Activated Sludge Process and biological Wastewater treatment system
Pengolahan air
1.
2. LATAR BELAKANG
KOAGULASI/ DISINFEKSI
FLOKULASI/ KLORIN
SARINGAN
SEDIMENTASI
AIR BAKU
PASIR AIR
BERSIH
Padatan
patogen
tersuspensi
- PRODUK SAMPING DISINFEKSI
RESIDU
- PERTUMBUHAN MIKRO ORGANISME SENYAWA
- WARNA, RASA, BAU
ORGANIK
- MENINGKATKAN KEBUTUHAN DISINFEKTAN
No. 2
3. KOAGULASI/ OZONISASI
FLOKULASI/ PENGOLAHAN
SARINGAN
SEDIMENTASI BIOLOGIS
RAW
PASIR
WATER
Padatan
patogen
tersuspensi
PENGOLAHAN
DISINFEKSI TAMBAHAN
KLORIN
AIR
BERSIH No. 3
4. REAKSI MEMUTUSKAN IKATAN
LANGSUNG RANGKAP
ORGANIK
O3 + TERLARUT
MEMECAHKAN MOLEKUL
BESAR KECIL
REAKSI TIPE
MENINGKATKAN
RADIKAL
HYDROPHILICITY
PENGOLAHAN
BIODEGRADASI BIOLOGIS
OLEH
PRODUKSI
MIKROORGANISME BDOC
No. 4
5. OZONISASI DALAM JANGKA
PRODUKSI BDOC HASIL WAKTU LAMA TIDAK MAMPU
OZONISASI TERBATAS MENINGKATKAN BDOC
OZON TERKONSUMSI UNTUK
MENGOKSIDASI BDOC YANG TELAH
DIPRODUKSI SECARA SEMPURNA
MENJADI CO2 DAN H2O
TOTAL REDUKSI DOC
TIDAK SIGNIFIKAN
No. 5
6. PENYISIHAN BDOC PADA TAHAP AWAL
OZONISASI KEMUNGKINANNYA DAPAT
MENGHASILKAN BDOC BARU
PENGULANGAN
PENGOLAHAN PENGOLAHAN
OZON BIOLOGIS OZON BIOLOGIS
OZONISASI- PENGOLAHAN
BIOLOGIS MULTI-STAGE
DAPAT DIHASILKAN BDOC BARU KARENA
OZONASASI HANYA BERLANGSUNG PADA
SENYAWA ORGANIK NON-BDOC
No. 6
7. ARTIKEL 1
TUJUAN
MENGEVALUASI KINERJA PROSES OZONISASI DAN
PENGOLAHAN BIOLOGIS YANG DIOPERASIKAN SECARA
MULTI TAHAP UNTUK DIAPLIKASIKAN DALAM SISTEM
PENGOLAHAN AIR
AIR DAM (MINAGA RESERVOIR WATER)
AIR OLAHAN DARI PROSES LUMPUR
SUMBER
AKTIF (SECONDARY EFFLUENT)
AIR
BAHAN HUMIK (HUMIC SUBSTANCES)
PENGULANGAN
PENGOLAHAN PENGOLAHAN
OZON BIOLOGIS OZON BIOLOGIS
No. 7
9. Ozonation time : 15 min/treatment
12 Mineralized DOC
10 0.7 mg l-1 BDOC
8 2.7 mg l-1 non-BDOC
DOC (mg l-1)
6
4
2
0
0 1 2 3 4
Jumlah tahap
BDOC dapat diproduksi dari non-BDOC setelah BDOC
yang terbentuk pada ozonisasi sebelumnya disisihkan
Peningkatan daya sisih DOC disebabkan oleh produksi BDOC
No. 9
10. Satu tahap : Ozonisasi 15 menit
Multi tahap : Ozonisasi 3 x 5 menit
60
Single-stage Multi-stage
50
Penyisihan DOC (%)
40
30
Residual ozone (mg l-1)
20
10
0
h m s
Senyawa Minaga Reservoir Secondary
Humik water Effluent
No. 10
11. Ozonisasi-Pengolahan Biologis Multi tahap dapat
meningkatkan penyisihan DOC dibandingkan
dengan Ozonisasi-Pengolahan Biologis Satu tahap,
dengan waktu ozonisasi yang sama. Hal ini terjadi
karena ozon digunakan secara efektif untuk
memproduksi
Ozonisasi-Pengolahan Biologis tidak efisien
untuk air yang mengandung scavenger ozon.
