Different methods of biological treatment were used for treatment of landfill leachate and wastewater. Sequencing batch reactor SBR is a kind of biological treatment. This study was carried out to investigate the landfill leachate and domestic wastewater treatment by a novel adsorbent (powdered ZELIAC) augmented SBR technique. The ZELIAC includes zeolite, activated carbon, rise husk ash, lime stone, and Portland cement. The research was carried out in six 2000 ml breakers. The beakers were filled with 120 ml activated sludge, and 1080 ml landfill leachate and domestic wastewater in different ratios. The reactors were divided into 2 groups comprising 3 for normal SBRs, and 3 for powdered ZELIAC SBRs (PZ-SBR). Prior to aeration, 3.24g (3 g/L) of powdered ZELIAC (PZ) was added to each PZ-SBRs. Different aeration rates of 0.5 to 7.5 L/min, contact times of 2 to 24 h and leachate to wastewater of 20 to 80% were applied to both SBR and PZ-SBR. The evidences provided by current work indicated that the PZ-SBR showed higher performance in removal efficiencies while compared to SBR. At the optimum conditions of aeration rate (1.60 L/min), contact time (15.43 h) and leachate to wastewater ratio (20%) for the PZ-SBR, the removal efficiencies for colour, COD, NH3-N, and phenols were 82.04%, 71.56%, 98.27%, and 61.98%, respectively.
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Key words: Co-treatment, Landfill Leachate, Nickel, Phenols, Sequencing Batch Reactor, Wastewater, ZELIAC
Solid waste disposal ways contain open dump, sanitary landfill, incineration, composting, grinding and discharge to sewer, compaction, hog feeding, milling, dumping, reduction, and anaerobic digestion. Sanitary landfill is the most general urban solid waste (MSW). Presently, there are over 230 landfills in Malaysia, mostly old dumpsites. Most are simply dumping grounds without any environmental protection. The resulting leachate is discharged directly into water courses without any treatment, which can threaten the surrounding ecosystem, particularly in cases where landfills are located upstream of water intakes (Aziz et al., 2010).
Leachate is created while water penetrates through the waste in a landfill, carrying some forms of pollutants like ammonia-nitrogen (NH3-N), chemical oxygen demand (COD), biological oxygen demand (BOD5), colour, suspended solids and heavy metals. Leachate composition depends on some diversity parameters like sort of waste, site hydrology, landfill age, landfill operation and landfill type.
Landfill leachates are reflected one of the kinds of wastewater with the utmost environmental influence. The most serious features of leachate are connected of the high concentrations of some contaminants. Urban landfill leachates enclose contaminants which can be separated into four key groups including dissolved organic matter and inorganic compound like calcium, potassium, sodium, ammonium, calcium, magnesium, sulphates, chlorides, iron and heavy metals like nickel, lead, copper, chromium, cadmium, zinc, xenobiotic organic materials (Tengrui et al., 2007). Obviously, as landfill age increases, the biodegradable fraction of organic pollutants in leachate decreases due to anaerobic decomposition occurring in a landfill site.
In general, available landfill leachate treatment options include: (1) spray irrigation on adjacent grassland; (2) recirculation of leachate through the landfill; (3) co-treatment of sewage and leachate; (4) leachate evaporation using landfill-generated methane as fuel; and (5) biological or physical/chemical treatment (Mojiri, 2011).
Today, landfill leachates are often treated with municipal sewage in the municipal wastewater treatment plants. Due to stricter regulation for nitrogen release and problem with potential effect of recalcitrant leachate constituents on the biological treatment step an increase of demands for separate treatment and disposal of landfill leachate is detected. The solution which can lead to disconnection landfill leachate from the municipal sewage treatment may be co-treatment with domestic wastewater (Neczaj et al., 2008).
