Application of Box-Behnken Design (BBD) to Optimizing COD Removal from Fresh Leachate using Combination of Ultrasound and Ultraviolet

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 861-869

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

Application of Box-Behnken Design (BBD) to

Optimizing COD Removal from Fresh Leachate

using Combination of Ultrasound and Ultraviolet

Neamatollah Jaafarzadeh , Mohammad Hasan Zarghi , Mobina Salehin , Aliakbar

Roudbari , Amir Zahedi

¹Toxicology Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran

Student Research Committee, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran

Department of Environmental Health Engineering, Semnan University of Medical Sciences, Semnan, Iran

Center for Social and Behavioral Sciences Research, Shahroud University of Medical Sciences, Shahroud, Iran

Received: 16/04/2020 Accepted: 03/05/2020 Published: 20/09/2020

Abstract

Municipal Solid Waste (MSW) landfill leachate contains highly concentrated organic substances which must be treated before

discharged into aqueous environments. This study was done to optimize the removal of COD from fresh landfill leachate using

combination of ultrasound and ultraviolet. The sample of fresh landfill leachate was obtained from a municipal landfill, and its COD

was measured. Box-Behnken design was applied to analyze and optimize the removal of COD by different variables, including pH,

contact time, ultrasound frequency and UV intensity. Based on this, 29 samples and three replications were tested. The analysis of

variance indicated quadratic model was significant for removal of COD. According to the model, the removal efficiency of COD was

obtained 92.1 % at optimal conditions (pH at 9.2, contact time of 54min, ultrasound frequency of 54 kHz and UV intensity of 45w). The

removal efficiency of COD was 91.8 % in these conditions which agrees well with the predicted response value. The BOD5/COD ratio

increased to 0.38 after treatment. Also, the values of average oxidation state (AOS) and carbon oxidation state (COS) increased to +1.9

and 3.49, respectively. This means that the treated leachate was much easier to biodegrade than the initial leachate.

Keywords: COD, Leachate, Ultrasound, Ultraviolet, BBD

Introduction¹

Lifestyle changes and commercial and industrial growth

soil and mutagenic effect of human being as well as affecting

the ecology balance, etc [61].

The removal of organic matter based on COD (chemical

oxygen demand) is a common precondition before leachate

discharge into natural water bodies [8]. The concentration of

COD in young leachate is 36 times higher than in domestic raw

sewage. The pollutant potential of leachate is mainly related to

its organic load [62]. Most recently, a variety of physical,

biological and chemical processes have been widely used to

remove COD from landfill leachate [9, 10]. Advanced

oxidation processes (AOPs) as an innovative technique are

extremely promising, owing to their unique potential for the

generation of hydroxyl radicals (OH) that are highly reactive in

chemical solutions [9, 11, 12]. The produced hydroxyl radicals

in this process degrade the organic matter present in the

leachate of the landfill site [11]. AOPs include numerous

combinations of ultraviolet (UV) radiation, ultrasound (US),

photocatalysts, catalysts, fenton and strong oxidants [9, 13, 14].

Ultrasonic can degrade pollutants by applying thermal

dissociation (pyrolysis) and shear forces in addition to

producing hydroxyl radicals [15, 16]. The strong cavitations

and hot spots produced by ultrasound in an aqueous solution,

that causing shock waves (physical effect) and reactive free

radicals (chemical effect) by the violent collapse of the

capitation bubbles [17]. These effects accelerate the

decomposition of toxic chemicals [18]. Another method used

in many countries over the past years have led to a rapid

increase in the production of solid industrial and municipal

waste [1, 2]. The method of hygienic landfill for the final

disposal of solid waste material continues to be widely avowed

and used due to its economic benefits [3, 4]. The production of

leachate remains an unavoidable result of the waste disposal

[2]. The aqueous effluent produced as a result of the infiltration

of rainwater into the waste, together with biochemical

processes in the waste cells and the intrinsic water content of

the waste, constitute the leachate [5]. Leachate includes many

amounts of organic matter, which its humic constituents are

ammonia nitrogen, chlorinated organic, inorganic salts and

heavy metals [6, 7]. When leachate leaks out of them due to the

decomposition of waste materials, it carries all the biological

and chemical substances in the waste materials. The leachate of

the landfill is one of the most polluted types of sewage, which

has caused many health and environmental concerns due to the

extensive use of urban landfills for the final disposal of waste

[59]. Due to percolation of leachate through the soil and

migration of leachate by surface runoff contaminates the soil,

groundwater and surface water bodies in and around the landfill

site [60]. Discharge of landfill leachate to the environment

causes detrimental effect to the aquatic life, infertility of the

Corresponding author: Mohammad Hasan Zarghi, Student Research Committee, Ahvaz Jundishapur University of Medical Sciences,

Ahvaz, Iran. E-mail: mohandesmhz@gmail.com, zarghi.mh@ajums.ac.ir, phone: +989101107810.

