Leachates from landfills are one of the environmental challenges in developing countries, such as Iran that also will face water scarcity in the near future. Landfill leachate management to decrease the negative impact on water resources is indispensable. On the one hand, depending on the age of landfill, high ammonia concentration leachates could be a resource for use in agricultural purposes and on the other, treated leachate can be used as a valuable resource for agronomic irrigation. In order to investigate this hypothesis, landfill leachate was provided from the Sari municipal landfill in the north of Iran (COD = 7,045 mg/l; BOD5/COD = 0.36) and the performance of different combinations of biological, chemical and membrane processes were evaluated according to Iran's Agricultural Water Standard (IAWS). The treatment processes consisted of sequencing batch reactor (SBR), Fenton's process/SBR, and membrane/SBR/Fenton. Results indicated in addition to access IAWS, the treated leachate through Membrane/SBR/Fenton's process could be used as a nitrogen source for agricultural purposes. The removal efficiency of primary parameters, including COD, BOD5, turbidity, and color were 89%, 96%, 99% and 98%, respectively.

INTRODUCTION

One of the main solid waste management methods in Iran as a developing country is the landfill, into which about 84% of generated municipal solid waste (10 million tons per year) was disposed, with approximately, 0.5 m3/ton leachate production rate. The fundamental problem of solid waste landfilling is leachate production. Generally, land-fill leachates (LFL) are characterized by dark color, bad smell, high organic and nitrogen loads, heavy metals, humic substances and recalcitrant compounds which make leachate treatment challenging and complicated (Kamenev et al. 2002; Zouboulis et al. 2004).

The age of landfill and thus the degree of solid waste stabilization has a significant effect on LFL characteristics (Renou et al. 2008). Among the different LFL properties, the ratio BOD5/chemical oxygen demand (COD) is explanatory of LFL age due to its direct relationship to the biodegradability of LFL. Table 1, shows a classification of LFL characteristics expressed by Ahmad & Lan (2012). Consistent with this, biological treatments such as UASB, stabilization ponds, activated sludge, trickling filters, biodiscs and sequencing batch reactor (SBR), have shown to be very useful for young leachates treatment (Kang & Hwang 2000; Ding et al. 2001; Spagni & Marsili 2009; Yan & Hu 2009). For old or partially stabilized leachates, the most efficient way to treat them is physicochemical processes including coagulation-flocculation-sedimentation, membrane processes (reverse osmosis, ultra, and Nanofiltration), ammonia stripping and advanced oxidation processes (Rivas et al. 2004; Ntampou et al. 2005). High concentrations of COD and N-NH3 are the principal pollutants of LFL. In the past decade, many investigations were conducted to decrease COD and N-NH3 from LFL, by applying combined chemical, biological and physical processes to achieve desirable results (Wu et al. 2009; Yan & Hu 2009).

Table 1

Classification and composition of landfill leachate vs. age (adapted from (Ahmad & Lan 2012)

Parameter Young Intermediate Stabilized 
Age (years) <5 5–10 >10 
pH <6.5 6.5–7.5 >7.5 
BOD5/COD 0.5–1 0.1–0.5 <0.1 
COD (mg L–1>10,000 4,000–10,000 <4,000 
NH3-N (mg L–1<400 N.A. >400 
Heavy metals Low-medium Low Low 
Biodegradability High Medium Low 
Parameter Young Intermediate Stabilized 
Age (years) <5 5–10 >10 
pH <6.5 6.5–7.5 >7.5 
BOD5/COD 0.5–1 0.1–0.5 <0.1 
COD (mg L–1>10,000 4,000–10,000 <4,000 
NH3-N (mg L–1<400 N.A. >400 
Heavy metals Low-medium Low Low 
Biodegradability High Medium Low 

N.A., not applicable.

