Journal of Environmental Management 166 (2016) 493e498
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Research article
Performance of combined sodium persulfate/H2O2 based advanced oxidation process in stabilized landfill leachate treatment Ahmed H. Hilles a, Salem S. Abu Amr b, *, Rim A. Hussein a, Olfat D. El-Sebaie a, Anwaar I. Arafa a a b
Department of Environmental Health, High Institute of Public Health, Alexandria University, Egypt Malaysian Institute of Chemical and Bioengineering Technology, Universiti Kuala Lumpur (UniKL, MICET), Melaka, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 January 2015 Received in revised form 28 October 2015 Accepted 29 October 2015 Available online xxx
A combination of persulfate and hydrogen peroxide (S2 O2 8 /H2O2) was used to oxidizelandfill leachate. 2 The reaction was performed under varying S2 O2 8 /H2O2 ratio (g/g), S2 O8 /H2O2 dosages (g/g), pH, and reaction time (minutes), so as to determine the optimum operational conditions. Results indicated that under optimum operational conditions (i.e. 120 min of oxidation using a S2 O2 8 /H2O2 ratio of 1 g/1.47 g at a persulfate and hydrogen peroxide dosage of 5.88 g/50 ml and8.63 g/50 ml respectively, at pH 11) removal of 81% COD and 83% NH3eN was achieved. In addition, the biodegradability (BOD5/COD ratio) of the leachate was improved from 0.09 to 0.17. The results obtained from the combined use of (S2 O2 8 /H2O2) were compared with those obtained with sodium persulfate only, hydrogen peroxide only and sodium persulfate followed by hydrogen peroxide. The combined method (S2 O2 8 /H2O2) achieved higher removal efficiencies for COD and NH3eN compared with the other methods using a single oxidizing agent. Additionally, the study has proved that the combination of S2 O2 8 /H2O2 is more efficient than the sequential use of sodium persulfate followed by hydrogen peroxide in advanced oxidation processes aiming at treatingstabilizedlandfill leachate. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Landfill leachate Persulfate Advanced oxidation Biodegradability
1. Introduction Sanitary landfill is recognized as the most common and desirable method of urban solid waste management and as the most economical and environmentally acceptable method of municipal and industrial solid wastes disposal (Tengrui et al., 2007). However, the large quantity and highly polluted leachate that is produced from landfilling is recognized as a potential source of environmental contamination. Leachate contains large amount of organics, ammonia, heavy metals, and many other hazardous materials (Ghafari et al., 2005; Christensen et al., 2001). There are many important factors that affect leachate characteristics such as age and type of landfill, characterization of the dumped waste, weather and climate of the region. Stabilized leachate is generated from old landfills (>10 years) with stable characteristics. Stabilized leachate is characterized by a very strong organic content, has a high NH3-Nconcentration and a very low biodegradability (BOD5/
* Corresponding author. E-mail address: [email protected] (S.S. Abu Amr). http://dx.doi.org/10.1016/j.jenvman.2015.10.051 0301-4797/© 2015 Elsevier Ltd. All rights reserved.
COD < 0.1), (Schiopu and Gavrilescu, 2010; Azizi et al., 2004). Leachate requires an efficient treatment to reduce the high concentration of contaminants to an acceptable level prior tofinal discharge (Aziz et al., 2007, 2010; Goi et al., 2009). Different leachate treatment methods, including physical, chemical and biological processes have been reported (Abu Amr et al., 2013a,b & c; Abu Amr and Aziz, 2012; Bashir et al., 2011; Hagman et al., 2008). Persulfate is one of the chemical treatment processes that can be used in leachate treatment, and recently received an attention in chemical oxidation of water and wastewater (Huling and Pivetz, 2006; Shiying et al., 2009). The mechanism of persulfate oxidation is to initiate sulfate radical, which has strong oxidation potential (E ¼ 2.7 V) (Renaud and Sibi, 2001). Persulfate can be investigated naturally under the effect of different organic and inorganic compounds (i.e., iron oxides, manganese oxides, clay minerals, trace minerals, base and iron chelates) (Watts, 2011). Liu et al. (2012) used iron (Fe2þ) and Copper (Cu2þ) ions for persulfate activation. Persulfate can act as a direct oxidant; however, its effectivenessto treat high recalcitrant contaminants is limited (Watts, 2011; Liu et al., 2012). The effectiveness of persulfate alone in stabilized leachate treatment is relatively low (Abu Amr et al.,
494
A.H. Hilles et al. / Journal of Environmental Management 166 (2016) 493e498
2013a, b, c); however, its effectiveness can be improved using advanced oxidation materials and techniques. Shabiimam and Dikshit (2012) used low pH (2e4.5) to improve persulfate oxidation in removing Total organic carbon (TOC) and color from stabilized leachate. Xu et al. (2012) combined persulfate with activated carbon to enhance biodegradability and improve organic removal in stabilized leachate. Ghauch et al. (2012) used heated persulfate for ibuprofen and methylene blue degradation. Yang et al. (2011) used activated carbon as a catalyzing agent with sodium persulfate for azo dye acid orange7 removal. Abu Amr et al., (2013c, 2014) enhanced biodegradability of stabilized leachate by using the combination of ozone with persulfate. Thus, persulfate oxidation in combination with other treatment processes proves to be more efficient for stabilized leachate treatment. Consequently, the current study investigates the effectiveness of simultaneously employing S2 O2 and H2O2 in stabilized landfill 8 leachate treatment. The scope and benefit of this new method is an increase in the oxidation potential using S2 O2 8 with H2O2 in the advanced oxidation processes during the oxidation of leachate. The effect of the S2 O2 8 and H2O2 dosages, pH variation, and reaction time are investigated in the current work. Furthermore, the treatment efficiency of the simultaneous (persulfate/hydrogen peroxide) method was assessed and compared with those processes conducted separately (S2 O2 alone and H2O2 alone) and 8 sequentially (S2 O2 followed by H O ) under their experimental 2 2 8 conditions. 2. Materials and methods 2.1. Leachate sampling and characteristics Leachate samples were collected from the collection pond at Deir El-balah Landfill Site (DBLS), at Deir El-Balah city, Middle Governorate in Gaza Strip, Palestine. The leachate samples were collected from the area of the landfill that receives waste continually. The DBLS has an area of 7 ha, receiving approximately 450 tons of municipal solid waste daily (Solid Waste Management Council SWMC, 2012). In this study, afour leachate samples were manually collected from February 2014 to June 2014 and placed in 2-L plastic containers. The samples were immediately transported to the laboratory, characterized, and cooled to 4 C to minimize the biological and chemical reactions. The average characteristics of the leachate used in this study are presented in Table 1. Themethodology to characterize are according to the Standard Methods for the Examination of Water and Wastewater (2005). 2.2. Experimental procedures
All experiments were conducted at a room temperature of 28 Cusing 50 mL leachate samples in 250 ml-polyethylene bottles. Orbital Shaker (Luckham R100/TW Rotatest Shaker 340 mm 245 mm) was used for sample shaking at 350 rpm. S2 O2 8 as sodium persulfate (Na2S2O8) Molarity (M) ¼ 238.09 g/mol) and Hydrogen peroxide (H2O2 37%) were employed for advanced oxidation during the oxidation of leachate samples. To determine the optimum conditions, a four-stage experiment was gradually applied: (1) Persulfate and hydrogen peroxide with different ratios ranging from 1:0.3 to 1:2.46 were immediately added into the oxidation reactor before each run. Persulfate (S2 O2 8 ) dosage was fixed at 4.2 g, which was determined through a set of preliminary experiments using persulfate oxidation only, and thenH2O2reagent was added gradually to achieve the highest performance ratio for the treatment of leachate. .
