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Treatment of high organic carbon industrial wastewater using photocatalysis process
Environmental Nanotechnology, Monitoring & Management 8 (2017) 163–168
Contents lists available at ScienceDirect
Environmental Nanotechnology, Monitoring & Management journal homepage: www.elsevier.com/locate/enmm
Treatment of high organic carbon industrial wastewater using photocatalysis process T. Threrujirapaponga, W. Khanitchaidechab,c, A. Nakarukb,d,
T
⁎
a
Department of Materials and Production Technology Engineering, King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand Centre of Excellence for Innovation and Technology for Water Treatment, Faculty of Engineering, Naresuan University, Thailand c Department of Civil Engineering, Faculty of Engineering, Naresuan University, Thailand d Department of Industrial Engineering, Faculty of Engineering, Naresuan University, Thailand b
A R T I C L E I N F O
A B S T R A C T
Keywords: Actual industrial wastewater treatment High organic carbon wastewater Photocatalysis process
In Thailand, agricultural machinery manufacturing companies are known to generate high organic carbon wastewater from painting and leak testing processes. Chemical oxygen demand (COD) value in leak test wastewater is found to be in the range of 3000–5000 mg/l. In this study, three scales including lab-scale, pilot-scale and industrial-scale photocatalytic reactors were developed to investigate the efficiency of wastewater treatment. In lab-scale, the 800 ml reactors were set up to optimize the best condition for pH and TiO2 loading. The results suggested that the pH had no effects on the COD removal, whereas the COD removal efficiency was increased by TiO2 loading. The highest COD removal efficiency of 85% was found at the TiO2 loading of 1 g/l. The 200 l reactor of pilot-scale and the 3000 l reactor of industrial-scale were established and continuously operated for 30 days. The results revealed that the COD removal efficiency was > 90%, and the COD concentration was reduced to 250–300 mg/l in the treated wastewater. The COD value of treated wastewater met the standard set by the Industrial Estate Authority of Thailand to discharge into a central wastewater treatment plant, which verified the successful implementation of process to the actual industrial wastewater.
1. Introduction The agricultural machinery manufacturing industry is considered to be one of the key industrial sectors in Thailand. The most common products of the industry are tractors, agricultural implements and harvesters. There are several manufacturing processes including surface etching, painting, assembly and leak testing. During leak testing, grease which is used for preventing rust contaminates the water, called leak test wastewater, which is difficult to treat by traditional treatment processes. The leak test wastewater contains a high grease content of 40 mg/l and its chemical oxygen demand concentration (COD) which is referred to as organic carbon contamination is in the range of 3000–5000 mg/l (Siam Kubota Corporation, 2014). Normally, the industry treats leak test wastewater by chemical precipitation to reduce the organic carbon of about 80%, and then the wastewater is further treated in a central wastewater treatment plant of an industrial estate (Siam Kubota Corporation, 2014). According to the chemical precipitation process, the organic carbon content is efficiently removed, however the chemical solid waste which is a by-product of the process, is generated and requires further treatment and disposal. The industry spends millions of dollars every year for such chemical solid waste ⁎
treatment and disposal. To reduce the treatment and disposal costs, the industry is interested in finding more efficient and cheaper alternatives. The advanced technology of the photocatalysis process which has no toxic waste as a by-product is a potential process for the leak test wastewater treatment. Photocatalysis is known as one of the advanced oxidation processes, it is applicable in the treatment of high organic carbon wastewater (Chong et al., 2010; Ghaly et al., 2011). According to the conceptual photocatalysis process, a catalyst such as TiO2 is exposed to light and exhibited oxidative decomposition and super hydrophilic properties of %O2−, and %OH under an aeration. These two forms can decompose organic carbon from wastewater to intermediate forms and continued to become carbon dioxide (CO2) and water (H2O), as shown in Eq. (1) Banu et al. (2008). TiO2 + O2 light
Organic Compound ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ intermediates ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ CO2 + H2 O
(1)
However, the application of the photocatalysis process in actual industrial wastewater treatment, has been very limited. There are only a few reports available. For example, Ghaly et al. (2011) used photocatalysis and H2O2 oxidation to treat paper mill wastewater which
Corresponding author at: Department of Industrial Engineering, Faculty of Engineering, Naresuan University, Thailand. E-mail addresses: [email protected], [email protected] (A. Nakaruk).
http://dx.doi.org/10.1016/j.enmm.2017.07.006 Received 27 November 2016; Received in revised form 15 June 2017; Accepted 17 July 2017 2215-1532/ © 2017 Elsevier B.V. All rights reserved.
TiO2 + O2 light
Environmental Nanotechnology, Monitoring & Management 8 (2017) 163–168
T. Threrujirapapong et al.
Table 1 Characteristics of leak test wastewater from the agricultural machinery industry.
Table 2 Summary of operating conditions of photocatalytic reactors.