No. 11
12. KARAKTERISASI SENYAWA ORGANIK DALAM
ARTIKEL 2 PROSES OZONISASI DAN PENGOLAHAN BIOLOGIS
TUJUAN
KLARIFIKASI PERUBAHAN KARAKTERISTIK SENYAWA
ORGANIK PADA PROSES OZONISASI DAN PENGOLAHAN
BIOLOGIS
AIR DAM (MINAGA RESERVOIR WATER)
SUMBER
AIR OLAHAN DARI PROSES LUMPUR
AIR
AKTIF (SECONDARY EFFLUENT)
HYDROPHOBIC
BASE AND NEUTRAL HYDROPHOBIC
SUMBER AIR
3 ACIDS
pH 2
2
DAX 8
1 NaOH
pH 13
HYDROPHILIC No. 12
13. 5 5
Mineralized DOC Mineralized DOC
BDOC BDOC
4
4
Residual DOC Residual DOC
DOC (mg l -1)
DOC (mg l -1)
3 3
2 2
1 1
0 0
Before 1 2 3 Before 1 2 3
ozonation ozonation
TAHAP OZONISASI TAHAP OZONISASI
HYDROPHOBIC ACID No. 13 HYDROPHILIC
15. Ozonation- Humic substances
Biological Minaga Reservoir Water
Treatment Secondary Effluent X
AOPs ARE RECOMMENDED FOR DEGRADATION
OF OZONE RESISTANT ORGANIC CARBON
OBJECTIVE
TO EVALUATE DOC REMOVAL BY ADVANCED
OXIDATION PROCESS (AOP)- BIOLOGICAL
TREATMENT FOR LESS SUSCEPTIBLE DOC TO OZONE
No. 15
16. Ozone – Biological Treatment
Ozone/H2O2 (AOP) – Biological Treatment
Single-stage
15, 30, 45, 60 min 4days
Ozonation/AOP Biological Treatment
Multi-stages 1-3 times repeated
15 min 4days 15 min 4days
Ozonation/ Biological Ozonation/ Biological
AOP Treatment AOP Treatment
No. 16
17. 12
10
15
DOC (mg.l-1)
8
%
6 40
O3-BIO for MRW %
41
4 O3-BIO for SE %
2 AOP-BIO for MRW 62
AOP-BIO for SE %
0
0 15 30 45 60
OZONATION TIME (MIN)
No. 17
23. The single-stage AOP-biological treatment
could improve DOC removal than the single-
stage ozonation-biological treatment.
The multi-stage AOP-biological treatment
could improve DOC removal than the single-
stage AOP-biological treatment.
No. 23
32. Single stage : 15 min ozonation
Multi stage : 3 x 5 min ozonation
60
Single-stage Multi-stage
50
DOC removal (%)
40
30
20
10
0 h m s
Humic Minaga Reservoir Secondary
Substances water Effluent
No. 32
35. KESIMPULAN
KOMBINASI OZONISASI DAN PENGOLAHAN BIOLOGIS YANG
DIOPERASIKAN SECARA BERULANG (MULTI-STAGE DAPAT
MENINGKATKAN PENYISIHAN DOC DALAM SUMBER AIR MINUM
DIBANDINGKAN DENGAN OZONISASI DAN PENGOLAHAN
BIOLOGIS SATU TAHAP (SINGLE STAGE).