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 861-869

to treat fluids in recent years is ultraviolet radiation (UV). This

ray is part of an electromagnetic wave with an amplitude range

of 100 to 400 nm [19]. The common benefits of both methods

include: 1. Non-production of mutagenic/carcinogenic side

products 2. No odor and taste problem 3. No need to use and

store dangerous chemicals [20, 21]. Combined methods appear

to be the most useful solution for the treatment of waters

containing high loads of pollutants. According to the

mentioned points, and while no research has yet been done to

remove COD by ultrasound and ultraviolet, this study was done

to optimize the removal of COD from fresh landfill leachate

using combination of ultrasound and ultraviolet.

5220-D, 5220-B, 4500-NH

pH was measured by Bench Top pH Meters (Cole-Parmer Co.

Ltd.) [25].

and 5310-B, respectively [24]. The

First, the raw leachate sample was filtered by filter paper

(0.45 μm) to remove any suspended solid impurities [23]. The

leachate sample of 1000 ml was placed in a cylindrical glass

vessel [23]. Ultrasound and ultraviolet were used

simultaneously to remove COD. For ultrasonic source used an

ultrasound generator (Model UGMA-5000) with 30, 45, and 60

kHz transducers having 120 w input power and a titanium

probe with 2 cm diameter [17]. UVC lamps (15 W-Philips)

were placed around the glass vessel at a distance of 3 cm to

provide ultraviolet radiation. The influence of UV light power

was tested by application of one, two, and three lamps

corresponding to 15, 30, and 45 W, respectively. The glass

vessel and the light sources were placed inward a black box to

prevent ultraviolet emission [22].

Materials and Methods

All of the main chemical reagent for COD analysis were

prepared from Merck Company (Germany), which included

sulfuric acid (H SO -99 %), silver sulfate (Ag SO -99.9 %),

mercury sulfate (HgSO -99 %), potassium dichromate

Cr -99.9 %), sodium hydroxide (NaOH–99 %),

ammonium chloride (NH Cl-99.8 %), and Potassium hydrogen

phthalate (C KO –99.5 %) [22]. Sample of fresh landfill

Box-Behnken design based on Response Surface Method

(RSM) was applied to analyze and optimize the removal of

(

2 7

COD by different variables, including pH, contact time,

ultrasound frequency and UV intensity on the removal of COD

from fresh landfill leachate [26, 27, 28].

leachate (<10 days old) was obtained Based on EPA guidelines

for sampling leachate from a municipal landfill (>10 years old)

located in Shahroud city (Semnan province, Iran) (Figure 1),

brought to the laboratory in a cold box within 2 h, stored at 4°C,

and tested within a maximum 6 days [23]. The UTM

coordinates (WGS84) of Shahroud are: Zone 40S E: 322121.87

The optimization by response surface reveals the effect of

operating variables and also interactive effects of independent

variables on the response [27, 29]. The coded levels of the

variables were shown in Table 1. Each individual variable was

varied over three levels between -1 and +1 at the determined

ranges [26]. The optimizing experiments were carried out

following a three-level-four-variable Box-Behnken design

based on RSM [26].

5 3

N: 4030834.19. Then, its features such as COD, BOD , NH -

N, TOC and pH were analyzed. COD, BOD, NH -N and TOC

measurements were determined following standard methods

Figure 2: Map of Shahroud municipal landfill

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 861-869

The number of experiments was obtained 29 steps using

equation (1):

3.1 Establishment of the response surface model

The application of response surface offers an empirical

relationship between the independent variables and the

response function [37]. In this research, the response value

푁 = 2퐾(퐾 − 1) + 퐶₀

(1)

(removal efficiency of COD) was fitted by a quadratic model

Where C

is the number of repetitions at the central point

[26], which was shown in equation 3 (in terms of coded

factors):

(C =5) and K is the number of variables studied (K=4) [30, 31].

