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Keywords:

  • ozonation;
  • persulfate;
  • biodegradable;
  • soluble;
  • advanced oxidation;
  • stabilized leachate

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. ACKNOWLEDGMENT
  8. LITERATURE CITED

This study investigated the effects of O3 and O3/S2O82− in the advanced oxidation process (AOPs) on the biodegradable and soluble characteristics of semiaerobic stabilized solid waste leachate. The biodegradability (BOD5/COD) ratio improved from 0.034 to 0.05 and 0.29 following O3 and O3/ S2O82−, respectively. Fractions of biodegradable COD(bi) (24%), nonbiodegradable COD(ubi) (76%), soluble COD(s) (59%), biodegradable soluble COD(bsi) (38%), nonbiodegradable soluble COD(ubsi) (62%), and particulate COD (PCOD) (41%) in stabilized leachate were also investigated. The fraction of COD (bi) increased to 28 and 39% after applying O3 and O3/ S2O82− in AOPs, respectively. COD(S) increased to 65 after O3 and to 72% after O3/AOPs, whereas COD (bsi) increased to 38 and 55% after O3 and O3/AOPs, respectively. The removal efficiency of total COD was obtained at 15 after O3 alone and improved to 72% following ozone-based AOPs, whereas PCOD reduced from 41 to 35 after O3 and 28% after ozone-based AOPs. Ozone/Prsulfate is an efficient method for degradation of stabilized leachate, enhanced biodegradability and improved biodegradable and soluble characteristics of stabilized leachate. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 184–191, 2014


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. ACKNOWLEDGMENT
  8. LITERATURE CITED

Continuous population growth and industry development have led to increased waste generation. To date, land filling remains to be the preferred option for disposal and management of solid urban waste [1]. Despite the advantages offered by land filling, this method produces highly polluted industrial wastewater, which has elicited significant concern, especially because it is the most prevalent solid waste disposal technique [2]. Landfill leachate is defined as liquid that seeps through solid waste in a landfill, producing extracted, dissolved, or suspended materials [3]. It is a potential pollutant that may cause harmful effects on groundwater and surface water that surround a landfill site, unless returned to the environment in a carefully controlled manner [4]. Leachate contains high amounts of organic compounds, ammonia, heavy metals, a complex variety of materials, and many other hazardous chemicals. It is recognized as a potential source of groundwater and surface water contamination [3-5]. Regardless of changes in the concentration of landfill leachate, its complexity can be categorized based on four major groups of pollutants, depending on a complex set of interrelated factors: dissolved organic matter, inorganic macro-components, heavy metals, and xenobiotic organic compounds [6].

Determination and evaluation of leachate quality is a very important aspect of evaluating the risk of nonbiodegradable characteristics in the environment. Thus, fractionation of chemical oxygen demand (COD) is the most important factor in determining leachate quality. The total value of COD cannot express the exact data that can be used for further research because it only measures the total amount of organic matter without the differentiating biodegradable characteristics [7]. Doğruel et al. [8] evaluated the biodegradation and treatability of COD fractions based on particle size destripution of organics in leachate. COD is divided into two main fractions, namely, biodegradable and nonbiodegradable, which are further subdivided into particulate and soluble fractions [8]. Soluble COD(S) contains two fractions: biodegradable soluble COD(bsi) and nonbiodegradable soluble COD(ubsi). Soluble COD in the effluent obtained from a leachate treating process includes biodegradable and nonbiodegradable compounds from the raw leachate and microbial activities in the treatment system [9].

