dorcas gora AES360 final draft

Heavy metal leaching from ash and soil from an unsanitary waste dump 2014

ABSTRACT

Heavy metal leaching from unsanitary solid waste dumps has potential to cause groundwater and soil pollution. Despite the researches done, the relationship between leaching of pollutants from solid waste dumpsites and groundwater pollution is still unclear. This study was aimed at assessing the leaching potential of zinc, lead, nickel and cadmium from the University of Zimbabwe waste dump and effect of pH of leaching solution. It was found that fresh ash, old ash and soil beneath the waste dump had significantly higher concentrations of heavy metals leaching than the control indicating that they could be sources of ground water contamination. The mobility of the cations was dependent on the pH of leaching solution and decreased with increasing pH for Zn, Pb and Ni. Cd however, increased its mobility in old ash with increasing pH. Heavy metals leached were below the WHO limit values for hazardous waste: 10 mg/l for Ni, 3 mg/l for Pb, and 50 mg/l for Zn with the exception of Cd, 0.3mg/l in fresh ash. This implies Cd leaching may be a cause for concern as it may affect surrounding soil and groundwater quality. It may thus be recommended that the waste dump is lined to minimize leaching of Cd. Detailed characterization of materials and retention mechanisms in different materials may be conducted in further research to assess leaching of these heavy metals from an unsanitary waste dump.

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CHAPTER ONE: INTRODUCTION

1.1 Background

Unsanitary disposal of solid waste is predominant in developing countries such as Zimbabwe and poses serious threats to the environment. Zimbabwe’s population is increasing rapidly and thus ultimately waste generated annually is increasing. Zimbabwe generates an average of 2.5 million tons of solid waste annually (TARSC, 2007). Currently solid waste is being disposed of in non-engineered landfills which are not properly lined, unsanitary and overloaded. This poses a threat to the soil and ground water as the risk of leaching of contaminants like heavy metals, is heightened. Air pollution from landfill emissions, health problems due to breeding of disease causing pests and social problems such as decreasing land values and aesthetic appeal of an area, are some associated problems. Typically, the solid waste dumps consist of domestic, organic, electronic, industrial, clinical, agricultural and other types of wastes.

In Harare, the capital city of Zimbabwe, many of these open pits are located near residential areas. The major dumpsites such as the Pomona dumpsite are not even designed for their purpose. There are just mere landfills in which waste is disposed of in. Landfills have been identified as one of the major threats to quality of groundwater water (Fatta et al., 1999; US EPA, 1984). The absence of containment systems at the sites allows the possible percolation of leachate into groundwater (Aderemi and Falade, 2012). Leachate is liquid containing innumerable organic and inorganic compounds which accumulates at the bottom of a landfill and percolates through the soil. Leachability is an indication of potential migration or mobilization of contaminants from solid waste by moving water or infiltrating water. The leachate generated will have the tendency to move in a downward motion through the underlying soils (UNEP, 2005).

The environmental problem posed by heavy metals is that they are non-biodegradable like organic waste and have toxic effects on living organisms when exceeding a threshold concentration (Esakku et al., 2003). Areas close to landfills have a greater possibility of groundwater contamination because of the potential pollution source of leachate originating from the nearby dumpsite. Groundwater forms as a part of the natural water cycle present in aquifers. This contamination of groundwater resource poses a considerable risk to local resource users and the natural environment (Mor et al, 2005). This is particularly important in Zimbabwe where both rural and urban populations are dependent on groundwater for drinking and domestic uses.

Several studies have been done on the leaching behavior of heavy metals. Examples include Buy et al, (2003) investigated the leaching behavior of magnesium phosphate cements containing high quantities of heavy metals and their environmental implication on groundwater quality. Robinson (2009) and Wiles (1996) stated that e-waste is a major source of leachable Pb, Ni, Hg, Cd. Hjelmar (1990) and Bosshard et al (1996), carried out studies on municipal incineration ash and found out that metals present in the leachate decrease as the number of pores increase with the average percentage of leachable toxic metals. Also the impact of fly ash on ground water seems to be mainly dependent on site conditions. Wasay (2005) studied the leaching characteristics of Cr (III), Cr (VI), Hg (II) and as of a fly ash sample at various pH values and found 40% of these toxic elements in the leachate at pH 7.0. Johnson et al (1996) studied the

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leaching behavior and solubility controlling solid phases of heavy metals in municipal solid waste incinerator ash.

