Combining Advanced Oxidation Processes in Attached Growth ... JWS-A-17-004.pdf · water treatment...

1 L. Li et al. / Journal of Water Sustainability 3 (2017) 205-213

Combining Advanced Oxidation Processes in Attached Growth

Membrane Bioreactor for Treating Polluted Surface Water

Lu Li, Thanwarat Chan, Chettiyappan Visvanathan*

School of Environment Resources and Development, Asian Institute of Technology, Pathumthani, 12120, Thailand

ABSTRACT

The continuous increment of organic pollution in surface water has brought new challenges to conventional drinking

water treatment processes. Attached growth membrane bioreactor (aMBR) has been reported as an attractive

technical solution, effective in removing biodegradable organic fractions. While the recalcitrant such as synthetic

organic matters (SOM), natural organic matters (NOM) and the other non-biodegradable components were remain

untreated. This study investigated the possibility of combining UV/O3 process as a recirculation phase into aMBR

system. Improving the biodegradability of recalcitrant in a MBR permeate by UV/O3 process and then send back to

be treated in a MBR system. The aMBR system combined with UV, O3 and UV/O3 system were tested and analyzed,

respectively. Results indicated that aMBR + UV/O3 process has much higher removal performance than aMBR + UV

or aMBR + O3. FEEM analysis and differential FDOM results indicated that UV/O3 was able to largely remove

recalcitrant and improve biodegradability of aMBR permeate. UV/O3 synergy provided higher contribution to

recalcitrant removal than simple addition of UV and O3. This study indicated that UV/O3 has potential to be used as a

recirculation phase in aMBR system for treating polluted surface water.

Keywords: Advanced oxidation processes (AOPs); UV/O3; fluorescence excitation emission matrix (FEEM);

attached growth membrane bioreactor (aMBR); polluted surface water

1. INTRODUCTION

Surface water pollution by agricultural runoff, industrial discharge and domestic sewage disposal has attracted high attention from worldwide. This has led to an increase of organic contamination of the surface water source and brought big challenges to water works in the world, especially for developing countries. aMBR which integrated biodegra-dation by naturally immobilized moving carrier and physical rejection by membrane module has been proven as an affordable and prospective technology (Li et al., 2017). The MBR process was not effective in treating recalcitrant organic matters, such as natural

organic matters (NOM) and synthetic organic matters (SOC). The SOC species and concen-tration of it have become more common in polluted surface water due to human activities (Padhye et al., 2014). The remaining untreated non-biodegradable organic matters could lead to the generation of disinfection byproducts once chlorination was used. Thus, it is necessary to improve the recalcitrant organic removal during the use of aMBR process in treating polluted surface water.

Advanced oxidation process (AOP) has been reported as an effective technology in treating recalcitrant organic matters and used in water treatment (Parsons, 2004; Toor and

Journal of Water Sustainability, Volume 7, Issue 3, September 2017, 205-213

© University of Technology Sydney & Xi’an University of Architecture and Technology

*Corresponding to: [email protected]

DOI: 10.11912/jws.2017.7.3.205-213


Mohseni, 2007). Few studies have focused on improving the biodegradability of AOP treated water, or combining it into aMBR process for treating polluted surface water. UV light irradiation is effective in treating UV absorptive components, and O3 has high oxidation properties. UV/O3 combination could provide a synergistic effect and high oxidation. Li et al. (2007) has compared the application of UV/O3-BAC and O3/BAC process in treating secondary effluents. They found that the presence of UV has improved the ozone utilization and biodegradability of the effluent. Hence, suitable UV/O3 reaction condition could partially oxidize the non-biodegradable organic matters and improve the biodegradability of treated water.

Fluorescence excitation emission matrix (FEEM) analysis is able to provide the infor-mation of fluorescence responsible dissolved organic matters (DOM) in water sample. It has been widely used in comparing the organic matter removal in water purification processes. FEEM and Liquid chromatography-organic carbon detection (LC-OCD) are two of the most promising DOM characterization methods. LC-OCD is able to quantify biopolymers, humic substances, building blocks, low molecular weight acids and neutrals. LC-OCD technique separates DOM into varies fractions based on the apparent molecular size. FEEM is able to detect aromatic proteins, humic acid-like substances, fulvic acid like substances and SMP. FEEM fractionation is based on the different structural and functional properties, which has significant effects of the chemical, physical and polyelectrolytic behaviors of DOM constituents (Chen et al., 2014; Huber et al., 2011). At the same time, FEEM analysis is also simpler than LC-OCD techniques.

