ENVIRONMENTAL ENGINEERING SCIENCE Volume 21, Number 5, 2004 © Mary Ann Liebert, Inc.
Chemical Pretreatment of Landfill Leachate Discharged into Municipal Biological Treatment Systems A. Pala* and G. Erden Department of Environmental Engineering Dokuz Eylül University 35160, Buca Izmir, Turkey
ABSTRACT Landfill leachate produced in the Harmandali Landfill in Izmir in Turkey was characterized and chemically treated to examine chemical oxygen demand (COD) and color removal efficiencies. The leachate was coagulated adding various doses of an organic flocculant (DEC). Chemical oxidation was carried out using Fenton’s reagent. Powdered activated carbon was used for adsorption to achieve improved COD and color removal in chemically treated leachate. The maximum removal efficiencies of 79% in COD and 98% in color were achieved by Fenton reagent and lime addition (at doses of 2,500 mg/L H2O2 1 2,500 mg/L FeSO4?7H2O2). The best DEC dose was found to be 4,600 mg/L, and COD and color removal efficiencies varied between 60–65% and 82–93%, respectively. A COD removal of 49% and a maximum color removal of 96% were obtained by lime slurry addition. Among the leachate samples, the highest COD and color removal was obtained using the Fenton’s oxidation. Activated carbon adsorption tests indicated that the color parameter was best fitted to the Langmuir Isotherm (r2 5 0.98). The isotherm constants were qmax 5 889 mg Pt–Co?g21, K 5 1,093. Oxygen uptake rate of the samples was also determined after lime and adsorption, Fenton and adsorption, DEC and adsorption, Fenton and lime, and DEC treatment, in raw landfill leachate and in its different dilutions with municipal wastewater. The oxygen uptake rate of municipal wastewater that is accepted as a reference value for biological treatability was found as 46 mg/L/h. In comparison to the OURs obtained from the different treatment alternatives, all alternatives were appropriate for biological treatment of leachate with the exception of discharging the raw leachate directly. Key words: landfill leachate; activated carbon adsorption; DEC, Fenton’s reagent; oxygen uptake rate (OUR) INTRODUCTION General
L
for the disposal of municipal solid wastes due to its low oper-
ANDFILL IS THE MOST COMMON METHOD
ation and maintenance costs (Diamondapoulos, 1994). Nevertheless, this type of waste disposal creates the leachate generation problem, as a result of liquid infiltration through the solid wastes. The leachate produced in landfills may contaminate aquifers. This contamina-
*Corresponding author: Dokuz Eylül University, Engineering Faculty, Department of Environmental Engineering, Kaynaklar Campus, 35160, Buca, Izmir, Turkey. Phone: 90 232 4531 008/1121; Fax: 90 232 453 1153; E-mail:
[email protected]
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550 tion is avoided by collecting and treating the leachate by different processes (Ramirez Zamora et al., 2000). Leachates are classified as young and old, depending on the age of the landfill area. Young leachates are characterized by chemical oxygen demand (COD) contents higher than 5 g/L and by a low nitrogen concentration (,400 mg/L of N). Old leachates are characterized by a high nitrogen content as ammonia (.400 mg/L of N), a high content of recalcitrant compounds, and a low biodegradable organic fraction (BOD5/COD # 0.1) (Diamondapoulos, 1994; Ramirez Zamora et al., 2000). There is a wide range of leachate treatment and disposal options available, including traditional anaerobic and aerobic biological processes as well as physical/chemical processes. Applicable types of treatment depend on the leachate influent quality, effluent quality desired, and quantity. Disposal options include discharge to a Publicly Owned Treatment Works, land application, discharge to surface waters, evaporation, and thermal methods (Knox and Schmalz, 1997). Comparison of a traditional (under anoxic/anaerobic conditions) and innovative landfill, which has a first phase under aerobic conditions (pretreatment) followed by a second phase under anoxic/anaerobic conditions (traditional landfilling) showed that the leachate COD concentration was 10 times lower in an innovative landfill (Boni et al., 1998). Organic carbon in