KOMBINASI OZONISASI DAN PENGOLAHAN BIOLOGIS YANG
DIOPERASIKAN SECARA BERULANG TIDAK EFEKTIF UNTUK
SUMBER AIR YANG MENGANDUNG ION KARBONAT, DIMANA ION
INI BERFUNGSI SEBAGAI PENGHAMBAT REAKSI OZON DENGAN
DOC MELALUI MEKANISME PEMBENTUKAN RADIKAL HIDROKSIL
KINERJA OZONISASI DAN PENGOLAHAN BIOLOGIS YANG
DIOPERASIKAN SECARA BATCH TELAH DIKONFIRMASIKAN PADA
OZONISASI DAN PENGOLAHAN BIOLOGIS YANG DIOPERASIKAN
SECARA SINAMBUNG
No. 35
Editor's Notes
This is the background of my study Conventional drinking water treatment process have been designed primarily to remove suspended solids and pathogens in water supply through coagulation-flocculation, sedimentation, sand filtration and disinfection by chlorine. However, the above treatment processes cannot be remove lower molecular weight dissolved organic matter (DOM) in raw water efficiently. The residual organic in finish water would threaten the quality and safety of drinking water. DOM produces disinfection by product, such as THMs during disinfention process and increases microorganism regrowth potential in distribution system. In addition, the existence of DOM result on color, taste, and odor problem to the consumers and also increasing disinfectant demand in disinfection process. Advanced drinking water treatment process is necessary to remove residual organic in conventional drinking water treatment process.
The combination of ozonation and biological treatment are promising unit process to remove residual organics, in addition to conventional drinking water treatment. Biological activated carbon or (BAC) treatment is recommended as a biological treatment because it can remove dissolved organic matter in raw water by biodegradation and simultaneously remove synthetic organic chemical by adsorption.
Ozone can react with dissolved organic matter or DOM in an aqueous environment by the following mechanisms; one is direct reaction of ozone molecule, and the other is radical type reaction. These reaction as a whole lead to the decrease in aromaticity and molecular weight, and increasing hydrophilicity of DOM, which eventually result in an increase in biodegradability of dissolved organic carbon, through the production of biodegradable dissolved organic carbon (BDOC). BDOC produced during ozonation would be removed by biological treatment such as Biological activated carbon. Therefore, the production of BDOC is considered to be essential factor that determines the performance of ozonation-biological treatment.
However, several researchers reported that the production of BDOC by ozonation is limited and longer ozonation could not be produce BDOC significantly. In the longer ozonation, ozone was mainly consumed for the oxidation of BDOC produced in the early stage of ozonation and was not utilized for the conversion of residual refractory DOC into BDOC. Consequently, higher DOC removal could not be expected by simple ozonation-biological treatment. Therefore, the simple ozonation and biological treatment should be modified in order to improve the DOC removal.
The removal of BDOC produce in the early stage of ozonation seems to be interesting to produce new BDOC, by further ozonation. It is considered that a multi-stage ozonation-biological treatment, which was a repeated process of ozonation-biological treatment, could possibly decrease more DOC than the conventional single-stage ozonation-biological treatment with the same total ozonation time. In the multi-stage ozonation-biological treatment, additional BDOC would be produced by the repeated ozonation after biodegradation of BDOC produced by the previous ozonation. The additional production of BDOC by the subsequent ozonation was expected because each ozonation in the multi-stage ozonation-biological treatment is carried out only for refractory DOC, without being consume by BDOC.
It is well known that ozonation followed by biological treatment is an effective process for the removal of dissolve organic carbon (DOC) in raw water for drinking water . Ozonation increase the biodegradable dissolved organic carbon in raw water, and remove it by biodegradation in biological treatment. However, several researchers reported that the production of BDOC by ozonation is limited and higher ozone dose could not be produce BDOC significantly. Consequently, higher DOC removal could not be expected by simple ozonation-biological treatment. Therefore, the simple ozonation and biological treatment should be modified in order to improve the DOC removal.
The multi-stage ozonation-biological treatment was carried out with 5 or 15 min ozonation. This figure shows DOC after biological treatment both in the continuous and the repeated ozonation-biological treatments. DOC decreased remarkably with the repeated ozonation-biological treatment both for 5 and 15 min ozonation. DOC after the 5 min ozonation and subsequence biodegradation repeated for 4 times was 5.1 mg l -1 . This is lower than the DOC observed in the same ozonation period, for the continuous ozonation-biological treatment, in which residual DOC was 7.4 mg/l. DOC after 15 min ozonation and biodegradation which repeated for 4 times was 3.6 mg l -1 . It was much lower than conventional treatment for 60 min (7.2 mg l -1 ). These results indicate that the repeated ozonation-biological treatment give higher DOC removal efficiency than the conventional single stage ozonation-biological treatment.