The different DOM has corresponding Ex/Em position on the FEEM spectrum: Region I (Ex: 200-250 nm, Em: 280-330 nm, aromatic protein I); Region II (Ex: 200-250 nm,

Em: 330-380 nm, aromatic protein II); Region III (Ex: 200-250 nm, Em: 380-540 nm, fulvic acid-like); Region IV (Ex: 250-400 nm, Em: 280-380 nm, soluble microbial by-product- like); Region V (Ex: 250-400 nm, Em: 380- 520 nm, humic acid-like) (Chen et al., 2003). Differential FDOM which is able to compare the intensity difference has been used in tracking fluorophores changes in earlier researches. Even small changes in each Ex and Em wavelength, it was able to be captured in the FEEM fingerprint (Lavonen et al., 2015).

In this study, the aMBR system combined with UV, O3 and UV/O3 were tested, respec-tively. The system removal performance of water quality parameters was compared. The inorganic nitrogen balance in varies combination system were also analyzed. FEEM analysis and differential FDOM were used to compare the removal performance in varies systems. The percentage of FDOM total intensity and average intensity in region IV and region V in different treatment processes were analyzed.

2. MATERIALS AND METHODS

2.1 Materials

2.1.1 System operation conditions

The feed water used in the whole system was diluted domestic wastewater with CODMn around 10 mg/L. The aMBR system was operated with 5% polyvinyl alcohol gel (PVA-gel) as bio-carrier in HRT 2.5 h, the schematic of aMBR system was shown in Fig. 2. Separate air lines were provided for aeration in carrier tank and scouring in membrane tank. A timer was used for maintaining 8 minutes on and 2 minutes off intermittent operation. The flowchart of the combination of aMBR and UV, O3, UV/O3 processes were shown in Fig. 1. The whole system was operated under ambient temperature and constant pressure.

L. Li et al. / Journal of Water Sustainability 3 (2017) 205-213 207

2.1.2 UV and O3 reactor operation conditions

The UV light used in this study was 8w low pressure ultraviolet lamp with wavelength 254 nm. The O3 generator (CH-ZTW3G, OZO

CENTERTM, China) used pure oxygen gas to produce ozone. The O3 concentration used was 1.5 mg/L and contact time used was 3 minutes by BDOC test. The BDOC test results were shown in Table 1.

Figure 1 Flowchart of aMBR + (UV, O3, UV/O3) system

Figure 2 Schematic of aMBR system setup.

Table 1 BCODMn test results

Ozonation time (min) 0 1 3 5 10 15 30

BCODMn (mg/L) 0.32 1.08 1.4 1.38 1 1.24 0.96

aMBR aMBR

permeate

UV

Feed O3

UV/O3

Feed tank

Air

Level

sensor

Timer

1. PVA-gel

2. Membrane module

3. Pressure gauge

4. Permeate

1

2

3

4


2.2 Methods

2.2.1 BDOC test

The aMBR system permeate was collected and treated with ozonation time of 0, 1, 3, 5, 10, 15 and 30 minutes, respectively. The fresh feed water was filtrated with 2 µm filter paper and used as inoculation solution. 500 mL O3 treated water was collected, 5 mL inoculation solution was added in each sample, respec-tively. After that, the sample bottles were sealed and incubated in ambient temperature (26oC). The CODMn of water samples was tested immediately after ozonation treatment, recorded as COD0. The CODMn of water samples after 28 days incubation was tested and recorded as COD28. The BCODMn value was calculated by Eq. 1, as a modified BDOC method.

BCODMn = COD0 - COD28 (1)

2.2.2 Water quality parameters

The water quality parameters tested in this study follows the standard methods (APHA, 2012). Potassium permanganate index-CODMn was used as organic matter index. The NH3-N was tested by Nessler’s method; NO2-N and NO3-N was tested by spectrophotometry methods.