old leachates is mainly due to substances with high molecular weight and recalcitrant characteristics (Diamondapoulos, 1994). The recalcitrant compounds in old leachates are not amenable to biological processes. The effective removal of these substances can only be achieved through the application of more sophisticated methods such as advanced oxidation and especially adsorption with activated carbon, or a combination of these with conventional physiochemical methods (Ramirez Zamora et al., 2000). Ramirez Zamora et al. (2000) reported the best conditions for color removal with Fenton’s method using a mathematical model based on an experimental design with a fractional factorial plan. According to this model, the best conditions for color removal using Fenton’s Method are pH 5 4, 30-min reaction time combined with 1,000 mg/L FeSO4 and 1,000 mg/L of H2O2. Several studies were conducted using aluminum compounds and ferric chloride as coagulants. Amokrane et al. (1997) examined the coagulation-flocculation as a pretreatment for reverse osmosis. They found that ferric chloride was better than aluminum sulfate in turbidity (95 and 87%) and COD (55 and 42%) removal. They also reported that preoxidation with the addition of both H2O2 (1.94 mg/L) and lime milk (0.31 g/L), coagulation using an optimal dose of ferric chloride (0.035 mol Fe/L) and flocculation using a nonionic polymer (40 mg/L) gave a
PALA AND ERDEN supernatant that was less fouling for the reverse osmosis membrane than the supernatant obtained without preoxidation. Pala and Sirin (2001) used polyaluminum chloride (PAX-XL60) (density, 1.32 g/cm3, 7.5% Al) as coagulant and an anionic polyelectrolyte at a concentration of 1/100 of each added PAC dosages during the flocculation phase of the chemical treatment. They reported that settling properties were very poor in the removal of COD in the concentration range of 1,320–13,200 mg PAXXL60/L. Tatsi et al. (2003) also reported that ferric chloride was more efficient than aluminum sulfate for COD removal. Landfill leachate is dark-brown colored wastewater with a high organic pollution. Many treatment techniques have to be employed consecutively to comply with the discharge limits. Conventional physicochemical and advanced oxidation methods can be applied in the pretreatment of landfill leachate to reduce the organic load and toxic substances inhibiting biological treatment. The objectives of this study were (1) to characterize the leachate, to compare with the discharge standards into sewage system (2), and to investigate its treatability to comply with the discharge standards by considering the municipal sewage system ends with a biological treatment plant for the removal of carbon, nitrogen, and phosphorus. Pretreatment of leachate using chemical methods such as conventional physiochemical treatment or advanced oxidation may reduce the size of following the biological treatment plant by decreasing organic loading. Organic compounds, which are inhibiting and toxic for biological treatment, may be removed or converted to relatively lower molecular weight organics that are amenable to biological processes. The standards (Table 1) may also be met using physicochemical treatment or advanced oxidation. In the present study, landfill leachate treatment was conducted by chemical precipitation with lime at pH 5 11, chemical coagulation with a specific organic flocculant (DEC), chemical oxidation with Fenton, and precipitation with lime at pH 5 11. Following these treatments, activated carbon adsorption was also applied. Oxygen uptake rates (OUR) of different treatment alternatives were determined to control the biological treatability of effluent wastewaters. Experimental findings and previous studies in the literature were evaluated to comply with the discharge limits into an urban sewage system ending with biological treatment.
The properties, capacity, and projection of Harmandali landfill After investigation of available areas for landfilling in the surrounding areas of Izmir, the Harmandali area, lo-
CHEMICAL PRETREATMENT OF LANDFILL LEACHATE DISCHARGE Table 1.
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Influent and effluent leachate characteristics (IZSU, 2003).