The main applicable methods of landfill leachate treatment are biological, chemical, membrane separation and thermal treatment processes. Sequencing batch reactor is one of the biological processed applied to remove several contaminants (Mojiri et al., 2011). Because landfill leachate has a high degree of variation in quality and quantity, the sequencing batch reactor (SBR), which has greater process flexibility among biological treatment methods, is therefore well fitted for leachate treatment (Lim et al. 2010). The high concentrations of organic matters, low biodegradability ratio, heavy metals, NH3-N, and other contaminants in leachate clearly affect SBR performance (Foo and Hameed, 2009).
In the literature, adsorbents like activated carbon were added to activated sludge and SBR for the improvement of the biological treatment of landfill leachate (Foo and Hameed 2009; Aziz et al. 2011b, c, d). A gap of knowledge can still be noticed in the literature, particularly in the removal of pollutants (such as phenols, heavy metals, and other contaminants), settleability of sludge, and nitrification and denitrification processes in different landfill leachates using low costs materials augmented SBR technology.
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Recently, application of several indigenous and low-cost materials for wastewater and leachate treatment has received greater interest (Foul et al., 2009). Some of these materials contain zeolite, limestone, activated carbon, rice husk ash, and Portland cement; ZELIAC was created from these materials.
The goals of this study is to examine the SBR performance in the absence and presence of powdered ZELIAC on the following: (1) the removal of phenols, ammonia (NH3-N), color, and chemical oxygen demand (COD) from Sungai Petani landfill leachates, and domestic wastewater from Bayan Baru Wastewater Treatment Plant in Malaysia; and (2) introduce a new low cost media namely ZELIAC.
2. Materials and Methods
2.1. Landfill Leachate Sampling
Leachate samples were collected from the Sungai Petani landfill site from June 2012 to January 2012. The landfill site (geographical coordinates, 05° 43′ N and 100° 29′ E) is located in Kedah, Malaysia. The landfill received about 350-400 tons of solid waste daily, it measure by using Weight Bridge. This open dumping site was actively used beginning 1990. Total landfill area of Sungai Petani is 11.24 ha. Leachates remain in the collection pond depending on retention time, and then are disposed of directly in the environment without any treatment. After collection, the samples were immediately transported to the laboratory and stored in a cold room at 4 °C prior to minimizing biological and chemical reactions (Aziz et al., 2011c). The characteristics of the samples are shown in Table 1. To determine the environmental risks of the leachates, the parameter values obtained were compared against the 2009 Regulations of the Malaysia Environmental Quality Act of 1974 (Environmental Quality, 2009).
2.2. Domestic Wastewater and Activated Sludge Sampling
The domestic wastewater and activated sludge were obtained from Bayan Baru wastewater treatment plant located in Penang, Malaysia. The characteristics of the wastewater and activated sludge are shown in Table 1.
2.3. Reactors characteristics
The six 2000mL beakers each having a working volume of 1200 mL, an inner diameter of 113mm, and a height of 200mm were used throughout the study. There was a magnetic stirrer for mixing in the bottom of reactors. The experiments were conducted at room temperature, and air was supplied to the reactors by 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). The air flow rate was manually regulated by an air flow meter (Dwyer Flow meter, Model: RMA-26-SSV).
2.4. Sludge Acclimatization
Based on Aziz et al. (2011c) studies, about 1080 mL of the activated sludge (90%) was mixed with 120 mL (10%) of the collected landfill leachate. After termination of the reaction and settling phases, 120 mL of the supernatant was withdrawn. In a new cycle, an additional 120 mL of raw leachate was added to the reactor. This process was sustained for at least 10 d to allow the system to adjust to the experimental conditions. The acclimated sludge was later used as seed in the SBRs.