In various studies (Modenes et al. 2012; Shrawan et al. 2013), the BOD5/COD ratio has been increased by Fenton's process followed by biological treatment in order to decreasing COD loading. Air stripping has been used as a conventional method for reducing ammonia concentration from LFL (Kilic et al. 2007; Hasar et al. 2009; Guo et al. 2010), whereas the existence of N-NH3, can be useful for agricultural purposes. Accordingly, there is no limitation in Iran's Agricultural Water Standard (IAWS) for ammonia. On the other hand, due to many economic barriers, implementation of advanced LFL treatment plant in developing countries is not executable. According to the UN Development Program (United Nations 1992), the level of Iran's per capita water resources has been predicted to fall to as little as 816 m³ in 2025, down from 2,030 m³ in 1990. It is clear Iran is facing an impending water crisis of staggering proportion (MOE 2010).

Therefore, the objective of current study is an investigation of LFL treatment feasibility in order to reuse for agricultural purposes as a new nutrient source. To achieve this target, all characteristics of Sari, Iran's landfill leachate were measured, and then combinations of biological (SBR), Chemical (Fenton's process) and physical (Ultrafiltration) processes have been evaluated for leachate treatment according to IAWS (MOE 2010).

MATERIALS AND METHODS

Leachate

Leachate was collected from Sari's municipal landfill located in the north of Iran and the characteristics were evaluated in triplicate and compared with the agricultural water standard of Iran (MOE 2010). According to Table 2, BOD5, raw COD, filtered COD, turbidity, Zn, Pb, TSS, N-NH3, and color have a higher value more than the standard limit, so in this study, the performance of treatment methods has been evaluated according to these parameters.

Table 2

Comparison between leachate characteristics and IAWS

Parameter Unit Leachate value IAWSa Parameter Unit Leachate value IAWSa 
pH – 6–8.5 Turbidity FTU 173 <50 
BOD5 mg/l 2,555 <100 Zn mg/l 2.46 <2 
Raw COD mg/l 7,045 <200 Ni mg/l <2 
Filtered COD mg/l 5,600 <200 Cr mg/l 0.08 <2 
BOD5/COD – 0.36 – Cd mg/l <0.05 
TOC mg/l 2,340 – Pb mg/l 1.77 <1 
EC μs 22,200 – N-NO3 mg/l 25 – 
TN mg/l 201.6 – SO4 mg/l 176 <500 
TP mg/l 126.9 – PO4 mg/l 108 – 
TSS mg/l 610 <100 N-NH3 mg/l 181.2 – 
  Color mg/l 3,715 <75 
Parameter Unit Leachate value IAWSa Parameter Unit Leachate value IAWSa 
pH – 6–8.5 Turbidity FTU 173 <50 
BOD5 mg/l 2,555 <100 Zn mg/l 2.46 <2 
Raw COD mg/l 7,045 <200 Ni mg/l <2 
Filtered COD mg/l 5,600 <200 Cr mg/l 0.08 <2 
BOD5/COD – 0.36 – Cd mg/l <0.05 
TOC mg/l 2,340 – Pb mg/l 1.77 <1 
EC μs 22,200 – N-NO3 mg/l 25 – 
TN mg/l 201.6 – SO4 mg/l 176 <500 
TP mg/l 126.9 – PO4 mg/l 108 – 
TSS mg/l 610 <100 N-NH3 mg/l 181.2 – 
  Color mg/l 3,715 <75 

aIran's Agricultural Water Standard (MOE 2010).

Bacteria adaptation

For adaptation of bacteria to leachate, activated sludge from municipal wastewater treatment plant was fed with synthetic wastewater containing KH2PO4, CO(NH2)2, C6H12O6 + H2O, and required trace elements for 7 days. After this period, 5% (v/v) of synthetic wastewater was diminished and replaced with leachate for 20 days to prepare activated sludge for using in SBR and membrane SBR (MSBR).

