w a t e r r e s e a r c h 7 1 ( 2 0 1 5 ) 8 5 e9 6
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/watres
Post-treatment of biologically treated wastewater containing organic contaminants using a sequence of H2O2 based advanced oxidation processes: Photolysis and catalytic wet oxidation rquez a,*, M. Sillanpa €a € b, P. Pocostales c, A. Acevedo a, J.J. Rueda-Ma M.A. Manzano a a Department of Environmental Technologies, Faculty of Marine and Environmental Sciences, Cadiz University, diz, Spain Avda. Repu´blica Saharaui S/N, Puerto Real, 11510, Ca b Laboratory of Green Chemistry, Lappeenranta University of Technology, Sammonkatu 12, 50100, Mikkeli, Finland c R&D Department, Abengoa Water, C/ Don Redondo, Dos Hermanas, 41703, Seville, Spain
article info
abstract
Article history:
In this paper the feasibility of a multi-barrier treatment (MBT) for the regeneration of
Received 13 September 2014
synthetic industrial wastewater (SIWW) was evaluated. Industrial pollutants (orange II,
Received in revised form
phenol, 4-chlorophenol and phenanthrene) were added to the effluent of municipal
25 December 2014
wastewater treatment plant.
Accepted 29 December 2014 Available online 8 January 2015
The proposed MBT begins with a microfiltration membrane pretreatment (MF), followed by hydrogen peroxide photolysis (H2O2/UVC) and finishing, as a polishing step, with catalytic wet peroxide oxidation (CWPO) using granular activated carbon (GAC) at ambient
Keywords: AOP
conditions. During the microfiltration step (0.7 mm) the decrease of suspended solids concentration,
Accumulated UVC dose
turbidity and Escherichia coli in treated water were 88, 94 and 99%, respectively. Also, the
Disinfection
effluent's transmittance (254 nm) was increased by 14.7%. Removal of more than 99.9% of
UVC dose equation
all added pollutants, mineralization of 63% of organic compounds and complete disinfec-
Toxicity test
tion of total coliforms were reached during the H2O2/UVC treatment step (H2O2:TOC w/w
Operational cost
ratio ¼ 5 and an UVC average dose accumulated by wastewater 8.80 WUVC s cm2). The power and efficiency of the lamp, the water transmittance and photoreactor geometry are taken into account and a new equation to estimate the accumulated dose in water is suggested. Remaining organic pollutants with a higher oxidation state of carbon atoms (þ0.47) and toxic concentration of residual H2O2 were present in the effluent of the H2O2/ UVC process. After 2.3 min of contact time with GAC at CWPO step, 90 and 100% of total organic carbon and residual H2O2 were removed, respectively. Also, the wastewater toxicity was studied using Vibrio fischeri and Sparus aurata larvae. The MBT operational and maintenance costs (O&M) was estimated to be 0.59 V m3. © 2015 Elsevier Ltd. All rights reserved.
* Corresponding author. Faculty of Marine and Environmental Sciences, Cadiz University (CACYTMAR), Avda. Repu´blica Saharaui S/N, diz, Spain. Tel.: þ34 956016587. Puerto Real, 11510, Ca rquez). E-mail address: [email protected] (J.J. Rueda-Ma http://dx.doi.org/10.1016/j.watres.2014.12.054 0043-1354/© 2015 Elsevier Ltd. All rights reserved.
86
1.
