Journal of Environmental Management 139 (2014) 1e14

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Powdered ZELIAC augmented sequencing batch reactors (SBR) process for co-treatment of landfill leachate and domestic wastewater Amin Mojiri a, Hamidi Abdul Aziz a, *, Nastaein Q. Zaman a, Shuokr Qarani Aziz b, Mohammad Ali Zahed c a b c

School of Civil Engineering, Engineering Campus, University Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia Department of Civil Engineering, College of Engineering, University of Salahaddin, Erbil, Iraq Department of Civil Engineering, Auburn University, Auburn, AL 36849, USA

a r t i c l e i n f o

a b s t r a c t

Article history: Received 13 October 2013 Received in revised form 4 February 2014 Accepted 17 February 2014 Available online

Sequencing batch reactor (SBR) is one of the various methods of biological treatments used for treating wastewater and landfill leachate. This study investigated the treatment of landfill leachate and domestic wastewater by adding a new adsorbent (powdered ZELIAC; PZ) to the SBR technique. ZELIAC consists of zeolite, activated carbon, lime stone, rise husk ash, and Portland cement. The response surface methodology and central composite design were used to elucidate the nature of the response surface in the experimental design and describe the optimum conditions of the independent variables, including aeration rate (L/min), contact time (h), and ratio of leachate to wastewater mixture (%; v/v), as well as their responses (dependent variables). Appropriate conditions of operating variables were also optimized to predict the best value of responses. To perform an adequate analysis of the aerobic process, four dependent parameters, namely, chemical oxygen demand (COD), color, ammoniaenitrogen (NH3eN), and phenols, were measured as responses. The results indicated that the PZ-SBR showed higher performance in removing certain pollutants compared with SBR. Given the optimal conditions of aeration rate (1.74 L/min), leachate to wastewater ratio (20%), and contact time (10.31 h) for the PZ-SBR, the removal efficiencies for color, NH3eN, COD, and phenols were 84.11%, 99.01%, 72.84%, and 61.32%, respectively. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: Co-treatment Landfill leachate Wastewater Phenols Sequencing batch reactor ZELIAC

1. Introduction Solid waste disposal methods include open dump, sanitary landfill, composting, incineration, grinding and discharging to sewer, compaction, dumping, hog feeding, milling, reduction, and anaerobic digestion. Sanitary landfill is the most general urban solid waste disposal method. To date, more than 230 landfills, which are mostly old dumpsites, exist in Malaysia. Most of these landfills are simply dumping grounds that lack any environmental protection. Thus, the resulting leachate is directly discharged into water courses without treatment. This discharged leachate can threaten the surrounding ecosystem, especially in cases where landfills are located upstream of water intakes (Aziz et al., 2010). Leachate is formed when water penetrates through the waste in a landfill and carries some forms of pollutants, such as ammoniae nitrogen (NH3eN), biochemical oxygen demand (BOD5), chemical oxygen demand (COD), color, heavy metals, and suspended solids. * Corresponding author. Tel.: þ60 45996215; fax: þ60 45941009. E-mail addresses: [email protected], [email protected] (H.A. Aziz). http://dx.doi.org/10.1016/j.jenvman.2014.02.017 0301-4797/Ó 2014 Elsevier Ltd. All rights reserved.

Leachate composition depends on different factors, such as the kind of waste and site hydrology, as well as age, type, and operation of the landfill (Foul et al., 2009). Landfill leachates are one of the types of wastewater with great environmental effect. The most critical feature of leachates is linked to the high concentrations of some contaminants. The composition of urban landfill leachates can be divided into four main groups, namely, dissolved organic substances, inorganic compounds (e.g., calcium, potassium, sodium, ammonium, magnesium, sulfates, chlorides, and iron), heavy metals (e.g., nickel, copper, lead, cadmium, chromium, and zinc), and xenobiotic organic materials (Tengrui et al., 2007). As a landfill ages, the biodegradable fraction of the organic contaminants in the leachate decreases because of the occurrence of anaerobic decomposition in the landfill site. In general, the following landfill leachate treatment options are available: (1) spray irrigation on abutting grassland, (2) leachate recirculation through the landfill, (3) sewage and leachate cotreatment, (4) leachate evaporation using landfill-generated methane as fuel, and (5) biological or physical/chemical treatment (Mojiri, 2011).

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Table 1 Characteristics of landfill leachate, domestic wastewater and sludge. No.