The data obtained from the BBD experiments were analyzed by

Design Expert 9.0.6 software, and a statistical model with

response surface curves was given [26]. The model could be

described by a second-order regression equation (2).

푌 = 76.98 + 4.ꢁ2푋 + 1ꢁ.98푋 + 14.33푋 + 3.66푋 +

ꢂ

ꢀ

ꢃ

ꢄ

ꢁ.ꢁꢁ푋 푋 − ꢁ.28푋 푋 − ꢁ.5푋 푋 + ꢁ.48푋 푋 +

ꢂ

ꢀ

ꢂ

ꢃ

ꢂ

ꢄ

ꢀ

ꢀ ꢃ

ꢀ

ꢃ

ꢁ.ꢁ25푋 푋 + ꢁ.1푋 푋 + 1.23푋 − 7.9푋 − 8.53푋 −

ꢀ

ꢄ

ꢃ

ꢄ

ꢂ

ꢀ

.69푋_ꢄ

ꢀ

푌 = 푏 + ∑ 푏 푥 + ∑ 푏 푥 + ∑ 푏 푥 푥

(2)

푖

푖푖

푖

푖푗

푖

푗

where Y is COD removal efficiency (%), X

contact time (min), X

is UV intensity (w). Among the coefficients of the variables in

this equation, the coefficient of X has the highest value,

which states ultrasound frequency has the greatest effect on

the model equation.

is pH, X

Where Y is the response value (COD removal efficiency),

and X are the i, jth variable which are called the independent

variable in coded values, b is the offset term (constant), b is

the coefficient of the linear parameter X , bij is the coefficient

, and bii is the coefficient

[32, 26]. Analysis of variance

3 4

is ultrasound frequency (kHz) and X

of the interaction parameters X

of the quadratic parameters X

and X

was done to evaluate the adequacy of the response surface

model and the significance of independent variables and

interaction parameters in the model [29, 26]. All experimental

data are expressed in terms of arithmetic averages obtained

from three repetitions [22]. In the end, the biodegradability

potential of the treated leachate was estimated by the

BOD5/COD ratio, average oxidation state (AOS) and carbon

oxidation state (COS) indices [33, 34].

3.2 Analysis of variance (ANOVA) for response surface

model

ANOVA results of the model presented in Table 3 indicate

that it can be used to navigate the design space [38]. The model

F-value of 1041.96 with a low probability value (P value

<0.0001) in Table 3 implies that the model is significant for

COD removal. Adequate precision indicates the signal to noise

ratio and generally a ratio greater than 4 indicates the model is

desirable [39, 40]. Therefore, in the model of COD removal,

the ratio of 123.585 indicates there is adequate signal for the

model obtained to navigate the design space. The satisfaction

of the fit of the model was checked by the determination

Table 1: RSM design for variable and levels

Level

Variable

Code

coefficient (R ). The closer the R value is to 1, the model is

stronger and it predicts better the removal of COD. The value

of the determination coefficient (R =0.9990 for COD removal)

indicates that 99.9% (COD removal) of the variability in the

response was explained by the model. Also, the value of the

Contact time (min)

adjusted determination coefficient (Radj =0.9981) was very

Ultrasound frequency (kHz)

UV intensity (W)

high for COD removal, showing a high significance of the

model. The adjusted determination coefficient (Radj ) corrects

the determination coefficient (R ) for the sample size and the

number of terms in the model. If there are many terms in the

Results and discussion

model and the sample size is not very large, the Radj value may

Characteristics of the fresh landfill leachate sample were

be noticeably smaller than the R value [39]. In this study, the

Radj value was very close to the R value, which is similar to

COD=4830 mg/l, BOD

=715 mg/l, NH

-N=530 mg/l,

TOC=1130 mg/l and pH of 7.9 derived from the arithmetic

mean of three repetitions. The design matrix in coded units and

the experimental results of COD removal efficiency are

presented in Table 2. The five steps of the experiments are at

the central point (repeatable) to determine the amount of error

the reports by Zhang et al. (2011). In addition, the value of

predicted R is also high to support a high significance of the

model [41]. The predicted R of 0.9949 is in reasonable

agreement with the adjusted R of 0.9981 for COD removal.