Parameter
Concentration
Unit
Analysis method
Reactor
pH Biochemical Oxygen Demand (BOD5) Chemical Oxygen Demand (COD) Suspended Solids (SS) Total Dissolved Solids (TDS) Total Kieldahl Nitrogen (TKN) Oil and grease
9.2 170
– mg/l
Electrometric method 5-day BOD test
Lab-scale Effect of pH
3200
mg/l
Close reflux
150 3940
mg/l mg/l
Dried at 103–105 °C Dried at 103–105 °C
198
mg/l
Macro-Kjeldahl method
36
mg/l
Liquid-liquid, partition gravimetric
Effect of TiO2 loading
Pilot-scale Industrial-scale
pH
TiO2 loading (g/l)
Reactor volume (l)
6 7 8 No No No No No No No No
1 1 1 1 0 0.1 1 5 10 0.1 0.1
0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 200 3000
adjustment adjustment adjustment adjustment adjustment adjustment adjustment adjustment
2. Methodology
contains the high COD level of 2000 mg/l, the COD removal efficiency was approximately 75%. Further, the effective photocatalytic reactor was established to treat the effluent from an anaerobic bioreactor in the dairy industry; the COD and nitrogen concentrations in the wastewater were approximately 300 mg/l and 60 mg/l (Banu et al., 2008). However, both wastewater in previous studies had no oil and grease contamination which possibly negatively effects on the performance of photocatalysis process. The intention of the present study is to investigate the efficiency of the photocatalysis process for industrial wastewater containing high non-biodegradable organic carbon. The COD removal efficiency is used as an indicator to identify the performance of organic carbon removal. Firstly, lab-scale of photocatalytic reactors were used to study and clarify the optimal pH and TiO2 loading. Later, the pilot-scale and industrial-scale of photocatalytic reactors were implemented at the industry site for investigating performance under long-term operational conditions.
Leak test wastewater from the agricultural machinery industry is used as a case study in this study. The characteristics of the wastewater is summarized in Table 1 (Siam Kubota Corporation, 2014). In the experiments, commercial TiO2 particles were used as a catalyst. The characteristics of TiO2 particles are shown in previous study (Yuangpho et al., 2015). The various scales of photocatalytic reactors as developed, are indicated as follows: 2.1. Lab-scale reactor In the lab-scale reactors, the effects of pH and TiO2 loading were studied. The pH of wastewater was adjusted to 6, 7 and 8 using H2SO4. Then, 800 ml of adjusted wastewater was added into three 1 l beakers. Wastewater with no pH adjustment was used as a control. Although the enhancement of photocatalysis activity was reported at a low pH value (Akpan and Hameed, 2009), the cost-effectiveness of chemicals
Fig. 1. Schematic diagram of (a) lab-scale, (b) pilot-scale and (c) industrial-scale of photocatalytic reactors for actual industrial wastewater treatment.
164
Environmental Nanotechnology, Monitoring & Management 8 (2017) 163–168
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Fig. 2. Reduction of organic carbon in industrial wastewater at various pH values.
2.4. Water quality analysis
consumption for pH adjustment and neutralization was a factor of concern for the industry. Hence, only pH values of 6, 7 and 8 were studied. Then, the TiO2 loading was controlled at 1 g/l for the four reactors. All reactors were placed in the closed system which contains two lamps of UV-C (210 nm, 40 W) on the top and stirrers at the bottom (as shown in Fig. 1a) for 5 days. For the study of the effects of TiO2 loading, various TiO2 loadings of 0–10 g/l were added to the wastewater with no pH adjustment, then the above procedure was followed to study the pH effect.
The performance of the photocatalytic reactors for the treatment of actual industrial wastewater was evaluated by the reduction of the COD value which is commonly referred to as the organic carbon content of the wastewater. The COD value was measured by using Chemical Oxygen Demand (COD) analyzer (AL200 COD Vario, Aqualytic). The other parameters such as Biochemical Oxygen Demand (BOD5), Suspended Solids (SS) and Total Dissolved Solids (TDS) were measured by an environmental consultant company; the methods of measurement are presented in Table 1. The pH and dissolved oxygen (DO) values were regularly detected by using a pH meter (Eutech Instruments) and a DO meter (CyberScan DO 110 Model) while the reactors were operating.
2.2. Pilot-scale reactor The pilot-scale reactor was setup using a 200 l polyethylene tank with a height of 70 cm and a diameter of 65 cm (Fig. 1b). The reactor consisted of six lamps of UV-C (210 nm, 40 W) along the reactor height and an air pump at the bottom for circulation (Fig. 1b). During operation, the TiO2 loading was maintained at 0.1 g/l. After two days, approximately 160 l of treated water was replaced with fresh wastewater.
