Treatment of Landfill Leachate using Granular Multi-Stage Anaerobic Reactor: Optimisation through Response Surface Methodology

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 567-572

J. Environ. Treat. Tech.

ISSN: 2309-1185

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

Treatment of Landfill Leachate using Granular

Multi-Stage Anaerobic Reactor: Optimisation

through Response Surface Methodology

Aida Batrisyia Jasni , Shreeshivadasan Chelliapan , Mohd Fadhil Md Din and Nithiya

Arumugam²

School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Skudai, 81310, Johor, Malaysia

Department of Engineering, Razak Faculty of Technology and Informatics, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, 54100 Kuala Lumpur,

Malaysia

Centre for Environmental Sustainability and Water Security (IPASA), Research Institute for Sustainable Environment, Universiti Teknologi Malaysia,

Skudai, 81310, Johor, Malaysia

Received: 16/09/2019

Accepted: 11/02/2020

Published: 20/05/2020

Abstract

One of the most hazardous sources of pollution these days is landfill leachate. This harmful wastewater is not only affecting the

environment, but also the health of beings surrounding the landfills. Numerous treatments have been used to treat this recalcitrant wastewater;

however, anaerobic treatment has been in focus in recent years. In this study, we investigated the interactive effects of chemical oxygen

demand (COD), leachate percentage and pH on the performance of a granular multi-stage anaerobic reactor (GMSAR) treating landfill

leachate. Response surface methodology (RSM) was utilised to project the interaction effects of the operating conditions of the treatment

system in terms of COD removal and biogas yield. The optimum region of the GMSAR was acquired at influent COD of 1239 mg/L, a

leachate percentage of 14.2% and a pH of 7.3. These variables resulted in a 71.9% COD removal and 65.9mL/d of biogas yield. The

percentage of leachate and COD influent resulted respectively in the most effective parameters on the COD removal and biogas yield of

GMSAR.

Keywords: Landfill leachate, Anaerobic treatment, Multi-stage anaerobic reactor, Response surface methodology, Biogas yield

(

3). Leachate formed from water runoff at landfill often causes

Introduction¹

pollution to the soil, groundwater and surface water (4). Leachate

enters the surroundings from the bottom of the landfill through

unsaturated soil stratum and flows to the groundwater and

eventually to surface water via hydraulic connections. The

discharge of treated or raw leachate from the treatment facility

may also taint the environment and affect public health (5).

.1 Landfill leachate

Most of the developing countries are facing a major problem

in terms of waste disposal. The disposal of municipal solid waste

MSW) by dumping or burying it in a designated site is called

(

landfilling. This, however, does not solve the problem as it

basically transfers the MSW from urban areas to landfills (1). The

disposal and improper management of MSW in landfills provide

the opportunity for toxic substances in MSW to degrade into a

liquid form called landfill leachate. Generally, landfills can be

classified into five levels which are levels 0, I, II, III and IV. Table

Table 1: Classes of landfill sites in Malaysia (6, 7).

Level

Type of Landfill

Open Dumping

Controlled tipping

shows the classifications of landfill sites in Malaysia. Out of

58 landfills nationwide, only 17 sites are categorised as sanitary

III

Sanitary landfill with bund and daily cover

Sanitary landfill with leachate recirculation system

Sanitary landfill with leachate treatment facilities

landfills whereas the rest of the sites are classified as unsanitary

landfills. Level II is regarded as a semi-sanitary landfill due to the

absence of leachate treatment facilities (2). The first two levels of

landfills are the most worrisome as the numbers of these type of

landfills are the highest in the country. These landfills are today’s

main cause of groundwater pollution as they do not have any layer

of protection to keep the leachate from seeping into the ground

Leachate is liquid rich in organic matter which can be

distinguished by its colour, mainly brownish or viscous black.

The quality of the leachate is influenced by several determinants

such as age, precipitation, weather variation, waste type and

Corresponding author: Aida Batrisyia Jasni, School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Skudai,

1310, Johor, Malaysia; E-mail: aida@civil.my.