This figure shows fractionations of DOC the multi-stage ozonation-biological treatment. The first ozonation removed 0.7 mg l -1 of DOC and produced 2.7 mg l -1 of BDOC for 15 min ozonation. All the BDOC was removed by the following biological treatment. The second ozonation for the residual non-BDOC fraction removed DOC directly and produced another BDOC. Total BDOC removals by the 4 times of ozonation- biological treatment were 77% of total DOC removal for 15 min ozonation. These results indicate that BDOC can be reproduced from non-BDOC by removing BDOC produced by ozonation. Therefore, the higher DOC removal in multi-stage ozonation-biological treatment is mainly due to the production of BDOC by ozonation. In the single-stage ozonation-biological treatment, BDOC produced during the early stage of ozonation could further consume ozone for it’s complete oxidation. Consequently, ozone is competitively consumed both by BDOC and the remaining refractory organics during further stage of ozonation. On the other hand, in the repeated ozonation-biological treatment, BDOC was completely removed by biological treatment, and ozone was consumed by the refractory DOC without being consumed by BDOC. Therefore, the production of BDOC could be improved by the multi-stage ozonation-biological treatment.
This figure shows percentage of DOC removal in different waters during the single- and multi-stage ozonation-biological treatments. Ozonation was carried out for 15 min in the single-stage ozonation-biological treatment and 5 min ozonation and biodegradation were repeated for 3 times in the multi-stage ozonation-biological treatment. DOC removal was significantly improved by the multi-stage ozonation-biological treatment for humic substance and Minaga reservoir water. However, DOC removals for the secondary effluent were almost similar for the single and the multi-stage ozonation-biological treatments. In addition the DOC removal on the secondary effluent was much smaller than those on the humic substance and the Minaga reservoir water.
The following conclusions is derived from this study:
Previous experimental results indicate that repeated ozonation-biological treatment could improve DOC removal efficiency than the conventional single stage ozonation-biological treatment.However, repeated ozonation and biological treatment of various DOM solution resulted in different DOC removal efficiency. Characteristic changes of DOM during conventional single-stage ozonation-biological treatment and multi-stages ozonation-biological treatment should also be evaluated to help basic understanding of the ozonation and biological treatment.
To clarify the role of each fraction for BDOC production, the multi-stages ozonation-biological treatment was conducted separately on hydrophobic acid and hydrophilic fractions from Minaga reservoir water. This figure shows BDOC production after ozonation in the multi-stages ozonation-biological treatment for hydrophobic acid and hydrophilic fractions, respectively. For hydrophobic acid fraction, further ozonation in the multi-stage ozonation-biological treatment, could signicantly produce additional BDOC. On the other hand, in hydrophilic fraction significant amount of BDOC only produce in the the 1st ozonation. It is most likely that further BDOC production in the multi-stages ozonation-biological treatment in comparison with the single-stage ozonation biological treatment was mainly attributed by the decrease in hydrophobic acid fraction.
The contribution of hydrophobic acid on BDOC production of MR is shown in the above figure. The contribution of hydrophobic acid in continuous ozonation was steadily maintaining at 50 % of total BDOC production, in a certain period of ozonation time. It is suggests that the mechanism of BDOC formation during ozonation of DOM are occurs as follows: Ozone simultaneously react with hydrophobic acid, which is known as non-BDOC and non biodegradable hydrophilic fraction. However, of hydrophobic acid tends to transform into non biodegradable hydrophilic fraction before transform to biodegradable hydrophilic one. Therefore, the formation of BDOC during ozonation was contributed both by decrease in hydrophobic acid and the transformation non biodegradable hydrophilic fraction in biodegradable hydrophilic fraction.
In the previous study, ozone is not an efficient oxidant for the water containing much ozone resistant organic compound such as secondary effluent in previous study. Advanced oxidation processes which treat organic contaminant basically by hydroxyl radicals are well recommended to be applied for degradation of organic contaminant that is not reactive to ozone .
