Reduction of COD and ammoniacal nitrogen from stabilized landfill leachate by using green mussel and zeolite as composite adsorbent

ABSTRACT

Landfill leachate is a liquid generated due to rainwater percolation through the waste in a landfill or dumping site that may contain high levels of organic matter, both biodegradable and non-biodegradable, which are the major sources of water pollution. Chemical oxygen demand (COD) and Ammoniacal Nitrogen (NH₃-N) contents have been relevant indicators of severity and pollution potential of landfill leachate. The reductions of COD and NH₃-N were investigated in this study using different combinations of media ratios of green mussel (GM) and zeolite (ZEO). Generally, ZEO is considered as a renowned adsorbent but with a relatively high in cost. In Malaysia, mussel shell is abundantly available as a by-product from the seafood industry, is regarded as waste, and is mostly left at the dumpsite to naturally deteriorate. Its quality and availability make GMs a cost-effective material. In this research study, leachate samples were characterized and found to contain high concentrations of COD and NH₃-N. The adsorption process was conducted to find out the best combination media ratio between GM and ZEO. The removing efficiency was determined at different amounts of composite media ratios. The optimal adsorbent mixture ratios between (GM: ZEO) of 1.0:3.0 and 1.5:2.5 were considered as a more efficient technique in removing COD and NH₃-N compared to exploiting these adsorbents individually. The optimal extenuation removal reduction was found at an approximately 65% of COD and 78% of NH₃-N. The adsorption Isotherm Langmuir model exhibited a better fit with high regression coefficient for COD (R² = 0.9998) and NH₃-N (R² = 0.9875), respectively. This means that the combination of GM: ZEO adsorption of landfill leachate in this analysis is homogeneous with the monolayer. The mixture of GMs and ZEO was observed to provide an alternative medium for the reduction of COD and NH₃-N with comparatively lower cost.

Implications: The concentration of organic constituents (COD) and ammoniacal nitrogen in stabilized landfill leachate have significantly strong influences of human health and the environment. The combination of mixing media green mussel and zeolite adsorbent enhancing organic constituents (COD) and ammoniacal nitrogen reduction efficiency from leachate. This would be greatly applicable in future research as well as conventionally minimizing high cost materials like zeolite, thereby lowering the operating cost of leachate treatment.

Introduction

Landfilling is the most efficient method and a widely used technique for organizing waste disposal in most countries. It is the most economical and environmentally acceptable technique for eliminating and disposing of municipal and industrial solid wastes (Bashir et al. 2012; Daud et al. 2016; Naveen and Malik 2019; Sharma and Katoch 2019). The leachate is generally characterized by an elevated concentration of dissolved organic matters (chemical oxygen demand, COD), inorganic macro constituents, halogenated hydrocarbons, ammonia, xenobiotic organic substances, suspended solids, and a substantial concentration of heavy metals in addition to inorganic salts (Bashir et al. 2012). Leachate is discharged directly into the atmosphere, becaming percolate into soil and subsoil, posing serious threats to humans and the ecosystem. If inadequately managed, the landfill leachate may become the source of hydro-geological pollution. Therefore, over the recent decade, the reduction of pollutant has become the most important concern in the treatment of leachate (Naveen and Malik 2019). There are several factors that influence the characterization of leachate from landfills, i.e., landfill age, hydro-geological site, climate and season, quantity and quality of waste, rainwater precipitation and percolation, landfill conditions, landfill’s morphology, biology and chemical processes occurring at landfill site, depth of waste, and operation facilities (Sharma and Katoch 2019). Stabilized or old landfill leachate characterization has a (less biodegradability) ratio that is difficult to proceed biologically. Variations of biodegradable ratio (BOD₅/COD) in landfill leachate were categorized to different groups of landfill leachate according to landfill age and decomposition of leachate. In general, the biodegradability ratio of young leachate (< 1 years), intermediate leachate (1–5 years) and stabilized leachate (> 5 years) as reported are 0.5–1.0, 0.1–0.55, and <0.1, respectively (Alvarez‐Vazquez, Jefferson, and Judd 2004). Table 1 shows characteristics of leachate versus the age of landfill (Li, Zhou, and Hua 2010).