Parameter

Leachate average value

Wastewater average value

Activated sludge average value

Standard discharge limit for leachatea

1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

Temperature ( C) pH EC (ms/cm) Salinity (g/L) Total solids (mg/L) Suspended solids (mg/L) Total Hardness (mg/L CaCO3) Color (Pt. Co) BOD5 (mg/L) COD (mg/L) BOD5/COD TDS (%) ORP (mV) MLVSS/MLSS Nitrite (mg/L NO2eN-HR) Total phosphorus (mg/L PO3 4 ) NH3eN (mg/L) Total organic carbon (mg/L TOC) Sulfide (mg/L) Total iron (mg/L) Total manganese (mg/L) Total Zinc (mg/L) Total copper (mg/L) Total aluminum (mg/L) Total nickel (mg/L) Total chromium (mg/L) Total cobalt (mg/L) Total lithium (mg/L) Total molybdenum (mg/L) Total cadmium (mg/L) Total calcium (mg/L) Total magnesium (mg/L) Phenols (mg/L)

28.7 8.25 3.94 2.10 5723 710 1912 1690 269.0 1301 0.20 5.72 11.6 e 54.10 17.8 532.0 44.2 0.300 6.03 1.98 1.89 1.17 0.034 4.94 0.21 0.81 0.64 0.78 2.71 121.45 25.34 1.69

28.6 6.87 1.00 0.02 e e e 6.00 64.2 156 0.41 1.03 e e 10.1 81.13 149.0 29.0 0.600 1.21 0.67 1.71 1.11 0.031 0.51 0.12 0.02 0.51 0.30 0.39 25.11 8.404 0.04

28.6 6.60 1.09 0.03 10,711 9234 e e 87.5 218 0.40 1.44 126.0 0.82 e e 160.0 36.0 0.654 1.95 0.91 1.89 1.82 0.047 0.78 0.12 0.27 0.52 0.33 0.39 102.0 34.0 0.07

40 6e9 e e e 50 e 100 20 400 0.05 e e e e 5.0 e 0.5 5.0 0.20 2.0 0.20 e 0.20 0.20 e e e 0.01 e e 0.001

a Environmental Quality (Control of Pollution from Solid Waste Transfer Station and Landfill) Regulations 2009, under the Laws of MalaysiaeMalaysia Environmental Quality Act 1974.

To date, landfill leachates are often treated in urban wastewater treatment plants. Given the strict regulation of nitrogen release and the issue on the potential effect of recalcitrant leachate components on the biological treatment stage, an increasing demand Table 2 Powdered ZELIAC characteristics. Parameter

Unit

Value

Surface area data MultiPoint BET Langmuir surface area BJH method cumulative adsorption surface area DH method cumulative adsorption surface area t-method external surface area t-method micropore surface area DR method micropore area

m2/g m2/g m2/g m2/g m2/g m2/g m2/g

6.760eþ01 1.328eþ02 9.638eþ00 1.019eþ01 3.421eþ01 3.338eþ01 1.153eþ02

Pore volume data Total pore volume for pores with Diameter less than 4.06 nm at P/P0 ¼ 0.501894 BJH method cumulative adsorption pore volume DH method cumulative adsorption pore volume t-method micropore volume DR method micropore volume HK method cumulative pore volume SF method cumulative pore volume

cc/g

4.029e-02

cc/g cc/g cc/g cc/g cc/g cc/g

9.930e-03 1.011e-02 1.803e-02 4.098e-02 3.172e-02 3.222e-02

Pore size data Average pore Diameter BJH method adsorption pore Diameter (Mode DV (d)) DH method adsorption pore Diameter (Mode Dv9d)) DA method pore Diameter (Mode) HK method pore Diameter (Mode) SF method pore Diameter (Mode)

nm nm nm nm nm nm

2.384eþ00 3.652eþ00 3652eþ00 1.760eþ00 3.675e-01 4.532e-01

exists for separate treatment and disposal of landfill leachate. One solution to separate landfill leachate from the urban sewage treatment is co-treatment with domestic wastewater (Neczaj et al., 2008). The main applicable methods of landfill leachate treatment include chemical, biological, membrane separation, and thermal treatment processes. Sequencing batch reactor (SBR) is one of the biological processes used to remove several contaminants (Aziz et al., 2011a). Given that landfill leachates have high degree of variation in quantity and quality, the SBR, which has greater process flexibility than other biological treatment methods, is well fitted for leachate treatment (Lim et al., 2010). The high concentrations of organic matters, low biodegradability ratio, NH3eN, heavy metals, and other pollutants in leachate affect the SBR performance (Foo and Hameed, 2009).