2.2.3 FEEM

FEEM was tested by fluorescence spectrome-ter (Cary Eclipse, USA) equipped with a xenon lamp. The scanning wave ranges were 300-600 nm for excitation and 250-445 nm for emission. Intervals were set as 5 nm in excitation and 4 nm in emission with a scanning speed of 2400 nm/min and high photomultiplier voltage. Excitation and emission slit were 5 nm and averaging time was 0.1 s. Pure water (Milli-Q, Millipore Co. Ltd) was used as the blank sample for all fluorescence analysis.

2.2.4 Differential FDOM

Differential EEMs (ΔEEMs) were calculated as follows:

ΔEEM = EEM of removed FDOM = EEM before – EEM after (2)

Removed fraction (%):

EEM% removed = ΔEEM / (EEM before) (3)

Based on the Eq. 2 and Eq. 3, the differential FDOM compared in this study were listed as follows:

ΔEEM1 = EEM of aMBR permeate – EEM of aMBR permeate after treated by UV;

EEM1% removal =ΔEEM1 / EEM of aMBR permeate;

ΔEEM2 = EEM of aMBR permeate – EEM of aMBR permeate after treated by O3;

EEM2% removal =ΔEEM2 / EEM of aMBR permeate;

ΔEEM3 = EEM of aMBR permeate – EEM of aMBR permeate after treated by UV/O3;

EEM3% removal = ΔEEM3 / EEM of aMBR permeate;

By this differential analysis between feed and treated sample, the removal of different fluorescence response components was compared and displayed by FEEM fingerprint in terms of intensity and percentage, visually. The percentage of total intensity in region IV and V in each sample in varies system were also calculated. Besides which, the average intensity of region IV and V in varies system were also compared.

3. RESULTS AND DISCUSSION

3.1 Removal performance

The removal performance in terms of CODMn, UV254 and color of aMBR permeate treated by UV, O3 and UV/O3 were compared and presented in Table 2. UV/O3 combination has provided much higher CODMn and UV254


removal than simple UV or O3 process in treating aMBR permeate. UV light has some effects in treating UV254, and nearly no effects in removing CODMn. This indicated that UV/O3 combination process has higher removal performance in treating aMBR permeate. Whether this process could improve the biodegradability of treated water have to be discussed.

Inorganic nitrogen in terms of ammonia, nitrite and nitrate was also tested in each system and shown in Table 3. Results indicated that the total inorganic nitrogen was reduced after treated by UV or UV/O3 for aMBR permeate, and has a small increase when treated by O3. This indicated that UV/O3 combination process was more effective in reducing total inorganic nitrogen than O3 alone in treating aMBR permeate.

3.2 FEEM analysis

The FEEM of water samples from aMBR + (UV, O3, UV/O3) systems, including feed, aMBR permeate and aMBR permeate after treated by UV, O3 and UV/O3 respectively were shown in Fig. 3. The highest intensity of FDOM in feed water was found in region V (Ex: 250-360 nm, Em: 380-500 nm), the humic

acid-like components. After treated by aMBR process, as shown in Fig. 3b, the humic acid-like region intensity was slightly reduced. aMBR, as a biological process, was not effective in treating the humic acid-like recalcitrant. The small reduction of region V might be attributed to carrier adsorption and membrane rejection. Some of the region V components has been retained in the system, and become decomposed or part of the membrane fouling layer. The UV treated aMBR permeate as displayed in Fig. 3c, has shown that the humic acid-related FDOM removal had increased a bit. While the protein-like components (region IV, Ex: 250-300 nm; Em: 300-380 nm) had increased. This indicated that the hydrophilic components were increased and hydrophobic components were decreased by UV treatment of aMBR permeate. As shown in Fig. 3d and 3e, the region V has the highest reduction and region IV has the highest increase after treated by UV/O3 process. The hydrophilicity of treated water had increased after treated by UV, O3 and UV/O3 process. This indicated that UV/O3 process was largely reduced recalcitrant and improved the biodegradability in treating aMBR permeate as compared with UV or O3 alone.