[

35]. According to this table, the highest COD removal

efficiency (88%) was obtained at pH=10 (X =1), contact

time=40 (X =0), ultrasound frequency=60 (X =1) and UV

intensity=30 (X =0) that indicate the high ultrasound frequency

3.3 Effect of variables on the response

Figure 2 is showing the effect of the interaction variable

at the response surface. It was observed in Fig.2 (a, b and c),

that the removal efficiency of COD increased with increasing

pH, but the effect of pH is relatively low. Since there are

different types of organic compounds in leachate and the

optimum pH for sonolysis of different organic compounds is

quite different, the optimum pH for sonochemical

decomposition may be different for leachate in different

landfills [42]. Similar results were also observed by Wang et al.

and contact time have a significant effect on the increase of

COD removal efficiency. Wang et al. (2008) in their study

indicated that all studied variables (ultrasound power, pH,

initial concentration and contact time) have a strong effect on

COD removal. But, ultrasound power was the most influential

parameter [36].

(2008).

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 861-869

Table 2: Design matrix in coded units and experimental responses

X3: Ultrasound

frequency

X4: UV

intensity

COD removal efficiency

(%)

Run No.

X1: pH

X2: Contact time

-1

67.6

49.1

34.7

55.8

-1

86.9

76.3

-1

77.4

85.2

55.4

74.5

77.1

59.2

81.9

56.8

52.4

60.7

63.5

77.3

84.6

76.8

76.5

-1

77.2

62.9

80.1

53.4

77.5

-1

The results in Fig.2 (a, d and e) show that contact time

increases COD removal efficiency so far due to the increase of

cavitation of the organic compound. According to this figure,

although the removal efficiency of COD increases but its speed

decreases. The results of this study are consistent about contact

time with the results of Mahvi et al. (2012) study [23]. Figure

at or above the cavity threshold, the bubbles form easily and

the cavities collapse extremely, according to the sonochemistry

theory. Increasing the ultrasonic frequency causes cavitation

energy and the amount of cavitation bubbles to increase. It also

reduces the cavitation threshold limit. In other words, the

higher intensity causes the molecules to be more degraded

because of the higher hydroxyl radical concentration and mass

transfer [43, 44]. Similar results were also observed by Goel et

al. (2004) [45].

(b, d and f) shows the ultrasound frequency significantly

influences on the removal efficiency of COD. Also, the

efficiency of COD removal increases as the increasing of

ultrasound frequency [36]. When the intensity of ultrasound is

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 861-869

Table 3: Analysis of variance for Response Surface Quadratic model

Sum of

Squares

Mean

Square

p-value

Prob > F

Source

Model

A-x1

B-x2

C-x3

D-x4

Value

5111.31

365.09

1041.96

< 0.0001

significant

194.41

1447.60

2465.33

160.60

0.000

0.30

194.41

1447.60

2465.33

160.60

0.000

0.30

554.83

4131.37

7035.91

458.35

0.000

0.86

< 0.0001

1.000

0.3686

0.1133

0.1308

0.9339

0.7405

0.0001

< 0.0001

1.00

2.85

0.90

2.58

2.5E-3

0.040

9.89

2.5E-3

0.040

9.89

7.13E-3

0.11

A²

28.24

1156.07

1346.16

52.87

B²

405.08

471.69

18.53

4.91

405.08

471.69

18.53

0.35

C²

D²

Residual

Lack of Fit

Pure Error

Cor Total

4.42

0.44

3.62

0.1132

Not significant

0.49

0.12

5116.22

R-Squared (R )=0.9990

Adj R-Squared=0.9981

Pred R-Squared=0.9949

Adeq Precision=123.585

Figure 2 (c, e and f) displays an increase in COD removal

efficiency with increase in light intensity. This increase causes

an increase in the reaction rate of photocatalytic degradation of

molecules [9, 46]. This observation was in good agreement

with Jia et al. (2011) study [47].

by aiding ultrasound with additional AOP, such as the UV

process [50]. Mahmuni and Adewuyi (2010) showed that by

combining sonolysis with the additional AOP, the cost of

wastewater treatment could be reduced by 110-fold [51].

Combined methods appear to be the most useful solution for

the treatment of waters containing high loads of complex

pollutants. However, these processes require further

investigation.