Table 3 XRF results for ZELIAC. Compounds/elements

Composition (%)

C CaO SiO2 Al2O3 Fe2O3 K2O MgO Na2O P2O5 SO3 Others

14.350 32.401 42.002 7.300 1.502 1.005 1.000 0.100 0.030 0.030 0.280

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Fig. 1. The XRD results for ZELIAC.

Many studies reported the addition of adsorbents, such as activated carbon, to activate sludge and SBR at the end of the enhancement of the biological treatment of landfill leachate (Foo and Hameed, 2009; Aziz et al., 2011b, 2011c, 2012). However, a knowledge gap can still be observed in the literature, especially in the removal of pollutants (e.g., heavy metals, phenols, and other contaminants), settleability of sludge, nitrification and denitrification processes in different landfill leachates using the SBR technology, and availability of low cost materials. Recently, more attention has been focused on the application of several domestic and low-cost materials for wastewater and leachate treatment (Environmental Quality, 2009). Some of these materials include zeolite, limestone, rice husk ash, activated carbon, and Portland cement, which comprise the powdered ZELIAC (PZ). This study aims to examine the SBR performance in the presence and absence of PZ on the following processes: (1) the removal of phenols, color, NH3eN, and COD from the landfill leachates of Sungai Petani and the domestic wastewater from the Bayan Baru

Wastewater Treatment Plant in Malaysia and (2) introduction of a new, inexpensive media called ZELIAC. 2. Materials and methods 2.1. Landfill leachate sampling 10 leachate samples were collected from the Sungai Petani landfill site from June 2012 to March 2013. The landfill site (geographical coordinates, 05 430 N and 100 290 E) is located in Kedah, Malaysia. Sungai Petani landfill receives nearly 350 tonse 400 tons of solid wastes daily, measured using a weight bridge. This open dumping site has been actively used since 1990. The total landfill area of Sungai Petani is 11.24 ha. The leachates remain in the collection pond depending on retention time, and then discharged directly into the environment without treatment. Samples were collected in 24 L plastic containers and were immediately transferred to the laboratory after collection and maintained in a cold room at 4  C to minimize the biological and chemical reactions

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A. Mojiri et al. / Journal of Environmental Management 139 (2014) 1e14 Table 5 Experimental variables and results for the PZ-SBR. COD Ammonia Phenols Run Aeration Contact Leachate to Color rem. (%) time (h) wastewater rem. (%) rem. (%) rem. (%) rate ratio (%) (L/min) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

4.0 7.5 0.5 0.5 0.5 0.5 4.0 7.5 4.0 4.0 7.5 4.0 7.5 4.0 0.5 7.5 4.0 4.0 4.0 4.0

12 22 22 22 12 2 12 12 2 22 22 12 2 12 2 2 12 12 12 12

80 20 80 20 50 20 50 50 50 50 80 50 80 50 80 20 50 50 20 50

68.15 78.57 62.39 82.31 74.31 78.85 77.11 74.31 75.59 75.26 65.47 77.84 65.53 79.31 66.61 79.59 78.60 75.31 86.46 75.58

52.34 67.94 50.22 69.40 67.38 73.30 66.52 63.07 65.30 63.52 56.29 66.06 53.22 66.40 48.72 69.53 68.22 66.29 71.18 67.12

89.06 95.21 79.42 96.89 90.88 96.11 95.98 93.10 96.04 91.13 82.74 94.89 79.52 95.97 80.67 97.00 92.11 92.00 98.27 91.09

46.29 61.63 48.17 63.71 55.13 62.34 53.25 52.89 55.13 55.13 47.29 52.18 45.23 52.88 46.01 60.61 52.37 52.64 62.23 51.93

2.2. Domestic wastewater and activated sludge sampling The activated sludge and domestic wastewater were collected from the Bayan Baru wastewater treatment plant in Penang, Malaysia. Table 1 shows the characteristics of the activated sludge and wastewater. 2.3. Reactor characteristics

Fig. 2. SEM images from surface of ZELIAC.

(Aziz et al., 2011c). Table 1 shows the characteristics of the samples. To determine the risks of leachates to the environment, the obtained parameter values were compared with the 2009 Regulations of the Malaysia Environmental Quality Act of 1974 (2009).

Six 2000 mL beakers were used throughout the study. Each beaker had a working volume of 1200 mL, an inner diameter of 113 mm, and a height of 200 mm. A magnetic stirrer placed at the bottom of the reactors was used to mix the media. The experiments were carried out at room temperature, and an air pump (YASUNAGA, Air pump Inc.; voltage: 240 V, frequency: 50 Hz, input power: 61 W, model: LP-60A, pressure: 0.012 MPa, air volume: 60 L/ min; Serial no.: 08110014, made in China) was used to provide the reactors with air. The air flow speed was manually regulated using an air flow meter (Dwyer Flow meter, Model: RMA-26-SSV).

