Characteristics and Pollution Potential of Leachate from Municipal Solid Waste Landfills

Abstract

Landfill leachate occurs as one of the by-products of waste deterioration. It is the mineralization of pollutants within the waste stream which gives rise to a very concentrated, dark and toxic chemical mix, depending on the type of waste disposed, age of dumpsite and climatic conditions of the site. Leachate is generally collected at the bottom of the landfills, in unlined landfills, leachate usually migrates through the underground strata and may travel down to the groundwater table. Some lateral migration of the leachate is also possible depending on the surface and subsurface geology. The migrating leachate can dissolve soluble chemicals, many with toxic constituents that may result in soil and water resources pollution. Hence proper leachate management procedures should be developed and incorporated into the design of landfills.

9.1 Introduction

Uncontrolled waste dumps in municipalities of developing nations/cities have in recent times given rise to various forms of nuisance such as rodents’ proliferation, air pollution (odor), soil pollution (percolation/infiltration) as well as water pollution (overland flow) [1]. The open dumping of municipal solid waste in landfills is one of the oldest and most common disposal methods adopted in most of the countries, particularly developing ones [2] Landfill leachate is generated when rainwater percolates through the waste layers in a landfill, in which process organic and inorganic constituents of the waste get dissolved, transported and deposited at the bottom of the landfill by gravity [3] Some of the components of landfill leachate may be categorized as a water-based solution of four groups of contaminants dissolved organic matter, inorganic macro-components, heavy metals, and xenobiotic organic compounds [4]. The most important potential environmental concern associated with landfill is the formation of leachate and the subsequent contamination of soil and water resources [5, 6]. A landfill leachate may be regarded therefore as an enormously contaminated solution comprising of both organic and inorganic components emanating from a direct deposition of solid waste in a landfill. Landfill sites therefore poses a direct threat to the soil, ground and surface water resources as a result of the leaching effects of contaminants from municipal solid wastes deposited on it. This effect is determined by the landfill's age, climatic conditions, and the sort of waste generated as a result of the residents’ lifestyle [1]. Jagloo [7], said that there are three essential attributes that distinguish any source of water resources contamination, the degree of localization, the loading history, and the kind of contaminants emanating from them. According to Al Sabahi and Abdul Rahim [5], the primary problem associated with landfills is the formation of leachate and eventual contamination of water sources and soil because of contaminant migration.

A landfill is a point source of environmental pollution, it can also be a non-point source of surface water pollution. The loading history describes how the concentration of a contaminant or its rate of production varies as a function of time at the source. Leachate rates at a landfill site are controlled by seasonal factors or by a decline in source strength as components of the waste such as organics, biodegrade. The sorts of waste put in the landfill, the amount of precipitation in the area, and other site-specific circumstances all influence leachate composition [7].

Through interactions within the hydrologic cycle, a leachate contaminated environment can have an impact on soil, ground and surface water quality. In a hydrologic continuum, groundwater and surface water are connected by their transitional zone, and contamination of one frequently affects the other [8].

9.2 Landfill By-Products

Initially, the biochemical reactions in a landfill take place under aerobic condition (where oxygen is the terminal electron acceptor), producing carbon dioxide (CO₂) as the principal gas. As most of the available oxygen (O₂) is depleted, decomposition reactions continue under partial aerobic to mostly anaerobic conditions, where the principal landfill gases generated are CO₂, methane (CH₄), trace amounts of ammonia (NH₃), and hydrogen sulfide (H₂S) [9].

The two main by-products generated during the life of a landfill are leachate and landfill gases. The composition and amount of leachate and gas generated varies spacio-temporily depending on the nature of waste and design of the landfill. This utilization of leachate and landfill gases are dependent on the associated management system that is needed for proper functioning of a sanitary landfill.

9.3 Formation of Leachate Plume

Infiltration from precipitation is caused by gravity to move leachates through the landfill, to the bottom and sides, and through the underlying soil until it reaches the groundwater zone or aquifer. Some of the key processes of leachate formation are presented below, (see Fig. 9.1).