Conventional SBR reactor

A reactor with a total volume of 3 L and a working volume of 2 L was used. Air was supplied at the bottom of the reactor to maintain dissolved oxygen concentration between 2 and 4 mg/l. The system was operated at approximately 8-hour cycles including 7-hour aeration, and 1 hour sedimentation. The volume exchange ratio was 50%. The reactor operated at room temperature (20–27°C) without pH control.

Membrane SBR

A membrane separation process was coupled to a SBR for using simultaneously biological oxidation and physical separation processes in a reactor. The separation module was made with propylene hollow fiber membranes (100-nm pore size, 6 m2 surface area) vertically submerged in the 218 L (useful volume) bioreactor with SBR operation by hydraulic retention time of 24 hr. A blower with a diffuser was placed under the membrane to avoid fouling of the membrane through promoting shear over its surface and produced stable dissolved oxygen concentration of 2–5 mg/l in the bioreactor. Required suction was provided by a vacuum pump and the membrane module was also backwashed with effluent for 10 min every day to remove deposits on the membrane surface.

Fenton process

A bench-scale jar-testing apparatus equipped with 1,000-mL beakers was used to conduct optimization Fenton experiments. Before starting the experiments, leachate was brought to room temperature at approximately 23°C, and leachate was diluted to 50% (v/v) for decreasing COD strength. First, the mixing speed and pH was adjusted to 200 rpm and 3 respectively, then the desired amount of H2O2 was added to each sample jar-test beaker. Approximately 1 min later, the desired amount of FeSO4-7H2O was added in a single step. A 30 min oxidation period was provided, followed by coagulation by increasing the pH to 8.3 using 10 M NaOH for 5 min. Afterward, 15 min of flocculation time was given by reducing the mixing speed to 30 rpm. Finally, a 30 min sedimentation period was provided to settle iron sludge, the supernatant was collected and stored for analysis and using in downstream treatment.

RESULT AND DISCUSSION

Optimization of Fenton process

In order to assess the performance of the Fenton process for leachate treatment in combination with other systems (SBR & MSBR), it was necessary to study the optimal operational conditions of the Fenton process to achieve maximum COD, color, and turbidity removal. It was conducted one variable at a time by modifying the value of one particular variable while keeping all other variables close to the favourable conditions (Zhang et al. 2005; Di Laconi et al. 2006).

Effect of pH

Many authors have described the effect of pH as one of the major factors limiting the performance of the Fenton processes in the wastewater treatment because its affect on the activity of both oxidant and the substrate (Gulsen & Turan 2004; Zhang et al. 2005). Therefore, in this study, the effect of pH was evaluated. Figure 1, shows the effect of pH on COD, color and turbidity removal of leachate by the Fenton process. The results indicated that the best removal efficiency was obtained at pH 3. Results agreed well with other studies (Gulsen & Turan 2004; Zhang et al. 2005). In pH higher than optimum condition, the iron precipitate in the form of Fe(OH)3, and H2O2 decomposes into oxygen (Lunar et al. 2000; Fu et al. 2009). At pH lower than optimum value, due to the formation of [Fe(II)(H2O)6]2+ complex, which reacts with H2O2 more slowly than [Fe(II)(OH)(H2O)5]+, thus produced less OH radical (Gallard et al. 1999).
Figure 1

The effect of pH on COD, Color, and Turbidity removal.

Figure 1

The effect of pH on COD, Color, and Turbidity removal.

Effect of reaction time

Reaction time has a direct impact on treatability and power consumption during the Fenton process (Deng & Englehardt 2007). In this study, the effect of reaction time on COD, color and turbidity removal during Fenton process was evaluated at 30, 45, 75, 90 and 120 min (Figure 2). The results indicated that optimum reaction time was 75 min. After this period removal efficiency was increased due to the regeneration of Fe2+ and destruction of produced flocs. The reaction time for Fenton's process in various studies has fluctuated between 30 min and 3 hours (Kang & Hwang 2000; Zhang et al. 2005; Tengrui et al. 2007).
Figure 2

The effect of time reaction on COD, color, and turbidity removal.