Table 1 General characteristics of landfill leachate from DELS. Parameter
Results
COD (mg/L) BOD (mg/L) BOD/COD ratio EC (mS) TDS (mg/L) Nitrate (mg/L) Ammonia (mg/L) Chloride (mg/L) Sulfate (mg/L) Alkalinity (mg/L) Hardness (mg/L) Calcium (mg/L) Magnesium (mg/L) Potassium (mg/L) Sodium (mg/L) pH Turbidity NTU Cupper (mg/L) Lead (mg/L) Nickel (mg/L) Manganese (mg/L) Cadmium (mg/L) Zinc (mg/L)
19,180e20,448 830e1821 0.05e0.09 40,800 22,356e25,296 2020e3602 2450e3400 6150e6953 780e856 22,500e24,000 6980e7283 1620 785 4345.5 6000 7.9e8.42 537.5 0.44 0.143 4.63 0.08 0.259 5.84
(2) Based on the optimum S2 O2 8 /H2O2 ratio (1:1.47) obtained from the previous oxidation step; different dosages of S2 O2 8 /H2O2 ranging from 2.52 g/3.7 g to 10.08/14.8 g were added gradually to the 50 mL of leachate sample in the reactor to determine the optimum persulfate dosage according to the efficiencies inCOD and NH3eN removal. In this stage, pH wasnot adjusted and all runs were performed with natural leachate pH (8.5) within 60 min of shaking and oxidation. (3) The performance of pH variation on oxidation of the leachate samples was performed and assessed. pH value of leachate samples were adjusted gradually from 3 to 11 using 5 Molar sulfuric acid solution and 5 Molar sodium hydroxide solution. Optimum dosage of S2 O2 8 /H2O2 (5.88 g/8.63 g) obtained from step 2 was used throughout all runs. All runs in step 1, 2 and 3 were performed for 60 min of oxidation. (4) The reaction time was examined from 10 min to 240 min (shaking at 350 rpm) at the optimal pH value (11) which was obtained from step No. 3. All samples were filtered through a 0.45 mm membrane prior to analysis. Persulfate oxidation alone, Hydrogen peroxide oxidation alone and sequential persulfate and hydrogen peroxide oxidation were conducted on a 50 mL sample reactor and the results were compared with simultaneous (S2 O2 8 /H2O2) process. 2.3. Analytical methods Chemical oxygen demand (COD) and NH3eN, were immediately tested before and after each run of the experiments in accordance with the Standard Methods for the Examination of Water and Wastewater (2005). The leachate was stirred uniformly before being analyzed. NH3eN concentration was measured by the Phenol Method No. (4500) using a UV-VIS spectrophotometer at 640 nm with a light path of 1 cm, (ATI UNICAM 8625 UV/VIS spectrometer). The pH was measured using a portable digital pH/Mv meter. The COD concentration was determined by the open reflux method No (5220) using COD REACTOR P/N 45600-00, HACH). The test values are presented as the average of the three
A.H. Hilles et al. / Journal of Environmental Management 166 (2016) 493e498
measurements, and the difference between the measurements of each value was less than 3%. The removal efficiencies of COD and NH3eN were obtained using the following equation (1):
Removal % ¼
. i h Xi 100 Xi Xf
(1)
where Xi and Xf refer to the initial and final concentrations for both COD and NH3eN. 3. Results and discussion 3.1. Effect of S2 O2 8 /H2O2 ratio To evaluate the performance of hydrogen peroxide in enhancing persulfate oxidation, the persulfate/H2O2 ratios (g/g) were fixed at ten different ratios, namely,1:0.3, 1:0.6, 1:0.89, 1:1.17, 1:1.23, 1:1.47, 1:1.76, 1:2.06, 1:2.34 and1:2.64 during 60 min of oxidation of the leachate (Fig. 1). Although persulfate reagent can act alone as an oxidant, its effectiveness is limited for oxidation of stabilized leachate. Persulfate oxidation can be enhanced by the initiation of sulfate radicals which have powerful effects on the oxidation of organics (Deng and Ezyske, 2011 and Kolthoff and Stenger, 1947). The generation of sulfate radicals during persulfate oxidation can be significantly investigated using different applications, such as heat, UV radiation, Iron ions as shown in equations (2)e(4), which were found to enhance the persulfate oxidation potential (Gao et al., 2012; Shiying et al., 2009; Rastogi et al., 2009). S2 O2 8 þ Initiator/SO4 þ SO4
(2)
S2 O2 8 þ Thermal Activation/SO4 þ SO4 30 C < T < 90 C
(3) 2þ Fe3þ þ S2 O2 8 /2SO4 þ Fe
(4)
SO-4
may initiate production of other intermediate highly reactive oxygen species (ROS) such as hydroxyl radicals (OH) as shown in Eq. (5), (Huie et al., 1991; Berlin, 1986). SO2 4 þ H2 O/HSO4 þ OH
(5)
To investigate the performance of H2O2 in initiating sulfate radical formation from persulfate during the oxidation process, the
495
influence of S2 O2 8 /H2O2 ratios on COD and NH3eN removal was investigated under the optimal operational conditions which were fixed at 28 C, reaction time 60 min, shaking speed of 350 rpm and an initial pH of 8.5. The maximum removal efficiencies of COD and NH3eN were 58% and 49%, respectively, at 1 g/1.47 g of S2 O2 8 /H2O2 ratio (Fig. 1). The removal efficiencies of the targeted parameters were improved by increasing the H2O2 dosages (Fig. 1). The activation mechanism that plays an important role in S2 O2 8 /H2O2 process is the initial formation of hydroxyl radical (OH) by the decomposition of the hydrogen peroxide followed by the activation of the persulfate to produce sulfate radicals (Block et al., 2004; Crimi and Taylor, 2007). Both sulfate and hydroxyl radicals may have played a significant role in the degradation of COD and NH3eN. Moreover, the temperature of oxidation is monitored and ranged between 40 and 50 C during oxidation. The increasing of temperature was observed when H2O2 dosage was increased. The heat resulted from decomposition of H2O2 contributed to initiate sulfate radicals. Shiying et al. (2009) utilized Microwave for persulfate activation used in wastewater treatment. Xu et al. (2012) activated persulfate at high temperature (150 C) using K2S2O8 in treating stabilized leachate. 3.2. Effect of S2 O2 8 /H2O2 dosage (g/g) Hydrogen peroxide reagent is used to improve persulfate oxidation efficiency during the oxidation of leachate. The amount of both persulfate and hydrogen peroxide used to improve oxidation efficiency has been determined. To investigate the optimum amount of both reagents in the oxidation of leachate, different 2 dosages of (S2 O2 8 /H2O2) were tested by fixing the S2 O8 /H2O2 ratio at 1:1.47, with varying amounts of both reagents (Fig. 2). By increasing the persulfate and hydrogen peroxide dosages, the performance of oxidation for treating leachate has improved. The maximum removal of COD was 72% at S2 O2 8 /H2O2 dosage 5.88 g/ 8.63 g, while the maximum removal of NH3eN (81%) was obtained using 7.56 g/11.09 g of S2 O2 8 /H2O2 dosage. 3.3. Effect of pH To determine the optimal pH for the S2 O2 8 /H2O2 system, the pH of the initial leachate sample was gradually adjusted from 3 to 11, maintaining the optimal S2 O2 8 /H2O2 dosage at5.88 g/8.63 g (as obtained from the previous reaction step). Fig. 3 shows that by increasing the pH, the removal efficiencies for COD, and NH3eN
Fig. 1. Effect of persulfate/hydrogen peroxide ratio (g/g) in removing of COD and NH3eN during 60 min oxidation of leachate (pH: 8.5, shaking at 350 rpm), S.D for COD (%) and NH3eN (%): 0.158, 0.156, respectively.
496
A.H. Hilles et al. / Journal of Environmental Management 166 (2016) 493e498
Fig. 2. Effect of persulfate/hydrogen peroxide dosage (g/g) in removing COD and NH3eN during 60 min oxidation of stabilized leachate [pH: 8.5, 350 rpm, S2 O2 8 /H2O2 ratio (1 g/ 1.47 g)] S.D for COD (%) and NH3eN (%): 0.23 and 0.22, respectively.