Despite the researches done, the relationship between leachability of pollutants from solid waste

dumpsites and groundwater pollution is still unclear. Most of these studies were carried out in developed countries where proper landfills and incinerators are available. By comparison, there is limited reliable information specific to developing countries on heavy metal and nitrate leachability from waste dumps (UNEP, 2005).Therefore, this study seeks to investigate the leaching of heavy metals from solid waste dumps using column and batch experiments.

1.2 Problem Statement and Justification

Zimbabwe produces approximately over 2.7 million tons of solid waste annually (TARSC, 2010) and has currently no properly engineered dumpsite for disposal of solid waste. This is mainly due to several economic constraints such as lack of capital, personnel and reliable information applicable to the nation (UNEP, 2005). Due to lack of properly designed sanitary landfills, the bulk of which is disposed of in unsanitary dumpsites which could potentially cause environmental problems like groundwater pollution. The bulk of solid waste generated in Zimbabwe is disposed of in unlined waste dumps which could potentially cause environmental problems like groundwater pollution.

However, the impacts of the leachable heavy metals on groundwater quality are still poorly understood. Information on leachability of heavy metal and nitrate content from solid waste dumpsites will facilitate the development of suitable remedial measures (Esakku et al., 2003). It is thus important to assess leaching of heavy metals which are major components of urban solid waste. Although a few studies have investigated the leachability of heavy metals in developing countries, limited information is available. Although there is existing research on urban solid waste management in Zimbabwe which stretches over a decade, limited information on environmental problems such as soil and ground water contamination by leaching of heavy metals associated with poor waste disposal (Tevera, 1991 and Mandimutsa, 2009).

The study site which is the University of Zimbabwe dumpsite is located at the main campus which is surrounded by the Mt pleasant and Alexandra Park residential areas. Due to water supply issues in the city of Harare, most residents have drilled boreholes as sources of water. This is also the case with the university which accommodates over 5000 students and staff members. Thus the threat of contamination of ground water by leachate from the dumpsite poses serious public health risks. Therefore this study seeks to investigate the leaching of and heavy metals from the University of Zimbabwe solid waste dump and the results will help pollution remediation and reduction measures as well as designing of sanitary landfills.

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1.3 Hypotheses

1.3.1 Soil and ash from solid waste dumps has significantly higher concentrations of leachable heavy metals than the control

1.3.2 Leaching of heavy metals in ash and soil is significantly related to the pH of the leaching solution.

1.4 Objectives

1.4.1 Main Objective

The main objective of the study is to investigate the leaching of heavy metals from unsanitary solid waste dumps and its dependence on pH of leaching solution

1.4.2 Specific Objectives

To investigate the leaching of heavy metals from soil and residual ash from a solid waste dump.

To evaluate the effect of pH of leaching solution on the leaching of heavy metals from soil and ash from a solid waste dump

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CHAPTER TWO: LITERATURE REVIEW

2.1 The Problem of Waste Generation Solid waste is mainly generated from households and industrial activities. Thus whenever people exist, waste must be generated and managed either fully or partially (Taylor et al, 2006). The EPA (1972) defines solid waste as useless, unwanted or discarded material with insufficient liquid content to be free flowing. Truthfully, there are no ways of dealing with waste that have not been known for many years. Principally, incineration, source reduction, recycling, composting and landfills are usually common. The site onto which solid wastes are often dumped include valleys, old quarries sites, excavations, or a selected portion within the residential and commercial areas in many urban settlement where the capacity to collect, process, dispose of, or re-use solid waste in a cost-efficient, safer manner is limited (Eludoyin and Oyeku, 2010).