Establishing efficient treatments for large quantities of polluted leachate is one of the main problems that affect landfill management. The environmental impact of leachate is affected by its strength, proper collection, and efficiency of treatment. Leachate requires treatment to minimize the amount of pollutants to an acceptable level prior to being discharged into water courses [10]. To date, a number of leachate treatment techniques, including biological, physical, and chemical processes, have been applied [11, 12]. Ozonation is one of the chemical processes used in the treatment of stabilized landfill leachate to reduce leachate strength and the amount of nonbiodegradable organics. Several studies have been conducted on ozone and Fenton applications for color, COD removal, and improvement of biodegradability (BOD5/COD) for different types of solid waste leachate [[11-19]]. Persulfate (S2O82−) is the newest oxidant used in chemical oxidation of groundwater and soil cleanup [20] and recently received attention in landfill leachate treatment because of its effectiveness in removing organics and ammonia [20], which has standard oxidation potential (E0 = 2.01 V) compared with ozone (E0 = 2.07 V) [21]. Furthermore, S2O82− has an ability to initiate sulfite radical based-AOPs that are strong oxidants (E0 = 2.7 V) [22]. However, the effect of ozone and ozone/Persulfate in AOP on the fraction of COD in stabilized leachate was not investigated. In addition, the performance of ozone in improving biodegradable, soluble, and biodegradable soluble COD on stabilized leachate remains undocumented.

The objective of this study is to investigate the effects of O3 and O3/Persulfate in the advanced oxidation processes (AOPs) on the biodegradable and soluble COD of semiaerobic stabilized solid waste leachate. The fractions of biodegradable, nonbiodegradable, soluble, and particulate COD were determined before and after each ozonation process.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. ACKNOWLEDGMENT
  8. LITERATURE CITED

Leachate Sampling and Characteristics

The leachate samples used in this study were collected from the aeration pond of a semiaerobic stabilized leachate of the Pulau Burung landfill site in Nibong Tebal, Penang, Malaysia. The total landfill site area is 62.4 ha; however, only 33 ha is currently utilized to receive approximately 2200 tons of solid waste daily [23]. This landfill produces a dark-colored liquid with pH > 7.0, and is classified as stabilized leachate with high COD and NH3–N concentrations, as well as a low BOD5/COD ratio [24]. Samples were collected manually and stored in 20 L plastic containers. Table 1 shows the different characteristics of the leachate sample.

Table 1. Characteristics of semi-aerobic landfill leachate from PBLS
ParametersValue
COD (mg/L)2480
BOD (mg/L)93
NH3-N (mg/L)792
Color (PT Co.)3450
pH8.5
Suspended solids (mg/L)203
Conductivity, (μS/cm)19,450

Experimental Procedure

All experiments were performed on a 2 L volume of the sample using an ozone reactor with a height of 65 cm and an inner diameter of 16.5 cm (Figure 1). The reactor is supported by a cross-column ozone chamber to enhance ozone gas diffusion. Ozone was produced using a BMT 803 generator (BMT Messtechnik, Germany) fed with pure dry oxygen at the recommended gas flow rate of 1000 mL/min ± 10%. The input ozone concentration was 30 g/m3 NTP ± 0.5% under 1 bar pressure. The gas ozone input and output concentrations (in g/m3 NTP) were measured using an ultraviolet gas ozone analyzer (BMT 964). A water bath and a cooling system supported the ozone reactor to maintain the internal reaction temperature at <15°C. S2O82– as Na2S2O8 (M = 238 g/mol) was used in the advanced oxidation during the ozonation of stabilized leachate. Optimal operational conditions (O3 = 30 g/m3, pH 10, persulfate dosage = 1 g/1 g COD/S2O82– and 210 min reaction time) were used. These conditions were determined from the optimization step in the response surface methodology (RSM) application and central composition design (CCD) using the experimental design software 6.0.7. In this study, the CCD and RSM were applied to optimize the experimental parameters and assess the relationships among the four significant independent variables, as presented in Table 2: (1) ozone dosage (30–80 g/m3), (2) persulfate dosage (1/1–1/7 g/g COD0/S2O82–), (3) variation in pH (3–11), and (4) reaction time (30–210 min). Each independent variable was varied over three levels between –1 and +1 within ranges determined based on a set of preliminary experiments and the ozone generator manual for ozone dosage. Performance was evaluated by analyzing the COD removal efficiency. The total number of experiments conducted for the four factors was 30 (=2k + 2k + 6, where k is the number of factors, i.e., 4). A total of 24 experiments were enhanced with six replications to assess the pure error. The effect of the O3/S2O82– system was compared with the effect of O3 on leachate quality after the ozonation process.

image

Figure 1. Schematic diagram of ozone equipment and experiments procedures.