Parameter Temperature pH Salinity (% 0) Conductivity (mS/cm) COD (mg/L) BOD5 (mg/L) NH4-N (mg/L) Suspended solids (mg/L) Oil and grease (mg/L) T. phosphorus (mg/L) T. cyanide (mg/L) T. chromium (mg/L) Lead (mg/L) Cadmium (mg/L) Copper (mg/L) Zinc (mg/L) Mercury (mg/L) Sulfate (mg/L) Nickel (mg/L) Iron (mg/L) Arsenic (m/L) Calcium (mg/L) Boron (mg/L) Phenol (mg/L) Free chlorine (mg/L) Anionic surface Active agentb (mg/L) Sulfide (mg/L)
Influent Effluent Influent Effluent Influent Effluent (23.01.01) (23.01.01) (12.09.00) (12.09.00) (24.07.03) (24.07.03)
Concentration rangec Standards (mg/L) (IZSU)
— 8.2 — 27,400 38,950 — — 1,442 — 4.3 4.4 2.4 0.7 0.2 0.6 3.1 — — — — n.d. — — — —
— 9.5 — 18,700 17,860a — — 3,270a — 1.0 0.45 0.20 2.2 0.2 0.1 3.6a — — — — n.d. — — — —
— — — — 18,642 — — 137 — 12 — 1.0 0.3 0.06 0.1 1.5 — — — — n.d. — — — —
— — — — 16,770a — — 110 — 3.40 0.56 0.8 1.0a 0.05 0.20a 1.00 — — — — n.d. — — — —
— 8.2 20.9 33,300 20,865 1.325 2,040 156 266 7.5 2.8 0.4 0.7 0.1 0.5 0.8 0.01 360 0.5 15 n.d. 130 95 115 0
— 5.6a 24.2a 38,200 16,087a 120 680 14 40 2.0 1.7 0.1 0.5 0.1 0.06 0.2 0.01 300 0.4 0.5 n.d. 475a 75 65 0
— 1.5–9.5 — 480–72,500 0–195,000 480–72,500 0–1,250 — — 0–234 0–6 0–22.5 0–14.2 0–1.16 0–9.9 0–1,000 0–3 0–1,850 0–7.5 0–42,000 0–70.2 5–4,080 0.413 0.17–6.6 —
40 6.5–10 — — 4,000 — — 500 250 — 10 5 3 2 2 10 0.2 1,000 5 — 3 — 3 10 10
— —
— —
— —
— —
7 —
1.3 —
— —
— 2
aThe
values do not comply with the discharge standards and indicates improper operation of treatment system. is inhibited to discharge nonbiologically degradable surfactants. cReported values by El-Fadel et al. (2002). n.d., not detectable. bIt
cated at the northern part of the city, was chosen because of its geological properties and width. Operation of the Harmandali Landfill was started in April 1992, after the closure of the six old landfills. Its area is 900,000 m2, and it was designed to serve for 15 years. The domestic, medical, and industrial solid wastes are landfilled in separate clusters in the area. According to the geological investigations conducted by Hacettepe University in Turkey, the area is far from the groundwater sites and the permeability coefficient of the site is 1028–10210 m/s. Industrial and medical wastes are disposed in pits opened in the areas with minimum permeability. Domestic solid wastes are leveled first and then topped by soil daily. Three million tons of domestic solid wastes have been disposed of in Harmandali Landfill until the end of 2000, and a biogas utilization unit has been oper-
ated since 1996 to burn methane gas produced in the Landfill. Although the biogas unit has a capacity of 1,250 m3/h, only 250–300 m3/h biogas can be collected from the landfill body (Pala and Sirin, 2001).
Characteristics of Harmandali leachate, present leachate treatment method, and national standards for sewage network discharge Landfill leachate is collected in a lagoon and transferred into an equalization tank by gravity. According to the original design of the treatment plant, leachate used to be pumped to a neutralization unit to decrease the pH to 3 by H2SO4 addition. This neutralization process was designed to break the oil structures and dissolve the organics in leachate. However, the results of the operation ENVIRON ENG SCI, VOL. 21, NO. 5, 2004
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indicated that this neutralization process was useless, and it was canceled. The present treatment system consists of a three-stage chemical treatment: rapid mixing with 20% lime in a rapid mixing tank, flocculation by adding anionic polyelectrolyte in a slow mixing tank, and settling in a sedimentation tank. The operational problems are difficulties in lime dosing by pumps, foam formation by mixing, and excess amounts of sludge. The capacity of the present treatment system is 250 m3/day, and it commenced operation in October 1999. The influent and effluent leachates of the present treatment plant were characterized by samples taken on different dates and the results are summarized in Table 1. The influent leachate characteristics are variable. High COD concentration, high ammonium nitrogen concentration, and low BOD5 concentration are characteristic properties. The low BOD5-to-COD ratio of 0.06 indicates a very low biodegradable organic fraction and an inappropriate influent for biological treatment (Table 1). El-Fadel et al. (2002) also reported that BOD5/COD ,0.1 is an indication of an old stable landfill. They also reported that leachate characteristics are highly variable. Salinity and conductivity of leachate is extremely high. Suspended solid concentration is low, and heavy metal concentration is not as high as expected. Residence time of approximately 8 h in the equalization tank does not provide consistency in influent characteristics. Also, operation of the chemical treatment system is not appropriate to obtain a consistent effluent and to comply with some of the standards (i.e., COD, phenol) to discharge landfill leachate into the sewage system.