3. Results and discussion 3.1. Effect of pH The pH of leak test wastewater from the agricultural machinery industry was approximately 9. It was adjusted to a pH of 6, 7 and 8 to study the effect of pH on the photocatalytic activity for the organic carbon removal. At pH 6, the COD concentration in the wastewater was reduced from 1270 mg/l to 960 mg/l on the first day of operation and continued to decrease to 750 mg/l on day 2 and reached to the lowest value of 340 mg/l on day 5, as shown in Fig. 2. The trends of COD reduction at higher pH levels were similar as for the pH 6, i.e. the pH decreased to 650–750 mg/l on day 2 and to 340–400 mg/l on day 5. The overall COD removal efficiency was around 75%–80% at all pH values. The results revealed that the pH level had no effect on COD removal efficiency for the leak test wastewater. Although high COD
2.3. Industrial-scale reactor The industrial-scale of photocatalytic reactor was developed using a 3000 l polyethylene tank with 200 cm height and 165 cm diameter (Fig. 1c). The reactor consisted of 20 lamps of UV-C (210 nm, 58 W), two water pumps and an air pump. The TiO2 loading was also maintained at 0.1 g/l. Approximately 2000 l of treated water was discharged every two days. The operating conditions of three scales reactors are summarized in Table 2. 165
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Fig. 3. Efficiency of COD removal at various TiO2 loadings.
The aggregation of TiO2 particles at high loading was another significant reason to decrease the active surface site. Compared to previous studies, the optimal TiO2 loading was also found in the range of 0.75–2 g/l (Ghaly et al., 2011; Saquib et al., 2008). From Fig. 3, the COD removal efficiency of 57% was observed when there was no TiO2 in the wastewater. This is due to strong oxidation from UV-C light which is able to decompose some of the organic carbon content, as reported in previous study (Ruppert et al., 1994). Further, O3 can be generated via the reaction of O2 and UV light, as shown in Eqs. (2) and (3) (Van Sonntag et al., 1993). Therefore, the hybrid process of TiO2 photocatalysis, UV and O3 oxidation occurred in the photocatalytic reactors for organic carbon removal.
removal efficiency was reported at low pH values of around 2–4, the degradation of dyes from a particular synthetic dye wastewater such as bromocresol purple and methylene blue were investigated (Akpan and Hameed, 2009; Lin et al., 2013; Baran et al., 2008). At low pH levels, a strong adsorption of the dyes on TiO2 particles resulted in the increase in electrostatic attraction of positively charged TiO2 with the dyes. This phenomenon enhanced the activity of photocatalysis on dye degradation. However, the different composition of synthetic dyes in the wastewater and the actual industrial wastewater is a significant reason for the dissimilar results. Due to the effluent standard of the Industrial Estate Authority of Thailand, the COD concentration of treated water has to be less than 750 mg/l before discharge into a central wastewater treatment plant (PCD, 2016). The results suggest that the retention time of 2 days was sufficient for wastewater treatment using the photocatalytic reactor.
O2(g ) → 2Og
(2)
O(g ) + O2(g ) → O3(g )
(3)
3.2. Effect of TiO2 loading
3.3. Performance of pilot- and industrial- scale reactors
As the above experiment, the adjusted pH wastewater had no effect on increasing the photocatalysis activity. In this experiment, the leak test wastewater with no pH adjustment was used. Under various TiO2 loading of 0–10 g/l, the COD removal efficiency was increased by TiO2 loading; the efficiency was 75% at low TiO2 loading of 0.1 g/l and increased to 85% at the higher TiO2 loading of 1 g/l, as shown in Fig. 3. The COD removal efficiency was stable at approximately 85% of the TiO2 loading of 5 and 10 g/l. These results present the enhancement of photocatalytic activity to remove organic carbon by increasing TiO2 loading. The optimal TiO2 loading was 1 g/l to treat the leak test wastewater. At the high TiO2 loading of 5 and 10 mg/l, photocatalytic activity cannot be enhanced because the dense TiO2 particles decreased light penetration to generate the oxidizing agents of %O2−, and %OH.
The pilot-scale of 200 l photocatalytic reactor was built on the factory site, and operated in the fed-batch mode with a retention time of 2 days. The reactor design was modified from the lab-scale reactor to enhance photocatalytic activity. To save on operating costs, the TiO2 loading was started at 0.1 g/l in the photocatalytic reactor. During operation, the COD concentration was reduced from 3800 mg/l in the wastewater to 280 mg/l in the treated water, which was around 90% removal efficiency (data not presented as a graph). The good COD removal efficiency was observed on the first day of the operation and the efficiency was kept stable until the end of the experiment. The performance of the photocatalytic reactor at low TiO2 loading of 0.1 g/l was due to complete circulation and high oxygen levels during treatment, which resulted from improved design of the reactor. 166
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Fig. 4. Efficiency of organic carbon removal for industrial-scale photocatalytic reactor.
concentrations met the effluent standard of the Industrial Estate Authority of Thailand. This present study indicates that the photocatalytic reactor is an effective treatment system for industrial wastewater containing high levels of non-biodegradable organic carbon and oil and grease. The developed system is extremely cost-effective for wastewater treatment and industrial waste disposal. It is simple to operate and easy to maintain on site.