w a t e r r e s e a r c h 7 1 ( 2 0 1 5 ) 8 5 e9 6
Introduction
Wastewaters from industries such as pulp and paper, textile, chemical and petrochemical contain a cocktail of organic contaminants which may be non-biodegradable or environmentally toxic. They must be treated in order to satisfy the stringent water quality regulations and the demand for water recycling in the industrial processes. Conventional technologies, including biological, physical and chemical treatments, are usually applied to remove aqueous pollutants (Kim and Ihm, 2011). Despite widespread use of biological methods for the residual wastewater treatment, this approach is not suitable for the removal of nonbiodegradable or toxic compounds. This limitation has encouraged the development of more efficient and environmental-friendly systems for wastewater treatment. One possibility for industrial wastewater decontamination is combination of biological and chemical treatments, firstly eliminating the highly biodegradable part and then degrading the recalcitrant contaminants by a post-treatment based on advance oxidation processes (AOPs). AOPs are considered as highly competitive water treatment processes for removal of organic pollutants that are resistant to conventional techniques due to their high chemical stability and/or low biodegradability (Oller et al., 2011). Several processes like Fenton, photo-Fenton, wet oxidation, ozonation or photocatalysis are included in the AOPs and the main difference between them is the way of producing hydroxyl radicals ($OH). The most widely applied methods are based on generation of hydroxyl radicals via photolysis of hydrogen peroxide, as well as ozone and titanium dioxide (Coleman et al., 2007). With regard to H2O2 photolysis, the role of UV irradiation is to catalyze the oxidation process in two ways: one through excitation of the target pollutant, thereby increasing its reactivity towards oxidants and the other through promotion of H2O2 homolysis to form hydroxyl radicals (Eq. (1)), which are very strong oxidizing species (Catalkaya and Kargi, 2007; Chen, 2010). H2 O2 þ hn/2$OH
(1)
At high H2O2 concentration, the following reactions (2, 3) may additionally occur, (Borghei and Hosseini, 2008; Tabrizi and Mehrvar, 2006), which can scavenge $OH and inhibit the process. H2 O2 þ $OH/H2 O þ HO2 $
(2)
HO2 $ þ $OH/H2 O þ O2
(3)
The use of hydrogen peroxide as an oxidant in H2O2/UVC treatment has a number of advantages: (i) it is readily available, easy to store, relatively safe to handle and environmentally friendly; (ii) it is a cost-effective source of hydroxyl radicals, two hydroxyl radicals being formed per each photolyzed H2O2 molecule and (iii) peroxyl radicals (HO2$) are generated after $OH attack on most organic substrates, thus, facilitating oxidation reactions (Legrini et al., 1993; Pan et al.,
1993). Apart from these advantages, phase transfer and sludge formation problems are not encountered in this process. The main disadvantages of H2O2 photolysis are the presence of residual hydrogen peroxide in the effluent and the possible generation of toxic by-products during the treatment, which can be removed by activated carbon (AC) (Heringa et al., 2011). Moreover, the use of H2O2 photolysis as the only treatment method would not make economic sense, since both capital and operational costs are relatively high (Del Moro et al., 2013). Therefore, H2O2 photolysis could be used after the biological step (if wastewater is not toxic for bio-treatment) and prior to a polishing step through GAC (CWPO) aiming to remove residual organic pollutants and excess H2O2 for wastewater discharge. Although, the GAC adsorption method without H2O2 is effective for removal of organic compounds, the GAC can be saturated easily in the process, and requires regeneration or complete replacement. Hydrogen peroxide decomposition is one of the most known reactions to be catalyzed by carbon materials (Serp and Figueiredo, 2009). Recent research demonstrated that AC is active in the degradation of some dissolved organic pollutants in the presence of H2O2, providing evidence that AC can promote hydrogen peroxide decomposition through the formation of hydroxyl radicals (Eq.(4) and (5)) (Lu¨cking et al., 1998; Oliveira et al., 2004; Rey et al., 2011; Santos et al., 2009). AC þ H2 O2 /$OH þ OH þ ACþ
(4)
ACþ þ H2 O2 /AC þ $OOH þ Hþ
(5)
Georgi and Kopinke (2005) concluded that the predominant pathway of the degradation reaction during CWPO is the attack by $OH of organic contaminant fraction that is freely dissolved in the pore volume of the AC. In contrast, the adsorbed fraction is nearly non-reactive. Consequently, sorption on AC has an adverse effect on the oxidation of organic compounds via $OH radical even though the radicals are formed directly on the AC surface. The CWPO process after H2O2/UVC treatment is useful because molar mass and hydrophobicity of the organic pollutants are decreasing and increasing, respectively (Lu¨cking et al., 1998). Also, during the CWPO step the residual H2O2 from the hydrogen peroxide photolysis process is consumed, bkova et al., leading to the effluent's toxicity removal (Dra 2007). It should be noted that a few installations combining H2O2/ UV followed by GAC are currently operated, and most of them are for drinking water production (Heringa et al., 2011; Kruithof et al., 2007). Hence, the aim of this work was to evaluate the feasibility of a multibarrier (MBT) approach (MF, H2O2/UVC and CWPO) to obtain safer effluent after MBT wastewater treatment. Also, toxicity evolution during MBT treatment was assessed with sea water species to estimate the impact of discharge to the environment. Target economic parameters, such as reagent consumption, electricity and replacement of installation parts were used to estimate the operating cost of the MBT process (V m3).