The treatment processes are ozonation-biological treatment and AOP-biological treatment. The AOP selected in this study is the combination of ozonation and hydrogen peroxide oxidation. The treatment processes were conducted in single-stage and multi-stages treatment. In the single-stage treatment, ozonation or AOP was conducted for 15, 30, 45, and 60 min., followed by biological treatment. In the multi-stages treatment, ozonation or AOP were conducted for 15 minutes, followed by biological treatment, which was repeated for 1-3 times.
This figure shows DOC removal in the single-stage ozonation-biological treatment and AOP-biological treatment for Minaga reservoir water and secondary effluent. Horizontal axis shows ozonation time, and vertical axis shows DOC concentration. The square symbol represent ozonation-biological treatment and the circle symbol represent AOP-biological treatment. In the ozonation-biological treatment, DOC concentration decreased significantly after 15 min ozonation followed by biological treatment, both in the Minaga reservoir water and the secondary effluent. However, it leveled off even with the longer ozonation. DOC removal in the Minaga reservoir water and the secondary effluent after 60 min were 40% and 15%, respectively. In the AOP-biological treatment, the better DOC removal was noted with the longer period of AOP than 15 min. DOC removals after 60 min were 62% and 41% in the Minaga reservoir water and the secondary effluent,respectively. The single-stage AOP-biological treatment showed better DOC removal than the single-stage ozonation-biological treatment.
This figure shows DOC fractionation in the single-stage ozonation-biological treatment for the secondary effluent. Secondary effluent contained about 5 % BDOC. Ozonation for 15 min mineralized approximately 2 % of DOC and increased BDOC up to 12 % of the initial DOC. However, the increase in ozonation time up to 60 min decreased BDOC along with the increase in mineralized DOC. The result indicates that the long term ozonation could not increase BDOC production. BDOC produced in the early stage of ozonation was mineralized by further ozonation and residual NBDOC was not oxidized by further ozonation than 15 min.
This figure shows DOC fractionation in the single-stage AOP-biological treatment for the secondary effluent. AOP for 15 min produced BDOC up to 15 % and mineralized 5 % of the initial DOC. Continuous oxidation for more than 30 min decreased DOC concentration mainly by mineralization and decreased BDOC. After 60-min oxidation, 35 % of DOC was removed by mineralization, and decreased BDOC down to 6 % of initial DOC. In the single-stage ozonation-biological treatment, BDOC produced by early stage of ozonation was mineralized by further ozonation and NBDOC was not oxidized by ozonation. However in the single-stage AOP-biological treatment, the AOP for more than 15 min could mineralize both BDOC and NBDOC resulting in the better DOC removal than ozonation-biological treatment.
This figure shows the comparison of DOC removals between the single-stage and the multi-stages treatments for ozonation and AOP-biological treatments for the secondary effluent. In the ozonation-biological treatment, the multi-stage treatment showed little improvement in DOC removal. DOC removal by cumulative ozonation time more than 30 min was almost the same as that for 15 min both in the single and multi-stages ozonation-biological treatments. However, the multi-stage AOP-biological treatment significantly reduced DOC and achieved 71% of DOC removal by 4 times repetition, whereas DOC removal was 41% in the single-stage AOP-biological treatment for the same oxidation time. This result indicates that the efficiency of DOC removal by AOP-biological treatment was higher in the multi-stage than in the single-stage.
This figure shows DOC fractionation in the multi-stage ozonation-biological treatment for the secondary effluent. The multi-stage ozonation-biological treatment for the secondary effluent produced sigificant BDOC only in the 1 st stage treatment. The total DOC removal by the 4 times repetition was only 20%, indicating that the multi-stage ozonation-biological treatment is not efficient for waters with high concentration of ozone scavengers like secondary effluent employed in this study.
This figure shows DOC fractionation in the multi-stage AOP-biological treatment for the secondary effluent. The first stage oxidation in the multi-stage AOP-biological treatment produced higher BDOC than mineralized for the secondary effluent. The BDOC was removed by subsequent biological treatment and the remaining NBDOC was oxidized by the 2nd stage oxidation, which is equivalent to 30 min oxidation time. The 2nd and subsequent stages of oxidation produce little BDOC and remove DOC by direct mineralization. In the single-stage AOP-biological treatment, BDOC produced during the early stage of treatment could further oxidize by OH radical produced in AOP. Consequently, OH radical is competitively consumed both by BDOC and the remaining refractory organics during further oxidation. On the other hand, in the multi-stage AOP-biological treatment, BDOC was completely removed by biodegradation, and the oxidation only conducted on the refractory DOC without being consumed by BDOC. Therefore, The different in DOC removal efficiency between the single-stage treatment and the multi-stage treatment can be explained that BDOC was removed by biological treatment in the early stage of oxidation in the multi-stage treatment.