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Table 2. Independent variables of the CCD design
Level of valueOzone (g/m3)COD0/S2O82- ratio (g/g)pHReaction time (min)
−1301/1310
0551/46.5120
+1801/711210

Analytical Method

The samples were immediately transferred, characterized, and refrigerated for 1 week at 4°C in compliance with the Standard Methods for the Examination of Water and Wastewater [25]. The COD concentration was measured using a DR/2800 spectrophotometer based on the closed reflux and colorimetry of Method No. 5220D [19, 24]. The color value was reported as true color, filtered using GC-50 filters, papers (Advantec Toyo Kaisha, Japan) with 0.45 µm pore size, assayed at 455 nm using DR2800 HACH spectrophotometer [19, 24]. Method No.2120C reports color in Platinum-cobalt (PtCo), the unit of color being produced by 1 mg platinum/L in the form of the chloroplatinate ion. The effect of filtration on color removal was corrected by means of a control sample, the hue (Brown, dark brown) is designated by the dominant wavelength 455 nm, the degree of brightness by “luminance,” and the saturation by “purity.” pH value was adjusted to 7.6 by using sulfuric acid (H2SO4) and sodium hydroxide (NaOH) of such concentrations that the resulting volume change was not exceed 3%, as the original pH was 8.5. The concentration of NH3[sbond]N was measured through the Nessler method (Method No. 8038) using a Hach DR/2800 spectrophotometer. The pH was measured using a portable digital pH/Mv meter. Meanwhile, BOD5 was measured based on standard methods [25], and the biodegradability (defined as BOD5/COD) was also determined. The fractions of biodegradable and nonbiodegradable COD were determined using the initial COD of a 1 L aerated sample. An air pump was used, and COD was gradually measured until a constant value deemed as the final COD concentration was reached. The sample size was maintained at 1 L during aeration. Water loss in the sample was compensated for by adding distilled water. Biodegradability was calculated using the following equation:

  • display math(1)

where COD(bi) represents biodegradability, CODi represents the initial total COD in the sample, and CODf denotes the constant amount of COD after optimal aeration.

Hu et al. [26] discussed the determination of soluble COD(s) using the ZnSO4 coagulant method. About 1 mL of 0.6 M ZnSO4 solution was added to 100 mL of the sample. The pH was adjusted to approximately 10.5 ± 0.3 using 5 M sodium hydroxide and sulfuric acid before adding the coagulant material. The sample was mixed using a magnetic stirrer for 1 min at high speed (approximately 200 rpm) followed by 5 min at low speed (30 rpm). Subsequently, the sample was allowed to settle for 1 h. About 30 mL of the sample was withdrawn and filtered through a pre-rinsed 0.45 µm mixed cellulose ester membrane filter (Millipore, MA). The COD was then measured as COD(s), and the difference between COD(s) and CODi was determined as particulate COD (PCOD). The value of COD(bi) was considered as the soluble biodegradable COD(sbi), whereas the soluble nonbiodegradable COD(subi) was determined by the difference between COD(sbi) and COD(S). Test values are presented as the average of three measurements, and the difference between measurements was <3%.