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 567-572

composition, depending on the lifestyle of the surrounding

population and tip structure. Kurniawan et al. (8) mentioned that

the composition of the landfill leachate depends greatly on the age

of the leachate. As the harmful chemical substances found in

leachate vary, they resulted in the increment of COD value,

making them difficult to treat. The high COD value which not

only contains organic matter but also inorganic matter requires a

very intricate treatment system to treat the landfill leachate.

and statistical tool, is applied for process modelling and

optimisation studies (19). RSM has been extensively used in

various studies as the design of experiment (DOE) and

optimisation tools in anaerobic digestion (18–22). There is no

information available on literature to the extent of the author’s

knowledge, on the treatment of landfill leachate using a stage

granular anaerobic reactor. Therefore, this study used a unique

four-stage granular multi-stage anaerobic reactor (GMSAR) for

the treatment of landfill leachate, focusing on the COD removal

and biogas yield. RSM was applied as a statistically based DOE

to study the effects of COD influent, percentage of leachate and

pH on the removal of COD and biogas yield. The optimal

operating parameters for the COD removal and biogas yield were

determined.

.2 Stage anaerobic treatment

Various landfill leachate treatment methods have been studied

such as physical, chemical and biological which consist of aerobic

and anaerobic treatments. Recent years have shown a grown

interest in the area of anaerobic treatments (9–11). Anaerobic

digestion is a process carried out by microorganisms that are able

to live in an oxygen-deprived environment. The disintegration of

organic substance happens in four stages: hydrolysis,

acidogenesis, acetogenesis, and methanogenesis.

Materials and Methods

.1 Wastewater characteristics

In terms of the feed substrate, this study used a mixture of meat

In pursuance of optimising the environment in the reactor for

the anaerobic bacteria and to boost the specific conversion

reactions, physical separation is added in the sludge bed of a

staged anaerobic treatment reactor. According to Lier et al. (12),

studies have been conducted for the treatment of carbohydrate

wastewater under mesophilic conditions by segregating the

anaerobes involved in anaerobic digestion. The convenience of

staging in this study is accredited to the high sludge yield of the

carbohydrate fermenting bacteria. As the carbohydrate is

fermented or pre-acidified in the first stage, a high volumetric

fraction is passed on to the next stage for the methanogens to

increase the methane yield of the anaerobic treatment system (12).

The advantage of a staged anaerobic treatment system is also

supported by Zhao et al. (13) who agreed that the anaerobic

treatment is enhanced and needed only half of the amount of

biomass in the conventional treatment system to double the

activity of the anaerobes in the staged treatment system.

Intanoo et al. (14) mentioned that the arrangement of a stage

anaerobic reactor provides an ideal surrounding for the

breakdown of intermediates such as propionate, which is

beneficial both in mesophilic and thermophilic treatment

conditions. However, the type and sequence of stages should be

thoroughly studied in the preliminary stage to select the optimum

arrangement for a specific application. Nasr et al. (15) applied a

staged process in an up-flow anaerobic sludge bed (UASB)

reactor which resulted in a more stable thermophilic treatment

system. Very low volatile fatty acids concentration and low

hydrogen partial pressure were obtained in the last compartments.

The simplest arrangement of a staged anaerobic reactor can be

achieved by arranging two or more up-flow reactor in series. In

recent years, an integrated staged reactor comprising of vertically

and horizontally oriented reactor has been introduced in order to

enhance the plug flow pattern and spatial biomass separation

and yeast extract for a start-up. In anaerobic treatment, the start-

up of the reactor is an important phase for the stabilisation of the

reactor. The substrate used for the reactor stabilisation is crucial

in determining a successful start-up process. Various substrates

have been used by researchers in order to smoothen and reduce

the time taken for the start-up process. Most of the researchers

used glucose as their substrate during the acclimatisation period.