w a t e r r e s e a r c h 7 1 ( 2 0 1 5 ) 8 5 e9 6
2.
Materials and methods
2.1.
Synthetic industrial wastewater (SIWW)
The SIWW was the effluent of a domestic wastewater treatment plant spiked with model industrial organic pollutants (Table 1). The urban wastewater (UWW) was purchased from the effluent of wastewater treatment plant (WWTP) in Chi diz, Spain) where physical and bioclana de la Frontera (Ca logical treatment is applied for water purification. For preparation of SIWW, the UWW was used as a matrix. It was done in order to simulate the conditions of real industrial wastewater, the main problems of which are organic compounds recalcitrant to biological treatment, presence of suspended solids, salinity, coloration, microorganism and turbidity. The following industrial organic compounds were added to UWW: 4-chlorophenol, phenol, phenanthrene and orange II. The 4-chlorophenol is a halogenated aromatic compound considered as priority pollutant by USEPA since 1976. It is known to be endocrine disruptor, toxic and nonbiodegradable, and it is present in wastewater as byproduct of pulp and paper, dyestuff, pharmaceutical and agrochemical industries (Pozan and Kambur, 2013). Phenol is a major component of organic waste streams such as dye manufacture wastewater, pulp and paper manufacture wastewater, and it is also found in wastewaters from the petrochemical industry and municipal solid waste (Onwudili and Williams, 2007). Phenanthrene is a polycyclic aromatic hydrocarbon considered as priority pollutant due
Table 1 e The main characteristics of SIWW. Parameter (unit) 1
COD (mg O2 L ) TOC (mg C L1) SS (mg L1) Turbidity (NTU) Transmittance (254 nm, %) pH Conductivity (mS cm1/mg TDS L1) E. coli (CFU 100 mL1) Total coliforms (CFU 100 mL1) Nematodes (eggs 10 L1) 4-Chlorophenol (mg L1) Phenol (mg L1) Phenanthrene (mg L1) Orange II (mg L1) a
Value 146 40 25 6.7 43.6 7.14 1900/1222 104 107 4-chlorophenol > phenol. It should be noted that, these compounds were completely degraded with a dose 5.53 WUVC s cm2. C ¼ C0 *ek*D
Fig. 3 e Average oxidation state of carbon atoms (AOSC) during H2O2/UVC process as a function of UVC average dose accumulated by the wastewater. Note that a þ4 oxidation state corresponds to inorganic carbon (CO2) and a ¡4 oxidation state corresponds to methane.