Fig. 9.1

Process of leachate formation [10]

Immediately after solid waste materials are deposited in disposal sites, the process of stabilization begins. This process, which forms the leachate within the site, occurs mainly through physical, chemical and biological processes. These processes brings about four key stages which include hydrolysis of solid waste, biological degradation of organic waste, solubilization of soluble salts contained within the waste mass and the transportation of waste as colloids or particulate matter [11].

As leachate is transported to the sides and base of the landfill through gravity, a percentage of it spreads across the surface of nearby soils which in excess, negatively affects available farmlands. Some part of the remaining leachate migrate to receiving surface water sources through runoffs from landfills that causes overland flows that finally ends up polluting sources of surface water. The rest leachate gets through the subsurface by infiltration and percolation, then mixes with groundwater held in soil voids forming a plume of contaminated groundwater that moves along the groundwater’s flow pattern.

The leachate toxins initially reach the unsaturated zone before being transferred to the saturated zone's groundwater table, resulting in groundwater pollution that can later affect other water sources due to the geologic formation.

9.4 Leachate Composition and Effects on the Environment

As a heavily contaminated “black chemical soup”, landfill leachate comprises both organic and inorganic components that originate directly from deposited solid waste materials. It is known generally to contain significantly more contaminant loads than raw sewage or many industrial wastes [12]. Below is a pictorial view of a typical landfill leachate collected in depression at the base of Yenagoa central waste dump site, Bayelsa State, Nigeria (Fig. 9.2).

Fig. 9.2

A typical leachate collected in a depression at a landfill in Bayelsa State, Nigeria

The relative quality of leachate varies widely depending on a series of complex but interrelated factors. Table 9.1 presents some of the organic and inorganic leachate constituents.

Table 9.1 Leachate parameters [12]

Leachate contains a host of toxic and carcinogenic chemicals, which may cause harm to both humans and environment as shown in Table 9.2. Furthermore, contaminated water from leachate can have a negative impact on domestic, industrial and agricultural activities that rely on it. Irrigating with contaminated water reduces soil productivity, brings about contaminated crops, and potentially moves hazardous pollutants up the food chain as animals and humans consume crops grown in contaminated water [7]. It can take years before groundwater pollution reveals itself and chemicals in the leachates often react synergistically and often in unexpected ways to affect the ecosystem but as for soil and subsurface water are concerned, leachate effects are immediate.

Table 9.2 Health effects of landfill leachate (EPA 2003)

9.5 Effects of Leachate on Water Quality (Surface Water and Ground Water)

According to Omole [13], the number one source of contamination of water resources, particularly ground water comes from leachates generated from wastes of industrial origin deposited in a landfill. Leachates from non-hazardous waste in a landfill can also contain organic compounds, chlorinated hydrocarbons and metals of various concentrations which could pose a danger to both surface and ground water resources.

The quantity of leachate produced in a landfill and its subsequent impact on the environment is essentially dependent on the metrological and hydrological factors governing the area in addition to the waste disposal methods. According to Chapman [14], the volume of leachate generated is consequently expected to be excessively high in humid regions with high rainfall or high runoff and shallow water table Previous researches have noted that most landfills have high levels of BOD, COD, Ammonia, chloride, sodium, Potassium, Hardness and Boron with respect to the time and age of the landfill because its conditions often vary from aerobic to anaerobic thus allowing different chemical processes to take place [15].

9.6 Effects of Leachate on Soil and Farmlands

Recently, leachate contamination and subsequent pollution of soils and farmlands has been on the table of global environmental discuss. Figure 9.3, shows the adverse effects of landfill leachate on nearby soil which affected an Okra farm beside an uncontrolled municipal waste dump site. The picture shows the early stages of leachate effects of crops wilting on the farmland occasioned by the spread of leachate across the parcel of land. Therefore, the part encircled in red was the most affected at the time of this evidence.

Fig. 9.3

A picture showing the early stages of leachate effect of an okra farm close to a dumpsite

A closer view of the effects of landfill leachate pollution on a farmland is shown in Fig. 9.4. While Fig. 9.5 shows a researcher/farmer in a landfill leachate polluted Okra farm. The figure shows the advanced stages of leachate pollution and its wilting effects on the crops.