EXPERIMENTAL STUDIES Material and methods The materials used in the experiments were FeSO4?7H2O, H2O2, lime slurry [20% Ca(OH)2] and DEC. DEC is an organic flocculant (density, 1.15 g/cm3) made from polymethylpolyamine cationic resin. It was provided from Marwichem S.R.L Company (Italy). It is stable in water, reacts with dyes forming an insoluble complex easily settling with the activated sludge. It is also used as a primary coagulant to remove COD and all the dyes available. It works at pH 6.5–8.5. The activated carbon used was powdered 410/S PW type provided from Kemwater Company (Izmir, Turkey). It was produced by physical activation of selected sawdust charcoal. It was dried at 103°C before use. The properties of this carbon were as follows: apparent density, 360 g/L; moisture, 3%, ash content, 6%; phenol value, 1.3 g/L; internal surface area, 1,100 m2/g. All experiments were carried out in a Jar test appara-
tus using glass beakers. Mixing speed of the apparatus was adjustable between 0 and 250 rpm. Hydrogen peroxide (H2O2 ) forms an extremely efficient oxidizing agent by reacting with ferrous (II) salts in acidic media. A factor of decisive importance for this oxidizing agent, which was discovered in 1894 by H.J.H. Fenton, and was named after him as the “Fenton’s Reagent,” is the hydroxyl radical OH, the oxidizing capacity of which exceeds that of ozone, and is only slightly inferior to that of fluorine. In wastewater techniques, Fenton’s Reagent is used in the treatment of oxidizable substances in wastewater, which inhibit the biological treatment of wastewater or have a toxic effect. The reaction proceeds batchwise, and can be generally described as follows: (a) adjusting the pH with acid to approximately 3, (b) adding ferrous (II) salt, (c) adding hydrogen peroxide, (d) reaction (30 min at 20°C), neutralizing with caustic soda solution or lime milk, separating the solids (in a settling basin or centrifuge) if necessary. The disadvantage of the Fenton procedure is the production of excess amounts of sludge as well as other chemical coagulation processes. Experiments were conducted using 50% H2O2 and 20% FeSO4?7H2O solutions. Raw leachate pH of 6.96 was reduced to 3 using 95–98% H2SO4 (10.98 g/L). Then, different dosages of H2O2 and FeSO4?7H2O were added to the samples (500 mL). Samples were mixed at 100–120 rpm for 30 min. Samples were settled for 15 min and transferred to 300-mL beakers. The pH of the samples was adjusted to 11 with a 20% lime solution, since the best sedimentation was obtained at this pH rather than other pH values such as 7, 8, 9, and 10. Mixing at pH 5 11 was carried out for 20 min at a speed of 30 rpm. After a settling period of 4 h, samples were kept in an oven at 50°C for 30 min to remove the interference of residual H2O2 on COD measurements. A simple permanganate test was also applied to check the presence of residual H2O2. The measured parameters of wastewater, during the experiments, were total and soluble COD (mg/L), suspended solid concentration TSS (mg/L), color as Pt–cobalt and pH. COD and TSS were measured according to the Standard Methods. OUR was determined by the BOD bottle technique as recommended by the Standard Methods (APHA, 1992). Mixed liquor samples taken from the aeration basin were aerated to increase the DO concentration to approximately 7 mg/L. Then, they were immediately transferred to BOD bottles, keeping the bottle contents mixed using a magnetic stirrer. The decrease in DO with time to 2 mg/L was monitored. The OUR was determined from the slope of the linear regression line of DO vs. time. pH measurements were carried out by using 890 MD pH meter. The pH meter was
CHEMICAL PRETREATMENT OF LANDFILL LEACHATE DISCHARGE calibrated by using the standard pH solutions before use. Conductivity was measured with a YSI model 33, S-CT meter.
