オゾン/過酸化⽔素促進酸化による⽣物学的⼆次処理⽔中有機物の分解過程
Characterization and removal of organic compounds in Effluent from Sewage Biological Treatment
by O3/H2O2 Advanced Oxidation Process○Nanthapong Chantaraprachoom*, Bingzi Chen*, Tatsuhide Hamasaki*,
Shogo Taniguchi* and Tadao Mizuno***: Osaka Sangyo University，**: Setsunan University
Abstract

Even though O3/H2O2 based advanced oxidation process (AOP) has been proven to be an effective
polishing treatment for sewage effluent, some of organic compounds were still found after treatment
as the TOC value of treated sample was around 1 mg/L. In pursue of identifying these remaining
substances, High Performance Size Exclusion Chromatography with Organic Carbon Detector(HPSEC-OCD) was used to determine range of apparent molecular weight (AMW) of the remaining
substances. In this study, four HPSEC-OCD results were observed and compared: (a) sewage effluent
before AOP, (b) after ozone only treatment, (c) after ozonation with hydrogen peroxide addition in
the beginning, (d) after ozonation with hydrogen peroxide continuously added. HPSEC-OCD
chromatograms show that biopolymer in AMW range of 30,000 Da and low-molecular weight (LMW)
neutrals in AMW range of 500 Da were removed in all cases. However, humic substances and building
blocks in AMW range of 2,700 and 2,000 Da are only removed in presence of hydrogen peroxide.
LMW acids in which has AMW range of 1,100-1,200 Da were found irremovable. Furthermore,concentration in this AMW range increased after all treatment. The increase was hypothesized to be
by-products of AOP reactions with larger molecules.
Keywords: Sewage Treatment, Advance Oxidation Process (AOP), HPSEC-OCD
1. Introduction

O3/H2O2 based advanced oxidation process (O3/H2O2 AOP) has been proven to be an effective
polishing process for treating refractory organic compounds from biological sewage treatment1).
However, previous study2) shows that not all organic compounds can be removed by O3/H2O2 AOP
as some of organic compounds were still found in treated sample, indicated by TOC value around 1
mg/L. It is important to identify these irremovable substances as they will accumulate in nature overtime and may pose risk to human and environment in the upcoming future. In pursue of identifying
these untreatable substances, High Performance Size Exclusion Chromatography with Organic
Carbon Detector (HPSEC-OCD) is used extensively in this study to roughly determine apparent
molecular weight (AMW) range and concentration of such irremovable organic substances.
2. Methodology

2.1 Sample collection
The sewage effluent used in this study was collected from final settling basin at a sewage treatment
plant in Kansai area, where anaerobic-anoxic-aerobic method with nitrified liquor recirculation isutilized. Sampled water was then vacuum-filtered with glass fiber filter (GA-100, ADVANTEC) toremove any remaining suspended solid. Sample was then stored under refrigeration to minimize
degradation.

2.2 O3/H2O2 advanced oxidation process setup
Semi-batch type reactor from the previous studies2) was used. The setup consisted of ozone generator(SGA-01A-PSA4, Sumitomo Precision Products), flow meter (RK-1350V, KOFLOC), three 1L glassbottles, each for: backflow prevention, NOx trap (filled with water), and moisture trap respectively,
1L glass reactor (internal dimensions: ⌀ 8.2 cmx19 cm) with bottom gas diffuser (⌀ 100-200 µmpores), sampling tap, and H2O2 inlet connected to peristaltic pump discharge. The ozone transfer
capacity of the reactor was previously tested at 0.27 L/min. The gas outlet of the reactor wasconnected to ozone monitor (EG-60, Ebara Jitsugyo) for monitoring ozone concentration after thereactor. A data logger was used to record reading from ozone monitor to obtain ozone concentration
profile during experiment. Sewage effluent used in the experiment was taken out of refrigerator andleft to room temperature prior to the experiment. The water was treated by AOP in 3 conditions: (a)Ozonation with ozone-rich gas, ozone concentration 50 mg/L, at flow rate 0.5 L/min for 30 minutes;(b) Ozonation same as (a) with 30 mg/L hydrogen peroxide solution added to water right before
ozonation; (c) Ozonation same as (a) with hydrogen peroxide continuously added into reactor at 1.0
mg/L/min. The ozone concentration of ozone-rich gas generated by the ozone generator
was confirmed prior to each experiment by iodine titration method3). The reading of ozone monitor
was then linearly offset to match the value obtained by iodine titration to ensure accurate reading.