The single and multi-stages AOP-biological treatments were evaluated to apply for drinking water treatment, especially for the water containing less susceptible DOC to ozone, comparing with the ozonation-biological treatment. The multi-stage AOP-biological treatment could improve DOC removal than the single-stage AOP-biological treatment. The improvement of DOC removal by the multi-stage treatment was due to BDOC removal by subsequent biological treatment in the early stage of oxidation.
This is the procedure for preparation of DOM solutions. Minaga reservoir water, secondary effluent and humic substances were used as DOM solutions. Minaga reservoir water and secondary effluent were concentrated to have about 20 mg DOC l -1 with a rotary evaporator at 40 o C. It is follows by removal of higher molecular weight DOM by addition of poly aluminium chloride, because high molecular weight DOM is removed by coagulation process in actual drinking water treatment and is not flowed into ozonation process. The supernatant was biodegraded and filtrated through a 1.2 u m glass fiber filter, and was adjusted to 10 mg DOC l -1 with distilled water. Humic substances were extracted from a commercial leaf mold for horticulture. The dried leaf mold was added into 0.1N NaOH solution and the mixture was boiled in water bath at 100 0 Cfor 30 min. PAC was added into the supernatant, following the same procedure as the DOM solutions. The filtrate that contained a large amount of BDOC was biodegraded to remove BDOC, and was diluted to 10 mg DOC l -1 .
Ozone was generated from a Fuji Electric ozone generator, which continuously supplied to a glass cylinder ozone reactor at ozone dose 5.2 mg/min or 2.3 mg/min. Biodegradation was performed according to the bioassay procedure. Water sample was sterilized by filtration through a 0.2 μ m polycarbonate filter. One milliliter of river water filtered through a 2 μ m polycarbonate filter was added into 100 ml of the sterilized sample, as an inoculum. The sample was incubated at 20 o C in the dark for 4 days. BDOC concentration was defined as the difference between initial DOC and DOC after incubation.
The treatment processes are ozonation-biological treatment and AOP-biological treatment. The AOP selected in this study is the combination of ozonation and hydrogen peroxide oxidation. The treatment processes were conducted in single-stage and multi-stages treatment. In the single-stage treatment, ozonation or AOP was conducted for 15, 30, 45, and 60 min., followed by biological treatment. In the multi-stages treatment, ozonation or AOP were conducted for 15 minutes, followed by biological treatment, which was repeated for 1-3 times.
This figure shows DOC concentrations after ozonation and biodegradation in the single-stage ozonation-biological treatment. The horizontal axis shows ozonation time and vertical axis is DOC concentration DOC decreased gradually from 10.4 to 9.2 mg l -1 after the ozonation at 120 min. Biological treatment after the ozonation was more effective for DOC removal than the ozonation only. DOC after biological treatment decreased down to 7 mg l -1 in 5 min ozonation, whereas significant decrease in DOC concentrations was not noted after 5 min until 120 min of ozonation. Ozonation for more than 5 min was not effective to decrease DOC in the conventional single stage ozonation-biodegradation treatment. Maximum DOC removal in this treatment was 31% for ozone dose of 5.2 mg O 3 l -1 .
The multi-stage ozonation-biological treatment was carried out with 5 or 15 min ozonation. This figure shows DOC after biological treatment both in the continuous and the repeated ozonation-biological treatments. DOC decreased remarkably with the repeated ozonation-biological treatment both for 5 and 15 min ozonation. DOC after the 5 min ozonation and subsequence biodegradation repeated for 4 times was 5.1 mg l -1 . This is lower than the DOC observed in the same ozonation period, for the continuous ozonation-biological treatment, in which residual DOC was 7.4 mg/l. DOC after 15 min ozonation and biodegradation which repeated for 4 times was 3.6 mg l -1 . It was much lower than conventional treatment for 60 min (7.2 mg l -1 ). These results indicate that the repeated ozonation-biological treatment give higher DOC removal efficiency than the conventional single stage ozonation-biological treatment.