2.5. ZELIAC Preparation
For preparation of ZELIAC, zeolite, activated carbon, rice husk ash, lime stone, and Portland cement were grinded and passed through a 300 µm mesh sieve. Totality of them was mixed, and then was mixed with water. After evenly, the mixing was poured in the mold. The materials were removed from the mold after 24 hours, after that they were soaked in water for curing process for three days. The materials were dried within two days, and then they were crushed and passed through a sieve. Table 2 shows the characteristics ZELIAC with the autosorb (Quantachrome AS1wintm, version 2.02) testing. Table 3 and Figure 1 show the results of XRF, and XRD testing of ZELIAC, respectively. In this study, powdered ZELIAC of size 75-150 μm (passing sieve No. 100 and retained on sieve No. 200) was used as adsorbent in the PZ-SBR (Aziz et al., 2011a).
2.6. Operation of Reactors
SBR phases contain fill, react, settle, draw and idle. In all experiments, the duration for filling and mixing (20 min), settling (90 min), drawing, and idle (10 min) was fixed. Different contact times of 2, 12, and 22 h, aeration rates of 0.5, 4, and 7.5 L/min, and different ratio of leachate to wastewater (20 to 80%; v/v) were used to both SBR, and PZ-SBR. The beakers were filled with 120 mL (10%) of acclimated sludge and 1080 (90%) of domestic wastewater and Sungai Petani landfill leachate (in different ratio), using a mixing ratio of 25% to 75% (v/v). The main characteristics of leachate, wastewater and activated sludge are presented in Table 1.
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The reactors were divided into 2 groups comprising 3 for SBR (normal SBR) and 3 for PZ-SBR (powdered ZELIAC augmented SBR). Based on preliminary experiments, 3.24g of PZ (i.e. PZ dosage = 3 g/L) was added to each PZ-SBR before aeration. The PZ (powdered ZELIAC) used for adsorption pollutants in the PZ-SBR pre-dried at 103-105 -C and sized 75-150µm (passing sieve No. 100, retained on sieve No. 200). Table 2 was showed the characteristics of PZ.
The removal efficiency of COD, colour, NH3-N, and phenols were monitored in the experiments. Removal efficiency was determined by measuring the target parameters before and after treatment. The following equation was used for calculating removal efficiency (Eq. 1):
Removal (%) = (Eq. 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). YSI 556 MPS (YSI incorporated, USA) was used for recording the values of pH, electrical conductivity (ms/cm), temperature (-C), salinity (g/L), TDS (%), and oxidation reduction potential i.e. ORP (mV). A spectrophotometer (DR/2500 HACH) was used for measuring phenols (mg/L), colour (Pt. Co), ammonia NH3-N (mg/L), total phosphorus (PO43− mg/L), Total Nitrogen (mg/L), Nitrite (mg/L), total organic carbon (mg/L TOC), COD (mg/L), sulfide (mg/L S2−), total iron (mg/L Fe), manganese (mg/L Mn), copper (mg/L Cu), zinc (mg/L Zn), aluminum (mg/L Al), chromium (mg/L Cr), and nickel (mg/L Ni).The ICP (ICP Varian, OES 715) was used for measuring cadmium (mg/L Cd), cobalt (mg/L Co), molybdenum (mg/L Mo), lithium (mg/L Li), magnesium (mg/L), and calcium (mg/L CaCO3).
2.8. Experimental design and data analysis
Central composite design and response surface methodology were employed in order to illustrate the nature of the response surface in the experimental design and elucidate the optimal conditions of the independent variables. CCD was established through Design Expert Software (6.0.7). The behavior of the system is described through Eq. (2) an empirical second-order polynomial model:
where Y is the response; Xi and Xj are the variables; β0 is a constant coefficient; βj, βjj, and βij are the interaction coefficients of linear, quadratic and second-order terms, respectively; k is the number of studied factors; and e is the error. The results were completely analyzed by analysis of variance (ANOVA) in the Design Expert Software.