Figure 2

The effect of time reaction on COD, color, and turbidity removal.

Effect of chemical reagents

Chemical reagents are significant operational cost items for many wastewater treatment facilities (Zhang et al. 2005). The removal of organic contaminants can be improved by increasing reagents concentration, which will be negligible when the reagent's dosage is increased above a certain threshold level (Deng & Englehardt 2007). Besides, an extra dosage of Fe2+ can contribute to increase total dissolved solids and electrical conductivity in the effluent that require further treatment before discharge to receiving water (Gogate & Pandit 2004; Hermosilla et al. 2009). As well, Excessive application of hydrogen peroxide generates gas bubbles, which inhibits sludge sedimentation (Hermosilla et al. 2009). Therefore, the optimal concentration of H­2O2 and Fe2+ must be determined for economical evaluation of Fenton process. Figure 3 shows the effect of Fe2+ concentration on the COD, color, and turbidity removal during Fenton process. It can be seen that the Fenton treatment efficiency of COD, color, and turbidity removal increases with augmenting Fe2+ concentration and optimum value is 1,750 mg/L. Maximum removal efficiency for COD, color, and turbidity were obtained 75%, 98%, and 99%, respectively. Excessive concentration of Fe2+ reacts with hydroxyl radicals and drives them out of the reaction's environment and therefore COD removal efficiency has been decreased (Equation (1)). It must be noted that excessive iron dosage leads to Fe(OH)3 production that has a brown color and therefore, color and turbidity removal has been decreased (Antonio 2006).
Figure 3

The effect of Fe2+ concentration on COD, Color, and turbidity removal.

Figure 3

The effect of Fe2+ concentration on COD, Color, and turbidity removal.

 
formula
1
 
formula
2
Similarly, the optimum concentration of H2O2 was determined by changing the value between 500 to 5,000 mg/l. Maximum removal efficiency for COD, color and turbidity were obtained 75%, 98%, and 99%, respectively (Figure 4). According to Equation (2), excessive concentration of H2O2 reacts with radical hydroxyls and so leads to decreased removal efficiency (Deng & Englehardt 2006). Meanwhile, Excess H2O2 lead to iron sludge flotation, owing to O2 off-gassing caused by auto decomposition of excess H2O2 (Kim et al. 2001; Lau et al. 2001), and residual H2O2 inhibits downstream biological treatment. Hereupon in this study, pH of Fenton process effluent was increased to 8.3 and then subjected to high temperature (50°C) for 30 min.
Figure 4

The effect of H2O2 on COD, color, turbidity.

Figure 4

The effect of H2O2 on COD, color, turbidity.

According to optimum operational parameters, pH = 3, reaction time = 75 min, Fe2+ = 1,750 mg/l and H2O2 = 3,000 mg/l, the Fenton process was performed, and the effluent was stored for using in the SBR reactor. Characteristics of the Fenton process effluent are presented in Table 3. As it has been shown, except for COD and BOD, other parameters are the sub-standard limits. The BOD5/COD ratio of the effluent leachate from the Fenton reactor was improved from 0.36 to 0.78, which could be sufficient to have an efficient biological treatment. Since this effluent was connected to SBR reactor for further treatment.

Table 3

Characteristic of Fenton process effluent and comparison with IAWS

Parameter Unit Effluent value IAWSa Parameter Unit Effluent value IAWSa 
pH – 8.3 6–8.5 Turbidity FTU <50 
BOD5 mg/l 877.7 <100 Zn mg/l 0.63 <2 
Raw COD mg/l 735 <200 Pb mg/l 0.21 <1 
Filtered COD mg/l 655 <200 Color mg/l 60 <75 
BOD5/COD – 0.78 – TSS mg/l <100 
Parameter Unit Effluent value IAWSa Parameter Unit Effluent value IAWSa 
pH – 8.3 6–8.5 Turbidity FTU <50 
BOD5 mg/l 877.7 <100 Zn mg/l 0.63 <2 
Raw COD mg/l 735 <200 Pb mg/l 0.21 <1 
Filtered COD mg/l 655 <200 Color mg/l 60 <75 
BOD5/COD – 0.78 – TSS mg/l <100 

aIran's Agricultural Water Standard (MOE 2010).