2.3 Water Quality Analysis
Sample were collected from reactor every 5 minutes. For each collection, the followings were
performed: (1) dissolved ozone concentration measurement by the indigo colorimetric method4),
immediately after collection; (2) hydrogen peroxide concentration measurement by DMP method5),
immediately after collection; (3) Non-purgeable total organic carbon (NPOC) measurement (TOCVCSH, Shimadzu, Japan); (4) HPSEC-OCD analysis. Except for dissolved ozone concentration
measurement, samples were purged with nitrogen before measurement to get rid of remaining ozone
in order to stop further reaction.

2.4 HPSEC-OCD Analysis
HPSEC-OCD was used to determine AMW of dissolved organic compounds contained in each sample.
The system consists of high-performance liquid chromatography unit (LaChrom Elite w/ L-2130
pump, Hitachi), custom-made chromatographic column (21.5 (ID) × 200 (L) mm, Tosoh) packed
with hydroxylated methacrylic polymer chromatographic resin with a pore size of 12.5 nm and particle
size of 30 µm (Toyopearl HW-50S, Tosoh). The column temperature was kept constant at 25ºC, using
thermostat-equipped ribbon heater. The column was periodically flushed with purified water toensure contamination-free. An OCD (Modified Sievers M9, Suez Water Technologies & Solutions)
was connected downstream to measure TOC of column outlet stream. The measurement was in 4second interval (Turbo mode) with 5.0 µL/min acid flow rate and 2.0 µL/min oxidant flow rate. Theeluent used in analysis was phosphate buffer (2.4 mM NaH2PO4 + 1.6 mM Na2HPO4) in 25 mM

sodium sulphate solution to achieve ionic strength 100 mM which is recommended by manufacturer
to minimize unwanted interaction between elutes and resin. Slight amount of 0.1M NaOH was added
to adjust pH of eluent to 6.8. The eluent flow rate was 1 mL/min. Prior to injection, the samples were
syringe-driven through a 0.2-μm filter (Millex-LG, Merck Millipore) to ensure particle-free. Sample
was then introduced into system via manual injector with 5ml loop (7725i, Rheodyne). Data fromOCD were streamed and recorded to PC via ethernet port and communication software (PuTTY,open-source). The streaming started in synchrony with sample injection and marked a start ofchromatogram. Chromatograms were plotted and analyzed in MS Excel spreadsheet, in which area
and retention time of each peak were calculated. Polyethylene glycol (PEG) with molecular weight
ranging from 200 to 20,000 Da were used to make semi-log calibration curve for AMW calculation(figure 2). PEG was selected as standard as it was reported to have low undesirable interactions withToyopearl HW resin6). Relationships between TOC value from NPOC analysis and sums ofchromatogram peak areas for each experiment were plotted (figure 3). The concentration of eachpeak in chromatogram was then estimated from these graphs.
5OZONE + H2O2 AT BEGINNING (INTERCEPT=0)
4.5

44

3.5

3.5

33TOC (PPM)

log MW

4.5

2.5
2
1.5
12040

y = 3E-06x
R² = 0.998

10.5

002
1.5

y = -0.023x + 5.93
R² = 0.99

0.5

2.5

60

80

10012014016000.E+00180

2.E+05

4.E+056.E+05

8.E+05Retention time (min)1.E+06

1.E+06

1.E+06

2.E+06

AREA

Figure 2: Semi-log calibration curve from PEG measurement

Figure 3: Example of relationships between total peak Area and TOC

3. Results and Discussion

According to literature7), SEC-OCD chromatograms can be generally classified by the descending
retention time into biopolymers, humic substances (HS), building blocks which are low molecularweight HS-like materials resulted from degradation of HS, low-molecular weight (LMW) acids, andLMW neutrals (alcohols, aldehydes, ketones, and amino acids). From figure 4, five peaks can beclassified in chromatogram of untreated sewage effluent: biopolymer at 30,000 Da, HS and building
blocks at 2,700 and 2,000 Da, LMW acids at 1,100 Da, and LMW neutrals at 500 Da range. After
treatment, biopolymers and LMW neutrals were completely removed in all cases. However, HS andbuilding blocks were only removed in presence of hydrogen peroxide. In all cases, peaks of LMW
acids are observed to be higher than initial concentration before treatment.
20002000