(9)
Higher UVC dose accumulated by water is required for mineralization and/or oxidation of organic pollutants than for degradation. Hence, 8.80 WUVC s cm2 of UVC average dose accumulated by wastewater was necessary to remove 76% of COD. The decrease of COD and TOC means an increase of organic pollutant oxidation during the H2O2 process. The average oxidation state of carbon atoms (AOSC) in the reaction mixture (Fig. 3) was calculated by means of Eq. (10), reported by Scott and Ollis (1995). AOSC ¼ 4 1:5
COD TOC
(10)
According to Fig. 3, the residual organic molecules are oxidized, increasing values of AOSC from 1.5 (mostly non oxygenates hydrocarbons and alcohols) to þ0.45 (organic compound with a carbonyl group) with UVC accumulated dose by the wastewater at 8.80 WUVC s cm2. Finally in this step, total coliforms disinfection (
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/watres
Post-treatment of biologically treated wastewater containing organic contaminants using a sequence of H2O2 based advanced oxidation processes: Photolysis and catalytic wet oxidation rquez a,*, M. Sillanpa €a € b, P. Pocostales c, A. Acevedo a, J.J. Rueda-Ma M.A. Manzano a a Department of Environmental Technologies, Faculty of Marine and Environmental Sciences, Cadiz University, diz, Spain Avda. Repu´blica Saharaui S/N, Puerto Real, 11510, Ca b Laboratory of Green Chemistry, Lappeenranta University of Technology, Sammonkatu 12, 50100, Mikkeli, Finland c R&D Department, Abengoa Water, C/ Don Redondo, Dos Hermanas, 41703, Seville, Spain
article info
abstract
Article history:
In this paper the feasibility of a multi-barrier treatment (MBT) for the regeneration of
Received 13 September 2014
synthetic industrial wastewater (SIWW) was evaluated. Industrial pollutants (orange II,
Received in revised form
phenol, 4-chlorophenol and phenanthrene) were added to the effluent of municipal
25 December 2014
wastewater treatment plant.
Accepted 29 December 2014 Available online 8 January 2015
The proposed MBT begins with a microfiltration membrane pretreatment (MF), followed by hydrogen peroxide photolysis (H2O2/UVC) and finishing, as a polishing step, with catalytic wet peroxide oxidation (CWPO) using granular activated carbon (GAC) at ambient
Keywords: AOP
conditions. During the microfiltration step (0.7 mm) the decrease of suspended solids concentration,
Accumulated UVC dose
turbidity and Escherichia coli in treated water were 88, 94 and 99%, respectively. Also, the
Disinfection
effluent's transmittance (254 nm) was increased by 14.7%. Removal of more than 99.9% of
UVC dose equation
all added pollutants, mineralization of 63% of organic compounds and complete disinfec-
Toxicity test
tion of total coliforms were reached during the H2O2/UVC treatment step (H2O2:TOC w/w
Operational cost
ratio ¼ 5 and an UVC average dose accumulated by wastewater 8.80 WUVC s cm2). The power and efficiency of the lamp, the water transmittance and photoreactor geometry are taken into account and a new equation to estimate the accumulated dose in water is suggested. Remaining organic pollutants with a higher oxidation state of carbon atoms (þ0.47) and toxic concentration of residual H2O2 were present in the effluent of the H2O2/ UVC process. After 2.3 min of contact time with GAC at CWPO step, 90 and 100% of total organic carbon and residual H2O2 were removed, respectively. Also, the wastewater toxicity was studied using Vibrio fischeri and Sparus aurata larvae. The MBT operational and maintenance costs (O&M) was estimated to be 0.59 V m3. © 2015 Elsevier Ltd. All rights reserved.
* Corresponding author. Faculty of Marine and Environmental Sciences, Cadiz University (CACYTMAR), Avda. Repu´blica Saharaui S/N, diz, Spain. Tel.: þ34 956016587. Puerto Real, 11510, Ca rquez). E-mail address: [email protected] (J.J. Rueda-Ma http://dx.doi.org/10.1016/j.watres.2014.12.054 0043-1354/© 2015 Elsevier Ltd. All rights reserved.
86
1.