RESULTS AND DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. ACKNOWLEDGMENT
  8. LITERATURE CITED

Effect of Ozone and Ozone/Persulfate on Biodegradability

The effect of ozone and ozone/persulfate in the advanced oxidation process (O3/S2O8) on the biodegradability of stabilized leachate was investigated and determined for future research. COD, BOD5, and BOD5/COD were tested before and after ozonation of stabilized leachate. Figure 2 presents the effect of O3 and O3/S2O8 on COD, BOD5, and BOD5/COD. To investigate the performance of the O3/S2O8 system and compare it with other treatment techniques, biodegradability was also examined after persulfate oxidation only and persulfate oxidation followed by ozonation. Accordingly, the system O3/S2O82– in AOPs was found to be more efficient in enhancing the biodegradability of stabilized leachate than other treatment techniques. As shown in Figure 2, COD decreased from 2480 to 695 mg/L with a total removal efficiency of 72%, and BOD5 was increased from 107 to 202 mg/L. Consequently, the biodegradability described in terms of BOD5/COD increased from 0.043 to 0.29, whereas the ratio only improved to 0.05, 0.12, and 0.16 after ozonation only, persulfate oxidation only, and persulfate oxidation + ozonation, respectively. Although ozonation reduces and converts large refractory organic molecules found in mature leachates into smaller more biodegradable molecules [14], the combination of ozone and persulfate is more efficient in increasing BOD and enhancing biodegradability. Persulfate, as a new oxidant, can severely destroy organic molecules, and the degradation products are easily biodegraded. Xu et al. [27] improved the biodegradability index of leachate from 0.13 to 0.95 using potassium persulfate combined with activated carbon adsorption. Cortez et al. [14] obtained an improvement in biodegradability from 0.01 to 0.17 using O3/H2O2 in the advanced oxidation process.

image

Figure 2. Effect of ozone and persulfate in AOPs on COD, BOD5 and biodegradability of stabilized leachate. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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In the O3/S2O82– system, S2O82– releases sulfate radicals (Eqs. (2) and (3)), which powerfully oxidizes organic molecules [19, 21].

  • display math(2)
  • display math(3)

The generation of sulfate radicals during S2O82– oxidation can be significantly enhanced by some catalysts, such as heat and UV radiation (Eq. (4)), which can initiate sulfate radical generation [28, 29].

  • display math(4)

The performance of O3/S2O82– was higher at high pH (8–11) because O3 can initiate the formation of hydroxyl radical, whose oxidation potential (E0 = 2.80) was higher than that of O3 (E0 = 2.07) in a direct reaction under an acidic condition [30, 31]. Furthermore, S2O82– was more active at high pH. Deng and Ezyske [21] reported the same result, and low removal rates of COD and NH3–N are obtained when S2O82– oxidation is applied at pH 4. The removal efficiency improves with increased pH to 8.3.

Biodegradability can also be measured by removing COD through aeration, which can be defined as CODi – CODf during lab-scale aeration (Eq. (2)). Control over the process depends on the regulation of aeration to satisfy oxygen requirements, which are closely linked to organic matter biodegradability and biodegradation kinetics. Therefore, better knowledge of biodegradation kinetics enables the prediction of composting time.

The effect of ozone and ozone/S2O82– in the advanced oxidation process on the biodegradable COD fraction in stabilized leachate was investigated. Figure 3 presents the degradable COD in the batch aeration method before and after applying the ozone/persulfate process of stabilized leachate. The initial kinetic removal of COD in the first 5 days of aeration gradually increased for both samples. Furthermore, during this period, the degradation of COD after O3/persulfate was slightly higher than that in raw leachate. The increased removal of COD stabilized in raw leachate on the fifth day of aeration, whereas removal of COD continued to increase after ozonation and stabilized on the eighth day of aeration.

image

Figure 3. Biodegradation of COD in batch method for stabilized leachate before and after treatment by ozone and ozone/persulfate (AOP). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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The biodegradable and nonbiodegradable COD fractions were also calculated after the aeration process (Eq. (1)). The biodegradable COD improved from 24 to 39% after the ozone/persulfate process, whereas the nonbiodegradable fraction decreased from 76 to 61% (Figure 4). These results revealed that the O3/S2O8 system improved the removal of COD through extended aeration. Therefore, the biological processes were observed to be generally affected by new leachate, containing mainly volatile fatty acids, but were less effective for stabilized leachate [32]. Bilgili et al. [33] obtained 40 and 30% removal of COD using aerobic and anaerobic reactors of the leachate treatment system, respectively. These results revealed that the O3/S2O8 system improved the removal of COD using extended aeration.