This figure shows fractionations of DOC the multi-stage ozonation-biological treatment. The first ozonation removed 0.7 mg l -1 of DOC and produced 2.7 mg l -1 of BDOC for 15 min ozonation. All the BDOC was removed by the following biological treatment. The second ozonation for the residual non-BDOC fraction removed DOC directly and produced another BDOC. Total BDOC removals by the 4 times of ozonation- biological treatment were 77% of total DOC removal for 15 min ozonation. These results indicate that BDOC can be reproduced from non-BDOC by removing BDOC produced by ozonation. Therefore, the higher DOC removal in multi-stage ozonation-biological treatment is mainly due to the production of BDOC by ozonation. In the single-stage ozonation-biological treatment, BDOC produced during the early stage of ozonation could further consume ozone for it’s complete oxidation. Consequently, ozone is competitively consumed both by BDOC and the remaining refractory organics during further stage of ozonation. On the other hand, in the repeated ozonation-biological treatment, BDOC was completely removed by biological treatment, and ozone was consumed by the refractory DOC without being consumed by BDOC. Therefore, the production of BDOC could be improved by the multi-stage ozonation-biological treatment.
This figure shows percentage of DOC removal in different waters during the single- and multi-stage ozonation-biological treatments. Ozonation was carried out for 15 min in the single-stage ozonation-biological treatment and 5 min ozonation and biodegradation were repeated for 3 times in the multi-stage ozonation-biological treatment. DOC removal was significantly improved by the multi-stage ozonation-biological treatment for humic substance and Minaga reservoir water. However, DOC removals for the secondary effluent were almost similar for the single and the multi-stage ozonation-biological treatments. In addition the DOC removal on the secondary effluent was much smaller than those on the humic substance and the Minaga reservoir water.
To clarify why DOC was hardly removed in secondary effluent, residual ozone was monitored during conventional treatment of various DOM solutions. This figure shows residual ozone concentrations during the conventional single-stage ozonation. Residual ozone concentrations both in the humic substance and the Minaga reservoir water increased with ozonation time, whereas residual ozone in the secondary effluent was almost zero for 30 min. Therefore, ozone seemed to be consumed by scavengers such as carbon dioxide in the secondary effluent and were not used to convert refractory DOC to BDOC. Inorganic carbon concentrations in the humic substance, the Minaga reservoir water and the secondary effluent were 4.5, 18.5 and 30.7 mg l -1 , respectively. It is likely that the multi-stage ozonation-biological treatment is not efficient for waters with high concentration of ozone scavengers like secondary effluent employed in this study. Ozonation was continued to 120 min for the secondary effluent. Residual ozone was detected at 2.2 mg l -1 , however BDOC still hardly produced. Therefore, DOC in the secondary effluent must have lower reactivity for ozone than DOC in humic substance solution and Minaga reservoir water.
This figure shows the influent and effluents DOC from ozone-BAC treatment and ozone-BAC treatment with recycling. The horizontal axis shows experimental operating time and the vertical axis shows DOC concentration. The green symbol is influent, blue symbol shows DOC in BAC effluent, and the red symbol shows DOC in BAC with recycling. The average DOC concentration in influent is 9.1 mg l -1 . Initially, DOC of effluents in both ozone-BAC treatment and ozone-BAC treatment with recycling were 55 % and 40 % of initial DOC, respectively. However, DOC removal efficiency in both effluents were gradually decreased with ozonation time, and almost reached stability after 312 hrs continuous operation. The average DOC removal efficiency from 312hrs - 672 hrs continuous operation in ozone-BAC treatment and ozone-BAC treatment with recycling were 6.6 mg l -1 and 5.8 mg l -1 , respectively. In this condition, DOC removal efficiency in ozone-BAC treatment with recycling was 37 % higher than DOC removal efficiency in ozone-BAC treatment. This result indicates that recycling of effluent could improve DOC removal efficiency in ozone-BAC treatment.