Table 1. Characterization of leachate at different age of landfills (Li, Zhou, and Hua 2010)

Type of leachate	Unit	Young	Intermediate	Old
Age		<5	5–10	>10
pH		<6.5	6.5–7.5	>7.5
COD	(mg/L)	>10,000	4,000–10,000	<4,000
BOD5/COD		0.5–1.0	0.1–0.5	<0.1
Ammoniacal nitrogen	(mg/L)	<400	N. A	>400
TOC/COD		<0.3	0.3–0.5	>0.5
Heavy metal	(mg/L)	Low to medium	Low	Low
Biodegradability		Important	Medium	Low
Organic Compounds		80% volatile fatty acids	5%-30% VFA + Humic and fulvic acids	Humic and fulvic acids

Adsorption is relatively a physiochemical technique widely used for stabilized landfill leachate treatment. Adsorption is basically a process of mass transferring substance from liquid to solid surface and to become bounded by physical-chemical interactions. Nowadays, focus have been increasing since the usage of low cost material (e.g., natural polymer or agricultural waste and industrial process by product) to achieve adequate leachate treatment as an alternative approaches to the conventional adsorbent for the treatment of water because of its availability locally and eco-friendly material. Application of zeolite (ZEO)-based adsorbents has certain advantages over conventional method used for treating the water. ZEO typically hydrated mineral aluminosilicate that belong to tectosilicates minerals and porous material (Latiff and Rahman 2016). ZEO has an advantage of natural – VE charge which allows it to adsorb cation. ZEO have potential as an efficient adsorbent in various treatment process of drinking water (Lakdawala and Patel 2015), reduction of ammoniacal nitrogen, color, dissolved organic matter, heavy metal from landfill leachate (Aziz et al. 2010; Rosli et al. 2017), and many others.

It is noted that the mixture of green mussel (GM) and ZEO has been used effectively for the reduction of COD and ammoniacal nitrogen from leachate (Aziz et al. 2010; Rosli et al. 2017). The utilization of GM and ZEO mixture in the application of leachate treatment is not well known. Author (Rosli et al. 2017) reported that the composite materials have been produced to many applications, like improvising the adsorption property or producing cost effective adsorbent. In accordance to the above studies, the combination of two minerals improves the adsorption property and reduce treatment costs by partial replacement of ZEO with GM. This study explores the impact of GM and ZEO mixing ratio against the reduction of COD and ammoniacal nitrogen. This was obtained by identifying the optimum composition of the adsorbate medium using batch technique. In addition, adsorption capacity was analyzed using Langmuir and Freundlich isotherm models. Therefore, the finding results will be used in evaluating the pattern of reduction of each parameter in leachate.

The aim of this present research study, leachate was characterized and checked its concentration of COD and ammoniacal nitrogen. Adsorption was performed to determine the combination of different media ratios between GM and ZEO. The removing efficiency was determined at different amounts of composite media ratios for removing concentration of COD and ammoniacal nitrogen.

Materials and method

Site location

The research study was carried out on leachate samples that were collected from the Simpang Renggam Landfill Site (SRLS) found at lat. 10 53ʹ 41.64” N and lon. 1030 22ʹ 34.68” E in Kluang district, Johore, Malaysia. A total land area of SRLS is distributed approximately 6-hectares, and the aerated logoon technique method is used for the treatment of leachate. The SRLS is operated over 12 years and about 250 tonnes of waste is collected from three designated regions namely Simpang Renggam district, Kluang district, and Batu Pahat district, respectively (Bashir et al. 2012; Le and Le 2019).

Landfill Leachate Sampling

The leachate sample has been taken manually into 30-L high density polyethylene plastic container (HDPE) from (SRLS) according to the procedure guidelines described in standard Water and Wastewater Examination Method (Standard Methods for the Examination of Water and Wastewater 2012). The collected samples of leachate were immediately transported to the laboratory and preserved for experimental purposes in a cold storage room at room temperature, preventing deterioration or minimizing further characterization changes. In this study all chemical analyses for leachate characterization were of analytical grade. The leachate characterization are presented in Table 2.

Table 2. Characterization of leachate obtained from SRLS

Parameter	Unit	Minimum	Maximum	Average	MEQA (1974) (Environmental Quality 2010)
pH	-	7.65	8.27	7.96	6.0–9.0
SS	mg/L	316	367	341.5	50
NH3-N	mg/L	404.07	406.68	405.37	5
COD	mg/L	1,595	1,829	1,712	400
Color	-	4685	4788	4,736.5	-
BOD5	mg/L	140	163	138.66	20
BOD5/COD	-	0.07	0.08	0.07	-

Preparation of adsorbents

Green mussel and zeolite adsorbent is used in this study. Green mussel were collected from Ceria Maju Restaurant located in Parit Raja, Johor and zeolite were purchase from PT. Anugerah Alam Sdn. Bhd at a rate of  RM4000 and RM400 per ton, respectively” (Aziz et al. 2010; Rosli et al. 2017; Zukri et al. 2018). The preparation was carried out in accordance with the procedure mentioned in (Aziz et al. 2010; Rosli et al. 2017). The adsorbent density media has been calculated conventionally (i.e., mass by media volume). Both GM and ZEO has been ground to achieve particle size <150 µm using ceramic ball mill.