image

Figure 4. Effect of ozone and ozone/persulfate on biodegradable and non-biodegradable COD fractions in stabilized leachate. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Effect of O3 and O3/Persulfate on Soluble and PCOD

The fractionation of COD is the most important parameter for evaluating the quality of leachate. Soluble COD is one of the main fractions, and PCOD is the other important fraction of COD. Determining soluble COD is important in identifying other COD fractions. In this study, soluble COD was obtained through ZnSO4 coagulation and filtration [26]. The fractions of soluble and PCOD are given by the following equations:

  • display math(5)
  • display math(6)

where COD is the total COD (mg/l), PCOD is the PCOD (mg/l), and COD(s) is the total soluble COD (mg/L; passed through a 0.45 μm filter after coagulation).

Figure 5 presents the effect of O3 and O3/persulfate on soluble and PCOD of semiaerobic stabilized leachate. Soluble COD was improved from 59% in raw leachate to 72% after O3/S2O8 process under optimal operational conditions, whereas PCOD was reduced from 41 to 35% and 28% after O3 and O3/S2O82–, respectively. These results indicated that the new treatment process was efficient for improving the removal efficiency of PCOD and converting nonsoluble COD to soluble COD. In addition to the ability of ozone to reduce soluble inert COD in wastewater and increase residual soluble COD [34], persulfate can react with aromatic and aliphatic components, and then abstract hydrogen by breaking the C[sbond]H bond [35], resulting in the reduction of high-strength nonsoluble organics. The results revealed that the combination of ozonation and persulfate efficiently reduced nonsoluble COD and increased soluble COD in stabilized leachate. Previous studies showed a 60% increase in soluble COD using the Fenton process in the pretreatment of stabilized activated sludge [15]. The removal efficiency of total COD in stabilized leachate through ozone alone was 15%, which then improved to 72% through the O3/persulfate-based advanced oxidation process. Previous studies reported a COD removal of 47 and 65% [16, 17] using the Fenton process, 96% [18] using the photo-assisted Fenton process (UV/Fenton), and 27 and 50% [19] using ozone and ozone/H2O2 in advanced oxidation, respectively.

image

Figure 5. Effect of ozone and ozone/persulfate on Soluble and Particulate COD fractions in stabilized leachate. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Effect of Ozone Applications on Biodegradable Soluble COD(Sbi) and Nonbiodegradable Soluble COD(Subi)

COD(s) contains biodegradable soluble COD(Sbi) and nonbiodegradable soluble COD(Subi) in stabilized leachate. The fractions of COD(Sbi) and COD(Subi) were determined using the following formulas:

  • display math(7)
  • display math(8)

where COD(Sbi) is the biodegradable soluble COD (mg/L), COD(Subi) is the nonbiodegradable soluble COD (mg/L), COD(bi) is the biodegradable COD (mg/L) in a batch aeration system, and COD(s) (mg/L) is the total soluble COD (mg/L).

The obtained fractions of COD(Sbi) and COD(Subi) of the stabilized leachate were 38 and 62%, respectively. The COD(Sbi) fraction in stabilized leachate was generally very low (Figure 6). Bilgili et al. [36] showed that fresh aerobic landfill leachate contains approximately 40% of COD(Sbi) and approximately 60% of COD(Subi). The effects of ozone applications on COD(Sbi) and COD(Subi) in semiaerobic stabilized leachate are presented in Figure 6. The biodegradability of leachate during ozonation is enhanced because of the fragmented organic compounds with long chains to decrease chains degraded to carbon dioxide [31]. The most biodegradable organic material was produced after oxidation using ozone alone [37]. The results obtained in the current study showed improved COD(Sbi) fraction in stabilized leachate from 38 to 43% after 60 min of O3 alone and to 55% after ozonation using O3/S2O8. Meanwhile, the COD(Subi) fraction decreased to 57 and 45% using O3 and O3/S2O8, respectively. Previous studies showed that the Fenton process enables 19.5% removal of nonbiodegradable COD [38]. In the current work, the results revealed that ozonation converts nonbiodegradable organics to biodegradable components, suggesting the enhanced availability of applying the biological treatment of stabilized leachate after ozonation.