Table 4 Experimental variables and results for the SBR. COD Ammonia Phenols Run Aeration Contact Leachate to Color rem. (%) time (h) wastewater rem. (%) rem. (%) rem. (%) rate ratio (%) (L/min) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

4.0 7.5 0.5 0.5 0.5 0.5 4.0 7.5 4.0 4.0 7.5 4.0 7.5 4.0 0.5 7.5 4.0 4.0 4.0 4.0

12 22 22 22 12 2 12 12 2 22 22 12 2 12 2 2 12 12 12 12

80 20 80 20 50 20 50 50 50 50 80 50 80 50 80 20 50 50 20 50

38.11 55.46 35.13 52.30 52.49 47.29 46.29 48.31 44.11 49.10 30.00 46.00 27.43 47.21 29.10 49.10 45.91 45.25 58.26 44.98

38.73 40.17 25.64 41.29 40.14 43.19 41.18 39.40 44.24 40.66 25.65 42.11 32.45 41.18 30.70 46.29 40.71 40.84 43.29 40.63

82.13 92.29 71.26 90.18 79.73 87.49 96.04 89.18 79.44 94.11 79.48 96.03 90.00 95.14 76.11 90.50 95.17 94.13 96.11 95.61

21.95 30.19 14.97 30.91 26.95 26.13 24.43 30.98 16.11 30.98 16.11 30.98 13.93 29.42 16.98 23.18 30.18 28.91 33.17 30.23

Fig. 3. The design expert statistical plots e predicted versus actual plot: Color in the Normal-SBR. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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Fig. 4. The design expert statistical plots e predicted versus actual plot: COD in the Normal-SBR.

Fig. 7. The design expert statistical plots e predicted versus actual plot: Color in the PZ-SBR. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 5. The design expert statistical plots e predicted versus actual plot: Ammonia in the Normal-SBR.

Fig. 8. The design expert statistical plots e predicted versus actual plot: COD in the PZSBR.

Fig. 6. The design expert statistical plots e predicted versus actual plot: Phenols in the Normal-SBR.

Fig. 9. The design expert statistical plots e predicted versus actual plot: Ammonia in the PZ-SBR.

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In another cycle, an additional 120 mL of the raw leachate was added to the reactor. This procedure was sustained for at least 10 d to allow the system to adapt to the experimental condition. The adjusted sludge was later used as seed in the SBRs. 2.5. ZELIAC Preparation

Fig. 10. The design expert statistical plots e predicted versus actual plot: Phenols in the PZ-SBR.

2.4. Sludge acclimatization According to the study of Aziz et al. (2011c), 120 mL (10%) of the collected landfill leachate was mixed with approximately 1080 mL of the activated sludge (90%). After the termination of the reaction and the settling phases, 120 mL of the supernatant was withdrawn.

To prepare the ZELIAC, zeolite, activated carbon, lime stone, rice husk ash, and Portland cement were ground, passed through a 300 mm mesh sieve, and then mixed. The mixture was then evenly poured in the mold after the addition of water. After 24 h, the materials were removed from the mold and soaked in water for three days for the curing process. After allowing the materials to dry within two days, they were crushed and passed through a sieve. Table 2 shows the features of the ZELIAC with the autosorb (Quantachrome AS1wintm, version 2.02) test. The results of the XRF and XRD analyses of ZELIAC are shown in Table 3 and Fig. 1, respectively. The SEM image in Fig. 2 shows several pores on the ZELIAC surface, which can increase the adsorption surface. Zeolite and activated carbon are present in the ZELIAC; thus ZELIAC can act as both adsorbent and ion exchanger. In this study, PZ with a size ranging from 75 mm to 150 mm (passing sieve no. 100 and retained on sieve no. 200) was used as adsorbent in the PZ-SBR (Aziz et al., 2011a).

Fig. 11. The 3D surface plots of color removal in Normal-SBR. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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Fig. 12. The 3D surface plots of COD removal in Normal-SBR.