Table 3 Characteristics of treated water. Parameter
Concentration
Effluent standard of the Industrial Estate Authority of Thailand
Unit
pH Biochemical Oxygen Demand (BOD5) Chemical Oxygen Demand (COD) Suspended Solids (SS) Total Dissolved Solids (TDS) Total Kieldahl Nitrogen (TKN) Oil and grease
7.8 19
5.5–9 500
– mg/l
210
750
mg/l
57 956
200 3000
mg/l mg/l
16
100
mg/l
4
10
mg/l
4. Conclusions The actual industrial wastewater from the leak test process of an agricultural machinery company has high pH values and contains a high organic carbon content. The leak test wastewater was effectively treated by photocatalysis using TiO2 with no pH adjustment. The optimal TiO2 loading was 1 g/l in the lab-scale reactor which obtained 85% of COD removal. The COD removal efficiency increased to 90–92% in the pilot-scale and industrial-scale reactors at the low TiO2 of 0.1 g/l. This is because both reactors were designed for good circulation and high oxygen levels during the treatment, which were significant factors for achieving high performance photocatalytic activity. The treated water contained a low COD concentrations of 250 mg/l which met the effluent industrial standard of Thailand. It can be said that this study succeeded in applying the photocatalysis process to treat actual industrial wastewater without requiring any additional pre- and posttreatments.
The pilot-scale of the photocatalytic reactor was scaled up to a 3000 l industrial-scale reactor with some modifications to the water circulation system and the UV-C position. The reactor was operated in the fed-batch mode. The TiO2 loading was controlled at 0.1 g/l and the retention time was 2 days. The industrial-scale reactor was operated continuously for a month. The results are represented in Fig. 4. The excellent COD removal of 92% was consistently achieved from the first day. The COD concentration in the treated water was only 250 mg/l which reduced from an initial concentration of 3500–5000 mg/l in the wastewater. The other parameters of the water quality measured are summarized in Table 3. It can be seen that the overall quality of treated water including nitrogen, dissolved solids and oil and grease 167
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of TiO2. Dyes Pigm. 76, 226–230. Chong, M.N., Jin, B., Chow, C.W.K., Saint, C., 2010. Recent developments in photocatalytic water treatment technology: a review. Water Res. 44, 2997–3027. Ghaly, M.Y., Jamil, T.S., El-Seesy, I.E., Souaya, E.R., Nasr, R.A., 2011. Treatment of highly polluted paper mill wastewater by solar photocatalytic oxidation with synthesized nano TiO2. Chem. Eng. J. 168, 446–454. Lin, C.P., Chen, H., Nakaruk, K., Koshy, P., Sorrell, C.C., 2013. Effect of annealing temperature on the photocatalytic activity of TiO2 thin films. Energy Procedia 34, 627–636. Pollution Control Department (PCD), Thailand, 2016, URL: http://www.pcd.go.th. Ruppert, G., Bauer, R., Heisler, G., 1994. UV-O3, UV-H2O2, UV-TiO2 and the photo-fenton reaction – comparison of advanced oxidation processes for wastewater treatment. Chemosphere 28, 1447–1454. Saquib, M., Tariq, M.A., Faisal, M., Muneer, M., 2008. Photocatalytic degradation of two selected dye derivatives in aqueous suspensions of titanium dioxide. Desalinatioin 219, 301–311. Siam Kubota Corporation, 2014. Annual Report. Van Sonntag, C., Mertens, G.M.R., Schuchmann, M.N., Schuchmann, H.P., 1993. UV radiation and/or oxidants in water pollution control. Aqua 42, 201–211. Yuangpho, N., Le, S.T.T., Treerujiraphapong, T., Khanitchaidecha, W., Nakaruk, A., 2015. Enhanced photocatalytic performance of TiO2 particles via effect of anatase–rutile ratio. Physica E. 67, 18–22.