2 Fig. 3. Effect of initial pH on COD and NH3eN removal during 60 min oxidation of stabilized leachate at optimum S2 O2 8 /H2O2 ratio (1 g/1.47 g), S2 O8 /H2O2 dosage (5.88 g/8.63 g) and 350 (rpm) shaking speed. S.D for COD (%) and NH3eN (%): 0.23 and 0.21, respectively.
were also increased. The maximum removal efficiencies were 78% and 81% for COD and NH3eN respectively. At high pH conditions (pH ¼ 11), alkaline activation is very productive in generating sulfate and hydroxyl radicals. Both radicals (SO 4 and OH) have high oxidation potential (E ¼ 2.80 and E ¼ 2.70, respectively) (House, 1962). The effect of alkalinity on persulfate oxidation has been reported (Furman et al. 2011; Ocampo, 2009). At high pH value, hydroxyl radical can be act to activate persulfate and initiate sulfate radical (Eq. (6)) 2 S2 O2 8 þ OH /HSO4 þ SO4 þ 1=2 O2
(6)
Even though the optimal removal efficiency in the present study was obtained at the optimal temperature of 28 C and high pH (11), a significant removal efficiency was obtained also at natural pH (6e9) (Fig. 3). Deng and Ezyske (2011) obtained higher removal of COD and NH3eN from leachate at low pH (4) using persulfate alone. Shabiimam and Dikshit (2012) reported lower organic compounds removal in stabilized leachate at acidic medium (pH 2.5) using sodium persulfate reaction. Furthermore, Lin et al. (2011) obtained the best removal of Phenol from wastewater at high pH (11) using UV for persulfate activation.
3.4. Effect of reaction time The effect of reaction time on the S2 O2 8 /H2O2 oxidation process was investigated in terms of COD and NH3eN removal (Fig. 4). The reaction time was varied between 10 min and 240 min, and the initial pH and S2 O2 8 /H2O2 dosage were maintained constant at 11 and 5.88 g/8.63 g, respectively. The removal of organics and NH3eN were improved as the reaction time increased (Fig. 4). The maximum removal efficiencies for COD and NH3eN obtained 81%, and 83%, respectively after 120 min of oxidation. Thus, the optimum reaction time for S2 O2 8 /H2O2 oxidation process is considered to be 120 min Xu et al., 2012 used potassium persulfate in treating of stabilized leachate and achieved maximum removal efficiency of COD (78%) at 4 h as an optimal reaction time. 3.5. Treatment efficiency and effect on biodegradability The treatment efficiency of the S2 O2 8 /H2O2 oxidation was compared with other treatment processes (i.e., persulfate alone, hydrogen peroxide alone, and persulfate followed by hydrogen peroxide) under experimental conditions (Table 2). The efficiency of persulfate alone was found to beinsufficient for the removal of
A.H. Hilles et al. / Journal of Environmental Management 166 (2016) 493e498
497
2 Fig. 4. Effect of reaction time on COD and NH3eN removal during oxidation of stabilized leachate at optimum S2 O2 8 /H2O2 ratio (1 g/1.47 g), S2 O8 /H2O2 dosage (5.88 g/8.63 g) and 350 rpm and pH (11). S.D for COD (%) and NH3eN (%): 0.26 and 0.25, respectively.
Table 2 Comparing the performance of S2 O2 8 /H2O2 based on advanced oxidation with other processes used for the treatment of stabilized leachate. Process
Condition
Removal (%) COD
NH3eN
H2O2 alone S2 O2 8 alone S2 O2 8 followed by H2O2 H2O2 followed by S2 O2 8 S2 O2 8 /H2O2
H2O2: 8.63 g, pH (11), RT*: 120, SS*: 350 rpm S2 O2 8 :4.2 g, pH (7), RT*: 60, SS*: 350 rpm S2 O2 8 :4.2 g, pH (7), RT*: 60, SS*: 350 rpm, H2O2: 8.63 g, pH (11), RT*: 120, SS*: 350 rpm H2O2: 8.63 g, pH (11), RT*: 120, SS*: 350 rpm, S2 O2 8 :4.2 g, pH (7), RT*: 60, SS*: 350 rpm S2 O2 8 5.88 g, H2O2: 8.63 g, pH (11), RT*: 120, SS*: 350 rpm
31% 45% 62% 55% 81%
28% 46% 50% 42% 83%
RT*: reaction time in minutes. SS*: shaking speed.
COD and NH3eN (45% for both). Compared with that of the other processes, these limitedremovals were attributed to the limited oxidation potential of persulfate alone against high organic concentration in leachate. However, increasing of the persulfate dosage higher than 4.2 g did not improve removal efficiency. Although the efficiency of H2O2 after S2 O2 8 was improved (62% COD removal, and 50% NH3eN removal), the results showed lower removal efficiency than the combination method. These findings helped to ensure that the combined S2 O2 8 and H2O2work better as oxidants if they are added together than working separately. These results are close to those obtained from the oxidation process when adding S2 O2 8 after H2O2(55% COD removal, and 42% NH3eN removal). Best removal efficiency was obtained from the advanced oxidation system (S2 O2 8 /H2O2) and reached 81% and 83% for COD and NH3eN, respectively, under optimal conditions. Comparing the results with ozone/persulfate oxidation (Abu Amr et al., 2013a, b, c) obtained 70% and 72% removal efficiencies for COD and NH3eN, respectively. In the O3/persulfate oxidation, sulfate ions cannot react directly with ozone. However, ozone has a significant role in the process by increasing hydroxyl radicals at high pH, which directly activates persulfate and initiate sulfate radicals (Tizaoui et al., 2007). Although the optimal reaction time in the ozone/persulfate process (90 min) was shorter than that in the current process, the performance of cooperative hydroxyl and sulfate radicals in removing COD and NH3eN was much higher at 120 min of oxidation. As for the effect of persulfate/hydrogen peroxide oxidation on the biodegradability of leachate, the COD, BOD5, and BOD5/COD ratio of leachate were tested before and after the oxidation process. Based on the results, persulfate/Hydrogen peroxide was more efficient in enhancing the biodegradability of leachate than other oxidation processes. The biodegradability (BOD5/COD) ratio increased from 0.09 to 0.17, whereas the ratio only improved to 0.1
after S2 O2 oxidation. Operational cost for using persulfate/ 8 hydrogen peroxide oxidation is summarized and calculated for large scale volume (50 L of leachate); As the major cost of the oxidation process is related to chemicals used, the cost were 0.4 USD/L 37% H2O2 and 0.8 USD/kg sodium persulfate, since about 5.8 kg of persulfate and 16.7 L of 37% H2O2 are required to remove 1 kg COD (in 50 L of leachate). Around 10.73 USD is required to remove 81% of organics from 50 L of stabilized leachate using S2 O2 8 /H2O2 oxidation process. Although the cost of proposed process is higher than Ozone/Fenton oxidation (Abu Amr and Aziz, 2012), however, the process achieved significant removal in organic (81%) while ozone/Fenton reported lower removal (65%). Furthermore, the method can efficiently work at natural pH and doesn't required extra chemicals for pH adjustment, while the optimum pH for Fenton is 2e4.5 (Lopez et al., 2004; Deng, 2007; Mohajeri et al., 2010) which required extra chemicals and create critical risk for effluent discharge. Moreover, persulfate oxidation does not produce undesirable sludge needs to be settled comparing with Fenton oxidation. The study demonstrated that persulfate and persulfate/ H2O2 oxidation can improved biodegradability of organics in the leachate, and the application of biological methods as a post treatment process of leachate is applicable. 4. Conclusion The performance of an advanced oxidation process, consisting of the combined use of persulfate and hydrogen peroxide for the treatment of stabilized landfill leachate was investigated. The maximum removal efficiency for COD and NH3 - N was 81% and 83%, respectively. The results demonstrated that the combined persulfate/H2O2 process can efficiently use for stabilized leachate treatment at natural leachate pH (7e9). Moreover, the biodegradability of the leachate was improved. The combination of persulfate
498
A.H. Hilles et al. / Journal of Environmental Management 166 (2016) 493e498