Landfills have historically been the primary method of waste disposal due to its convenience and the threat of groundwater contamination was not initially recognized. However, modern landfills are far different from a simple hole in the ground into which waste is disposed of in developed nations. Examples of waste disposed of in dumpsites are shown in Figure 2.1;

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(a) (b)

(c) (d)Figure 2.1. Typical examples of solid waste; (a)(http://harmonyfdn.ca/?p=349),(b) http://www.rnw.nl/africa/article/zimbabwes-growing-electronic-waste-becomes-a-real-danger-0):e-waste , (c)http://www.infrastructurene.ws/2013/10/31/offenders-pay-the-price-in-illegal-dumping-clampdown/ and (d) http://dchigundu.blogspot.com /: unsorted general waste

The ever-increasing population, industrialization and changing consumption patterns in Zimbabwe have resulted in the generation of increasing amounts of solid waste and diversification of the type of the solid waste generated. Visvanathan and Ulrich (2006) stated that the environmental degradation caused by inadequate disposal of waste can be expressed by the contamination of surface and groundwater through leachate, soil contamination through direct waste contact or leachate, air pollution by burning of wastes, spreading of diseases by different vectors like birds, insects, rodents or uncontrolled release of methane by anaerobic decomposition of waste.

Disposal of solid waste in landfills has been acknowledged as a major source of groundwater contamination (Afzal et al., 2000). Waste that is disposed of in unsanitary landfills or in refuse dumps immediately becomes part of the prevailing hydrological system. Fluid derived from rainfall, snowmelt and groundwater, together with liquids generated by the waste itself through processes of hydrolysis and solubilisation, brought about by a whole series of complex

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http://harmonyfdn.ca/wp-content/uploads/2012/06/ewaste2.jpeg

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biochemical reactions during degradation of organic wastes, percolate through the deposit and mobilize other components within the wastes. The resulting leachate subsequently migrates either through direct infiltration on site or by infiltration of leachate-laden runoff offsite (Taylor and Allen, 2006).

2.2 Solid Waste Management in Zimbabwe

Solid waste disposal in Zimbabwe is regulated by the Environmental Management Act of 2007 under Effluent and Solid Waste Disposal Regulations, Statutory Instrument 6 of 2007 (Statutory Instrument 6 of 2007). The Environmental Management Agency under the Ministry of Environment, Water and Climate enforces the regulations. Section 22 of the SI 6:2007 states that disposal of waste in an unlicensed dumpsite is illegal and the characteristics for a legal dumpsite are stipulated. The statutory instrument (section 22.3), states that use of unlined dumpsites five years from date of the regulations’ publication is illegal. However, it’s been seven years since publication of the regulations and no properly engineered landfill exists in Zimbabwe with special reference to the capital, Harare. This is mainly due to economic hardships.

Solid wastes disposed of in Zimbabwean households are a mixture of domestic, industrial, electronic and clinical wastes. The co-disposal of household hazardous waste such as batteries, paint residues, ash, treated woods and electronic wastes increases the heavy metal content in municipal solid waste dumpsite environments (Pare et al., 1999). In Zimbabwe, the sanitary disposal of solid wastes is one of the most pressing challenges facing urban authorities. In recent years, there has been considerable increase in illegal waste dumping, which indicates that throughout the country, urban waste disposal systems are inefficient and environmentally unsafe.

While there are various studies, which have focused on solid waste management in Zimbabwe, existing research has concentrated mostly on: (i) large cities especially Harare and sidelined small towns; and (ii) some elements of the solid waste management system and accorded least attention to disposal (Masocha, 2004). Very little is known about the impacts of all these unsanitary landfills on soil and ground water contamination. Leaching or migration of contaminations poses public health risks especially in areas where communities depend on groundwater for domestic supply.