Though the glucose initially showed a good result in removing

COD, the performance of the reactor deteriorated as the pH levels

of glucose decreased abruptly (23–25). There are several

researchers who used a different substrate for the start-up process

such as meat extract (26). The characteristics of the meat extract

are suitable for the start-up process as it contains vitamins, fats,

carbohydrates, and protein. However, the COD removal was only

2% which was quite low (27). A study conducted by Zupancic

et al. (28) revealed that yeast extract is a good co-substrate which

enhances the biomethane production of wastewater. Therefore,

this study used a mixture of meat and yeast extracts as substrates

during the start-up and acclimatisation period. This combination

of both meat and yeast extracts is theoretically able to increase the

performance of the reactor during the start-up process in terms of

COD removal and biogas yield. The feed used in this study is a

matured landfill leachate supplied by Worldwide Landfill Sdn

Bhd, Jeram, Selangor. The characteristics of the leachate are

given in Table 2. The start-up of the GMSAR was accomplished

using a mixture dilution of Bovril soup stock and yeast extract and

the ingredients are shown in Table 3.

Table 2: Characteristics of matured leachate

Results

8.0

Units

Temperature

COD

26.0

2500

486

°C

mg L^-¹

(16,17).

mg L^-¹

_m_g_L-1

The efficiency of anaerobic treatment is further increased by

BOD @ 20°C

providing the optimal conditions for wastewater treatment.

Nonetheless, the optimisation process is conducted in an obsolete

way where a parameter is changed while the others are kept

constant, which is too resource-consuming (18). To overcome this

problem, response surface methodology (RSM), a mathematical

Total Suspended Solids

Ammoniacal Nitrogen

220

mg L^-¹

(AN)

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 567-572

Figure 1: GMSAR configuration

2.2 Reactor configuration

Table 3: Ingredients of meat and yeast extract

Ingredients

Yeast Extract

Protein

Carbohydrates

Fat

Weight per 100 g

The GMSAR consisted of a working volume of 11.2 L and

equipped with sampling ports at 15 cm from the base that allowed

biological solid and liquid samples to be withdrawn from the

sludge bed (Figure 1). The influent wastewater entered through a

38.4 g

19.2 g

0.1 g

.7 cm internal diameter downcomer tube in the head plate that

extended to within 55 cm of the reactor base and allowed feed to

flow upward through the sludge bed. A temperature controller and

heater strip were installed to retain the temperature at 37°C.

Peristaltic pumps were used to control the influent feed rate to the

GMSAR (Masterflex L/S, Easy Load II Pump Head). The

GMSAR had anaerobic granular sludge as the sludge blanket.

Fiber

Sodium

3.1 g

4.3 g

Thiamine

Riboflavin

Niacin

Folic acid

Vitamin B12

Meat Extract

Protein

5.8 mg

7.0 mg

160.0 mg

2500 μg

15.0 μg

.3 Experimental procedure

The start-up of GMSAR lasted for 36 days. Initially, the reactor

13.3 g

was inoculated with the granular sludge with 40% of the reactor's

effective volume and then filled with tap water. After that, the

GMSAR was left for about 8 days for the acclimatisation of the

reactor. During the start-up of GMSAR, the feed was prepared

using 30 ml of meat and yeast extract mixture and 18 L of tap

water which gave a COD value of 300 mg/l. The pH profile of the

reactor during the start-up showed stable performance at an

average pH of 7.0, which confirmed that the reactor had a suitable

pH level. As for the COD removal efficiency, the removal

efficiency gradually increased to 90% and the leachate was

gradually introduced into the feed for the treatment of landfill

leachate.

The main objective of this study is to optimise selected variable

factors including COD, percentage of leachate, and pH to evaluate

the performance of the process by analysing COD removal and

biogas yield as responses. As the variables concerned were only

three, RSM was applied in the design of experiment using the

Carbohydrates

Fat

Potassium

Sodium

24.4 g

0.1 g

1200 mg

3510 mg

Anaerobic granular sludge was used to seed the GMSAR. The

utilisation of anaerobic granular sludge as the seed sludge in the

present study was due to the efficient methane yield and pollutant

removal as reported by Lu et al. (29). The anaerobic granular

sludge contained a total suspended solid of 46,730 mg/L and

4,940 mg/L of total volatile suspended solids. The reactor was

filled with tap water to the working volume. Subsequently, the

reactor was flushed with nitrogen gas to displace residual air in

the system before introducing the feed. The reactor was allowed

to stabilise at 37°C for 24 hours for 7 days without further

modification.

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 567-572

two-level full factorial design (FFD). In the two-level FFD, the

number of experiments is 2 , where k is the number of variables.