and hydrogen peroxide was found to be more efficient in leachate treatment compared with using persulfate alone or persulfate followed by hydrogen peroxide. Accordingly, the new treatment increased the oxidation potential of organics during oxidation. The study revealed that the new (persulfate/H2O2) oxidation is an efficient process in treating stabilized leachate. Acknowledgments The authors wish to acknowledge the indispensable role of the staff of the Public Health Laboratory at the Ministry of HealthPalestine and at the Municipality of Deir El-balahfor facilitating and supporting the implementation of the present work. Thanks and gratitude are due them all. References Abu Amr, S.S., Aziz, H.A., Adlan, M.N., Alkaseeh, J.M., 2014. Effect of ozone and ozone/persulfate processes on biodegradable and soluble characteristics of semi-aerobic stabilized leachate. J. Environ. Prog. Sustain. Energy 33, 184e191. Abu Amr, S.S., Aziz, H.A., Adlan, M.N., Bashir, M.J.K., 2013a. Pretreatment of stabilized leachate using ozone/persulfate oxidation process. Chem. Eng. J. 221, 492e499. Abu Amr, S.S., Aziz, H.A., Adlan, M.N., 2013b. Optimization of stabilized leachate treatment using ozone/persulfate in the advanced oxidation process. Waste Manag. 33, 1434e1441. Abu Amr, S.S., Aziz, H.A., Adlan, M.N., Aziz, S.Q., 2013c. Effect of ozone and ozone/ fenton in the advanced oxidation process on biodegradable characteristics of semi-aerobic stabilized leachate. Clean Air Soil Water 41 (2), 148e152. Abu Amr, S.S., Aziz, H.A., 2012. New treatment of stabilized leachate by ozone/ fenton in the advanced oxidation process. Waste Manag. 32, 1693e1698. APHA, WPCF, A.W.W.A Standard Methods for the Examination of Water and Wastewater, 21st ed., 2005. American Public Health Association (APHA), Washington, DC. Aziz, H.A., Alias, S., Adlan, M.N., Asaari, A.H., Zahari, M.S., 2007. Colour removal from landfill leachate by coagulation and flocculation processes. Bioresour. Technol. 98, 218e220. Aziz, H.A., Adlan, M.N., Zahari, M.S.M., Alias, S., 2004. Removal of ammoniacal nitrogen (N-NH3) from municipal solid waste leachate by using activated carbon and limestone. Waste Manag. Res. 22, 371e375. Aziz, S.Q., Aziz, H.A., Yusoff, M.S., Bashir, M.J.K., Umar, M., 2010. Leachate characterization in semi-aerobic and anaerobic sanitary landfills: a comparative study. J. Environ. Manag. 12, 2608e2614. Bashir, M.J.K., Aziz, H.A., Yusoff, M.S., 2011. New sequential treatment for mature landfill leachate by cationic/anionic and anionic/cationic processes: optimization and comparative study. J. Hazard. Mater. 186, 92e102. Berlin, A.A., 1986. Kinetics of radical-chain decomposition of persulfate in aqueous solutions of organic compounds. Kinet. Catal. 27, 34e39. Block, P.A., Brown, R.A., Robinson, D., 2004. Novel activation technologies for sodium persulfate in situ chemical oxidation. In: 4th Int. Conf. on the Remediation of Chlorinated and Recalcitrant Compounds, Battelle, Monterey, CA. Christensen, T.H., Kjeldsen, P., Bjerg, P.L., Jensen, D.L., Christensen, J.B.A., Baum, A., Albrechtsen, H., Heron, G., 2001. Biogeochemistry of landfill leachate plumes. Appl. Geochem. 16, 659e718. Crimi, M.L., Taylor, J., 2007. Experimental evaluation of catalyzed hydrogen peroxide and sodiumpersulfate for destruction of BTEX contaminants. Soil Sediment. Contam. 16, 29e45. Deng, Y., Ezyske, C.M., 2011. Sulfate radical-advanced oxidation process (SR-AOP) for simultaneous removal of refractory organic contaminants and NH3-Nin landfill leachate. Water Res. 45, 6189e6194. Deng, Y., 2007. Physical and oxidative removal of organics during Fenton treatment of mature municipal landfill leachate. J. Hazard. Mater. 146, 334e340. Furman, O., Teel, A., Ahmad, M., Merker, M., Watts, R., 2011. Effect of basicity on
persulfate reactivity. J. Environ. Eng. 137 (4), 241e247. Gao, Y., Gao, N., Deng, Y., Yang, Y., Ma, Y., 2012. Ultraviolet (UV) light-activated persulfate oxidation of sulfamethazine in water. Chem. Eng. J. 195e196, 248e253. Ghafari, S., Aziz, H.A., Isa, M.H., 2005. Coagulation process for semi-aerobic leachate treatment using poly-aluminum chloride. In: The AEESEAP International Conference “Engineering a Better Environment for Mankind”, Kuala Lumpur, Malaysia, June 7e9. Ghauch, A., Tuqan, A., Kibbi, N., 2012. Ibuprofen removal by heated persulfate in aqueous solution: a kinetics study. Chem. Eng. J. 197, 483e492. Goi, A., Veressinina, Y., Trapido, M., 2009. Combination of oxidation and the fenton processes for landfill leachate treatment: evaluation of treatment efficiency. Ozone Sci. Eng. 31, 28e36. Hagman, M., Heander, E., Jansen, J.L.C., 2008. Advanced oxidation of refractory organics in leachateepotential methods and evaluation of biodegradability of the remaining substrate. Environ. Technol. 29, 941e946. House, D.A., 1962. Kinetics and mechanism of oxidations by peroxydisulfate. Chem. Rev. 62, 185e203. Huie, R.E., Clifton, C.L., Neta, P., 1991. Electron transfer reaction rates and equilibria of the carbonate and sulfate radical anions. Radiat. Phys. Chem. 38, 477e481. Huling, S.G., Pivetz, B.E., 2006. In-situ Chemical Oxidation, (2006) (EPA/600/R-06/ 072). US EPA. Kolthoff, I.M., Stenger, V.A., 1947. Volumetric analysis In: Titration Methods: Acidbase, Precipitation, and Complex Reactions, second revised ed., vol. II. Interscience Publishers, Inc., New York. Lin, Y., Liang, C., Chen, J., 2011. Feasibility study of ultraviolet activated persulfate oxidation of phenol. Chemosphere 82, 1168e1172. Lopez, A., Pagano, M., Volpe, A., Di Pinto, A.C., 2004. Fenton's pre-treatment of mature landfill leachate. Chemosphere 54, 1005e1010. Liu, C.S., Shih, K., Sunc, C.X., Wang, F., 2012. Oxidative degradation ofpropachlor by ferrous and copper ion activated persulfate. Sci. Total Environ. 416, 507e512. Mohajeri, S., Aziz, H.A., Isa, M.H., Zahed, M.A., Adlan, M.N., 2010. Statistical optimization of process parameters for landfill leachate treatment using electroFenton technique. J. Hazard. Mater. 176, 749e758. Ocampo, A.M., 2009. Persulfate Activation by Organic Compounds. PhD thesis. Washington State University, Department of Civil and Environmental Engineering, pp. 1e77. Rastogi, A., Al-Abed, S.R., Dionysiou, D.D., 2009. Sulfate radical-based ferrous peroxymonosulfate oxidative system for PCBs degradation in aqueous and sediment systems. Appl. Catal. B Environ. 85, 171e179. Renaud, I.P., Sibi, M.P., 2001. Radicals in Organics Synthesis. Wiley-VCH, Weinheim. New York, pp. 479e488. Schiopu, A.M., Gavrilescu, M., 2010. Options for the treatment and management of municipal landfill leachate: common and specific issues. Clean Soil Air Water 12, 1101e1110. Shabiimam, M.A., Dikshit, A.K., 2012. Treatment of municipal landfill leachate by oxidants. Am. J. Environ. Eng. 2, 1e5. Shiying, Y., Ping, W., Xin, Y., Guang, W., Wenyi, Z., Liang, S., 2009. A novel advanced oxidation process to degrade organic pollutants in wastewater: microwaveactivated persulfate oxidation. J. Environ. Sci. 21, 1175e1180. Solid Waste Management Council (SWMC), 2012. Annual Report of Khan Younis and Deir AL-balah Governorates. Tengrui, L., AL-Harbawi, A.F., Bo, L.M., Jun, Z., 2007. Characteristics of nitrogen removal from old landfill leachate by sequencing batch biofilm reactor. J. Appl. Sci. 4, 211e214. Tizaoui, C., Bouselmi, L., Mansouri, L., Ghrabi, A., 2007. Landfill leachate treatment with ozone and ozone/hydrogen peroxide systems. J. Hazard. Mater. 140, 316e324. Watts, R.J., 2011. Enhanced Reactant-contaminant Contact through the Use of Persulfate in Situ Chemical Oxidation (ISCO). SERDP Project ER-1489. Washington State University. Xu, X., Zeng, G., Peng, Y., Zeng, Z., 2012. Potassium persulfate promoted catalytic wet oxidation of fulvic acid as a model organic compound in landfill leachate with activated carbon. Chem. Eng. J. 200 e 202, 25e31. Yang, S., Yang, X., Shao, X., Niub, R., Wang, L., 2011. Activated carbon catalyzed persulfate oxidation of azo dye acid orange 7 at ambient temperature. J. Hazard. Mater. 186, 659e666.