.4 Process

Recently, advanced oxidation processes coupled with

cavitation has been used in the treatment of contaminations

48]. The combinations of cavitation with AOPs are listed in

[

3.5 COD removal

the introduction used for the treatment. Cavitation is a good

alternative to the technologies used in wastewater treatment

technologies. But its operating cost is high because of the

energy consumption of ultrasonic generators [49, 48].

Economics has an impact on process suitability for industrial

applications. The results of the research discussed in this study

relate solely to the laboratory scale. Subsequent studies can be

carried out by scaling up the pilot-scale workflow to a real

scenario to evaluate its feasibility in industrial practice.

However, the cost of treatment of wastewater can be reduced

In this study, the optimum value of COD removal

efficiency was determined using the mentioned software. In the

software optimization step, the requested goal for each

operational variable (pH, contact time, ultrasound frequency

and UV intensity) was chosen “within the range”, while the

response (COD removal efficiency) was placed in “maximum”

to achieve the highest performance [29, 28]. This program

combines the individual desirability into a single number, then

searches to maximize this function [28]. A value of one

indicates that all responses are in desirable limits [52].

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 861-869

Figure 2: Response surface displaying effect of interaction of (a) pH×contact time, (b) pH×ultrasound frequency, (c) pH×UV intencity, (d) contact

time×ultrasound frequency, (e) contact time×UV intencity and (f) ultrasound frequency×UV intencity on COD removal efficiency (%)

The results showed the 92.1% removal of COD was

predicted according to the model under optimized operational

conditions (pH=9.2, contact time=54min, ultrasound

frequency=54 kHz and UV intensity=45w). The desirability

function value was 1 for these optimum conditions. In addition,

another experiment was performed to confirm the optimal

results obtained from the software [35]. The removal of COD

was obtained 91.8 from the laboratory experiment that was in

good agreement with the predicted response value. The study

of Gao et al. (2013) has assessed the performances of Fenton,

ultraviolet/Fenton, ultrasound/Fenton and tri-hybrid process to

remove COD from actual pharmaceutical industrial

wastewater. The ultraviolet/Fenton treatment showed a better

COD removal efficiency than using Fenton alone which can be

explained by the fact of synergetic effect. The combination of

ultrasound with 60-minute Fenton oxidation provides greater

COD removal efficiency, 61.1%, than that of ultrasound alone

and Fenton oxidation alone which suggests that the

combination of two individual processes can produce a

synergistic effect. The tri-processes hybrid method can

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 861-869

significantly increase the COD removal efficiency compared to

that of individual and bi-process combination. Increasing UV

exposure time can significantly increase the COD removal

efficiency. The highest COD removal rate, 91%, was found at

the tri-hybrid process with 120 min ultrasound, 90 min UV

irradiation [63]. The paper of Liu et al. (2014) explored the

effects of the Ultrasound/Ultraviolet - Aged Refuse Bioreactor

combined process on aged landfill leachate. The test results

showed that the COD removal effects by ultrasound or

ultraviolet radiation alone were unsatisfactory. But the

for AOS and COS respectively. Thus, both AOS and COS

values significantly increased after treatment by ultrasound and

ultraviolet, confirming that great improvement has been made

in the biodegradability of treated leachate [34, 33]. These

results also depict that the simultaneous use of US and UV, as

a pretreatment, can provide appropriate conditions for the

biological treatment of leachate. In the study of Mahvi et al.

(2012) an ultrasonic process was used for the pre-treatment of

landfill leachate with the objective of improving its overall

biodegradability, evaluated in terms of the BOD5/COD ratio,

up to a value compatible with biological treatment. Under

optimized experimental conditions, this method showed

suitability for the removal of chemical oxygen demand (COD).

The biodegradability was significantly improved (BOD5/COD

increased from 0.210 to 0.786) which allowed an almost total

removal of COD by a sequential activated sludge process [65].

ultrasonic and ultraviolet light has

a complementary

cooperation. The COD removal rate of the combined process

was over 80% as a whole without any pretreatment, and it has

positive significance for the treatment of aged leachate [64].

These two studies also agree with our research on the combined

effectiveness of ultrasound and ultraviolet in the removal of

COD.