Conflict of interest The authors declare that there is no conflict of interest regarding the publication of this paper. Acknowledgement The authors would like to thank Naresuan University Research Funding for financial and other support during this study. References Akpan, U.G., Hameed, B.H., 2009. Parameters affecting the photocatalytic degradation of dues using TiO2-based photocatalysts: a review. J. Hazard. Mater. 170, 52–529. Banu, J.R., Anandan, S., Kaliappan, S., Yeom, I., 2008. Treatment of dairy wastewater using anaerobic and solar photocatalytic methods. Sol. Energy 82, 812–819. Baran, W., Makowski, A., Wardas, W., 2008. The effect of UV radiation absorption of cationic and anionic dye solutions on their photocatalytic degradation in the presence
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Contents lists available at ScienceDirect
Environmental Nanotechnology, Monitoring & Management journal homepage: www.elsevier.com/locate/enmm
Treatment of high organic carbon industrial wastewater using photocatalysis process T. Threrujirapaponga, W. Khanitchaidechab,c, A. Nakarukb,d,
T
⁎
a
Department of Materials and Production Technology Engineering, King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand Centre of Excellence for Innovation and Technology for Water Treatment, Faculty of Engineering, Naresuan University, Thailand c Department of Civil Engineering, Faculty of Engineering, Naresuan University, Thailand d Department of Industrial Engineering, Faculty of Engineering, Naresuan University, Thailand b
A R T I C L E I N F O
A B S T R A C T
Keywords: Actual industrial wastewater treatment High organic carbon wastewater Photocatalysis process
In Thailand, agricultural machinery manufacturing companies are known to generate high organic carbon wastewater from painting and leak testing processes. Chemical oxygen demand (COD) value in leak test wastewater is found to be in the range of 3000–5000 mg/l. In this study, three scales including lab-scale, pilot-scale and industrial-scale photocatalytic reactors were developed to investigate the efficiency of wastewater treatment. In lab-scale, the 800 ml reactors were set up to optimize the best condition for pH and TiO2 loading. The results suggested that the pH had no effects on the COD removal, whereas the COD removal efficiency was increased by TiO2 loading. The highest COD removal efficiency of 85% was found at the TiO2 loading of 1 g/l. The 200 l reactor of pilot-scale and the 3000 l reactor of industrial-scale were established and continuously operated for 30 days. The results revealed that the COD removal efficiency was > 90%, and the COD concentration was reduced to 250–300 mg/l in the treated wastewater. The COD value of treated wastewater met the standard set by the Industrial Estate Authority of Thailand to discharge into a central wastewater treatment plant, which verified the successful implementation of process to the actual industrial wastewater.
1. Introduction The agricultural machinery manufacturing industry is considered to be one of the key industrial sectors in Thailand. The most common products of the industry are tractors, agricultural implements and harvesters. There are several manufacturing processes including surface etching, painting, assembly and leak testing. During leak testing, grease which is used for preventing rust contaminates the water, called leak test wastewater, which is difficult to treat by traditional treatment processes. The leak test wastewater contains a high grease content of 40 mg/l and its chemical oxygen demand concentration (COD) which is referred to as organic carbon contamination is in the range of 3000–5000 mg/l (Siam Kubota Corporation, 2014). Normally, the industry treats leak test wastewater by chemical precipitation to reduce the organic carbon of about 80%, and then the wastewater is further treated in a central wastewater treatment plant of an industrial estate (Siam Kubota Corporation, 2014). According to the chemical precipitation process, the organic carbon content is efficiently removed, however the chemical solid waste which is a by-product of the process, is generated and requires further treatment and disposal. The industry spends millions of dollars every year for such chemical solid waste ⁎
treatment and disposal. To reduce the treatment and disposal costs, the industry is interested in finding more efficient and cheaper alternatives. The advanced technology of the photocatalysis process which has no toxic waste as a by-product is a potential process for the leak test wastewater treatment. Photocatalysis is known as one of the advanced oxidation processes, it is applicable in the treatment of high organic carbon wastewater (Chong et al., 2010; Ghaly et al., 2011). According to the conceptual photocatalysis process, a catalyst such as TiO2 is exposed to light and exhibited oxidative decomposition and super hydrophilic properties of %O2−, and %OH under an aeration. These two forms can decompose organic carbon from wastewater to intermediate forms and continued to become carbon dioxide (CO2) and water (H2O), as shown in Eq. (1) Banu et al. (2008). TiO2 + O2 light
Organic Compound ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ intermediates ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ CO2 + H2 O
(1)
However, the application of the photocatalysis process in actual industrial wastewater treatment, has been very limited. There are only a few reports available. For example, Ghaly et al. (2011) used photocatalysis and H2O2 oxidation to treat paper mill wastewater which
Corresponding author at: Department of Industrial Engineering, Faculty of Engineering, Naresuan University, Thailand. E-mail addresses: [email protected], [email protected] (A. Nakaruk).
http://dx.doi.org/10.1016/j.enmm.2017.07.006 Received 27 November 2016; Received in revised form 15 June 2017; Accepted 17 July 2017 2215-1532/ © 2017 Elsevier B.V. All rights reserved.
TiO2 + O2 light
Environmental Nanotechnology, Monitoring & Management 8 (2017) 163–168
T. Threrujirapapong et al.
Table 1 Characteristics of leak test wastewater from the agricultural machinery industry.
Table 2 Summary of operating conditions of photocatalytic reactors.