2.3 Chemical Composition of Leachate Limited data is available on leachate quality in Zimbabwe. Studies done elsewhere show that rainfall that runs over solid waste or infiltrates through solid waste extracts dissolved and suspended constituents and thus becomes leachate (Robinson, 2009). As the waste decomposes through aerobic and anaerobic microbial action, waste-derived constituents increasingly become available to form leachate of greater concentration. Leachate from sanitary landfills can reach high organic concentrations well in excess of 20,000 mg/l of COD (chemical oxygen demand)

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and 10,000mg/l of BOD5 (five-day biological oxygen demand) in the first several years after land disposal. It can also have high concentrations of total dissolved solids, ammonia, nitrate, phosphate, chloride, calcium, potassium, sulfate, and iron, as well as numerous heavy metals (commonly including lead, zinc, cadmium, and nickel) and organic trace constituents (commonly including byproducts of decomposing solvents, pesticides, and polychlorinated biphenyls) . In addition, high numbers of fecal bacteria are typical, while viruses seldom survive in leachate because of their sensitivity to the low pH values common to leachate.

2.4 Public Health Risks

Figure 2.4. Public health and environmental hazard risks of inappropriate solid waste disposal

2.5 Effects of Heavy Metals on Soil and Groundwater Quality

Heavy metals in soil are considered to be distributed among several phases; soil solution phase, exchangeable phase, sorbed and organically bound phase, bound and occluded in oxides and secondary clay minerals phase, and residual, within the primary mineral lattice phase. Operationally distinct extractant solutions to tap into these phases have been developed and used to devise indices of heavy metal (bio)-availability based on the relationship between extracted metal and plant performance or metal uptake. In contrast to analysis of total metal, such extractants give an idea of the geochemical forms of the heavy metals in the soil. This, in turn, allows us to distinguish between metal derived from the mineral matrix and metal added to the soil in, for example, waste leachates, assuming that the latter has a different solubility and/or availability(Speir et al.,2002).

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2.6 Leaching Studies

Information of leaching of heavy metals from solid waste dumps is important to evaluate the risk of landfills to human health and environment (Scott et al., 1990). Leaching tests are frequently used in assessing worst case environmental scenario where components of the wastes turn out to be soluble and mobile. The mobility and toxicity of heavy metals present in landfills depend on the chemical form of the metals. It has been reported that a major portion of the total metal content in MSW is inert form, unlikely to undergo chemical reactions in landfills but leach from the waste bed (Tessier et al., 1979). The toxic effects of solid wastes are known to be greatly influenced by their heavy metal contents (Lottermoser, 1985).

Knowledge of heavy metal content, their speciation and the leachability at various environmental conditions from the dumpsite is a prerequisite for the assessment of reclamation and hazardous potential of the reclaimed waste, when it is used as compost for agricultural applications. Since the effect of heavy metals is influenced by their form of existence (Norvell, 1984). Assessment of the species of metal ions enables to evaluate the sustainability of mined waste as compost or cover material.

Batchelor (1999) stated that when a solid waste is in contact with a fluid, some contaminants will leach from the solid to the fluid. One can look at the process as a continuous one, measuring the concentration of the contaminant in the fluid and the flow rate of the fluid. Alternatively, a batch process may be considered and the volume of fluid measured instead of the flow. Two important issues to be considered in leaching tests are equilibrium and kinetics. When the flow of fluid through the waste is low, there is time for many of the contaminants in the waste to reach equilibrium with the fluid, and the concentration of a contaminant in the leachant reflects its solubility at equilibrium. Conversely, when the fluid flow is high, the concentration of the contaminants in the leachant is controlled by the rate at which they can dissolve or otherwise be transformed. In some cases the concentration of a contaminant is a function of both the equilibrium process and kinetics. A leaching test may be designed to gather information on the equilibrium aspects of the process, the kinetic aspects, or both.

2.7 Methods of Evaluating Leachability

Various leaching methods such as acid digestion, TCLP, ELT, SE and MEP,are used to remove soluble components from solid matrix have been cited in literature (Hesbach et al., 2001). A lot of these are regulatory methods, directed to characterize materials and others are approved by organizations for establishing compliance to particular standards and are related to hazardous waste. The methods vary depending upon the amount and particle size of leached samples, the type and volume of leachant solutions and the leachant delivery time (Kim, 2002).