2.6. Operation of reactors The SBR system includes fill, react, settle, draw, and idle phases. In all experiments, the durations of fill and mix (20 min), settle (90 min), draw, and idle (10 min) were fixed. Different aeration rates of 0.5, 4, and 7.5 L/min; contact times of 2, 12, and 22 h; and different ratios of leachate to wastewater (20e80%; v/v) were applied to both SBR and PZ-SBR methods. The beakers were filled with 120 mL (10%) of adjusted sludge and 1080 mL (90%) of domestic wastewater and Sungai Petani landfill leachate (in different ratios), with a mixing ratio of 20%e80% (v/v). Table 1 shows the main features of the wastewater, leachate, and activated sludge. The reactors were divided into two groups consisting of three reactors each for SBR (normal SBR) and PZ-SBR (PZ augmented SBR). Based on preliminary experiments, 3.24 g of PZ (i.e., PZ dosage ¼ 3 g/L) was added to each PZ-SBR reactor before aeration. The PZ used for the adsorption of pollutants in the PZ-SBR was predried at 103  Ce105  C with a size of 75 mme150 mm (passing sieve no. 100 and retained on sieve no. 200). Table 2 shows the characteristics of PZ. The removal efficiencies of COD, NH3eN, color, and phenols were observed by measuring the target parameters before and after

the treatment process. The removal efficiency was calculated based on the following equation:

Removalð%Þ ¼

ðCi  Cf Þ*100 Ci

(1)

where Ci and Cf are the initial and final concentrations of the parameters, respectively. 2.7. Analytical methods All tests were conducted in accordance with the Standard Methods for the Examination of Water and Wastewater (APHA, 2005). A YSI 556 MPS (YSI incorporated, USA) was used to record the pH, temperature ( C), electrical conductivity (ms/cm), salinity (g/L), TDS (%), and oxidation reduction potential (mV) values. A spectrophotometer (DR/2500 HACH) was used to measure phenols (mg/L), color (Pt. Co), total phosphorus (PO3 4 mg/L), ammonia NH3eN (mg/L), total nitrogen (mg/L), nitrite (mg/L), COD (mg/L), sulfide (mg/L S2), total organic carbon (mg/L TOC), total iron (mg/L Fe), copper (mg/L Cu), manganese (mg/L Mn), aluminum (mg/L Al), zinc (mg/L Zn), chromium (mg/L Cr), and nickel (mg/L Ni). ICP (ICP Varian, OES 715) was used to measure

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Fig. 13. The 3D surface plots of ammonia removal in Normal-SBR.

cadmium (mg/L Cd), molybdenum (mg/L Mo), cobalt (mg/L Co), magnesium (mg/L), lithium (mg/L Li), and calcium (mg/L CaCO3) levels.

2.8. Experimental design and data analysis The response surface methodology (RSM) and central composite design (CCD) are used to demonstrate the nature of the response surface in the experimental design and clarify the optimum conditions of the independent variables. CCD is established using the Design Expert Software. Eq. (2), an empirical second-order polynomial model, accounts for the behavior of the system:

Y ¼ b

k X i¼1

biXi þ

k X i¼1

biXi2 þ

k X k X i15 years). In addition, the concentration of pollutants exceeded the permissible limits issued by the 1974 Environmental Quality Act of Malaysia (2009). This

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Fig. 14. The 3D surface plots of phenols removal in Normal-SBR.

study co-treated the raw leachate of the Sungai Petani landfill with domestic wastewater using the PZ augmented SBR process to decrease the environmental risks caused by the SG. Petani landfill leachate. Figs. 3 to 10 show the design expert statistical plots d predicted versus actual plot (color, COD, ammonia, and phenols) e in the normal SBR and PZ-SBR. The 3D surface plots for the pollutant removal (color, COD, ammonia, and phenols) in normal SBR and PZ-SBR are shown in Figs. 11 to 18. 3.1. Reactor performance 3.1.1. COD removal Table 4 shows that the removal efficiency of SBR varied from 25.64% (contact time ¼ 22 h, aeration rate ¼ 0.5 L/min, and leachate to wastewater ratio ¼ 80%) to 46.29% (contact time ¼ 2 h, aeration rate ¼ 7.5 L/min, and leachate to wastewater ratio ¼ 20%). Azimi et al. (2005) showed that the increasing aeration rate from 25.2 L/h to 90 L/h leads to an increase in COD concentration of the treated wastewater from 10.4 mg/L to 10.9 mg/L. In the SBR method, an optimal COD removal efficiency of 46.36% was obtained at 9.29 h contact time, an aeration ratio of 4.43 L/min, and 21.01% leachate to wastewater ratio. The removal efficiencies of PZ-SBR varied from 50.22% (contact time ¼ 2 h, aeration rate ¼ 0.5 L/min, and leachate to wastewater ratio ¼ 80%) to 73.30% (contact time ¼ 22 h, aeration rate ¼ 0.5 L/ min, and leachate to wastewater ratio ¼ 20%) (Table 5). In the