Table 4 represents the value of factors in the experiment and the

responses accordingly.

and 85.19% of the variability in the COD removal and biogas

yield responses respectively. Kainthola et al. (31) stated that the

statistical model with R value in the range of 0.75 – 1 shows that

it is the best fit model. Adequate precisions in Table 5 measured

the signal to noise ratio and a value of more than 4 was desirable.

Adequate precision of the models was adequate as the values were

12.9235 and 8.3882 respectively. According to the model, the

effect on each factor on the removal of COD was the percentage

of leachate > pH > COD influent. On the other hand, the COD

influent affected the biogas yield the most.

Table 4: The experimental plan of GMSAR and its raw

responses result.

Factors

Responses

COD Percentage

Influent of Leachate pH

COD

Removal

(%)

Biogas

Yield

(mL/d)

11.2

84.23

27.35

16.2

Run

(

mg/L)

1239

270

1239

270

(%)

7.3

6.6

7.3

6.6

7.3

89.7

5.12

80.2

23.5

77.8

90.7

12.8

Table 5: ANOVA results for responses

Sum of

squares

Mean

square

Source

F-value p-value

COD Removal

Model

A-COD

1239

270

8662.44

2165.61 26.20

467.87 5.66

0.0114

0.0977

67.87

Influent

270

B-Percentage

of Leachate

C-pH

079.31

7079.31 85.65

0.0027

.4 Analytical methods

To assess the efficiency of the GMSAR, the COD was

537.59

577.66

0.9722

537.59

577.66

6.50

6.99

0.0839

0.0774

measured based on the Standard Close Reflux Method using a

HACH COD reactor described in the Standard Methods (No.

Adjusted R 0.9351

220) (APHA, 2005) while the biogas yield was determined using

Predicted R 0.8021

an optical bubble counter (30).

Adeq

2.9235

Precision

Biogas Yield

Model

Results and Discussions

3796.95

944.51

1898.47 14.38

2944.51 22.31

0.0084

0.0052

0.0518

.1 Statistical analysis

A-COD

Influent

C-pH

The FFD method was chosen to attain the correlation between

the manipulating parameters and the process responses. Table 4

shows the operating parameters involved (COD influent,

percentage of leachate and pH) in terms of absolute units and the

experimental data collected for the process responses (COD

removal and biogas yield). In this study, eight experimental runs

were performed by FFD in accordance with Table 4. The number

852.43

0.8519

852.43

6.46

Adjusted R 0.7927

Predicted R 0.6209

Adeq

Precision

.3882

of runs was determined using formulae 2 , where k is the number

of factors. The experimental results were then subjected to

response surface analysis to investigate the interactive effects of

parameters COD influent (A), percentage of leachate (B) and pH

3.2 COD removal and biogas yield

In this study of landfill leachate treatment using GMSAR, B,

AB, C and A were ascertained as significant model terms for the

COD removal. Percentage of leachate (B) had the highest effect

on COD removal with an F-value of 7079.31 followed by the

interaction between COD influent and percentage of leachate, pH,

and COD influent with F-values of 577.46, 537.59 and 467.87,

respectively.

The percentage of leachate played the biggest role in the

removal of COD in this configuration of the anaerobic treatment

system. As seen in Table 4, the COD removal decreased

tremendously as the percentage of leachate injected into the stock

solution increased. This result is corresponding to a study by

Berenjkar et al. (32), whereby it was observed that the removal of

COD decreased significantly with the increment of leachate into

sewage sludge. The response surface plot for the relationship

between the factors on the efficiency in removal of COD is shown

in Figure 2. As can be seen, the COD removal decreases as the

percentage of leachate increases. Though the COD influent was

low, the high percentage of leachate in the stock solution reduced

the removal of COD. This is consistent with the results of the

variance analysis (Table 5). A high COD removal may have been

(

C) on each factor. The regression model for the COD removal

and biogas yield in coded terms, respectively, are as follows:

COD Removal = -0.001754A -2.86536B + 23.42143C +

.001169AB – 76.88524

Eq. (1)

Eq. (2)