w a t e r r e s e a r c h 7 1 ( 2 0 1 5 ) 8 5 e9 6
Introduction
Wastewaters from industries such as pulp and paper, textile, chemical and petrochemical contain a cocktail of organic contaminants which may be non-biodegradable or environmentally toxic. They must be treated in order to satisfy the stringent water quality regulations and the demand for water recycling in the industrial processes. Conventional technologies, including biological, physical and chemical treatments, are usually applied to remove aqueous pollutants (Kim and Ihm, 2011). Despite widespread use of biological methods for the residual wastewater treatment, this approach is not suitable for the removal of nonbiodegradable or toxic compounds. This limitation has encouraged the development of more efficient and environmental-friendly systems for wastewater treatment. One possibility for industrial wastewater decontamination is combination of biological and chemical treatments, firstly eliminating the highly biodegradable part and then degrading the recalcitrant contaminants by a post-treatment based on advance oxidation processes (AOPs). AOPs are considered as highly competitive water treatment processes for removal of organic pollutants that are resistant to conventional techniques due to their high chemical stability and/or low biodegradability (Oller et al., 2011). Several processes like Fenton, photo-Fenton, wet oxidation, ozonation or photocatalysis are included in the AOPs and the main difference between them is the way of producing hydroxyl radicals ($OH). The most widely applied methods are based on generation of hydroxyl radicals via photolysis of hydrogen peroxide, as well as ozone and titanium dioxide (Coleman et al., 2007). With regard to H2O2 photolysis, the role of UV irradiation is to catalyze the oxidation process in two ways: one through excitation of the target pollutant, thereby increasing its reactivity towards oxidants and the other through promotion of H2O2 homolysis to form hydroxyl radicals (Eq. (1)), which are very strong oxidizing species (Catalkaya and Kargi, 2007; Chen, 2010). H2 O2 þ hn/2$OH
(1)
At high H2O2 concentration, the following reactions (2, 3) may additionally occur, (Borghei and Hosseini, 2008; Tabrizi and Mehrvar, 2006), which can scavenge $OH and inhibit the process. H2 O2 þ $OH/H2 O þ HO2 $
(2)
HO2 $ þ $OH/H2 O þ O2
(3)
The use of hydrogen peroxide as an oxidant in H2O2/UVC treatment has a number of advantages: (i) it is readily available, easy to store, relatively safe to handle and environmentally friendly; (ii) it is a cost-effective source of hydroxyl radicals, two hydroxyl radicals being formed per each photolyzed H2O2 molecule and (iii) peroxyl radicals (HO2$) are generated after $OH attack on most organic substrates, thus, facilitating oxidation reactions (Legrini et al., 1993; Pan et al.,
1993). Apart from these advantages, phase transfer and sludge formation problems are not encountered in this process. The main disadvantages of H2O2 photolysis are the presence of residual hydrogen peroxide in the effluent and the possible generation of toxic by-products during the treatment, which can be removed by activated carbon (AC) (Heringa et al., 2011). Moreover, the use of H2O2 photolysis as the only treatment method would not make economic sense, since both capital and operational costs are relatively high (Del Moro et al., 2013). Therefore, H2O2 photolysis could be used after the biological step (if wastewater is not toxic for bio-treatment) and prior to a polishing step through GAC (CWPO) aiming to remove residual organic pollutants and excess H2O2 for wastewater discharge. Although, the GAC adsorption method without H2O2 is effective for removal of organic compounds, the GAC can be saturated easily in the process, and requires regeneration or complete replacement. Hydrogen peroxide decomposition is one of the most known reactions to be catalyzed by carbon materials (Serp and Figueiredo, 2009). Recent research demonstrated that AC is active in the degradation of some dissolved organic pollutants in the presence of H2O2, providing evidence that AC can promote hydrogen peroxide decomposition through the formation of hydroxyl radicals (Eq.(4) and (5)) (Lu¨cking et al., 1998; Oliveira et al., 2004; Rey et al., 2011; Santos et al., 2009). AC þ H2 O2 /$OH þ OH þ ACþ
(4)
ACþ þ H2 O2 /AC þ $OOH þ Hþ
(5)
Georgi and Kopinke (2005) concluded that the predominant pathway of the degradation reaction during CWPO is the attack by $OH of organic contaminant fraction that is freely dissolved in the pore volume of the AC. In contrast, the adsorbed fraction is nearly non-reactive. Consequently, sorption on AC has an adverse effect on the oxidation of organic compounds via $OH radical even though the radicals are formed directly on the AC surface. The CWPO process after H2O2/UVC treatment is useful because molar mass and hydrophobicity of the organic pollutants are decreasing and increasing, respectively (Lu¨cking et al., 1998). Also, during the CWPO step the residual H2O2 from the hydrogen peroxide photolysis process is consumed, bkova et al., leading to the effluent's toxicity removal (Dra 2007). It should be noted that a few installations combining H2O2/ UV followed by GAC are currently operated, and most of them are for drinking water production (Heringa et al., 2011; Kruithof et al., 2007). Hence, the aim of this work was to evaluate the feasibility of a multibarrier (MBT) approach (MF, H2O2/UVC and CWPO) to obtain safer effluent after MBT wastewater treatment. Also, toxicity evolution during MBT treatment was assessed with sea water species to estimate the impact of discharge to the environment. Target economic parameters, such as reagent consumption, electricity and replacement of installation parts were used to estimate the operating cost of the MBT process (V m3).