Table 2 Removal rate of aMBR permeate treated by UV, O3 and UV/O3 processes (%)

CODMn UV254 Color

UV 1.1±3.42 17.22±10.23 7.71±11.12 O3 4.35±8.39 55.74±5.13 86.21±11.80 UV/O3 22.59±8.52 67.09±2.57 86.88±4.94

Table 3 Inorganic nitrogen balance in aMBR + (UV, O3, UV/O3) system (unit: mg/L )

NH3-N NO2-N NO3-N Total inorganic N

Feed 14.975±3.157 0.032±0.004 2.88±0.874 17.886±2.807

aMBR 0.331±0.037 0.043±0.003 12.516±0.362 12.891±0.322

aMBR+UV 0.403±0.033 0.074±0.005 11.277±0.945 11.753±0.855

aMBR+O3 0.714±0.049 0 12.342±0.75 13.056±0.683

aMBR+UV/O3 0.719±0.023 0.016±0.002 11.255±0.741 11.990±0.677


Figure 3 FEEM of samples from aMBR + (UV, O3, UV/O3) system. ((a) Feed water; (b) aMBR permeate; (c) aMBR + UV permeate; (d) aMBR + O3 permeate;

(e) aMBR + UV/O3 permeate) 3.3 FDOM differential analysis

The FDOM differential in aMBR + (UV, O3, UV/O3) systems were compared as displayed in Fig. 4. Fig. 4a, 4b and 4c have shown the FDOM reduction of aMBR permeate after treated by UV, O3 and UV/O3 respectively. The most distinct removal of humic acid-like components was found in UV/O3 process. Fig. 4d, 4e and 4f have shown the percentage of removal fraction by UV, O3 and UV/O3 respectively in FEEM fingerprint. Highest reduction was found in region V (Ex: 250-440 nm, Em: 400-600 nm) in UV/O3 process. The protein-like components (Region IV, Ex: 250-300 nm, Em: 300-380 nm) removal was low or even increased. This indicated that the UV, O3 and UV/O3 process was able to in-crease the hydrophilicity and biodegradability in treating aMBR permeates. This means that it can be used as a recirculation phase to treat the aMBR permeates and then sending back to be

treated in the aMBR system. Among them, the UV/O3 process can be selected.

3.4 FDOM total intensity distribution and average intensity comparison

The FDOM total intensity in region IV and V of water samples in aMBR + (UV, O3, UV/O3) systems were displayed in Fig. 5. The percentage of region IV total intensity has the highest value in UV/O3 treated aMBR permeate. This also indicated that UV/O3 process was able to improve the region IV total intensity in treating aMBR permeate. This could finally result in reduction of recalcitrant and increase of biodegradability. The average intensity in region IV and V of water samples in aMBR + (UV, O3, UV/O3) systems were displayed in Fig. 6. This indicated that UV, O3, UV/O3 process has led to FDOM average intensity reduction, the most distinct reduction was occurring in treated by UV/O3 process.

(a) (b) (c)

(d) (e)


Figure 4 FDOM differential in aMBR + (UV, O3, UV/O3) system. ((a) ΔEEM1; (b) ΔEEM2; (c) ΔEEM3; (d) EEM1% removal; (e) EEM2% removal; (f) EEM3% removal)

Figure 5 Percentage of FDOM intensity in region IV and V of water samples in aMBR + (UV, O3, UV/O3) system. (Region IV: Ex: 250-445 nm, Em: 300-380 nm, the protein-like components;

Region V: Ex: 250-445 nm, Em: 380-600 nm, the humic acid-like components)

(a) (b) (c)

(d) (e) (f)


Figure 6 Average intensity in region IV and V of water samples of aMBR + (UV, O3, UV/O3) system (Region IV: Ex: 250-445 nm, Em: 300-380 nm, the protein-like components; Region V:

Ex: 250-445 nm, Em: 380-600 nm, the humic acid-like components)

CONCLUSIONS

This study reveals the potential of AOP being used as a recirculation phase in aMBR process. UV/O3 combination has provided higher organic matter removal than UV or O3 alone. FEEM analysis shows that UV/O3 process has the highest ability in removing recalcitrant FDOM, improving the hydrophilicity and biodegradability of treated water. FDOM total intensity analysis has shown that the protein- like region was largely increased in UV/O3 treated water. While the FDOM average intensity indicated that AOP was able to oxidize or partially oxidize FDOM in treating aMBR permeates. To discover the optimum AOP operation condition which could provide the lowest mineralization and highest biodegradability in treating aMBR permeate requires further study.

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