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Research article
Performance of combined sodium persulfate/H2O2 based advanced oxidation process in stabilized landfill leachate treatment Ahmed H. Hilles a, Salem S. Abu Amr b, *, Rim A. Hussein a, Olfat D. El-Sebaie a, Anwaar I. Arafa a a b
Department of Environmental Health, High Institute of Public Health, Alexandria University, Egypt Malaysian Institute of Chemical and Bioengineering Technology, Universiti Kuala Lumpur (UniKL, MICET), Melaka, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 January 2015 Received in revised form 28 October 2015 Accepted 29 October 2015 Available online xxx
A combination of persulfate and hydrogen peroxide (S2 O2 8 /H2O2) was used to oxidizelandfill leachate. 2 The reaction was performed under varying S2 O2 8 /H2O2 ratio (g/g), S2 O8 /H2O2 dosages (g/g), pH, and reaction time (minutes), so as to determine the optimum operational conditions. Results indicated that under optimum operational conditions (i.e. 120 min of oxidation using a S2 O2 8 /H2O2 ratio of 1 g/1.47 g at a persulfate and hydrogen peroxide dosage of 5.88 g/50 ml and8.63 g/50 ml respectively, at pH 11) removal of 81% COD and 83% NH3eN was achieved. In addition, the biodegradability (BOD5/COD ratio) of the leachate was improved from 0.09 to 0.17. The results obtained from the combined use of (S2 O2 8 /H2O2) were compared with those obtained with sodium persulfate only, hydrogen peroxide only and sodium persulfate followed by hydrogen peroxide. The combined method (S2 O2 8 /H2O2) achieved higher removal efficiencies for COD and NH3eN compared with the other methods using a single oxidizing agent. Additionally, the study has proved that the combination of S2 O2 8 /H2O2 is more efficient than the sequential use of sodium persulfate followed by hydrogen peroxide in advanced oxidation processes aiming at treatingstabilizedlandfill leachate. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Landfill leachate Persulfate Advanced oxidation Biodegradability
1. Introduction Sanitary landfill is recognized as the most common and desirable method of urban solid waste management and as the most economical and environmentally acceptable method of municipal and industrial solid wastes disposal (Tengrui et al., 2007). However, the large quantity and highly polluted leachate that is produced from landfilling is recognized as a potential source of environmental contamination. Leachate contains large amount of organics, ammonia, heavy metals, and many other hazardous materials (Ghafari et al., 2005; Christensen et al., 2001). There are many important factors that affect leachate characteristics such as age and type of landfill, characterization of the dumped waste, weather and climate of the region. Stabilized leachate is generated from old landfills (>10 years) with stable characteristics. Stabilized leachate is characterized by a very strong organic content, has a high NH3-Nconcentration and a very low biodegradability (BOD5/
* Corresponding author. E-mail address: [email protected] (S.S. Abu Amr). http://dx.doi.org/10.1016/j.jenvman.2015.10.051 0301-4797/© 2015 Elsevier Ltd. All rights reserved.
COD < 0.1), (Schiopu and Gavrilescu, 2010; Azizi et al., 2004). Leachate requires an efficient treatment to reduce the high concentration of contaminants to an acceptable level prior tofinal discharge (Aziz et al., 2007, 2010; Goi et al., 2009). Different leachate treatment methods, including physical, chemical and biological processes have been reported (Abu Amr et al., 2013a,b & c; Abu Amr and Aziz, 2012; Bashir et al., 2011; Hagman et al., 2008). Persulfate is one of the chemical treatment processes that can be used in leachate treatment, and recently received an attention in chemical oxidation of water and wastewater (Huling and Pivetz, 2006; Shiying et al., 2009). The mechanism of persulfate oxidation is to initiate sulfate radical, which has strong oxidation potential (E ¼ 2.7 V) (Renaud and Sibi, 2001). Persulfate can be investigated naturally under the effect of different organic and inorganic compounds (i.e., iron oxides, manganese oxides, clay minerals, trace minerals, base and iron chelates) (Watts, 2011). Liu et al. (2012) used iron (Fe2þ) and Copper (Cu2þ) ions for persulfate activation. Persulfate can act as a direct oxidant; however, its effectivenessto treat high recalcitrant contaminants is limited (Watts, 2011; Liu et al., 2012). The effectiveness of persulfate alone in stabilized leachate treatment is relatively low (Abu Amr et al.,
494
A.H. Hilles et al. / Journal of Environmental Management 166 (2016) 493e498
2013a, b, c); however, its effectiveness can be improved using advanced oxidation materials and techniques. Shabiimam and Dikshit (2012) used low pH (2e4.5) to improve persulfate oxidation in removing Total organic carbon (TOC) and color from stabilized leachate. Xu et al. (2012) combined persulfate with activated carbon to enhance biodegradability and improve organic removal in stabilized leachate. Ghauch et al. (2012) used heated persulfate for ibuprofen and methylene blue degradation. Yang et al. (2011) used activated carbon as a catalyzing agent with sodium persulfate for azo dye acid orange7 removal. Abu Amr et al., (2013c, 2014) enhanced biodegradability of stabilized leachate by using the combination of ozone with persulfate. Thus, persulfate oxidation in combination with other treatment processes proves to be more efficient for stabilized leachate treatment. Consequently, the current study investigates the effectiveness of simultaneously employing S2 O2 and H2O2 in stabilized landfill 8 leachate treatment. The scope and benefit of this new method is an increase in the oxidation potential using S2 O2 8 with H2O2 in the advanced oxidation processes during the oxidation of leachate. The effect of the S2 O2 8 and H2O2 dosages, pH variation, and reaction time are investigated in the current work. Furthermore, the treatment efficiency of the simultaneous (persulfate/hydrogen peroxide) method was assessed and compared with those processes conducted separately (S2 O2 alone and H2O2 alone) and 8 sequentially (S2 O2 followed by H O ) under their experimental 2 2 8 conditions. 2. Materials and methods 2.1. Leachate sampling and characteristics Leachate samples were collected from the collection pond at Deir El-balah Landfill Site (DBLS), at Deir El-Balah city, Middle Governorate in Gaza Strip, Palestine. The leachate samples were collected from the area of the landfill that receives waste continually. The DBLS has an area of 7 ha, receiving approximately 450 tons of municipal solid waste daily (Solid Waste Management Council SWMC, 2012). In this study, afour leachate samples were manually collected from February 2014 to June 2014 and placed in 2-L plastic containers. The samples were immediately transported to the laboratory, characterized, and cooled to 4 C to minimize the biological and chemical reactions. The average characteristics of the leachate used in this study are presented in Table 1. Themethodology to characterize are according to the Standard Methods for the Examination of Water and Wastewater (2005). 2.2. Experimental procedures
All experiments were conducted at a room temperature of 28 Cusing 50 mL leachate samples in 250 ml-polyethylene bottles. Orbital Shaker (Luckham R100/TW Rotatest Shaker 340 mm 245 mm) was used for sample shaking at 350 rpm. S2 O2 8 as sodium persulfate (Na2S2O8) Molarity (M) ¼ 238.09 g/mol) and Hydrogen peroxide (H2O2 37%) were employed for advanced oxidation during the oxidation of leachate samples. To determine the optimum conditions, a four-stage experiment was gradually applied: (1) Persulfate and hydrogen peroxide with different ratios ranging from 1:0.3 to 1:2.46 were immediately added into the oxidation reactor before each run. Persulfate (S2 O2 8 ) dosage was fixed at 4.2 g, which was determined through a set of preliminary experiments using persulfate oxidation only, and thenH2O2reagent was added gradually to achieve the highest performance ratio for the treatment of leachate. .