Parameter
Concentration
Unit
Analysis method
Reactor
pH Biochemical Oxygen Demand (BOD5) Chemical Oxygen Demand (COD) Suspended Solids (SS) Total Dissolved Solids (TDS) Total Kieldahl Nitrogen (TKN) Oil and grease
9.2 170
– mg/l
Electrometric method 5-day BOD test
Lab-scale Effect of pH
3200
mg/l
Close reflux
150 3940
mg/l mg/l
Dried at 103–105 °C Dried at 103–105 °C
198
mg/l
Macro-Kjeldahl method
36
mg/l
Liquid-liquid, partition gravimetric
Effect of TiO2 loading
Pilot-scale Industrial-scale
pH
TiO2 loading (g/l)
Reactor volume (l)
6 7 8 No No No No No No No No
1 1 1 1 0 0.1 1 5 10 0.1 0.1
0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 200 3000
adjustment adjustment adjustment adjustment adjustment adjustment adjustment adjustment
2. Methodology
contains the high COD level of 2000 mg/l, the COD removal efficiency was approximately 75%. Further, the effective photocatalytic reactor was established to treat the effluent from an anaerobic bioreactor in the dairy industry; the COD and nitrogen concentrations in the wastewater were approximately 300 mg/l and 60 mg/l (Banu et al., 2008). However, both wastewater in previous studies had no oil and grease contamination which possibly negatively effects on the performance of photocatalysis process. The intention of the present study is to investigate the efficiency of the photocatalysis process for industrial wastewater containing high non-biodegradable organic carbon. The COD removal efficiency is used as an indicator to identify the performance of organic carbon removal. Firstly, lab-scale of photocatalytic reactors were used to study and clarify the optimal pH and TiO2 loading. Later, the pilot-scale and industrial-scale of photocatalytic reactors were implemented at the industry site for investigating performance under long-term operational conditions.
Leak test wastewater from the agricultural machinery industry is used as a case study in this study. The characteristics of the wastewater is summarized in Table 1 (Siam Kubota Corporation, 2014). In the experiments, commercial TiO2 particles were used as a catalyst. The characteristics of TiO2 particles are shown in previous study (Yuangpho et al., 2015). The various scales of photocatalytic reactors as developed, are indicated as follows: 2.1. Lab-scale reactor In the lab-scale reactors, the effects of pH and TiO2 loading were studied. The pH of wastewater was adjusted to 6, 7 and 8 using H2SO4. Then, 800 ml of adjusted wastewater was added into three 1 l beakers. Wastewater with no pH adjustment was used as a control. Although the enhancement of photocatalysis activity was reported at a low pH value (Akpan and Hameed, 2009), the cost-effectiveness of chemicals
Fig. 1. Schematic diagram of (a) lab-scale, (b) pilot-scale and (c) industrial-scale of photocatalytic reactors for actual industrial wastewater treatment.
164
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Fig. 2. Reduction of organic carbon in industrial wastewater at various pH values.
2.4. Water quality analysis
consumption for pH adjustment and neutralization was a factor of concern for the industry. Hence, only pH values of 6, 7 and 8 were studied. Then, the TiO2 loading was controlled at 1 g/l for the four reactors. All reactors were placed in the closed system which contains two lamps of UV-C (210 nm, 40 W) on the top and stirrers at the bottom (as shown in Fig. 1a) for 5 days. For the study of the effects of TiO2 loading, various TiO2 loadings of 0–10 g/l were added to the wastewater with no pH adjustment, then the above procedure was followed to study the pH effect.
The performance of the photocatalytic reactors for the treatment of actual industrial wastewater was evaluated by the reduction of the COD value which is commonly referred to as the organic carbon content of the wastewater. The COD value was measured by using Chemical Oxygen Demand (COD) analyzer (AL200 COD Vario, Aqualytic). The other parameters such as Biochemical Oxygen Demand (BOD5), Suspended Solids (SS) and Total Dissolved Solids (TDS) were measured by an environmental consultant company; the methods of measurement are presented in Table 1. The pH and dissolved oxygen (DO) values were regularly detected by using a pH meter (Eutech Instruments) and a DO meter (CyberScan DO 110 Model) while the reactors were operating.
2.2. Pilot-scale reactor The pilot-scale reactor was setup using a 200 l polyethylene tank with a height of 70 cm and a diameter of 65 cm (Fig. 1b). The reactor consisted of six lamps of UV-C (210 nm, 40 W) along the reactor height and an air pump at the bottom for circulation (Fig. 1b). During operation, the TiO2 loading was maintained at 0.1 g/l. After two days, approximately 160 l of treated water was replaced with fresh wastewater.