w a t e r r e s e a r c h 7 1 ( 2 0 1 5 ) 8 5 e9 6
2.
Materials and methods
2.1.
Synthetic industrial wastewater (SIWW)
The SIWW was the effluent of a domestic wastewater treatment plant spiked with model industrial organic pollutants (Table 1). The urban wastewater (UWW) was purchased from the effluent of wastewater treatment plant (WWTP) in Chi diz, Spain) where physical and bioclana de la Frontera (Ca logical treatment is applied for water purification. For preparation of SIWW, the UWW was used as a matrix. It was done in order to simulate the conditions of real industrial wastewater, the main problems of which are organic compounds recalcitrant to biological treatment, presence of suspended solids, salinity, coloration, microorganism and turbidity. The following industrial organic compounds were added to UWW: 4-chlorophenol, phenol, phenanthrene and orange II. The 4-chlorophenol is a halogenated aromatic compound considered as priority pollutant by USEPA since 1976. It is known to be endocrine disruptor, toxic and nonbiodegradable, and it is present in wastewater as byproduct of pulp and paper, dyestuff, pharmaceutical and agrochemical industries (Pozan and Kambur, 2013). Phenol is a major component of organic waste streams such as dye manufacture wastewater, pulp and paper manufacture wastewater, and it is also found in wastewaters from the petrochemical industry and municipal solid waste (Onwudili and Williams, 2007). Phenanthrene is a polycyclic aromatic hydrocarbon considered as priority pollutant due
Table 1 e The main characteristics of SIWW. Parameter (unit) 1
COD (mg O2 L ) TOC (mg C L1) SS (mg L1) Turbidity (NTU) Transmittance (254 nm, %) pH Conductivity (mS cm1/mg TDS L1) E. coli (CFU 100 mL1) Total coliforms (CFU 100 mL1) Nematodes (eggs 10 L1) 4-Chlorophenol (mg L1) Phenol (mg L1) Phenanthrene (mg L1) Orange II (mg L1) a
Value 146 40 25 6.7 43.6 7.14 1900/1222 104 107 4-chlorophenol > phenol. It should be noted that, these compounds were completely degraded with a dose 5.53 WUVC s cm2. C ¼ C0 *ek*D
Fig. 3 e Average oxidation state of carbon atoms (AOSC) during H2O2/UVC process as a function of UVC average dose accumulated by the wastewater. Note that a þ4 oxidation state corresponds to inorganic carbon (CO2) and a ¡4 oxidation state corresponds to methane.
(9)
Higher UVC dose accumulated by water is required for mineralization and/or oxidation of organic pollutants than for degradation. Hence, 8.80 WUVC s cm2 of UVC average dose accumulated by wastewater was necessary to remove 76% of COD. The decrease of COD and TOC means an increase of organic pollutant oxidation during the H2O2 process. The average oxidation state of carbon atoms (AOSC) in the reaction mixture (Fig. 3) was calculated by means of Eq. (10), reported by Scott and Ollis (1995). AOSC ¼ 4 1:5
COD TOC
(10)
According to Fig. 3, the residual organic molecules are oxidized, increasing values of AOSC from 1.5 (mostly non oxygenates hydrocarbons and alcohols) to þ0.45 (organic compound with a carbonyl group) with UVC accumulated dose by the wastewater at 8.80 WUVC s cm2. Finally in this step, total coliforms disinfection (