RESULTS AND DISCUSSION Leachate characteristics Leachate samples used in the study were taken from the effluent of the equalization tank. Characteristics of leachate are given in Table 2. The results show that COD, color, SS, TS, VTS concentrations in all leachate samples are very high, and pH values are about neutral.
Experiments with different pH In this part of the study, pH of the raw leachate (pH 5 6.96) was adjusted to different values using HCl and 20% lime to examine the differences in color and settling properties. Supernatant of the settled samples were used in the experiments. No significant difference in color and settling was observed at pH values between 2 and 10. However, at pH 5 11 there was a significant improvement in settling and color removal. The amount of lime used to adjust the pH from 6.96 to 11 was 11.5 g/L. Raw leachate color of 20,500 Pt–Co reduced to 745 Pt–Co with a removal efficiency of 96%. COD concentration of raw leachate reduced from 64,000 to 34,000 mg/L with 47% removal efficiency. Tatsi et al. (2003) also found a COD removal capacity varying from 30–45% at pH 5 12 with a dosage of 7 g Ca(OH)2/L. Also, Amokrane et al. (1997) reported that 1–15 g/L of lime is required in landfill leachate treatment.
Table 2.
Experiments with DEC addition Presettled leachate samples (500 mL) were placed in glass beakers. DEC was added in beakers at increasing doses (1,150, 2,300, 3,450, 4,600, 5,750, and 6,900 mg/L). One beaker was kept as a control without DEC addition. Then rapid mixing was applied at 120 rpm for 2 min. Then, slow mixing at 35 rpm was applied to provide flocculation. After 1-h precipitation, supernatant was drawn by an injector for experimental analysis. Effluent COD concentrations and removal efficiencies are presented in Table 3. It was observed that there was a significant increase in COD and color removal efficiencies up to addition of 4,600 mg DEC/L. Significant differences were not observed in removal efficiencies at higher DEC concentrations. The best dosage of DEC was 4,600 mg/L, COD and color removal efficiencies were 65 and 88%, respectively, at this concentration. There is no previous study using DEC for leachate treatment, but DEC was successfully used to remove color (from 40 to 78%) from a textile processing factory effluent wastewater by adding into an activated sludge unit at a very low amount of 120 mg/L. However, COD removal efficiencies did not increase, and they were similar to those obtained from previous operation of activated sludge (80–90%) (Pala and Tokat, 2002). Although high COD removal efficiencies were obtained by using DEC to treat the leachate, the high amount of DEC requirement limits its usage for practical applications.
Experiments with Fenton reagent The best combinations of Fenton’s Reagent obtained from many trials and COD removal efficiencies are given in Table 4. The maximum COD (79%) and color removal
Raw leachate sample characteristics.
Parameters Suspended solids (SS) (mg/L) Volatile suspended solids (VSS) (mg/L) Total COD (mg/L) pH Conductivity (mmho/cm) Salinity (%) Total solids (TS) (mg/L) Volatile total solids (VTS) (mg/L) Color (Pt–Co) Turbidity (JTU) aThere
553
Sample-1a
Sample-2
Sample-3
Sample-4
Average
1,511 1,400 64,000 6.96 33,600 22.20 34,208 16,364 20,500 2,600
970 650 25,600 8.33 25,000 19.00 18,200 8,400 12,000 1,600
785 480 22,400 7.71 30,000 17.25 20,072 9,032 9,000 2,200
1,700 1,510 14,400 8.02 27,000 19.00 15,452 —0. 12,500 1,800
1,152 880 20,800 8.02 27,333.3 18.42 17,908 8,716 11,167 1,867
was maintenance of the pumps at the treatment plant. Therefore, these data were omitted from the calculation of average
values.
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Table 3. Results of DEC experiments. DEC Addition (mg/L)
Influent COD (mg/L)
Effluent COD (mg/L)
COD efficiency (%)
Influent color (Pt–Co)
Effluent color (Pt–Co)
Color efficiency (%)
3,450 3,450 4,600 4,600 5,750 5,750 6,900 6,900
22,400 14,400 22,400 14,400 22,400 14,400 22,400 14,400
12,000 7,800 9,000 5,000 8,800 4,800 8,400 4,500
46 44 60 65 61 67 63 69
9,000 12,500 9,000 12,500 9,000 12,500 9,000 12,500
2,500 3,600 1,200 1,500 900 1,300 850 1,150
72 71 87 88 90 90 91 91
efficiencies (98%) were obtained with the addition of 2,500 mg/L H2O2 1 2,500 mg/L FeSO4?7H2O. Among the alternative chemical treatment methods, Fenton’s oxidation followed by sedimentation with lime at pH 5 11 resulted in the best removal efficiencies of COD and color. Gau and Chang (1996) reported that coagulation–resistant organics could be removed by Fenton oxidation. They obtained 0.4–0.6 g COD removal/g H2O2 for an initial COD range of 580–680 mg/L. In this study
Table 4.