The design consisted of k2 factorial points augmented by 2k axial points and a center point, where k is the number of variables. Four replicates at the central points were employed to fit the second order polynomial models and to obtain the experimental error for this study. Each of the 4 operating variables was considered at 3 levels, low (−1), central (0), and high (+1). In the present work, CCD and RSM were applied to appraise the association between the most important operating variables i.e. (Mojiri et al., 2013) aeration rate (L/min), contact time (h), and leachate to wastewater mixing ration (%; v/v) and their responses (dependent variables) in addition to optimizing the appropriate situation of operating variables to predict the best value of responses. Aeration rates (0.5, 4, and 7.5 L/min), contact times (2, 12, and 22 h), leachate to wastewater mixing ratio and (80, 50, and 20 v/v %) were used with SBR and PZ-SBR. To carry out an adequate analysis of the aerobic process, 4 dependent parameters (COD, colour, NH3-N, and phenols) were measured as responses (Tables 4 and 5).
3. Results and discussion
Table 1 shows that Sungai Petani leachate contained high-intensity colour (1690 Pt. Co), high concentration of COD (1301 mg/L). The concentration of NH3-N was also high (532 mg/L). An average BOD5 value of 269 mg/L was recorded (Table 1), which gave a low biodegradability ratio (BOD5/COD) of 0.20 (age > 15 years). Moreover, the concentration of phenols, suspended solids, BOD5, COD, BOD5/COD, NH3-N, and sulfide surpassed the allowable limits issued by the 1974 Environmental Quality Act of Malaysia (Environmental Quality, 2009). In the current work, raw leachate of SG. Petani landfill was treated as co-treatment with domestic wastewater by PZ (Powdered ZELIAC) augmented SBR process in order to reduce the environmental risks from the SG. Petani landfill leachate.
3.1. Reactor performance
3.1.1. COD removal
Chemical oxygen demand (COD) is the amount of oxygen used for complete chemical oxidation of the organic constituents to carbon dioxide and water (Tchobanoglous et al., 1991). It is obvious that correspondingly with the decrease in BOD5/COD ratio there is a decrease in treatment effectiveness (Kulikowska and Klimiuk, 2004).
The removal efficiency of SBR ranged from 25.64% (aeration rate = 0.5 L/min, contact time = 22 h, and leachate to wastewater ratio= 80 %) to 46.29% (aeration rate = 7.5 L/min, contact time = 2 h, leachate to wastewater ratio= 20 %) (Table 4). Azimi et al. (2005) reported that the increase in aeration rate from 25.2 to 90 L/h resulted in an increase in COD concentration of treated wastewater from 10.4 to 10.9 mg/L.
In SBR, an optimum COD removal efficiency of 46.36% was achieved at an aeration ratio of 4.43 L/min, 9.29 h contact time, and 21.01% leachate to wastewater ratio.
The removal efficiency of PZ-SBR ranged from 47.61% (aeration rate = 0.5 L/min, contact time = 2 h, and leachate to wastewater ratio= 80 %) to 72.19% (aeration rate = 0.5 L/min, contact time = 22 h, and leachate to wastewater ratio= 20 %) (Tables 5). The present results are in line with those reported in literature (Azimi et al, 2005; Aziz et al., 2011c). Using PZ with SBR clearly enhanced the COD removal efficiency. It is in accordance with the results reported in literature (Uygur and Kargi, 2004; Aziz et al., 2011c). Dhas (2008) reported the limestone and activated carbon mixture provides alternative medium for removing COD.
In PZ-SBR, an optimum COD removal efficiency of 72.01% was achieved at an aeration ratio of 0.50 L/min, 15.07 h contact time, and 20.0% leachate to wastewater ratio.
3.1.2. Ammonia removal
Leachates with such high NH4+-N content are generally difficult of access to conventional biological treatment processes (Li et al., 1999). The existence of high levels of NH3-N in landfill leachate over a long period of time is one of the most important problems faced by the landfill operators. This high quantity of unprocessed NH3-N leads to reduced performance efficiency of biological treatment methods, accelerated eutrophication, and increased dissolved oxygen reduction. Consequently, NH3-N is extremely toxic to aquatic organism (Bashir et al., 2010).