image

Figure 6. Effect of ozone and ozone/persulfate on biodegradable soluble and non-biodegradable soluble COD fractions. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Treatment Efficiency and Statistical Analysis

A total of 30 runs were executed using the CCD experimental design. Interactions between the four independent variables were considered in each run to investigate the validity of treating stabilized leachate using ozone and persulfate during advanced oxidation. The removal efficiencies of total COD ranged from 29 to 75.8% for COD, and the optimum removal of total COD was 72% under optimal operational conditions (O3 = 30 g/m3, pH 10, persulfate dosage = 1 g/1 g COD/S2O82–, and reaction time = 210 min). Table 3 presents the ANOVA regression parameters for the predicted response surface quadratic models and other statistical parameters for COD removal. The effect of initial pH variation was examined to determine the optimal pH for the O3/S2O8 system. The removal of COD increased with increased pH. These phenomena can be attributed to the ability of O3 to initiate the formation of hydroxyl radical at high pH, which has an oxidation potential (E0 = 2.80) higher than O3 (E0 = 2.07) in a direct reaction under an acidic condition [30]. Although S2O82– is more active at high pH, Deng and Ezyske [21] reported higher removal for COD and NH3–N at lower pH (4), higher temperature (40 °C), and higher persulfate dosage. In this study, the optimal removal efficiency was obtained at optimal ozone temperature (15 °C), high pH (10), and minimum persulfate dosage. Furthermore, the reaction time was varied between 30 and 210 min to determine optimal experimental conditions. The results demonstrated that the degradation of organics in the leachate improved with increased reaction time.

Table 3. ANOVA for analysis of variance and adequacy of the quadratic model for total COD removal
 SourceSum of squaresDegree of freedomMean squareF-ValueProb > F 
  1. *A:O3, B: COD0/S2O82- ratio (g/g), C: pH, D: reaction time.

COD Removal (%)Model4478.499497.6148.44< 0.0001Mean = 51.31
A61.60161.606.000.0237R2 = 0.9376
B56.89156.895.540.0289SD = 5.719
C3695.1313695.13359.73< 0.0001PRESS = 2027
D33.89133.893.300.0843Adj R2 = 0.9272
C2316.481316.4830.81< 0.0001Adeq. precision = 32.87
D2108.581108.5810.570.0040 
AB36.91136.913.590.0726 
BD173.581173.5816.900.0005 
CD91.68191.688.930.0073 
 Residual205.442010.27   
 Lack of Fit203.621513.5737.430.0004 
 Pure Error1.8150.36   

Table 3 demonstrates that all models were significant at a 5% confidence level and the P values were <0.05. The correlation coefficients obtained in this study for COD removal, that is, R2 = 0.9561, were greater than 0.80, the cutoff for a model with good fit. A high R2 value indicates good agreement between the calculated and observed results, as well as desirable and reasonable agreement with the adjusted R2 [39, 40]. The “adequate precision” (AP) ratio of the models varied between 16.29 and 32.87, which was adequate. AP values above 4 were desirable and confirmed that the predicted models can be used to navigate the space defined by the CCD. Figure 7 demonstrates the normal probability plots of the Studentized residuals for COD removal. The normal probability plots predicted that if the residuals followed a normal distribution, as shown in Figure 7, then the points would fall along a straight line for each case. However, some scattering is expected even with normal data; thus, the data can be considered to be normally distributed.