Response surface methodology is an important branch of

experimental design and has been applied as an efficient

experimentation technique in a vast range of fields including

food and drug industry, biological and chemical processes, etc

Conclusions

This study shows that the combination of ultrasound

waves and ultraviolet irradiation could effectively remove

COD from fresh landfill leachate. Box–Behnken statistical

experiment design was proved to be a suitable response surface

methodology to determine the effects of operative variables and

their interactions on the removal of COD from fresh landfill

leachate. According to the model, the removal efficiency of

COD was obtained 92.1 % at optimal conditions (pH at 9.2,

contact time of 54min, ultrasound frequency of 54 kHz and UV

intensity of 45 w). The removal efficiency of COD was 91.8 %

in these conditions which agrees well with the predicted

response value. Significant improvement of biodegradability

[53]. It is well known in assessing the effect of parameters on

treatment results [54]. The RSM is efficient to optimize

multiple variables with the minimum number of experiments

by using a set of designed experiments to get an optimal

response [55]. In Box–Behnken design there is not any

embedded factorial or fractional factorial points where the

treatment combinations are at the midpoints of the edges of the

experimental space and in the center [54]. Among all the RSM

designs, Box–Behnken requires a lower number of runs and

allows calculations of the response function at intermediate

levels and enables estimation of the system performance at any

experimental point within the range studied through careful

design and analysis of experiments [56]. In general, BBD can

be an effective approach to: 1) evaluate the performance of

composite systems; 2) analyze the relationship of input with an

output; 3) understand the interaction of parameters; and 4)

optimize the input parameters [57]. Also, due to rotatable

design features, BBD is considered an efficient technique [52].

For instance, Silveira et al. (2015) optimized the effect of

current density, time of treatment, and supporting electrolyte

dosage to the treatment of landfill leachate using BBD model

for treated leachate was observed by BOD /COD as well as

AOS and COS values. This method drastically reduces the

pollution load and reduces the risk of leachate toxicity and even

makes it much easier for natural and biological treatment.

Economics has an impact on process suitability for

industrial applications. The results of the research discussed in

this study relate solely to the laboratory scale. Subsequent

studies can be carried out by scaling up the pilot-scale

workflow to a real scenario to evaluate its feasibility in

industrial practice. Combined methods appear to be the most

useful solution for the treatment of waters containing high loads

of complex pollutants. However, these processes require

further investigation.

[53].

.6 Biodegradability

Acknowledgments

In this study, the biodegradability potential of the treated

The authors would like to thank Ahvaz Jundishapur

University of Medical Sciences for financial support.

leachate was evaluated by BOD /COD ratio, average oxidation

state (AOS) and carbon oxidation state (COS) indices [34, 33].

Characteristics of the treated leachate were: COD=381 mg/l,

BOD

Ethical issue

Authors are aware of, and comply with, best practice in

publication ethics specifically with regard to authorship

=143 mg/l, NH

/COD ratio of the initial leachate was 0.14, indicating that

/COD ratio

-N=165 mg/l and TOC=282 mg/l. The

leachate was difficult to biodegrade. The BOD

(avoidance of guest authorship), dual submission, manipulation

increased to 0.38 after 54 min of treatment by the US and UV.

This means that the treated leachate was much easier to

biodegrade than the initial leachate, which comes from

removing/reducing recalcitrant compounds as well as

producing simple-biodegradable materials [33, 43]. The values

of AOS and COS can be obtained using the following equations

of figures, competing interests and compliance with policies on

research ethics. Authors adhere to publication requirements

that submitted work is original and has not been published

elsewhere in any language.

and 4 [58]:

Competing interests

The authors declare that there is no conflict of interest that

would prejudice the impartiality of this scientific work.

ꢅꢆ퐷

퐴푂푆 = 4 − 1.5 [_푇_ꢆ_ꢅ

]

(3)

(4)

Authors’ contribution

All authors of this study have a complete contribution for

data collection, data analyses and manuscript writing.

ꢅꢆ퐷

푇ꢆꢅꢇ

퐶푂푆 = 4 − 1.5 [

]

The values of AOS and COS in the initial leachate were -

.41. After treatment, these values increased to +1.9 and 3.49

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 861-869

8. Bohdziewicz J, Neczaj E, Kwarciak A. Landfill leachate

treatment by means of anaerobic membrane bioreactor.

Desalination. 2008 Mar 1;221(1-3):559-65.

9. Song K, Mohseni M, Taghipour F. Application of

ultraviolet light-emitting diodes (UV-LEDs) for water

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