A previous study (Li and Zhao, 1998) confirmed that the performance of a conventional activated sludge process could be significantly affected by a high concentration of NH4+-N (Li et al., 1999).
The removal efficiency of SBR ranged from 71.26% (aeration rate = 0.5 L/min, contact time = 22 h, and leachate to wastewater ratio= 80 %) to 96.11% (aeration rate = 4.0 L/min, contact time = 12 h, leachate to wastewater ratio= 20 %) (Table 4). This result is in line with finding of Aziz et al. (2011b and c).
In SBR, an optimum ammonia removal efficiency of 97.97% was achieved at an aeration ratio of 5.09 L/min, 14.15 h contact time, and 23.95% leachate to wastewater ratio.
The removal efficiency of PZ-SBR ranged from 79.42% (aeration rate = 0.5 L/min, contact time = 22 h, and leachate to wastewater ratio= 80 %) to 98.27% (aeration rate = 4.0 L/min, contact time = 12 h, leachate to wastewater ratio= 20 %) (Table 5). ZELIAC can be effective as ion exchanger in ammonia removal because of zeolite presence in the ZELIAC composite. Ion exchange offers an alternative method in the removal of the ammonium ion (Jorgensen and Weatherley, 2002). Jorgensen and Weatherley (2002) reported zeolite can be effective in removing ammonia from wastewater.
In PZ-SBR, an optimum ammonia removal efficiency of 98.63% was achieved at an aeration ratio of 2.64 L/min, 7.24 h contact time, and 26.54% leachate to wastewater ratio.
The majority of NH3-N was removed biologically (Aziz et al., 2011c). However, according to Uygur and Kargi (2004), the addition of PAC to activated sludge reactors enhanced nitrification efficiency in biological treatment of landfill leachate.
3.1.3. Colour removal
Colour is a common pollutant in landfill leachate (Aziz et al., 2011). The decomposition of organic matter such as humic acid may cause the water to be yellow, brown or black. There are several techniques used for colour removal. These include chemical precipitation, adsorption through granular activated carbon, nanoï¬ltration, ozonation, radiation, UV photolysis, chemical coagulation, biological treatment with various additives, anaerobic process, ï¬‚uidized biofilm process, and advanced oxidation with UV/H2O (Aziz et al., 2007).
In the current study, minimum and maximum colour removal efficiency achieved by SBR reactors was 27.43% (aeration rate = 7.50 L/min, contact time = 2 h, leachate to wastewater ratio= 80 %) and 58.26% (aeration rate = 4.0 L/min, contact time = 12 h, leachate to wastewater ratio= 20 %), respectively (Table 4). In SBR, an optimum ammonia removal efficiency of 56.88% was achieved at an aeration ratio of 7.50 L/min, 15.29 h contact time, and 20.00% leachate to wastewater ratio.
Minimum and maximum colour removal efficiency achieved by PZ-SBR reactors was 60.19% (aeration rate = 0.50 L/min, contact time = 22 h, leachate to wastewater ratio= 80 %) and 84.26% (aeration rate = 4.0 L/min, contact time = 12 h, leachate to wastewater ratio= 20 %), respectively (Table 5). In PZ-SBR, an optimum ammonia removal efficiency of 82.98% was achieved at an aeration ratio of 3.51 L/min, 13.71 h contact time, and 20.00% leachate to wastewater ratio.
Aziz et al. (2011c) reported the results obtained demonstrated that the elimination of organic substances (indicated by COD and colour) was due to both biological and adsorption phenomenon (Aziz et al., 2011c). Treatment of low biodegradable leachate by SBR resulted in low removal of COD and colour. However, adding PAC (powdered activated carbone) to SBR considerably enhanced the removal efficiency. Activated carbon is the most effective adsorbent owing to its superior ability for removal of a wide variety of dissolved organic pollutants from wastewater. The high surface area, wide range of pore size distribution and hydrophobic surface helped activated carbon to adsorb organic pollutant from leachate (Aziz et al., 2011c).