PZ-SBR method, an optimal COD removal efficiency of 73.32% was obtained at 6.06 h contact time, an aeration ratio of 0.73 L/min, and 22.66% leachate to wastewater ratio. COD is defined as the amount of oxygen required to completely oxidize organic constituents to carbon dioxide and water (Tchobanoglous et al., 1991). The decrease in BOD5/COD ratio results also in the decrease in treatment efficacy (Kulikowska and Klimiuk, 2004). The findings of current study are in accordance with those stated in literature (Aziz et al., 2011c; Azimi et al., 2005). COD removal efficiency is clearly enhanced by PZ using the SBR method, supported by those reported in literature (Uygur and Kargi, 2004). Dhas (2008) reported that the mixture of activated carbon and limestone provides an alternative medium for COD removal. An optimum COD removal efficiency of 73.33% was achieved in the PZ-SBR method at 6.36 h contact time, aeration ratio of 1.23 L/min, and 20.0% leachate to wastewater ratio. 3.1.2. Ammonia removal Table 4 shows that the removal efficiency of SBR varied from 71.26% (contact time ¼ 22 h, aeration rate ¼ 0.5 L/min, and leachate to wastewater ratio ¼ 80%) to 96.11% (contact time ¼ 12 h, aeration rate ¼ 4.0 L/min, and leachate to wastewater ratio ¼ 20%). This result is in agreement with that of Aziz et al. (2011b, c). In the SBR method, an optimal NH3eN removal efficiency of 97.97% was obtained at 14.15 h contact time, an aeration ratio of 5.09 L/min, and 23.95% leachate to wastewater ratio.

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Fig. 15. The 3D surface plots of color removal in PZ-SBR. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

The removal efficiency of PZ-SBR varied from 79.42% (contact time ¼ 22 h, aeration rate ¼ 0.5 L/min, and leachate to wastewater ratio ¼ 80%) to 98.27% (aeration rate ¼ 4.0 L/min, contact time ¼ 12 h, aeration rate ¼ 0.5 L/min, and leachate to wastewater ratio ¼ 20%) (Table 5). In the PZ-SBR method, an optimal ammonia removal efficiency of 98.63% was obtained at 7.24 h contact time, an aeration ratio of 2.64 L/min, and 26.54% leachate to wastewater ratio. Leachates with high NHþ 4 -N content are generally difficult to treat in a conventional biological treatment process (Li et al., 1999). The presence of high levels of NH3eN in landfill leachate over a long period is one of the most significant problems faced by landfill operators. This high amount of unprocessed NH3eN can lead to the reduction of the performance efficiency of the biological treatment methods, acceleration of eutrophication, and increase of dissolved oxygen reduction. Thus, NH3eN is extremely poisonous to aquatic organism (Bashir et al., 2010). A previous study (Li and Zhao, 1998) confirmed that high NHþ 4 -N concentration can remarkably affect the performance of a conventional activated sludge procedure (Li et al., 1999). ZELIAC can be an efficient ion exchanger in ammonia removal because of the presence of zeolite. Ion exchange offers an alternative approach for ammonium ion removal (Jorgensen and Weatherley, 2002). Jorgensen and Weatherley (2002) reported that zeolite is effective in removing ammonia from wastewater. Most the NH3eN was removed biologically (Aziz et al., 2011c).

According to Uygur and Kargi (2004), the addition of powdered activated carbon (PAC) to the activated sludge reactors increases the nitrification efficiency in the biological treatment of landfill leachate. 3.1.3. Color removal In this study, the minimum and maximum color removal efficiencies obtained by the SBR reactors were 27.43% (contact time ¼ 2 h, aeration rate ¼ 7.50 L/min, and leachate to wastewater ratio ¼ 80%) and 58.26% (contact time ¼ 12 h, aeration rate ¼ 4.0 L/ min, and leachate to wastewater ratio ¼ 20%), respectively, as shown in Table 4. In the SBR method, an optimal color removal efficiency of 56.88% was obtained at 15.29 h contact time, an aeration ratio of 7.50 L/min, and 20.00% leachate to wastewater ratio. The minimum and maximum color removal efficiencies obtained by the PZ-SBR reactors were 62.39% (contact time ¼ 22 h, aeration rate ¼ 0.50 L/min, and leachate to wastewater ratio ¼ 80%) and 86.46% (contact time ¼ 12 h, aeration rate ¼ 4.0 L/min, and leachate to wastewater ratio ¼ 20%), respectively (Table 5). In the PZ-SBR method, an optimal color removal efficiency of 85.15% was obtained at contact time of 13.65 h, aeration ratio of 3.58 L/min, and 20.00% leachate to wastewater ratio. Aziz et al. (2011) reported that color is a common contaminant in landfill leachate. The decomposition of some organic matters such as humic acid may cause the water to turn yellow, brown, or