Fig. 9.4

A closer look at the early stages of leachate effect of an okra farm close to a dumpsite

Fig. 9.5

Advanced stages of landfill leachate pollution of an okra farm close to a dumpsite

9.7 Health Effects of Environmental (Water Resource) Contamination

Water has remained the most abundant and most important resource of man, every life depends on it for various reasons. It has prided itself over the years as the source of life on planet earth without which nothing survives. Plants need it for their uptake of minerals and nutrients, animals need it for drinking and bathing while humans need it for drinking, bathing, agriculture, industrial purposes, transportation, recreation, dust suppression etc.

Water covers about 71% of the earth surface yet many people throughout the earth have faced grave challenges of the lack of portable drinking water in which the Niger Delta is not an exemption.

Water needed by humans for consumption is by all means expected to meet the needs of potability, which means water must be odorless, colorless and tasteless. From a biological standpoint, water has many distinct properties that are critical for the proliferation of life. It helps to transport oxygen throughout the body, lubricate joints and helps to increase metabolic activities etc. The human body contains from 50 to 75% of water depending on the body size [16]. This means that an intake of polluted water will directly affect the human body system.

When foreign elements enter the water column, or when the minerals found in water exceed the acceptable amount, the water is said to be contaminated; water pollution describes the presence of materials in water that interfere unreasonably with one or more beneficial uses of water [17]. When this happens, some health concerns are raised, health hazards arising from waste management and disposal associated activities and their ability to pollute surface and ground water consequently need to be analyzed specifically for the conditions in a given setting.

Pollution takes place when pollutants are directly or indirectly introduced into the water bodies without adequate treatment to remove the harmful compounds. This has remained a source of concern to environmental stakeholders. According to Anne [16], the polluted ground water has an effect on the food chain, health and human environment. She stressed that both women and children are victims of pollution and that over 40,000 children die from disorders and other epidemic diseases everyday due to poor waste disposal. She pointed out that waste is an environmental disaster that also causes aesthetic decay. There are different sources of water pollution ranging from agricultural practices, releases from industries and waste management to say a few.

9.8 Impact of Landfill Leachate and Public Outcry

Migration of hazardous materials into nearby water resources is often a vital environmental concern in subject of landfill sites, which may represent a public health problem, especially when a site is located near aquifers supplying public drinking water. Landfill sites may be a source of airborne chemical infection via the off-site migration of gases and through particles and chemicals adsorbed in dust, especially during the period of active operation of the site [18]. Therefore, people residing within the vicinity of these sites are exposed to cases of landfill leachate interference with their everyday lives. In the early 1980s, pollutants from leaking underground storage tanks (USTs) were found to be affecting some drinking-water wells in the Santa Clara Valley area. Two of these wells were studied and discovered that Chlorinated solvents had leaked from an underground waste storage tank impacting negatively on the residents living near one of the contaminated wells who reported a cluster of adverse pregnancy outcomes, mainly spontaneous abortions and congenital heart defects [19]. A first investigation confirmed a significant excess of cardiac anomalies in the service area of the water company that operated the contaminated well compared to those among residents of an unexposed area. The excess was found within the potentially exposed time period and not in an unexposed time period after the well was closed.

More so, leakages from an industrial dump of chemical waste drums in New Jersey caused contamination of groundwater and well water with organic chemicals (including benzene, toluene, trichloroethylene, and lead) [20]. It was found that there were higher prevalence of respiratory diseases and seizures among the people living in a high-exposure area estimated on the basis of groundwater flow patterns. The people dwelling in these high-exposure areas used private drinking-water wells, eat homegrown food, and smoked more often than populations living in unexposed areas, and whilst these factors were adjusted, variations in health outcomes disappeared.