Table 1 General characteristics of landfill leachate from DELS. Parameter
Results
COD (mg/L) BOD (mg/L) BOD/COD ratio EC (mS) TDS (mg/L) Nitrate (mg/L) Ammonia (mg/L) Chloride (mg/L) Sulfate (mg/L) Alkalinity (mg/L) Hardness (mg/L) Calcium (mg/L) Magnesium (mg/L) Potassium (mg/L) Sodium (mg/L) pH Turbidity NTU Cupper (mg/L) Lead (mg/L) Nickel (mg/L) Manganese (mg/L) Cadmium (mg/L) Zinc (mg/L)
19,180e20,448 830e1821 0.05e0.09 40,800 22,356e25,296 2020e3602 2450e3400 6150e6953 780e856 22,500e24,000 6980e7283 1620 785 4345.5 6000 7.9e8.42 537.5 0.44 0.143 4.63 0.08 0.259 5.84
(2) Based on the optimum S2 O2 8 /H2O2 ratio (1:1.47) obtained from the previous oxidation step; different dosages of S2 O2 8 /H2O2 ranging from 2.52 g/3.7 g to 10.08/14.8 g were added gradually to the 50 mL of leachate sample in the reactor to determine the optimum persulfate dosage according to the efficiencies inCOD and NH3eN removal. In this stage, pH wasnot adjusted and all runs were performed with natural leachate pH (8.5) within 60 min of shaking and oxidation. (3) The performance of pH variation on oxidation of the leachate samples was performed and assessed. pH value of leachate samples were adjusted gradually from 3 to 11 using 5 Molar sulfuric acid solution and 5 Molar sodium hydroxide solution. Optimum dosage of S2 O2 8 /H2O2 (5.88 g/8.63 g) obtained from step 2 was used throughout all runs. All runs in step 1, 2 and 3 were performed for 60 min of oxidation. (4) The reaction time was examined from 10 min to 240 min (shaking at 350 rpm) at the optimal pH value (11) which was obtained from step No. 3. All samples were filtered through a 0.45 mm membrane prior to analysis. Persulfate oxidation alone, Hydrogen peroxide oxidation alone and sequential persulfate and hydrogen peroxide oxidation were conducted on a 50 mL sample reactor and the results were compared with simultaneous (S2 O2 8 /H2O2) process. 2.3. Analytical methods Chemical oxygen demand (COD) and NH3eN, were immediately tested before and after each run of the experiments in accordance with the Standard Methods for the Examination of Water and Wastewater (2005). The leachate was stirred uniformly before being analyzed. NH3eN concentration was measured by the Phenol Method No. (4500) using a UV-VIS spectrophotometer at 640 nm with a light path of 1 cm, (ATI UNICAM 8625 UV/VIS spectrometer). The pH was measured using a portable digital pH/Mv meter. The COD concentration was determined by the open reflux method No (5220) using COD REACTOR P/N 45600-00, HACH). The test values are presented as the average of the three
A.H. Hilles et al. / Journal of Environmental Management 166 (2016) 493e498
measurements, and the difference between the measurements of each value was less than 3%. The removal efficiencies of COD and NH3eN were obtained using the following equation (1):
Removal % ¼
. i h Xi 100 Xi Xf
(1)
where Xi and Xf refer to the initial and final concentrations for both COD and NH3eN. 3. Results and discussion 3.1. Effect of S2 O2 8 /H2O2 ratio To evaluate the performance of hydrogen peroxide in enhancing persulfate oxidation, the persulfate/H2O2 ratios (g/g) were fixed at ten different ratios, namely,1:0.3, 1:0.6, 1:0.89, 1:1.17, 1:1.23, 1:1.47, 1:1.76, 1:2.06, 1:2.34 and1:2.64 during 60 min of oxidation of the leachate (Fig. 1). Although persulfate reagent can act alone as an oxidant, its effectiveness is limited for oxidation of stabilized leachate. Persulfate oxidation can be enhanced by the initiation of sulfate radicals which have powerful effects on the oxidation of organics (Deng and Ezyske, 2011 and Kolthoff and Stenger, 1947). The generation of sulfate radicals during persulfate oxidation can be significantly investigated using different applications, such as heat, UV radiation, Iron ions as shown in equations (2)e(4), which were found to enhance the persulfate oxidation potential (Gao et al., 2012; Shiying et al., 2009; Rastogi et al., 2009). S2 O2 8 þ Initiator/SO4 þ SO4
(2)
S2 O2 8 þ Thermal Activation/SO4 þ SO4 30 C < T < 90 C
(3) 2þ Fe3þ þ S2 O2 8 /2SO4 þ Fe
(4)
SO-4
may initiate production of other intermediate highly reactive oxygen species (ROS) such as hydroxyl radicals (OH) as shown in Eq. (5), (Huie et al., 1991; Berlin, 1986). SO2 4 þ H2 O/HSO4 þ OH
(5)
To investigate the performance of H2O2 in initiating sulfate radical formation from persulfate during the oxidation process, the
495
influence of S2 O2 8 /H2O2 ratios on COD and NH3eN removal was investigated under the optimal operational conditions which were fixed at 28 C, reaction time 60 min, shaking speed of 350 rpm and an initial pH of 8.5. The maximum removal efficiencies of COD and NH3eN were 58% and 49%, respectively, at 1 g/1.47 g of S2 O2 8 /H2O2 ratio (Fig. 1). The removal efficiencies of the targeted parameters were improved by increasing the H2O2 dosages (Fig. 1). The activation mechanism that plays an important role in S2 O2 8 /H2O2 process is the initial formation of hydroxyl radical (OH) by the decomposition of the hydrogen peroxide followed by the activation of the persulfate to produce sulfate radicals (Block et al., 2004; Crimi and Taylor, 2007). Both sulfate and hydroxyl radicals may have played a significant role in the degradation of COD and NH3eN. Moreover, the temperature of oxidation is monitored and ranged between 40 and 50 C during oxidation. The increasing of temperature was observed when H2O2 dosage was increased. The heat resulted from decomposition of H2O2 contributed to initiate sulfate radicals. Shiying et al. (2009) utilized Microwave for persulfate activation used in wastewater treatment. Xu et al. (2012) activated persulfate at high temperature (150 C) using K2S2O8 in treating stabilized leachate. 3.2. Effect of S2 O2 8 /H2O2 dosage (g/g) Hydrogen peroxide reagent is used to improve persulfate oxidation efficiency during the oxidation of leachate. The amount of both persulfate and hydrogen peroxide used to improve oxidation efficiency has been determined. To investigate the optimum amount of both reagents in the oxidation of leachate, different 2 dosages of (S2 O2 8 /H2O2) were tested by fixing the S2 O8 /H2O2 ratio at 1:1.47, with varying amounts of both reagents (Fig. 2). By increasing the persulfate and hydrogen peroxide dosages, the performance of oxidation for treating leachate has improved. The maximum removal of COD was 72% at S2 O2 8 /H2O2 dosage 5.88 g/ 8.63 g, while the maximum removal of NH3eN (81%) was obtained using 7.56 g/11.09 g of S2 O2 8 /H2O2 dosage. 3.3. Effect of pH To determine the optimal pH for the S2 O2 8 /H2O2 system, the pH of the initial leachate sample was gradually adjusted from 3 to 11, maintaining the optimal S2 O2 8 /H2O2 dosage at5.88 g/8.63 g (as obtained from the previous reaction step). Fig. 3 shows that by increasing the pH, the removal efficiencies for COD, and NH3eN
Fig. 1. Effect of persulfate/hydrogen peroxide ratio (g/g) in removing of COD and NH3eN during 60 min oxidation of leachate (pH: 8.5, shaking at 350 rpm), S.D for COD (%) and NH3eN (%): 0.158, 0.156, respectively.
496
A.H. Hilles et al. / Journal of Environmental Management 166 (2016) 493e498
Fig. 2. Effect of persulfate/hydrogen peroxide dosage (g/g) in removing COD and NH3eN during 60 min oxidation of stabilized leachate [pH: 8.5, 350 rpm, S2 O2 8 /H2O2 ratio (1 g/ 1.47 g)] S.D for COD (%) and NH3eN (%): 0.23 and 0.22, respectively.
2 Fig. 3. Effect of initial pH on COD and NH3eN removal during 60 min oxidation of stabilized leachate at optimum S2 O2 8 /H2O2 ratio (1 g/1.47 g), S2 O8 /H2O2 dosage (5.88 g/8.63 g) and 350 (rpm) shaking speed. S.D for COD (%) and NH3eN (%): 0.23 and 0.21, respectively.
were also increased. The maximum removal efficiencies were 78% and 81% for COD and NH3eN respectively. At high pH conditions (pH ¼ 11), alkaline activation is very productive in generating sulfate and hydroxyl radicals. Both radicals (SO 4 and OH) have high oxidation potential (E ¼ 2.80 and E ¼ 2.70, respectively) (House, 1962). The effect of alkalinity on persulfate oxidation has been reported (Furman et al. 2011; Ocampo, 2009). At high pH value, hydroxyl radical can be act to activate persulfate and initiate sulfate radical (Eq. (6)) 2 S2 O2 8 þ OH /HSO4 þ SO4 þ 1=2 O2
(6)
Even though the optimal removal efficiency in the present study was obtained at the optimal temperature of 28 C and high pH (11), a significant removal efficiency was obtained also at natural pH (6e9) (Fig. 3). Deng and Ezyske (2011) obtained higher removal of COD and NH3eN from leachate at low pH (4) using persulfate alone. Shabiimam and Dikshit (2012) reported lower organic compounds removal in stabilized leachate at acidic medium (pH 2.5) using sodium persulfate reaction. Furthermore, Lin et al. (2011) obtained the best removal of Phenol from wastewater at high pH (11) using UV for persulfate activation.