image

Figure 7. Design Expert plot; normal probability plot of the studentized residual for COD removal. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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Compared with ozone/Fenton in AOPs, our previous work [41] obtained 65% for COD removal. Furthermore, the effect of ozone/Fenton oxidation on the biodegradable characteristics of stabilized leachate has been recently investigated [42]. The biodegradability (BOD5/COD ratio) only improved from 0.034 to 0.1 following O3/H2O2/Fe2+. The fractions of COD(bi), COD(S), and COD(bsi) increased to 36, 72, and 51% after O3/Fenton application in AOPs, respectively. COD(ubi), PCOD, and COD(ubsi) decreased to 68, 28, and 49%, respectively, following O3/Fenton application in AOPs. These results revealed that the new oxidation process (ozone/persulfate) was more efficient in improving the biodegradable characteristics of stabilized leachate than the ozone/Fenton process.

Statistical analysis of COD fractions before and after O3 and O3/persulfate was performed using the Statistical Package for Social Sciences, and the descriptive data are summarized in Table 4. The standard errors for all COD fractions (3.75–4.48) in the three leachate types (raw, after O3, and after O3/persulfate) were statistically applicable. The variances ranged between 42.333 and 63, which were relatively high, and revealed the significant effects of ozonation processes on the COD fractions of raw leachate.

Table 4. Summary of descriptive statistical analysis of COD fractions before and after ozonation processes
     95% confidence interval for mean    
 NMeanStd. deviationStd. errorLower boundUpper boundRangeVarianceMin.Max.
  1. *N: three processes; raw leachate, after ozone and after ozone/persulfate.

Biodegradable COD (%)330.33337.767454.4845411.037949.628815.0060.33324.0039.00
Nonbiodegradable COD (%)369.66677.767454.4845450.371288.962113.0042.33361.0076.00
Soluble COD (%)365.33336.506413.7564849.170581.496115.0060.33359.0072.00
Particulate COD (%)334.66676.506413.7564818.503950.829513.0042.33328.0041.00
Biodegradable soluble COD (%)346.00007.937254.5825826.282865.717215.0063.00040.0055.00
Nonbiodegradable soluble COD (%)354.00007.937254.5825834.282873.717215.0063.00045.0060.00

CONCLUSIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. ACKNOWLEDGMENT
  8. LITERATURE CITED

In this study, the effects of O3 and O3/Persulfate in the AOP on biodegradability and solubility of semiaerobic stabilized solid waste leachate were investigated. Biodegradability, defined as BOD5/COD, improved from 0.034 to 0.05 and 0.29 using O3 and O3/ S2O82−, respectively. The removal efficiency of total COD was improved from 15% after ozone only to 72% after O3/S2O82−. COD(S) increased to 65 after O3 and to 72% after O3/AOPs. The biodegradable fraction of COD improved from 24 to 28 and 39% after O3 alone and O3/ S2O82−, respectively. The fraction of biodegradable soluble COD(Sbi) increased from 38 to 43% after 60 min of O3 alone and to 55% using O3/S2O82−, whereas COD(bsi) increased to 38 and 55% after O3 and O3/AOPs, respectively whereas COD(Subi) fraction was reduced to 57 and 45% as effects of O3 and O3/ S2O82−, respectively. The results suggest the application of biological treatment as a post-treatment process after the O3/ S2O82−system in the AOP for semiaerobic stabilized leachate.

ACKNOWLEDGMENT

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. ACKNOWLEDGMENT
  8. LITERATURE CITED

The authors wish to express their deepest thanks to the School of Civil Engineering of the University of Malaysian Sciences (USM) for supporting and facilitating this research.

LITERATURE CITED

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. ACKNOWLEDGMENT
  8. LITERATURE CITED
  • 1
    Tengrui, L., AL-Harbawi, A.F., Bo, L.M., & Jun, Z. (2007). Characteristics of nitrojen removal from old landfill leachate by sequencing batch biofilm reactor. Journal of Applied Science 211214.
  • 2
    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, 79.
  • 3
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