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Fig. 16. The 3D surface plots of COD removal in PZ-SBR.

black. Different techniques are used for the removal of color, including chemical precipitation, adsorption via granular activated carbon, radiation, nanofiltration, ozonation, UV photolysis, chemical coagulation, anaerobic process, biological treatment with different additives, fluidized biofilm process, and advanced oxidation with UV/H2O (Aziz et al., 2007). Aziz et al. (2011c) reported that the removal of organic substances (indicated by COD and color) was an outcome of both biological and adsorption phenomena. The SBR method was not efficient enough to remove COD and color by treating low biodegradable leachate. However, the addition of PAC to SBR remarkably increased the removal efficiency. Activated carbon is considered the most effective adsorbent because of its superior ability for removing various kinds of dissolved organic contaminants from wastewater. Specific features of activated carbon, including high surface area, wide range of pore size distribution, and hydrophobic surface, helped this substance adsorb organic contaminants from leachate (Aziz et al., 2011c). 3.1.4. Phenol removal The minimum and maximum phenol removal efficiencies obtained in this study by the SBR reactors were 13.93% (contact time ¼ 2 h, aeration rate ¼ 7.50 L/min, and leachate to wastewater ratio ¼ 80%) and 33.17% (contact time ¼ 12 h, aeration rate ¼ 4.0 L/ min, and leachate to wastewater ratio ¼ 20%), respectively (Table 4). In the SBR method, an optimal phenol removal efficiency

of 34.23% was obtained at 20.41 h contact time, aeration ratio of 3.61 L/min, and 22.59% leachate to wastewater ratio. The minimum and maximum phenol removal efficiencies obtained by the PZ-SBR reactors were 45.23% (contact time ¼ 2 h, aeration rate ¼ 0.50 L/min, and leachate to wastewater ratio ¼ 80%) and 63.71% (contact time ¼ 22 h, aeration rate ¼ 0.50 L/min, leachate to wastewater ratio ¼ 20%) (Table 5). In the PZ-SBR method, an optimal phenol removal efficiency of 63.71% was obtained at an aeration ratio of 0.52 L/min, 21.96 h contact time, and 20.07% leachate to wastewater ratio. Landfill leachate contains a large number of dangerous compounds, such as aromatics, halogenated compounds, heavy metals, phenols, pesticides, and ammonium, which are considered dangerous even in small amounts. The harmful effects of these compounds are often caused by multiple and synergistic effects. Phenolic compounds released into the environment are particularly of high concern because of their potential toxicity. These compounds detected in the leachate include cresols, phenol, and substituted as well as chlorinated phenols. Cresols and phenol, which are short-chain phenols previously reported by Benfenati et al. (1999) in leachates of urban and industrial landfills, originate from various types of wastes. Phenol and its substitutes are commonly produced by the transformation of several pesticides (Varank et al., 2011). Kurata et al. (2008) measured 41 kinds of phenols in three landfill sites in Japan. The results achieved in the

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Fig. 17. The 3D surface plots of ammonia removal in PZ-SBR.

Fig. 18. The 3D surface plots of phenols removal in PZ-SBR.

PZ-SBR

*Prob.: Probability of error; R2: Coefficient of determination; Adj. R2: Adjusted R2; Adec. P.: Adequate precision; SD: Standard deviation; CV: Coefficient of variance; PRESS: Predicted residual error sum of square; Prob. LOF: Probability of lack of fit. **In final equations, where A is Aeration rate (L/min), B is contact time (h), and C is leachate to wastewater mixing ration (%; v/v).

403.84 370.62 1471.16 81.53 272.69 133.52 422.01 41.79

Prob. LOF PRESS CV

6.37 5.92 5.44 4.27 2.20 2.32 2.77 1.94

SD

2.84 2.31 4.81 1.11 1.65 1.48 2.54 1.05

Adec. P.