3.4. Effect of reaction time The effect of reaction time on the S2 O2 8 /H2O2 oxidation process was investigated in terms of COD and NH3eN removal (Fig. 4). The reaction time was varied between 10 min and 240 min, and the initial pH and S2 O2 8 /H2O2 dosage were maintained constant at 11 and 5.88 g/8.63 g, respectively. The removal of organics and NH3eN were improved as the reaction time increased (Fig. 4). The maximum removal efficiencies for COD and NH3eN obtained 81%, and 83%, respectively after 120 min of oxidation. Thus, the optimum reaction time for S2 O2 8 /H2O2 oxidation process is considered to be 120 min Xu et al., 2012 used potassium persulfate in treating of stabilized leachate and achieved maximum removal efficiency of COD (78%) at 4 h as an optimal reaction time. 3.5. Treatment efficiency and effect on biodegradability The treatment efficiency of the S2 O2 8 /H2O2 oxidation was compared with other treatment processes (i.e., persulfate alone, hydrogen peroxide alone, and persulfate followed by hydrogen peroxide) under experimental conditions (Table 2). The efficiency of persulfate alone was found to beinsufficient for the removal of
A.H. Hilles et al. / Journal of Environmental Management 166 (2016) 493e498
497
2 Fig. 4. Effect of reaction time on COD and NH3eN removal during oxidation of stabilized leachate at optimum S2 O2 8 /H2O2 ratio (1 g/1.47 g), S2 O8 /H2O2 dosage (5.88 g/8.63 g) and 350 rpm and pH (11). S.D for COD (%) and NH3eN (%): 0.26 and 0.25, respectively.
Table 2 Comparing the performance of S2 O2 8 /H2O2 based on advanced oxidation with other processes used for the treatment of stabilized leachate. Process
Condition
Removal (%) COD
NH3eN
H2O2 alone S2 O2 8 alone S2 O2 8 followed by H2O2 H2O2 followed by S2 O2 8 S2 O2 8 /H2O2
H2O2: 8.63 g, pH (11), RT*: 120, SS*: 350 rpm S2 O2 8 :4.2 g, pH (7), RT*: 60, SS*: 350 rpm S2 O2 8 :4.2 g, pH (7), RT*: 60, SS*: 350 rpm, H2O2: 8.63 g, pH (11), RT*: 120, SS*: 350 rpm H2O2: 8.63 g, pH (11), RT*: 120, SS*: 350 rpm, S2 O2 8 :4.2 g, pH (7), RT*: 60, SS*: 350 rpm S2 O2 8 5.88 g, H2O2: 8.63 g, pH (11), RT*: 120, SS*: 350 rpm
31% 45% 62% 55% 81%
28% 46% 50% 42% 83%
RT*: reaction time in minutes. SS*: shaking speed.
COD and NH3eN (45% for both). Compared with that of the other processes, these limitedremovals were attributed to the limited oxidation potential of persulfate alone against high organic concentration in leachate. However, increasing of the persulfate dosage higher than 4.2 g did not improve removal efficiency. Although the efficiency of H2O2 after S2 O2 8 was improved (62% COD removal, and 50% NH3eN removal), the results showed lower removal efficiency than the combination method. These findings helped to ensure that the combined S2 O2 8 and H2O2work better as oxidants if they are added together than working separately. These results are close to those obtained from the oxidation process when adding S2 O2 8 after H2O2(55% COD removal, and 42% NH3eN removal). Best removal efficiency was obtained from the advanced oxidation system (S2 O2 8 /H2O2) and reached 81% and 83% for COD and NH3eN, respectively, under optimal conditions. Comparing the results with ozone/persulfate oxidation (Abu Amr et al., 2013a, b, c) obtained 70% and 72% removal efficiencies for COD and NH3eN, respectively. In the O3/persulfate oxidation, sulfate ions cannot react directly with ozone. However, ozone has a significant role in the process by increasing hydroxyl radicals at high pH, which directly activates persulfate and initiate sulfate radicals (Tizaoui et al., 2007). Although the optimal reaction time in the ozone/persulfate process (90 min) was shorter than that in the current process, the performance of cooperative hydroxyl and sulfate radicals in removing COD and NH3eN was much higher at 120 min of oxidation. As for the effect of persulfate/hydrogen peroxide oxidation on the biodegradability of leachate, the COD, BOD5, and BOD5/COD ratio of leachate were tested before and after the oxidation process. Based on the results, persulfate/Hydrogen peroxide was more efficient in enhancing the biodegradability of leachate than other oxidation processes. The biodegradability (BOD5/COD) ratio increased from 0.09 to 0.17, whereas the ratio only improved to 0.1
after S2 O2 oxidation. Operational cost for using persulfate/ 8 hydrogen peroxide oxidation is summarized and calculated for large scale volume (50 L of leachate); As the major cost of the oxidation process is related to chemicals used, the cost were 0.4 USD/L 37% H2O2 and 0.8 USD/kg sodium persulfate, since about 5.8 kg of persulfate and 16.7 L of 37% H2O2 are required to remove 1 kg COD (in 50 L of leachate). Around 10.73 USD is required to remove 81% of organics from 50 L of stabilized leachate using S2 O2 8 /H2O2 oxidation process. Although the cost of proposed process is higher than Ozone/Fenton oxidation (Abu Amr and Aziz, 2012), however, the process achieved significant removal in organic (81%) while ozone/Fenton reported lower removal (65%). Furthermore, the method can efficiently work at natural pH and doesn't required extra chemicals for pH adjustment, while the optimum pH for Fenton is 2e4.5 (Lopez et al., 2004; Deng, 2007; Mohajeri et al., 2010) which required extra chemicals and create critical risk for effluent discharge. Moreover, persulfate oxidation does not produce undesirable sludge needs to be settled comparing with Fenton oxidation. The study demonstrated that persulfate and persulfate/ H2O2 oxidation can improved biodegradability of organics in the leachate, and the application of biological methods as a post treatment process of leachate is applicable. 4. Conclusion The performance of an advanced oxidation process, consisting of the combined use of persulfate and hydrogen peroxide for the treatment of stabilized landfill leachate was investigated. The maximum removal efficiency for COD and NH3 - N was 81% and 83%, respectively. The results demonstrated that the combined persulfate/H2O2 process can efficiently use for stabilized leachate treatment at natural leachate pH (7e9). Moreover, the biodegradability of the leachate was improved. The combination of persulfate
498
A.H. Hilles et al. / Journal of Environmental Management 166 (2016) 493e498