3.1.4. Phenols removal
Landfill leachate contain a large number of hazardous compounds, including aromatics, halogenated compounds, phenols, pesticides, heavy metals, and ammonium, which can be assumed to be hazardous even in small amounts and their detrimental effects are often caused by multiple and synergistic effects. Particularly, phenolic compounds released into the environment are of high concern because of their potential toxicity. These compounds found in the leachate include phenol, cresols and substituted and chlorinated phenols. Phenol, cresols, short-chain phenols previously reported in leachates of municipal and industrial landfills (Benfenati et al., 1999) may originate from different types of wastes. Phenol and substituted phenols are common transformation products of several pesticides (Varank et al., 2011).
Kurata et al. (2008) measured 41 types of phenols in three landfill sites in Japan. The results yielded in the present study agree with the literature (Kurata et al. 2008; Aziz et al. 2010). In this research, the 4-aminoantipyrine method was used to measure phenols by determining all ortho-substituted and meta-substituted phenols or napthols, but not para-substituted phenols.
In the current study, minimum and maximum phenols removal efficiency achieved by SBR reactors was 13.93% (aeration rate = 7.50 L/min, contact time = 2 h, leachate to wastewater ratio= 80 %) and 33.17% (aeration rate = 4.0 L/min, contact time = 12 h, leachate to wastewater ratio= 20 %), respectively (Table 4). In SBR, an optimum phenols removal efficiency of 34.23% was achieved at an aeration ratio of 3.61 L/min, 20.41 h contact time, and 22.59% leachate to wastewater ratio.
Minimum and maximum phenols removal efficiency achieved by PZ-SBR reactors was 45.01% (aeration rate = 0.50 L/min, contact time = 2 h, leachate to wastewater ratio= 80 %) and 62.71% (aeration rate = 0.50 L/min, contact time = 22 h, leachate to wastewater ratio= 20 %), respectively (Table 5). In PZ-SBR, an optimum phenols removal efficiency of 63.10% was achieved at an aeration ratio of 0.51 L/min, 21.03 h contact time, and 20.01% leachate to wastewater ratio.
3.2. Statistical analysis and Experimental condition optimization
Central composite design and response surface methodology were employed in order to illustrate the nature of the response surface in the experimental design and elucidate the optimal conditions of the independent variables. CCD was established through Design Expert Software (6.0.7). Aeration rate (L/min), contact time (h), and leachate to wastewater mixing ration (%; v/v) were independent factors; to carry out an adequate analysis of the aerobic process, 4 dependent parameters (COD, colour, NH3-N, and phenols) were measured as responses (Tables 4 and 5).
Table 7 shows the response values for each parameter. These constraints were chosen relatively close to the acquired maximum removal and practicability standards of treatment plants. The optimization of experimental conditions was identified by considering whether the rates of COD, colour, NH3-N, and phenols removal were higher than the arbitrarily chosen constraint values. The optimum conditions were predicted by the Design Expert Software. According to the model, the optimized conditions occurred for the SBR reactor at the aeration rate of 4.49 L/min, contact time of 12.05 h and leachate to wastewater ratio 20%, which resulted in 55.83%, 45.92%, 98.27%, and 33.56% removal rates for colour, COD, NH3-N, and phenols, respectively. The second predicted optimum conditions for the PZ-SBR reactor occurred at the aeration rate of 1.6 L/min, contact time of 15.43 h and leachate to wastewater ratio 20%, which resulted in 82.04%, 71.56%, 98.27%, and 61.98% removal rates for colour, COD, NH3- N, and phenols, respectively.
The authors would like to acknowledge the University Sains Malaysia (USM) for provides of research grant to conduct this work, and their supports.