14.189 11.892 7.979 25.777 18.825 23.547 10.976 24.998 0.8889 0.8381 0.6110 0.9666 0.9298 0.9589 0.8268 0.9665 0.0001 0.0003 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 46.454 þ 0.695A þ 1.276Be0.013C e 0.009A2 e 0.039B2 e 0.002C2 e 0.007AB e 0.014AC e 0.001BC 41.682 þ 2.496A þ 0.074B þ 0.043Ce0.267A2 e 0.006B2 e 0.002C2 e 0.021AB e 0.0002AC e 0.001BC 82.346 þ 3.868A þ 1.293Be0.087C e 0.443A2 e 0.031B2 e 0.008C2 e 0.023AB þ 0.020AB e 0.008BC 26.195 þ 1.227A þ 0.723B þ 0.716Ce0.276A2 e 0.221B2 e 0.002C2 þ 0.034AB þ 0.005AC e 0.003BC 83.43 þ 1.644A þ 0.574Be0.248C e 0.244A2 e 0.018B2 e 0.00002C2 e 0.001AB þ 0.005AC e 0.002BC 75.68e0.833A e 0.006Be0.0009C e 0.030A2 e 0.004B2 þ 0.013AB þ 0.018AC þ 0.004BC 98.74 þ 1.763A þ 0.193Be0.128C e 0.239A2 e 0.013B2 e 0.001C2 þ 0.006AB þ 0.003AC þ 0.001BC 69.02e0.499A e 0.297Be0.275C þ 0.021A2 þ 0.013B2 þ 0.00001C2 e 0.001AB þ 0.002AC þ 0.0007BC SBR

Color COD Ammonia Phenols Color COD Ammonia Phenols

0.9416 0.9148 0.7952 0.9824 0.9630 0.9784 0.9088 0.9824

Adj. R2 R2 Prob. Final equation in terms of actual factor Response SBR type

Table 6 ANOVA results for response parameters.

0.0015 0.0007 0.0161 0.0866 0.4616 0.0369 0.2913 0.1797

A. Mojiri et al. / Journal of Environmental Management 139 (2014) 1e14

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Table 7 The value of factors and responses at optimum conditions. Reactor Factors

Responses

COD NH3eN Phenols Aeration Contact Leachate to Color time (h) wastewater rem. (%) rem. (%) rem. (%) rem. (%) rate ratio (%) (L/min) SBR 4.49 PZ-SBR 1.74

12.05 10.31

20.00 20.00

55.83 84.11

45.92 72.84

98.27 99.01

33.56 61.32

present study agree well with the literature (Aziz et al., 2010; Kurata et al., 2008). In this study, the 4-aminoantipyrine method was used to measure phenols and determine all ortho-substituted and meta-substituted phenols or napthols, but not the parasubstituted phenols. 3.2. Statistical analysis and experimental condition optimization The CCD and RSM were used to demonstrate the nature of the response surface in the experimental plan and clarify the optimum conditions of the independent factors. The Design Expert Software (6.0.7) was used to establish CCD. The independent factors were contact time (h), aeration rate (L/min), and leachate to wastewater mixing ratio (%; v/v). To perform an adequate analysis of the aerobic procedure, four dependent parameters (COD, NH3eN, color, and phenols) were closely measured as responses (Tables 4 and 5). Table 6 shows the ANOVA results for the response parameters. The response values for each parameter are given in Table 7. These limits were selected relatively close to the obtained maximum removal and practicality standards of treatment plants. The experimental condition optimization was determined by considering whether the rates of NH3eN, COD, color, and phenol removal were more than the arbitrarily selected response values. The Design Expert Software predicted the optimum conditions. Based on the model, the optimized conditions for the SBR reactor occurred at 12.05 h contact time, aeration rate of 4.49 L/min, and leachate to wastewater ratio 20%. These conditions resulted in about 45.92%, 55.83%, 98.27%, and 33.56% removal rates for COD, color, NH3eN, and phenols, respectively. The second predicted optimal conditions for the PZ-SBR reactor occurred at the contact time of 10.31 h, aeration rate of 1.74 L/min, and leachate to wastewater ratio 20%, resulting in 72.84%, 84.11%, 99.01%, and 61.32% removal rates for COD, color, NH3eN, and phenols, respectively. 4. Conclusion The treatability experiment of the raw low biodegradable leachate (average BOD5/COD ratio ¼ 0.22) created at SG. Petani was carried out by SBR and PZ augmented SBR processes. A number of pollutants in Sungai Petani landfill leachate exceeded the permissible discharge limits, including COD, color, NH3eN, and phenols. In the SBR treatment, the obtained optimum removal levels of COD, color, NH3eN, and phenols were 45.92%, 55.83%, 98.27%, and 33.56%, respectively. Meanwhile, the PZ-SBR treatment obtained 72.84%, 84.11%, 99.01%, and 61.32% removals, respectively. Thus, the PZ-SBR method was more effective in treating low biodegradable landfill leachate than the traditional SBR method. Acknowledgment The authors would like to express their gratitude to the Universiti Sains Malaysia (USM) for providing the research grant (Grant no. 1001/PAWAM/8045052) for this study and all their support.

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