and hydrogen peroxide was found to be more efficient in leachate treatment compared with using persulfate alone or persulfate followed by hydrogen peroxide. Accordingly, the new treatment increased the oxidation potential of organics during oxidation. The study revealed that the new (persulfate/H2O2) oxidation is an efficient process in treating stabilized leachate. Acknowledgments The authors wish to acknowledge the indispensable role of the staff of the Public Health Laboratory at the Ministry of HealthPalestine and at the Municipality of Deir El-balahfor facilitating and supporting the implementation of the present work. Thanks and gratitude are due them all. References Abu Amr, S.S., Aziz, H.A., Adlan, M.N., Alkaseeh, J.M., 2014. Effect of ozone and ozone/persulfate processes on biodegradable and soluble characteristics of semi-aerobic stabilized leachate. J. Environ. Prog. Sustain. Energy 33, 184e191. Abu Amr, S.S., Aziz, H.A., Adlan, M.N., Bashir, M.J.K., 2013a. Pretreatment of stabilized leachate using ozone/persulfate oxidation process. Chem. Eng. J. 221, 492e499. Abu Amr, S.S., Aziz, H.A., Adlan, M.N., 2013b. Optimization of stabilized leachate treatment using ozone/persulfate in the advanced oxidation process. Waste Manag. 33, 1434e1441. Abu Amr, S.S., Aziz, H.A., Adlan, M.N., Aziz, S.Q., 2013c. Effect of ozone and ozone/ fenton in the advanced oxidation process on biodegradable characteristics of semi-aerobic stabilized leachate. Clean Air Soil Water 41 (2), 148e152. Abu Amr, S.S., Aziz, H.A., 2012. New treatment of stabilized leachate by ozone/ fenton in the advanced oxidation process. Waste Manag. 32, 1693e1698. APHA, WPCF, A.W.W.A Standard Methods for the Examination of Water and Wastewater, 21st ed., 2005. American Public Health Association (APHA), Washington, DC. Aziz, H.A., Alias, S., Adlan, M.N., Asaari, A.H., Zahari, M.S., 2007. Colour removal from landfill leachate by coagulation and flocculation processes. Bioresour. Technol. 98, 218e220. Aziz, H.A., Adlan, M.N., Zahari, M.S.M., Alias, S., 2004. Removal of ammoniacal nitrogen (N-NH3) from municipal solid waste leachate by using activated carbon and limestone. Waste Manag. Res. 22, 371e375. Aziz, S.Q., Aziz, H.A., Yusoff, M.S., Bashir, M.J.K., Umar, M., 2010. Leachate characterization in semi-aerobic and anaerobic sanitary landfills: a comparative study. J. Environ. Manag. 12, 2608e2614. Bashir, M.J.K., Aziz, H.A., Yusoff, M.S., 2011. New sequential treatment for mature landfill leachate by cationic/anionic and anionic/cationic processes: optimization and comparative study. J. Hazard. Mater. 186, 92e102. Berlin, A.A., 1986. Kinetics of radical-chain decomposition of persulfate in aqueous solutions of organic compounds. Kinet. Catal. 27, 34e39. Block, P.A., Brown, R.A., Robinson, D., 2004. Novel activation technologies for sodium persulfate in situ chemical oxidation. In: 4th Int. Conf. on the Remediation of Chlorinated and Recalcitrant Compounds, Battelle, Monterey, CA. Christensen, T.H., Kjeldsen, P., Bjerg, P.L., Jensen, D.L., Christensen, J.B.A., Baum, A., Albrechtsen, H., Heron, G., 2001. Biogeochemistry of landfill leachate plumes. Appl. Geochem. 16, 659e718. Crimi, M.L., Taylor, J., 2007. Experimental evaluation of catalyzed hydrogen peroxide and sodiumpersulfate for destruction of BTEX contaminants. Soil Sediment. Contam. 16, 29e45. Deng, Y., Ezyske, C.M., 2011. Sulfate radical-advanced oxidation process (SR-AOP) for simultaneous removal of refractory organic contaminants and NH3-Nin landfill leachate. Water Res. 45, 6189e6194. Deng, Y., 2007. Physical and oxidative removal of organics during Fenton treatment of mature municipal landfill leachate. J. Hazard. Mater. 146, 334e340. Furman, O., Teel, A., Ahmad, M., Merker, M., Watts, R., 2011. Effect of basicity on
persulfate reactivity. J. Environ. Eng. 137 (4), 241e247. Gao, Y., Gao, N., Deng, Y., Yang, Y., Ma, Y., 2012. Ultraviolet (UV) light-activated persulfate oxidation of sulfamethazine in water. Chem. Eng. J. 195e196, 248e253. Ghafari, S., Aziz, H.A., Isa, M.H., 2005. Coagulation process for semi-aerobic leachate treatment using poly-aluminum chloride. In: The AEESEAP International Conference “Engineering a Better Environment for Mankind”, Kuala Lumpur, Malaysia, June 7e9. Ghauch, A., Tuqan, A., Kibbi, N., 2012. Ibuprofen removal by heated persulfate in aqueous solution: a kinetics study. Chem. Eng. J. 197, 483e492. Goi, A., Veressinina, Y., Trapido, M., 2009. Combination of oxidation and the fenton processes for landfill leachate treatment: evaluation of treatment efficiency. Ozone Sci. Eng. 31, 28e36. Hagman, M., Heander, E., Jansen, J.L.C., 2008. Advanced oxidation of refractory organics in leachateepotential methods and evaluation of biodegradability of the remaining substrate. Environ. Technol. 29, 941e946. House, D.A., 1962. Kinetics and mechanism of oxidations by peroxydisulfate. Chem. Rev. 62, 185e203. Huie, R.E., Clifton, C.L., Neta, P., 1991. Electron transfer reaction rates and equilibria of the carbonate and sulfate radical anions. Radiat. Phys. Chem. 38, 477e481. Huling, S.G., Pivetz, B.E., 2006. In-situ Chemical Oxidation, (2006) (EPA/600/R-06/ 072). US EPA. Kolthoff, I.M., Stenger, V.A., 1947. Volumetric analysis In: Titration Methods: Acidbase, Precipitation, and Complex Reactions, second revised ed., vol. II. Interscience Publishers, Inc., New York. Lin, Y., Liang, C., Chen, J., 2011. Feasibility study of ultraviolet activated persulfate oxidation of phenol. Chemosphere 82, 1168e1172. Lopez, A., Pagano, M., Volpe, A., Di Pinto, A.C., 2004. Fenton's pre-treatment of mature landfill leachate. Chemosphere 54, 1005e1010. Liu, C.S., Shih, K., Sunc, C.X., Wang, F., 2012. Oxidative degradation ofpropachlor by ferrous and copper ion activated persulfate. Sci. Total Environ. 416, 507e512. Mohajeri, S., Aziz, H.A., Isa, M.H., Zahed, M.A., Adlan, M.N., 2010. Statistical optimization of process parameters for landfill leachate treatment using electroFenton technique. J. Hazard. Mater. 176, 749e758. Ocampo, A.M., 2009. Persulfate Activation by Organic Compounds. PhD thesis. Washington State University, Department of Civil and Environmental Engineering, pp. 1e77. Rastogi, A., Al-Abed, S.R., Dionysiou, D.D., 2009. Sulfate radical-based ferrous peroxymonosulfate oxidative system for PCBs degradation in aqueous and sediment systems. Appl. Catal. B Environ. 85, 171e179. Renaud, I.P., Sibi, M.P., 2001. Radicals in Organics Synthesis. Wiley-VCH, Weinheim. New York, pp. 479e488. Schiopu, A.M., Gavrilescu, M., 2010. Options for the treatment and management of municipal landfill leachate: common and specific issues. Clean Soil Air Water 12, 1101e1110. Shabiimam, M.A., Dikshit, A.K., 2012. Treatment of municipal landfill leachate by oxidants. Am. J. Environ. Eng. 2, 1e5. Shiying, Y., Ping, W., Xin, Y., Guang, W., Wenyi, Z., Liang, S., 2009. A novel advanced oxidation process to degrade organic pollutants in wastewater: microwaveactivated persulfate oxidation. J. Environ. Sci. 21, 1175e1180. Solid Waste Management Council (SWMC), 2012. Annual Report of Khan Younis and Deir AL-balah Governorates. Tengrui, L., AL-Harbawi, A.F., Bo, L.M., Jun, Z., 2007. Characteristics of nitrogen removal from old landfill leachate by sequencing batch biofilm reactor. J. Appl. Sci. 4, 211e214. Tizaoui, C., Bouselmi, L., Mansouri, L., Ghrabi, A., 2007. Landfill leachate treatment with ozone and ozone/hydrogen peroxide systems. J. Hazard. Mater. 140, 316e324. Watts, R.J., 2011. Enhanced Reactant-contaminant Contact through the Use of Persulfate in Situ Chemical Oxidation (ISCO). SERDP Project ER-1489. Washington State University. Xu, X., Zeng, G., Peng, Y., Zeng, Z., 2012. Potassium persulfate promoted catalytic wet oxidation of fulvic acid as a model organic compound in landfill leachate with activated carbon. Chem. Eng. J. 200 e 202, 25e31. Yang, S., Yang, X., Shao, X., Niub, R., Wang, L., 2011. Activated carbon catalyzed persulfate oxidation of azo dye acid orange 7 at ambient temperature. J. Hazard. Mater. 186, 659e666.