Evaluation Fenton process followed by SBR process

The SBR was operated in two different phases, the operation with diluted leachate (phase 1) and the operation with Fenton-treated effluent (phase 2). The cycle period for both phases was 24 hr and divided into five steps: filling (0.25 hr), aeration-reaction (22 hr), settling (0.75 hr), decant (0.25 hr) and idle (0.75 hr). Table 4 shows the characteristics of the effluent SBR reactor. Although these results indicated SBR reactor reduced the values of COD and BOD5 of leachate, it still could not meet the reuse standard for agriculture. Therefore, better biological treatment is needed to combine with the Fenton process. Guo et al. (2010), has investigated leachate treatment using a combined stripping, Fenton, SBR, and coagulation process. COD and N-NH3 of the SBR effluent which was operated after Fenton process was 700 mg/l and 25 mg/l with %57 and %16 removal efficiency, respectively (Guo et al. 2010).

Table 4

Characteristic of SBR effluent

Parameter Unit Effluent value IAWSa Parameter Unit Effluent value IAWSa 
pH – 8.3 6–8.5 Turbidity FTU 15.3 <50 
BOD5 mg/l 147 <100 Color mg/l 15 <75 
Raw COD mg/l 265 <200 TSS mg/l 12 <100 
Filtered COD mg/l 220 <200 BOD5/COD – 0.67 – 
Parameter Unit Effluent value IAWSa Parameter Unit Effluent value IAWSa 
pH – 8.3 6–8.5 Turbidity FTU 15.3 <50 
BOD5 mg/l 147 <100 Color mg/l 15 <75 
Raw COD mg/l 265 <200 TSS mg/l 12 <100 
Filtered COD mg/l 220 <200 BOD5/COD – 0.67 – 

aIran's Agricultural Water Standard (MOE 2010).

Evaluation of MSBR

Amongst several technologies available for the treatment of LFL, Ultrafiltration (NF) has emerged as an attractive option since complementary combinations with other pre/post-treatment (Melin et al. 2005). According to a literature review (Trebouet et al. 2001), membrane separation is not suitable as a single process in LFL treatment due to low rejection for the nitrogen component, but for the hypothesis of the present study, this is a hopeful point. Therefore, the combination of membrane separation and biological treatment can be as a suitable option for reuse of LFL in agricultural fields. Hence, MSBR with 24-hr HRT and 8-day SRT, followed by the Fenton process was performed. Optimal condition for effluent treatment of MSBR by Fenton process were attained according to jar test and summarized in Table 5. The results of the MSBR and the combination with the Fenton process are shown in Table 6 and for more explanations a clustered column is used in Figure 5.
Table 5

Optimal conditions for MSBR effluent treatment by Fenton process

Parameters H2O2 (mg/l) Fe2+ (mg/l) H2O2/Fe2+ pH Reaction time (min) 
Values 3,500 200 7.1 60 
Parameters H2O2 (mg/l) Fe2+ (mg/l) H2O2/Fe2+ pH Reaction time (min) 
Values 3,500 200 7.1 60 
Table 6