3. Results and discussion 3.1. Effect of pH The pH of leak test wastewater from the agricultural machinery industry was approximately 9. It was adjusted to a pH of 6, 7 and 8 to study the effect of pH on the photocatalytic activity for the organic carbon removal. At pH 6, the COD concentration in the wastewater was reduced from 1270 mg/l to 960 mg/l on the first day of operation and continued to decrease to 750 mg/l on day 2 and reached to the lowest value of 340 mg/l on day 5, as shown in Fig. 2. The trends of COD reduction at higher pH levels were similar as for the pH 6, i.e. the pH decreased to 650–750 mg/l on day 2 and to 340–400 mg/l on day 5. The overall COD removal efficiency was around 75%–80% at all pH values. The results revealed that the pH level had no effect on COD removal efficiency for the leak test wastewater. Although high COD
2.3. Industrial-scale reactor The industrial-scale of photocatalytic reactor was developed using a 3000 l polyethylene tank with 200 cm height and 165 cm diameter (Fig. 1c). The reactor consisted of 20 lamps of UV-C (210 nm, 58 W), two water pumps and an air pump. The TiO2 loading was also maintained at 0.1 g/l. Approximately 2000 l of treated water was discharged every two days. The operating conditions of three scales reactors are summarized in Table 2. 165
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Fig. 3. Efficiency of COD removal at various TiO2 loadings.
The aggregation of TiO2 particles at high loading was another significant reason to decrease the active surface site. Compared to previous studies, the optimal TiO2 loading was also found in the range of 0.75–2 g/l (Ghaly et al., 2011; Saquib et al., 2008). From Fig. 3, the COD removal efficiency of 57% was observed when there was no TiO2 in the wastewater. This is due to strong oxidation from UV-C light which is able to decompose some of the organic carbon content, as reported in previous study (Ruppert et al., 1994). Further, O3 can be generated via the reaction of O2 and UV light, as shown in Eqs. (2) and (3) (Van Sonntag et al., 1993). Therefore, the hybrid process of TiO2 photocatalysis, UV and O3 oxidation occurred in the photocatalytic reactors for organic carbon removal.
removal efficiency was reported at low pH values of around 2–4, the degradation of dyes from a particular synthetic dye wastewater such as bromocresol purple and methylene blue were investigated (Akpan and Hameed, 2009; Lin et al., 2013; Baran et al., 2008). At low pH levels, a strong adsorption of the dyes on TiO2 particles resulted in the increase in electrostatic attraction of positively charged TiO2 with the dyes. This phenomenon enhanced the activity of photocatalysis on dye degradation. However, the different composition of synthetic dyes in the wastewater and the actual industrial wastewater is a significant reason for the dissimilar results. Due to the effluent standard of the Industrial Estate Authority of Thailand, the COD concentration of treated water has to be less than 750 mg/l before discharge into a central wastewater treatment plant (PCD, 2016). The results suggest that the retention time of 2 days was sufficient for wastewater treatment using the photocatalytic reactor.
O2(g ) → 2Og
(2)
O(g ) + O2(g ) → O3(g )
(3)
3.2. Effect of TiO2 loading
3.3. Performance of pilot- and industrial- scale reactors
As the above experiment, the adjusted pH wastewater had no effect on increasing the photocatalysis activity. In this experiment, the leak test wastewater with no pH adjustment was used. Under various TiO2 loading of 0–10 g/l, the COD removal efficiency was increased by TiO2 loading; the efficiency was 75% at low TiO2 loading of 0.1 g/l and increased to 85% at the higher TiO2 loading of 1 g/l, as shown in Fig. 3. The COD removal efficiency was stable at approximately 85% of the TiO2 loading of 5 and 10 g/l. These results present the enhancement of photocatalytic activity to remove organic carbon by increasing TiO2 loading. The optimal TiO2 loading was 1 g/l to treat the leak test wastewater. At the high TiO2 loading of 5 and 10 mg/l, photocatalytic activity cannot be enhanced because the dense TiO2 particles decreased light penetration to generate the oxidizing agents of %O2−, and %OH.
The pilot-scale of 200 l photocatalytic reactor was built on the factory site, and operated in the fed-batch mode with a retention time of 2 days. The reactor design was modified from the lab-scale reactor to enhance photocatalytic activity. To save on operating costs, the TiO2 loading was started at 0.1 g/l in the photocatalytic reactor. During operation, the COD concentration was reduced from 3800 mg/l in the wastewater to 280 mg/l in the treated water, which was around 90% removal efficiency (data not presented as a graph). The good COD removal efficiency was observed on the first day of the operation and the efficiency was kept stable until the end of the experiment. The performance of the photocatalytic reactor at low TiO2 loading of 0.1 g/l was due to complete circulation and high oxygen levels during treatment, which resulted from improved design of the reactor. 166
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Fig. 4. Efficiency of organic carbon removal for industrial-scale photocatalytic reactor.
concentrations met the effluent standard of the Industrial Estate Authority of Thailand. This present study indicates that the photocatalytic reactor is an effective treatment system for industrial wastewater containing high levels of non-biodegradable organic carbon and oil and grease. The developed system is extremely cost-effective for wastewater treatment and industrial waste disposal. It is simple to operate and easy to maintain on site.