The Love Canal, New York State is another important issue to take into account when planning a landfill. During the 1930s and 1940s, large quantities of toxic materials (residues from pesticide production) were dumped at the landfill which was followed by the building of houses and a school on and around the landfill in the 1950s. By 1977 the site was leaking and chemicals were observed in neighborhood creeks, sewers, soil, and indoor air of houses. This caused one of the most well-known and publicized incidents of environmental pollution from landfill. Exposure of Love Canal citizens, although not well understood, may have occurred via inhalation of volatile chemicals in indoor air or via direct contact with soil on playgrounds or surface water [21]. The drinking water supply was not contaminated. Chemicals detected at Love Canal were primarily organic solvents, chlorinated hydrocarbons and acids, consisting of benzene, vinyl chloride, PCBs, dioxin, toluene, trichloroethylene, and tetrachloroethylene. Several researches had been carried out to detect whether Love Canal residents suffered adverse health effects. A cross-sectional study observed an increased incidences of seizures, learning problems, hyperactivity, eye irritation, skin rashes, abdominal pain, and incontinence in children living close to the Love Canal site compared to controls from other areas, as reported by the parents of the children, as noted in previous reviews [22].

Bringing it closer home, the Koko incident of June 1988 is yet another sad tale when issues of waste disposal, particularly hazardous waste are considered. Little wonder [23], stated that Nigeria responds to most environmental problems on an ad-hoc basis. According to him, the discovery of toxic waste dumps in Koko, a remote part of southern Nigeria in June 1988 and its attendant media and public outcry prompted the government to react swiftly. This informed the formation of the Federal Environmental Protection Agency 1988 (FEPA). It latter translated to the further formation of Harmful Waste (Special Criminal Provision) Act, 1988 to deal specifically with illegal dumping of harmful waste.

9.9 Different Methods of Landfill Leachate Treatment

Since leachate is made up of a complex mixture of organic and inorganic constituents, treatment methods will be according to the composition of landfill leachate. The removal of organic matter is the general premise of leachate treatment, including chemical oxygen demand (COD) removal, biological oxygen demand (BOD) removal and ammonia nitrogen removal [24]. Before the leachate is discharged into the natural water body, toxicity analysis should also be carried out by testing various organisms. At present, there are three kinds of convenient methods for leachate treatment: leachate transfer method, biodegradation method and physical and chemical method [25].

9.10 Case Study: Typical Landfill in Bayelsa State, Nigeria

9.10.1 Description of the Study Area

The study area was situated within the lower floodplain of the Niger Delta. The terrain is poorly drained with a gentle syncline to the Gulf of Guinea in a southwestern direction [26]. It is characterized by sedimentary formations with a thickness of about 8000 m. It includes Akata Formation, Agbada Formation, Benin Formation, from bottom to top, which is Oligocene to Pleistocene in age. It consists predominantly of freshwater continental friable sands and gravel that are excellent aquifer properties, with occasional intercalation of shales [27]. The Niger delta has two basic hydrological regimes which are Coastal and Inland [2] (Fig. 9.6).

Fig. 9.6

Map of Nigeria showing Bayelsa State

The landfill is specifically located off Edepie-Amassoma road, Etelebu in Yenagoa Local Government Area of Bayelsa State, and operated by Bayelsa State Environmental Sanitation Authority. As at the time of this study, the site which began operations from around 2008 had an average life span of about 11 years. The landfill also had a height of about 2 m and covers a total area of about thirty-six kilometers square (36 km²). The hydrogeological condition of the landfill site was consistent with the regional hydrogeological setting of Port-Harcourt area as depicted by [28]. A pictorial view of the landfill is presented in Fig. 9.7.

Fig. 9.7

An image showing a pictorial view of the waste dump

The waste dump was unlined and serviced wastes generated from the Yenagoa municipality which include industrial, agricultural, institutional, commercial and domestic wastes, as well as sewage.

9.10.2 Study Objectives

The aim of the study was to access the impact of a waste dump site on the quality of surface water in a nearby stream within the study area. The specific objectives were to;

• Evaluate the characteristics of surface water from a nearby stream consequent upon waste disposal.

• Determine the variation in the physico-chemical and biological properties of the surface water sampled at Downstream point (SW 1), Central point (SW 2) and Upstream point (SW 3) of the stream.

• Compare the levels of contaminants from collected samples with standard acceptable limits, ie Nigerian Standard of Drinking Water Quality (NSDWQ) and World Health Organization (WHO).