Characteristics of MSBR effluent and Fenton post-treatment

Parameter Unit Influent MSBR
 
Fenton process
 
Total removal IAWSa 
Effluent Removal Effluent Removal 
pH – 8.2 8.3 – 7.5 – – 6–8.5 
BOD5 mg/l 486 36.66 92% 18.8 49% 96% <100 
Raw COD mg/l 1,351 320 76% 148 54% 89% <200 
Filtered COD mg/l 1,250 303 75% 135 55% 89% <200 
Turbidity FTU 85.7 32.14 45% 0.5 98% 99% <50 
Color – 2,084 1,396 32% 41 97% 98% <75 
N-NH3 mg/l 25.8 9.3 64% 3.1 66% 88% – 
SO4 mg/l 25.1 3.94 84% 3.5 11% 86% <500 
PO4 mg/l 15.4 NA 100% NA – 100% – 
Pb mg/l 0.25 0.2 20% 0.02 90% 92% <1 
Zn mg/l 0.35 0.08 77% 0.04 50% 88% <2 
Parameter Unit Influent MSBR
 
Fenton process
 
Total removal IAWSa 
Effluent Removal Effluent Removal 
pH – 8.2 8.3 – 7.5 – – 6–8.5 
BOD5 mg/l 486 36.66 92% 18.8 49% 96% <100 
Raw COD mg/l 1,351 320 76% 148 54% 89% <200 
Filtered COD mg/l 1,250 303 75% 135 55% 89% <200 
Turbidity FTU 85.7 32.14 45% 0.5 98% 99% <50 
Color – 2,084 1,396 32% 41 97% 98% <75 
N-NH3 mg/l 25.8 9.3 64% 3.1 66% 88% – 
SO4 mg/l 25.1 3.94 84% 3.5 11% 86% <500 
PO4 mg/l 15.4 NA 100% NA – 100% – 
Pb mg/l 0.25 0.2 20% 0.02 90% 92% <1 
Zn mg/l 0.35 0.08 77% 0.04 50% 88% <2 

aIran's Agricultural Water Standard (MOE 2010).

Figure 5

COD, BOD5, and Color removal through different processes.

Figure 5

COD, BOD5, and Color removal through different processes.

As mentioned, the BOD5/COD ratio of raw leachate was 0.36 (Table 2) which means the biodegradability of leachate is low and therefore, the maximum removal efficiency of MSBR is regarding the biodegradable portion and remaining pollutants are non-biodegradable. Accordingly, final BOD5 and COD removal efficiency have been %92 and %76, respectively and therefore, BOD5/COD ratio of MSBR effluent decreased to 0.11, which agreed with other studies (Neczaj et al. 2005; Laitinen et al. 2006) In the Fenton process, effluent COD (54 mg/l) reached the standard limit by the destruction and oxidation of non-biodegradable compounds and the BOD5/COD ratio increased to 0.12 which is a little more than the MSBR system. The maximum removal efficiency of ammonia in MSBR was %64 which is due to nitrification reactions. Existence of denitrification process in biological flocs due to simultaneous nitrification and denitrification event is predictable (Pochana & Keller 1999) and membrane separation can affect nitrogen compounds rejection from the LFL stream (Trebouet et al. 2001). As expected, MSBR does not have suitable removal efficiency for turbidity (%45) and color (%32), these results are due to the ultrafiltration module. But the Fenton process increased dramatically the removal efficiency of turbidity and color to %98 and %97, respectively. These results have a perfect match with other investigations (Wang et al. 2012). Other parameters have received standard limits through the biological treatment and the membrane separation.

CONCLUSION

In this study, treatability of leachate by different processes was evaluated. The results indicated that the MSBR + Fenton process has a sufficient performance for treatment of leachate pollutants. The total removal efficiency of the main pollutants through this process, such as COD, BOD5, color, and turbidity was 89%, 96%, 98% and 99%, respectively. Total ammonia removal was 88% which means there is a remaining part of ammonia in the effluent, which can be useful for agricultural lands. However, evaluation of high ammonia-leachates through the MSBR + Fenton process is recommended. The results of the present investigations suggest the possibility of leachate-treated for using in agricultural purposes that are a promising strategy to tackle important environmental challenges and water scarcity in Iran.

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