4.3–7.0 g COD removal/g H2O2 was obtained for an initial COD range of 14,400–22,400 mg/L.
Experiments with powdered activated carbon (PAC) Following the chemical treatment of leachate, adsorption experiments with powder activated carbon (PAC) were carried out using three different samples. The first
Results of Fenton’s oxidation experiments. Influent COD (mg/L)
Effluent COD (mg/L)
COD efficiency (%)
Influent color (Pt–Co)
Effluent color (%)
COD efficiency (%)
2,500 mg/L H2O2 1 3,000 mg/L FeSO4 ? 7H2O
22,400
9,600
57
9,000
230
97
2,500 mg/L H2O2 1 3,000 mg/L FeSO4 ? 7H2O
14,400
6,400
56
12,500
390
97
1,500 mg/L H2O2 1 2,000 mg/L FeSO4 ? 7H2O
22,400
12,000
46
9,000
300
97
1,500 mg/L H2O2 1 1,500 mg/L FeSO4 ? 7H2O
22,400
6,400
71
9,000
270
97
1,500 mg/L H2O2 1 1,500 mg/L FeSO4 ? 7H2O
14,400
4,800
67
12,500
410
97
1,000 mg/L H2O2 1 2,000 mg/L FeSO4 ? 7H2O
22,400
9,600
57
9,000
300
97
2,500 mg/L H2O2 1 2,500 mg/L FeSO4 ? 7H2O
22,400
4,800
79
9,000
190
98
2,500 mg/L H2O2 1 2,500 mg/L FeSO4 ? 7H2O
14,400
3,600
75
12,500
310
98
Dosages (mg/L)
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555
Figure 1. Freundlich isotherms.
sample was the effluent of Fenton’s oxidation experiments with the addition of the best dosages of 2,500 mg/L H2O2 1 2,500 mg/L FeSO4?7H2O and with an influent COD concentration of 22,400 mg/L. The second sample was obtained by adjusting the raw leachate pH from 8.02 to 11 with lime slurry following by settling (influent COD 5 22,400 mg/L). The third sample was the effluent of leachate treated with the addition of 4,600 mg/L DEC, which was the best dosage, and with an influent COD concentration of 22,400 mg/L. In the adsorption ex-
periments 2, 4, 7.5, 10, and 15 g/L of PAC were added to 100-mL samples. The samples were agitated during 24 h at 25°C in a shaker and then they were periodically filtered through 0.45-mm Millipore membrane filters in to measure color and soluble COD values. Freundlich and Langmuir adsorption isotherm models were applied in color data analysis. The Freundlich equation is given below: qe 5 Kf ? Ce1/n
(1)
Figure 2. Langmuir isotherms.