• Ascertain the possible source of surface water pollution using correlational analysis.

• Discuss the potential adverse effects of ingesting or coming into daily contact with water from the stream.

Having regular contact with surface water from sources near municipal waste dump sites and possible ingestion of same, could result in endangering the individual as it has the potential to contain contaminants washed into it from the dumpsite.

9.11 Data and Methodology

9.11.1 Sample Collection

The study area was described using Geographic Information System (GIS). Every sampling point was picked with the help of a standard Global Positioning System (GPS). To determine the degree of surface water pollution, three surface water samples were taken around the dumpsite and labeled Downstream Point (SW 1), Central Point (SW 2) and Upstream Point (SW 3) respectively. Two samples were taken at the landfill’s Northernmost and Southernmost ends, while the third sample was taken at the center of the nearby stream, which provided inhabitants with protein (fish) and other forms of livelihood (Table 9.3).

Table 9.3 Details of sampling sites

At each sampling location, surface water samples were taken with the help of clean 1.5L plastic bottles after initially rinsing the bottles with same water to be taken. Non-conservable parameters such as pH, temperature and electrical conductivity were determined in-situ. The pH of water samples was measured with a pH meter previously calibrated with buffer solutions. Conductivity was measured with a conductivity meter calibrated with potassium chloride solution. Temperature was measured with a thermometer [29].

After collection, the samples were immediately placed in iced coolers for transportation to the laboratory and stored in refrigerator. The water quality parameters dealt with were physical, chemical and biological characteristics [30] and were analyzed in accordance with standard laboratory methods [29]. The parameters were; pH, Electrical Conductivity (EC), Total Dissolved Solids (TDS), Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Total Hardness (TH), Ammonium (NH4⁺), Sulphate (SO₄²⁻), Nitrate (NO₃⁻), Phosphate and Heavy Metals such as Cadmium (Cd), Chromium (Cr), Copper (Cu²⁺), Lead (Pb), Zinc (Zn), Calcium (Ca²⁺), Magnesium (Mg²⁺), Sodium (Na⁺), Iron (Fe²⁺) and Potassium (K⁺) ions, as well as Total coliform count.

In this study, a total of three surface water samples were taken for laboratory analysis. The three samples were analyzed for, Physico-chemical and microbiological characteristics. The variations of parameters from sampling points SW 1, SW 2 and SW 3 as compared with Nigerian Standard of Drinking Water Quality (NSDWQ) and World Health Organization (WHO) [31, 32] are shown in Table 9.2. The table also presents some descriptive statistics of the surface water parameters analyzed.

9.12 Result and Discussions

The average concentration of parameters and their standard deviations as presented in Table 9.4 of the three samples analyzed showed that EC, TDS, TA, TH and Phosphate had higher average concentrations as compared to the NSDWQ and WHO standards. The average concentrations were 1533.33µS/cm, 766.67 mg/l, 339.53 mg/l, 260 mg/l and 2.95 mg/l respectively. Standard Deviation of these parameters were 824.58, 412.29, 175.97, 10 and 3.94. Similarly, parameters such as DOD, COD, Fe, K and Total plate count also indicated higher average concentrations as compared to the standard acceptable values. The average concentrations were 15.33 mg/l, 18 mg/l, 4.73 mg/l, 36.49 mg/l and 2,673,333.33 mg/l. While the Standard Deviations were 1.15, 6.56, 4.32, 30.83 and 202,319.88 respectively.

Table 9.4 Summary of special variation and descriptive statistics of surface water parameters

Figures 9.8 and 9.9 showed the percentages of the Physico-chemical and microbial characteristics of the surface water samples analyzed during the sampling period.