0 min TOC 4.9 ppm

600

400

200

200

0300 g /mol 0.18 ppm

800

1200 g /mol 1.20 ppm

400

1000

2000 g /mol 1.25 ppm

600

2800 g /mol 0.07 ppm

800

1200

TOC (ppb)

1000

1400

500 g /mol 1.18 ppm

TOC (ppb)

1200

Ozonation only 30 min. TOC 2.86 ppm

1800

1600

1100 g /mol 0.95 ppm

1400

2700 Da 0.64 ppm

30000 Da 0.91 ppm

1600

2000 g /mol 1.02 ppm

1800

00102030

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

Retention time (min)Figure 4 (top-left): Chromatogram, untreated sewage effluent (0 min)0102030405060

7080

90

100

110

120

130

140

150

160

170180Retention time (min)Figure 5 (top-right): Chromatogram, 30 min after ozonation only.

2000

2000

200

1000

800

600

400

200

300 g /mol 0.24 ppm

4002000 g /mol 0.13 ppm

600

TOC (ppb)

800

1200

300 g /mol 0.16 ppm

2800 g /mol 0.07 ppm

1000

1100 g /mol 1.58 ppm

1400

1200 g /mol 0.73 ppm

1600

1400

2000 g /mol 0.22 ppm

1600

1200

TOC (ppb)

Ozonation+H2O 2 continuously 30 min. TOC 1.05 ppm
1800

Ozonation+H 2O 2 at beginning 30 min. TOC 1.07 ppm

1800

000102030405060708090100110120130140150160170180

Retention time (min)0102030405060708090100110120130140150160170180

Retention time (min)Figure 6 (bottom-left): Chromatogram, 30 min after ozonation and H 2O 2 added at the beginning.
Figure 7 (bottom-right): Chromatogram, 30 min after ozonation and H 2O 2 continuously added.

4. Conclusion

TOC values and SEC-OCD chromatograms of samples after AOP both confirm that ozone-hydrogenperoxide AOP treatment yield better result than ozonation alone. In all cases, LMW acids with AMWrange of 1,100-1,200 Da were found irremovable. Furthermore, its concentration

increased in allcases. This is supposably due to conversion of larger molecules into smaller molecules as per AOP. At
this stage, it is difficult to determine if this LMW acids peak are solely AOP by-product or irremovableorganic compounds from biological process or both combined. Thus, next challenge is to identify
compositions as well as origins of these organic compounds in order to deepen understanding ofO3/H2O2 AOP capability.
5. References

1) Manjari Srivastav, Meenal Gupta, Sushil Kumar Agrahari, and Pawan Detwal, Removal ofRefractory Organic Compounds from Wastewater by Various Advanced Oxidation Process - A
Review, Current Environmental Engineering, 6, 8-16 (2019)
2) Tatsuhide Hamasaki, Yunqi Chen, Tadao Mizuno and Hiroshi Tsuno, Decomposition of organic
matter in effluent of biological treatment of sewage by O3/H2O2 Advanced Oxidation Process,
Journal of Japan Sewage Works Association, Vol.57 No.687, 116-124 (2020)
3) A. N. Al-Baarri, A. M. Legowo, S. B. M. Abduh, A. A. Mawarid, K. M. Farizha and M. Silvia,
Production of Ozone and the Simple Detection using Potassium Iodide Titration Method, IOP
Conf. Ser.: Earth Environ. Sci, 292, 012062 (2019)4) Measuring Methods for Ozone Concentration, Japan Ozone Association (2016)
5) Baga, A. N., Johnson, G. R. A., Nazhat, N. B. and Saadalla-Nazhat, R. A.: A simple
spectrophotometric determination of hydrogen peroxide at low concentrations in aqueous solution.
Anal. Chim. Acta, 204, 349-353 (1998)
6) Namguk Her, Gary Amy, David Foss, Jaeweon Cho, Yeomin Yoon and Paul Kosenka, Optimizationof method for detecting and characterizing NOM by HPLC-size exclusion chromatography withUV and on-line DOC detection. Env Sci Tech, 36, 1069‒1076 (2002)
7) Stefan A. Huber, Andreas Balz, Michael Abert and Wouter Pronk, Characterisation of aquatic
humic and non-humic matter with size-exclusion chromatography‒organic carbon detection‒organic nitrogen detection (LC-OCD-OND). Wat Res, 45(2) ,879‒885 (2011)