Optimum ratio

In this analysis of research study, the optimum mixing ratio of GM: ZEO was determined by varying media ratio (by weight) based on the previous research studies. The total weight of mixing media used was 4.0 g for each volumetric glass. For the experimental purpose, the mixing ratios of GM: ZEO used were 0.0:0.4, 0.5:3.5, 1.0:3.0, 1.5:2.5, 2.0:2.0, 2.5:1.5, 3.0:1.0, 3.5:0.5, and 4.0:0.0. The static batch experiment was conducted at the combination of a fixed media ratio (as mentioned above) with 100 mL sample of leachate in a 250 mL volumetric glass shaken for 120 minutes with 200 rpm shaking speed at pH7 (Daud et al. 2020a, 2020b; Detho et al. 2021). The optimum mixing ratio of GM: ZEO was evaluated, which revealed optimal reduction of COD and NH₃-N parameters. For the experimental run, three replicates were performed for each sample, and the average result was utilized. The reduction percentages of parameters were determined using the following Equation (1)(1) $\mathrm{E}\left(\mathrm{\%}\right)=\left[\left(C_i-{\mathrm{C}}_{\mathrm{f}}\right)/C_f\right]\times 100$(1) :

(1) $\mathrm{E}\left(\mathrm{\%}\right)=\left[\left(C_i-{\mathrm{C}}_{\mathrm{f}}\right)/C_f\right]\times 100$(1)

where $C_i$ is the initial concentration and $C_f$ is the final equilibrium concentration and leachate in mg/L, respectively.

Adsorption equilibrium

The isotherm model experiment was conducted by contacting 4.0 g of the GM: ZEO adsorbent in 250 mL Erlenmeyer flask with 100 mL of varying leachate concentrations (100 to 10 degrees dilution) allowing adequate time, 2 hours adsorption equilibrium. The rates of adsorbed GM: ZEO were determined by mass balance Equation (2)(2) $q_e=\frac{\left(Co-Ce\right)V}{m}$(2) based on the following formula:

(2) $q_e=\frac{\left(Co-Ce\right)V}{m}$(2)

whereas q_e denotes adsorption equilibrium sorption capacity (mg/g), C_o denotes initial concentration, C_f denotes final equilibrium concentration of COD and NH₃-N in (mg/L), m denotes mass of adsorbent GM: ZEO in (g), and V denotes leachate volume (Lit). In order to define the relation between COD and NH₃-N amounts, Langmuir isotherm and Freundlich isotherm models were applied.

Adsorption isotherm models

Equilibrium data from adsorption experiment for COD and NH₃-N results were investigated in relations with Langmuir isotherm and Freundlich isotherm adsorption models (Halim and Mohd 2013).

The conventional parameters of the Langmuir isotherm equation was found suitable for the experiment results to the linear isotherm equation derived from Equation (3)(3) $\frac{1}{q_e}=\left[\frac{1}{q_m{K}_L}\right]\frac{1}{C_e}+\frac{1}{q_m}$(3) :

(3) $\frac{1}{q_e}=\left[\frac{1}{q_m{K}_L}\right]\frac{1}{C_e}+\frac{1}{q_m}$(3)

The parameters of q_m and K_L have been derived from a linear plot of 1/q_e versus 1/C_e, which gives slope as 1/q_e and intercept as 1/C_e, respectively.

The parameters of the Freundlich model equation was found suitable for the experiment results to the linear isotherm equation derived from Equation (4)(4) $ln{q}_e=ln{K}_F+\frac{1}{n}ln{C}_e$(4) :

(4) $ln{q}_e=ln{K}_F+\frac{1}{n}ln{C}_e$(4)

The parameters of $K_F$ and $\mathrm{n}$ were derived from a linear plot of lnq_e versus $\mathrm{l}\mathrm{n}{\mathrm{C}}_{\mathrm{e}}$, which gives slope as and intercept as $ln{K}_F$, respectively.

According to the prediction of adsorption capacity and the adsorption favorability process, the equilibrium dimensionless parameter was identified as separation factor ($R_L$). The $R_L$ was calculated using Equation (5)(5) $R_L=1/1+K_L{C}_o$(5) .

(5) $R_L=1/1+K_L{C}_o$(5)

For separation factor ($R_L$), four numbers of probabilities values indicate the nature of adsorption: ($R_L$=0) as irreversible; ($R_L$=1) as linear; (0 <$R_L$<1) as favorable; and ($R_L$>1) as un-favorable (Halim and Mohd 2013).