Table 3 Characteristics of treated water. Parameter
Concentration
Effluent standard of the Industrial Estate Authority of Thailand
Unit
pH Biochemical Oxygen Demand (BOD5) Chemical Oxygen Demand (COD) Suspended Solids (SS) Total Dissolved Solids (TDS) Total Kieldahl Nitrogen (TKN) Oil and grease
7.8 19
5.5–9 500
– mg/l
210
750
mg/l
57 956
200 3000
mg/l mg/l
16
100
mg/l
4
10
mg/l
4. Conclusions The actual industrial wastewater from the leak test process of an agricultural machinery company has high pH values and contains a high organic carbon content. The leak test wastewater was effectively treated by photocatalysis using TiO2 with no pH adjustment. The optimal TiO2 loading was 1 g/l in the lab-scale reactor which obtained 85% of COD removal. The COD removal efficiency increased to 90–92% in the pilot-scale and industrial-scale reactors at the low TiO2 of 0.1 g/l. This is because both reactors were designed for good circulation and high oxygen levels during the treatment, which were significant factors for achieving high performance photocatalytic activity. The treated water contained a low COD concentrations of 250 mg/l which met the effluent industrial standard of Thailand. It can be said that this study succeeded in applying the photocatalysis process to treat actual industrial wastewater without requiring any additional pre- and posttreatments.
The pilot-scale of the photocatalytic reactor was scaled up to a 3000 l industrial-scale reactor with some modifications to the water circulation system and the UV-C position. The reactor was operated in the fed-batch mode. The TiO2 loading was controlled at 0.1 g/l and the retention time was 2 days. The industrial-scale reactor was operated continuously for a month. The results are represented in Fig. 4. The excellent COD removal of 92% was consistently achieved from the first day. The COD concentration in the treated water was only 250 mg/l which reduced from an initial concentration of 3500–5000 mg/l in the wastewater. The other parameters of the water quality measured are summarized in Table 3. It can be seen that the overall quality of treated water including nitrogen, dissolved solids and oil and grease 167
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of TiO2. Dyes Pigm. 76, 226–230. Chong, M.N., Jin, B., Chow, C.W.K., Saint, C., 2010. Recent developments in photocatalytic water treatment technology: a review. Water Res. 44, 2997–3027. Ghaly, M.Y., Jamil, T.S., El-Seesy, I.E., Souaya, E.R., Nasr, R.A., 2011. Treatment of highly polluted paper mill wastewater by solar photocatalytic oxidation with synthesized nano TiO2. Chem. Eng. J. 168, 446–454. Lin, C.P., Chen, H., Nakaruk, K., Koshy, P., Sorrell, C.C., 2013. Effect of annealing temperature on the photocatalytic activity of TiO2 thin films. Energy Procedia 34, 627–636. Pollution Control Department (PCD), Thailand, 2016, URL: http://www.pcd.go.th. Ruppert, G., Bauer, R., Heisler, G., 1994. UV-O3, UV-H2O2, UV-TiO2 and the photo-fenton reaction – comparison of advanced oxidation processes for wastewater treatment. Chemosphere 28, 1447–1454. Saquib, M., Tariq, M.A., Faisal, M., Muneer, M., 2008. Photocatalytic degradation of two selected dye derivatives in aqueous suspensions of titanium dioxide. Desalinatioin 219, 301–311. Siam Kubota Corporation, 2014. Annual Report. Van Sonntag, C., Mertens, G.M.R., Schuchmann, M.N., Schuchmann, H.P., 1993. UV radiation and/or oxidants in water pollution control. Aqua 42, 201–211. Yuangpho, N., Le, S.T.T., Treerujiraphapong, T., Khanitchaidecha, W., Nakaruk, A., 2015. Enhanced photocatalytic performance of TiO2 particles via effect of anatase–rutile ratio. Physica E. 67, 18–22.
Conflict of interest The authors declare that there is no conflict of interest regarding the publication of this paper. Acknowledgement The authors would like to thank Naresuan University Research Funding for financial and other support during this study. References Akpan, U.G., Hameed, B.H., 2009. Parameters affecting the photocatalytic degradation of dues using TiO2-based photocatalysts: a review. J. Hazard. Mater. 170, 52–529. Banu, J.R., Anandan, S., Kaliappan, S., Yeom, I., 2008. Treatment of dairy wastewater using anaerobic and solar photocatalytic methods. Sol. Energy 82, 812–819. Baran, W., Makowski, A., Wardas, W., 2008. The effect of UV radiation absorption of cationic and anionic dye solutions on their photocatalytic degradation in the presence
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