Fig. 9.8

Percentage composition of surface water parameters within the sampling points

Fig. 9.9

Percentage composition of some metals and microbial load of surface water within the sampling points

All the sampled parameters showed variations across the sampling points. It was observed from the chart above that the values for pH of the surface water samples ranged from 6.96 to 7.18, but were within the WHO recommended range. The EC which ranged from 852 to 2450 µS/cm and Total Dissolved Solid (TDS) with range from 426 to 125 mg/l showed similar trends. They both had higher percentages of values that were greater than the regulatory standards at the Downstream (SW 1) and the Central point (SW 2). Concentration of Sulphate (SO₄²⁻), Nitrate (NO₃), Phosphate (PO₄³⁻) and Ammonium (NH₄) also showed similar patterns. They all had the same concentrations at the Upstream point (SW 3) and Central point (SW 2), however, the values at the Downstream point (SW 1) were higher. When compared with NSDWQ and WHO standards, they fell within permissible limits except phosphate. Total Alkalinity, BOD, COD and Total Hardness values ranged between 193.5–534.9 mg/l, 14–16 mg/l, 12–25 mg/l and 250–270 mg/l respectively. When compared with the regulatory standards, it was observed that they were all above WHO standards except for the TA value at the Upstream point (SW 3). The higher BOD₅ and COD values indicate the presence of organic matter in water [4].

Summarily, the surface water analysis across the Downstream point (SW 1) showed that parameters such as pH, EC, TDS, TA, TH, Na, K, Fe, BOD, COD, Phosphate and Total Coliform Count, recorded 7.18, 2450 μS/cm, 1225 mg/l, 534.9 mg/l, 270 mg/l, 122.92 mg/l, 69.42 mg/l, 9.48 mg/l, 25 mg/l, 16 mg/l, 7.5 mg/l and 2.80 X 10⁶ cfu/ml respectively. All these values were above NSDWQ and WHO recommended values for drinking water except pH. All the heavy metals in the surface water analyzed (Pb, Cu, Zn, Cd, and Cr) in this study were below instrument detectable limits (BDL) [4]. However, the microbial load within the surface water sampled at all points indicated a huge population much more than the acceptable NSDWQ and WHO standards for potability. The high concentration of parameters in the three surface water samples showed that the surface water was contaminated and poses a threat to those who access it for their needs.

Pearson's correlation was also used to obtain the common sources of contaminants within the samples of surface water analyzed. This was done to identify if the waste dump was indeed responsible for the presence of these contaminants within the stream. The correlation matrices for 18 measured variables during sampling analysis are illustrated in Table 9.5.

Table 9.5 Pearson’s correlation for surface water analysis using microsoft excel

A perfect positive correlation between TDS and EC (r = 1, p ≤ 0.01), NH₄ and NO₃ (r = 1, p ≤ 0.001) and PO₄³⁻ and NO₃ (r = 1, p ≤ 0.001) was observed and this meant that they had exactly the same contributor which could be mud and putrescible wastes brought in by the infiltrating rain water and organics [4].

The strong positive correlation between EC and pH, TDS and pH, TA and EC, TA and TDS, COD and EC (r = 0.98, p ≤ 0.01) signified that they had nearly the same contributors (the dissolved ions). A significant negative correlation was also observed between TA, COD, Fe, Mg, K, Na and SO₄ (r = − 0.9615, − 0.92447, − 0.92447, − 0.97246, − 0.92518, − 0.93204) respectively, indicating the opposing distribution of these pair variables.

9.13 Summary and Conclusions

When compared to samples from the Central Point (SW 2) and Upstream Point (SW 3) sampling locations, the Downstream Point (SW 1) samples had higher concentration of parameters. However, some metals and heavy metals were below equipment detectable limits for all sampled locations. It was confirmed therefore that SW 1, was the most contaminated among the three sampled surface water points, in this study. The microbial load within all the samples greatly exceeded the recommended WHO and NSDWQ standards for drinking water. The Pearson’s correlation results also showed that some pollutants analyzed came from the same source.

Since the stream was the main resource that provided protein (fish) to nearby residents and other local farmers who came in contact with the water daily, its contamination may lead to a serious dislocation of the ecological balance. This may also result to a potential threat of bioaccumulation of pollutants as a result of fishers ingesting their catch and having dermal contact with the microbes infested water daily.

Therefore it was recommended that siting of landfills should be done after a proper study of the environment by policy makers since landfills had been confirmed to contribute contaminants into the environment. The surface water sources within landfills should also be properly monitored to avoid ingestion of contaminated water.