Leachate analysis

COD analysis was conducted by using Model HACH DR6000 spectrophotometer according to the procedure described in the standard method (Standard Methods for the Examination of Water and Wastewater 2012). Meanwhile, NH₃-N analysis was conducted by using Nessler’s method, using the Model HACH DR6000 spectrophotometer. All experiments were conducted in triplicates to obtain consistent results at room temperature 25 ± 2°C.

Results and discussion

Leachate characteristics

Many previous research studies described variations of leachate qualities from different landfills (Aopreeya et al. 2013). Leachate characteristics utilized in this study were shown in Table 2. The leachate has a high volume of NH₃-N and COD, as seen in the Table 2. The average value of COD and BOD₅ are (1829 mg/L) and (163 mg/L), respectively. The raw leachate has a biodegradability ratio (BOD₅/COD) that ranges from 0.07 to 0.08 with an average of 0.07, as shown in Table 2. The results show that the value of COD and BOD₅ demonstrate that the leachate was clearly stabilized. The physicochemical properties of the composite adsorbents (GM and ZEO) have been presented in Table 3.

Table 3. Physicochemical characteristics of composite adsorption media

Physio-chemical properties of composite media
Specific gravity (g/cm^3)	2.45
BET Surface area (m^2/g)	95.95
Porosity (%)	57.40
Water absorption (%)	52.62
Methylene blue number (mg/g)	7.97
Iodine number (mg/g)	21.93
Cation Exchange Capacity (meq/g)	0.80

Stabilized leachate has high concentration of COD (<3,000 mg/L) and NH₃-N (>400 mg/L) but low concentration of BOD₅/COD (Aziz and Mojiri 2014). The pH concentrations of leachate range from 7.65 to 8.27 with an average of 7.96, and it was increasing usually with time (Aeslina et al. 2014). A previously published study described that the concentration of pH of a stabilized leachate was higher than 7.5 (Foo and Hameed 2009; Moideen et al. 2020).

Optimum ratio

Effect of different ratio toward COD

Figure 1 shows COD reduction efficiency against varying ratio of GM and ZEO. The use of ZEO as a single media resulted in the reduction of COD at 39.48% with an intensity value of 1140 mg/L from stabilized leachate. The use of GM as a single media with a mixing ratio of (4.0:0.0 g) was producing very low results of 30% COD reduction as compared to the ZEO mixing ratio (0.0:4.0 g) as a single adsorbent. Both adsorbents have various mixing ratios. The lowest ratio of ZEO which achieved the greatest reduction of COD was known as optimal mixture. The obtained result indicated that the ideal optimum mixing ratio of GM: ZEO was 1.0:3.0 g. It consisted of 25% GM and 75% ZEO, whereas the reduction of COD remain unchanged (although ZEO percentage increases) with the reduction of COD at 65%. In another words, 25% of ZEO was replaced by GM at the maximum reduction of COD.

Figure 1. Reduction Percentage of COD against varying ratio of green mussel and zeolite

Effect of different ratio toward NH₃-N

According to Figure 2, the lowest ratio of ZEO that achieved the highest reduction of NH₃-N was considered as the optimal mixture. A mixture of GM: ZEO adsorbent with a media ratio of 1.5:2.5 g resulted in a reduction of NH₃-N at 78% with an intensity value of 4,748 mg/L. This optimal mixture consisted of 37.5% of GM and 62.5% of ZEO. The reduction percentage of NH₃-N remained unchanged although ZEO percentage increased. In other words, approximately 37.5% of ZEO was replaced by GM at the maximum reduction of NH₃-N, while the use of GM as a single media with a mixing ratio of (4.0:0.0 g) produced a very low result with 48% of COD reduction.

Figure 2. Reduction percentage of NH₃-N against varying ratio of green mussel and zeolite

Adsorption isotherm

As presented in Figures 3 and 4, Langmuir adsorption isotherm data better fits the model as compared to Freundlich adsorption. The regression coefficient (R²) value in terms of Langmuir adsorption for COD (0.9998) and NH₃-N (0.9875) shows higher results as compared to Freundlich adsorption for COD (0.9849) and for NH₃-N (0.9663). This indicates that the adsorption of both parameters onto GM: ZEO experienced adsorption of monolayer to a homogeneous surface in adsorption equilibrium (affinity). The maximum uptake capacities (${\mathrm{q}}_{\mathrm{m}}$) of COD and NH₃-N are shown in Table 4.