ENVIRON ENG SCI, VOL. 21, NO. 5, 2004
556 Table 5.
PALA AND ERDEN
Oxygen uptake rate experiments
Langmuir model constants for color removal. Langmuir
Treatment alternatives
qmax
K
r2
Fenton 1 PAC Lime 1 PAC DEC 1 PAC
889 258 605
1093 792 1634
0.98 0.97 0.92
where qe is the adsorption capacity of the activated carbon at equilibrium condition (mg Pt–Co g21 PAC), Ce is the equilibrium color (mg Pt–Co/L), and Kf and 1/n are Freundlich exponent and slope. The Langmuir equation is: 1/qe 5 1/qm 1 (K/qm ? 1/Ce)
(2)
where qm and qe are adsorption capacities at maximum and at equilibrium conditions (mg Pt–Co/g PAC), Ce is the equilibrium concentration of the solute in liquid phase (mg Pt–Co L21), and K is the Langmuir model constant. Figures 1 and 2 illustrate the Langmuir and Freundlich isotherms. The corresponding adsorption constants were calculated and are given in Table 5. The Langmuir model was more satisfactory in describing the data than the Freundlich model. The isotherm constants for color removal following the Fenton oxidation were found to be qm 5 889 mg Pt–Co/g and K 5 1093 with the highest value of r2 5 0.98. Ramirez Zamora et al. (2000) also found a higher adsorption capacity (442.8 mg Pt–Co/g) for color removal after Fenton’s oxidation than the adsorption capacity (93.45 mg Pt–Co/g) obtained after chemical coagulation. However, COD removal was slightly effective in Fe and PAC treatment when compared to DEC and PAC treatment and Lime and PAC treatment. But COD removal was apparently less for all treatment alternatives with addition of 2, 4, 7.5, and 10 g PAC/L, which are very high amounts of activated carbon for adsorption studies. But color removal efficiencies were high in both Fe and PAC and Lime and PAC treatments (Table 6).
OUR experiments were applied to the effluent samples collected from Fe and PAC, Lime and PAC, DEC and PAC, Fe and lime, and DEC treatments, raw leachate sample, and 2% (v/v) raw leachate-pretreated municipal wastewater mixture. The activated sludge culture used in the experiments with a total volatile solid concentration of 4,491 mg/L was taken from a biological oxidation pond at the Izmir Municipal Wastewater Treatment Plant. All the experiments were carried out under the same conditions at pH 5 7.0, and with the same volumes of activated sludge culture. The OUR value of pretreated municipal wastewater of 46 mg/L/h was accepted as a reference value for comparison. The OUR values were 55 mg/L/h for Fe and PAC, 50 mg/L/h for Lime and PAC, 91 mg/L/h for DEC and PAC, 50 mg/L/h for Fe and lime, 85 mg/L/h for DEC, 42 mg/L/h for raw leachate, and 47 mg/L/h for 2% (v/v) raw leachate pretreated municipal wastewater mixture. All the OUR values except for the raw leachate were higher than the reference value indicating biological treatability. Among these values, the OUR obtained from DEC treatment was the highest, indicating the highest biological treatability. The dilution of raw leachate with the municipal wastewater is not an acceptable solution in terms of environmental pollution control studies. The present chemical treatment system with lime addition is not operated well, and also does not comply with the discharge standards. Either Fenton and PAC or DEC and PAC alternatives before discharging into the main sewage system ending with biological treatment can be considered. But DEC and AC are expensive and also exported chemicals. Therefore, Fenton oxidation and sedimentation with lime slurry at pH 5 11 can be suggested for pretreatment before biological treatment. This alternative may also comply with the discharge standards.
SUMMARY This study indicated that treatment of landfill leachate depends on its characteristics and discharge standards to
Table 6. Color removal efficiencies. COD removal (%) PAC (g/L) 2 4 7.5 10 15
Color removal (%)
Fe 1 PAC
DEC 1 PAC
Lime 1 PAC
Fe 1 PAC
DEC 1 PAC
Lime 1 PAC
7 12.5 25 39.5 53.3
8.3 12 24 38 51
9 15 24 35 49
61 79 84 89 92
36 48 69 79 82
70 76 84 87 90
CHEMICAL PRETREATMENT OF LANDFILL LEACHATE DISCHARGE
557
the receiving media. Before biological treatment of the old stable or partially stable landfill leachates, chemical treatment should be employed as pretreatment. Lime is an effective coagulant to effectively remove impurities from leachate. DEC is an effective but expensive coagulant for COD removal. Fenton’s oxidation can improve the COD and color removal efficiencies up to 79% and 98%, respectively. Carbon adsorption requires high amounts of activated carbon for color and COD removal. The highest activated carbon adsorption capacity for color removal was obtained after Fenton treatment as 889 mg Pt–Co/g PAC. However, activated carbon was not effective for COD removal as it was for color removal. Oxygen uptake tests gave very important information on the biological treatability of the leachate. Compared OUR test results showed that all the chemical treatment alternatives were applicable for biological treatment of leachate with the exception of discharging the raw leachate directly into receiving media.
DIAMONDAPOULOS, E. (1994). Characterization and treatment of recirculation-stabilized leachate. Water Res. 28(12), 2439–2445.
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