation of the apparatus, the microbial community diversity on the membrane surface was restored, but it could not reach the level on the RO membrane surface without chlorination.

Table 6

The Shannon and Simpson indices of feed water and RO membrane samples

SamplesShannonSimpson
0 mg-Cl2/L-F 5.109 0.019 
5 mg-Cl2/L-F 1.633 0.479 
0 mg-Cl2/L-M 3.670 0.060 
5 mg-Cl2/L-M 3.035 0.108 
SamplesShannonSimpson
0 mg-Cl2/L-F 5.109 0.019 
5 mg-Cl2/L-F 1.633 0.479 
0 mg-Cl2/L-M 3.670 0.060 
5 mg-Cl2/L-M 3.035 0.108 

The microbial communities of the foulants on the membranes and water samples were analyzed. At phylum level, Proteobacteria (48.6%) was the predominant phylum in the feed water sample without chlorination. After chlorination, Actinobacteriota (72.6%) became dominant in the feed water, which was only 2.4% in the feed water without chlorination. Meanwhile, the abundance of Proteobacteria decreased to 6.6% (Figure 6(a)). This is because Proteobacteria are Gram-negative bacteria. The cell wall is less rigid in structure, which leads to the cells being easily lysed by chlorination. In contrast, Actinobacteriota are Gram-positive bacteria with dense cell walls, which are more resistant to chlorination. Although the microbial communities of feed water samples were obviously different, the microbial communities of RO membranes were relatively similar, with Proteobacteria as the predominant phylum (Figure 6(a)). This result was consistent with the previous study at ambient temperature (25 °C) (Wang et al. 2019). This is because the microbial community structures tend to be similar under the same environmental pressure. At the class level, Gammaproteobacteria was dominant in the feed water sample without chlorination. After chlorination, Actinobacteria became dominant in the feed water. When it comes to the fouled membranes, Gammaproteobacteria became dominant on the membranes whether chlorinated or not (Figure 6(b)). At the family level, Flavobacteriaceae and Pseudomonadaceae were predominant families in the feed water sample without chlorination with the relative abundance of 12.5 and 7.9%, respectively. After chlorination, Mycobacteriaceae became dominant in the feed water with the relative abundance of 71.7%, which was reported as CRB (Poitelon et al. 2010). When it comes to the fouled membranes, the microbial communities in the foulants on RO membranes showed significant differences from those of feed water samples. Hydrogenophilaceae, Halothiobacillaceae, Comamonadaceae and Flavobacteriaceae were predominant families, with the relative abundance of 20.0, 14.6, 10.1 and 6.4% on the RO membrane without chlorination and 31.4, 18.2, 6.2 and 13.2% on the RO membrane with chlorination, respectively (Figure 6(c)).
Figure 6

Microbial communities of feed water samples and the foulants on the membranes with and without chlorination at the (a) phylum level, (b) class level and (c) family level. ‘Others’ in the legend indicates the sum of unidentified bacteria and other minor bacteria.

Figure 6

Microbial communities of feed water samples and the foulants on the membranes with and without chlorination at the (a) phylum level, (b) class level and (c) family level. ‘Others’ in the legend indicates the sum of unidentified bacteria and other minor bacteria.

Close modal
The heatmap showed the major genera of feed water samples and the foulants on the membranes with and without chlorination (Figure 7). The microbial communities in the foulants on RO membranes showed significant differences from those of feed water samples. In the feed water with chlorination, the relative abundance of Mycobacterium was much higher than that in the feed water without chlorination. It had been pointed out in the literature that Mycobacterium had a high relative abundance after disinfection (Chen et al. 2021). Besides, there were certain differences in the microbial communities on the RO membranes with chlorination or not. For instance, the relative abundances of Pseudomonas, Sphingomonas and Acinetobacter on the membrane with chlorination, which were reported as CRB at ambient temperature, were much higher than those on the membrane without chlorination (Chen et al. 2021; Luo et al. 2021b). In addition, Caulobacter and Shinella were also more likely to accumulate on the membrane with chlorination than those without chlorination. The review by Luo et al. (2021b) counted 20 genera of CRB. However, Caulobacter and Shinella have not been reported as CRB in the literature, which indicated that these two genera might be resistant to chlorination only at low temperature. From another perspective, these bacteria screened out by chlorination might be more suitable for the low-temperature membrane environment. In addition, differences in microbial communities might contribute to the differences in foulant contents and components on the RO membranes.
Figure 7

Heatmap of feed water samples and the foulants on the membranes with and without chlorination at the genus level. Genera in top 20 relative abundances were counted.

Figure 7

Heatmap of feed water samples and the foulants on the membranes with and without chlorination at the genus level. Genera in top 20 relative abundances were counted.

Close modal

In this work, the effects of chlorine disinfection on the RO membrane biofouling at low feed water temperature (10 °C) were investigated. At low temperature, chlorination could not alleviate the RO membrane fouling. Besides, it would increase the RO membrane fouling potential of the feed water. At low temperature, the biofilm on the membrane with chlorination was thinner and denser than that without chlorination. In addition, the membrane with chlorination contained more foulants and dissolved organic matter than that without chlorination. Chlorination failed to continuously prevent the bacteria accumulation on the RO membrane at low temperature but screened out bacteria that were potentially more suitable for the low-temperature membrane environment.

This study was supported by the Research Institute for Environmental Innovation (Suzhou), Tsinghua (No. 00010272), the Higher Educational Science and Technology Program of Shandong Province, China (2020KJD003) and the Taishan Scholars Program of Shandong Province, China (No. tsqn201812091).

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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