Biogas yield = 0.039598A + 29.49286C – 198.47919

Eqs. (1) and (2) were figured out to attain the optimum value

of each of the operating parameters to maximise the COD removal

and biogas yield in the anaerobic treatment of landfill leachate

using GMSAR. The adequacy and significance of the

mathematical regression model were determined by analysis of

variance (ANOVA). The results of the ANOVA are exhibited in

Table 5. The F-value of the model for COD removal was 26.20,

while the F-value for the biogas yield model was 14.38 which

implied that both the models were significant. There were only

.14% and 0.84% of chance, respectively, that the F-values this

large could occur due to noise. The R value of 0.9722 revealed

that these particular mathematical models could explain 97.22%

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 567-572

prevented by the toxicity of the landfill leachate itself which

inhibited the acclimatisation of the microorganism to the

recalcitrant wastewater (3).

Figure 3: Surface plot of effects of COD influent and pH on the biogas

yield

Conclusions

In this research, the GMSAR was found to be effective in

biologically treating the landfill leachate. The RSM data showed

the significant and interactive effects of the variables, COD

influent, percentage of leachate and pH on the COD removal and

biogas yield of the treatment. The results of the experiments

revealed that GMSAR had the capability of treating the heavily

polluted landfill leachate. The optimum conditions of the

GMSAR were obtained at COD influent = 1239 mg/L, leachate

percentage of 14.2% and pH at 7.3, at which the COD removal

efficiency and biogas yield were 71% and 65 mL/d.

Figure 2: Surface plot of effects of COD influent and percentage of

leachate on COD removal

Figure 3 displays the surface plot of the interaction of factors,

COD influent and pH, on the biogas yield of this configuration of

the landfill leachate treatment system. The most significant model

term for the biogas yield was the COD influent which had an F-

value of 2944.51, followed by pH with an F-value of 852.43. As

discerned in Table 4 and variance analysis, the percentage of

leachate did not affect the biogas yield. The largest contributor to

the biogas yield was the COD influent. The higher the COD

influent, the higher the biogas yield. The pH level also contributed

to the amount of biogas yielded as the microorganism worked best

in a near-neutral condition. The highest collection of the biogas

yield in this study was recorded at 84 mL/d when the COD

influent was 1239 mg/L and the pH was 7.3. The stages of

GMSAR were for a better separation of acidogenesis and

methanogenesis which theoretically, would be able to yield a high

amount of biogas. However, the methanogens in the

methanogenesis phase grew very slowly which reduced the

consumption of volatile fatty acids (VFA), products from the

acidogenesis stage. This resulted in the accumulation of VFA and

inhibited the production of biogas (33, 34). This is similar to this

study in which the biogas yield could be considered in the average

region in comparison to the other types of anaerobic treatment

system of landfill leachate (35,36).

Acknowledgement

The journal editorial board thanks the following reviewers to

review this article. The authors would like to thank Universiti

Teknologi Malaysia and Razak Faculty of Technology and

Informatics for funding this research. The research was carried

out using Vote Number Q. K130000.3040.01M17 and Q.

K130000.2540.20H05.

Ethical issue

The authors are aware of and comply with the best practices

in publication ethics specifically with regard to authorship

(avoidance of guest authorship), dual submission, manipulation

of figures, competing interests and compliance with policies on

research ethics. The authors adhere to publication requirements

that submitted work is original and has not been published

elsewhere in any language.

.3 Process optimisation

An experiment was conducted in the optimised condition as

Competing interests

The authors declare that there is no conflict of interest that

would prejudice the impartiality of this scientific work.

predicted by the model to validate its accuracy and the

experimental data corresponded to the prediction of the model

(

Table 4). Under these optimal conditions (COD influent = 1239

Authors’ contribution

All authors of this study have a complete contribution for data

collection, data analyses, and manuscript writing

mg/L, leachate percentage = 14.2% and pH = 7.3), the maximum

COD removal and biogas yield were obtained as 71% and

5mL/d, respectively. These results validated the accuracy of the

model as the responses were comparable to the predictive values.

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 567-572

rotating disc electrocoagulation on cadmium removal: Parameter

optimization and response surface methodology. Sep Purif Technol.

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