Table 4. Langmuir and Freundlich adsorption isotherm parameters

Isotherm (Langmuir) COD	${\mathrm{R}}^2$	${\mathrm{q}}_{\mathrm{m}}$	${\mathrm{K}}_{\mathrm{L}}$
	0.9998	3.72$\times {10}^{-2}$	6.22$\times {10}^{-4}$
Isotherm (Langmuir) NH3-N	R^2	$\mathrm{n}$	${\mathrm{K}}_{\mathrm{F}}$
	0.9875	1.44	4.82$\times {10}^{-4}$
Isotherm (Freundlich) COD	${\mathrm{R}}^2$	${\mathrm{q}}_{\mathrm{m}}$	${\mathrm{K}}_{\mathrm{L}}$
	0.9849	8.37$\times {10}^{-3}$	3.2$\times {10}^{-3}$
Isotherm (Freundlich) NH3-N	${\mathrm{R}}^2$	$\mathrm{n}$	${\mathrm{K}}_{\mathrm{F}}$
	0.9663	172.4	1.25$\times {10}^{-4}$

Figure 3. Isotherm models for COD reduction (a) Langmuir and (b) Freundlich

Figure 4. Isotherm models for NH₃-N reduction (a) Langmuir and (b) Freundlich

In the present study, the value of $\mathrm{n}$ was higher than the unity that indicates the process of adsorption was highly favorable under study condition (Aziz et al. 2010; Aopreeya et al. 2013).

Conclusion

In this present research study, the experimental results show that the combination of GM and ZEO possessed an ability for the reduction of COD and NH₃-N from leachate. It was found that the optimum mixing ratio of the adsorbent of GM: ZEO was at 1.0:3.0, which shows the maximum reduction of COD at 65%, while the optimum mixture ratio of 1.5:2.5 shows the maximum reduction of NH₃-N of 78%. It was observed from the equilibrium data that the Langmuir--Freundlich isotherm models was better fitted to the results. The adsorption capacity obtained for COD and NH₃-N indicates that the potential use of GM: ZEO for the adsorption process. For further research, therefore, it is proposed that kinetic adsorption is taken into consideration to examine the adsorption process of COD and NH₃-N on GM: ZEO.

Acknowledgment

The authors would like to express their gratitude to Ministry of Higher Education Malaysia, Universiti Tun Hussein Onn Malaysia under Research Fund E15501, Research Management Centre (RMC) UTHM, and Quaid-e-Awam University of Engineering, Science & Technology (QUEST) Nawabshah, Sindh, Pakistan.

Disclosure Statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Amir Detho

Amir Detho works as a Lab Engineer at Energy & Environment Engineering Department, Quaid-e-Awam University of Engineering, Science & Technology, Nawabshah, Pakistan. He received his Bachelor of Engineering (Mechanical Engineering) in the year 2010 and Master of Engineering (Energy & Environment Engineering) in the year 2018 from Quaid-e-Awam University of Engineering, Science & Technology Nawabshah, Sindh, Pakistan. He is currently pursuing Ph.D. in Faculty of Civil Engineering and Built Environment, Universiti Tun Hussein Onn Malaysia. His current research interest includes landfill leachate/water and wastewater treatment technology. He is a registered member of the Pakistan Engineering Council (PEC).

Zawawi Daud

Zawawi Daud works as an Associate Professor at Faculty of Civil Engineering and Built Environment, Universiti Tun Hussein Onn Malaysia. Dr. Zawawi received his Ph.D. in Civil Engineering (Environment) from Universiti Sains Malaysia in 2009. Dr. Zawawi’s research focuses on alleviating problems associated with water pollution issues from industrial wastewater and landfill leachate. His latest interest is on natural adsorbent material in water and wastewater treatments.

Mohd Arif Rosli

Mohd Arif Rosli is currently a lecturer in the Faculty of Engineering Technology, Universiti Tun Hussein Onn Malaysia. His current research interest includes landfill leachate/water and wastewater treatment technology, building services and performance; water, air, noise and indoor environmental quality. Mohd Arif holds a Ph.D. degree in Civil Engineering from Universiti Tun Hussein Onn Malaysia. He is a member of The Clean Air Forum Society of Malaysia (MyCAS).

Halizah Awang

Halizah Awang received the Ph.D. in Educational Curriculum from Universiti Sains Malaysia in 2010. Since January 2011, she has been with Faculty of Technical and Vocational Education, Universiti Tun Hussein Onn Malaysia as an Associate Professor. Her research focuses on Curriculum and Instruction in Technical and Vocational Education and Training (TVET), Job and career development in TVET and teaching and learning in TVET.