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Toxicity characteristics leaching procedure (TCLP) developed by the United States Environmental Protection Agency (USEPA) is widely used to classify hazardous solid wastes and evaluate the worst leaching conditions in a landfill environment (USEPA, 1986). The TCLP is designed to determine the mobility of both organic and inorganic analytes present in liquid, solid, and multiphasic wastes. When applied to solid waste, i.e., waste containing greater than or equal to 0.5% solids, the liquid, if any, is separated from the solid phase and stored for later analysis; the particle size of the solid phase is reduced, if necessary. The solid phase is extracted with an amount of extraction fluid equal to 20 times the weight of the solid phase. The extraction fluid employed is a function of the alkalinity of the solid phase of the waste. A special extractor vessel is used when testing for volatile analytes. Following extraction, the liquid extract is separated from the solid phase by filtration through a 0.6 to 0.8 μm glass fiber filter (USEPA, 1984).

Multiple extraction procedure (MEP) was designed to simulate the leaching from repetitive precipitation of acid rain on an improperly designed sanitary landfill (Testing methods, Canada, 1986). The repetitive extractions reveal the highest concentration of each constituent that is likely to leach in a natural environment. This method is applicable to liquid, solid, and multiphase samples (USEPA, 1984). Equilibrium leach test (ELT) is meant for the evaluation of the maximum leachate concentration under mild conditions (Prudent et al., 1996).

Leaching tests can be used to compare the effectiveness of various solid-solid processes. Leaching of waste constituents from stabilized matrix will be influenced by the following factors:

Chemical composition of stabilized matrix and leaching medium Physical engineering properties of stabilized matrix Hydraulic gradient across the waste Polarity and leaching sum and waste type Redox conditions and competing reaction kinetics Bulk chemical diffusion of the waste or reactive species within the leachate pore solution

or solid matrix Concentration of reactive species, and Accumulation of waste in the pore solution at particle surface

(Suthersan, 1996)Leachability testing is used to predict the degree to which this objective has been met (Wilson, 1993).

Numerous leaching tests have been established to test solid waste. Extraction tests refer to a leaching test that generally involves agitation of ground or pulverized waste forms in a leaching solution which may be acidic or neutral. Extraction tests are generally used to determine the maximum leachate concentrations under a given set of environmental conditions. A typical example is the ELT extraction test (Sutherson, 1996). Leach tests involve the monolithic waste mass. They may be run under 2 conditions: (1) static conditions were leaching velocities are low, because leaching takes place under static hydraulic conditions and, (2) dynamic conditions in which leaching takes place under non-equilibrium conditions because leaching solution is replaced periodically with new solution (Sharma,1994). In column leach tests waste is initially pulverized and then placed in a column at a predetermined density, and the leaching solution is

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finally passed under pressure in an upward flow mode. This method is more representative of field conditions. However, simple care is required during set up to avoid errors due to certain factors like channeling effects, non-uniform packing of waste, biological growth, and changing of the column (Sharma,1994). Batch and column experiments thus complement each other.

CHAPTER THREE: MATERIALS AND METHODS

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3.1 Description of study site and soil sampling

The study site was the University of Zimbabwe dumpsite which is located at the main campus behind the Crop Science Department (31º02’56.13” E; 17º46’50.13”S). Waste disposed of at the dumpsite includes electronic and electrical waste, office waste papers, domestic waste from halls of residence and staff quarters, litter from university grounds, solid laboratory waste and demolition waste. The dumpsite has been in operation for over 50 years and is a non-sanitary dump as it is not lined. Waste management practices such as burning of waste occur every 5-6 weeks.

The study included four treatments, (1) fresh ash from recently burnt waste, (2) aged ash that had accumulated over the years from burning of waste, (3) soil from beneath the dump and (4) soil unaffected by the dump as the control. Fresh ash, aged ash and soil from beneath the waste where randomly collected from five sampling sites. Fresh ash from waste burnt three weeks prior to sampling was collected from the five selected sites. About 4 kg samples were collected from each sampling site and mixed to make a 20 kg composite sample.

Aged ash was collected after scrapping off fresh ash and some waste from the five sampling sites in the same manner as fresh ash. The aged ash was dark in colour, moist and had accumulated over the years as burning of waste is a frequent activity at the dumpsite. Soil beneath the dump was collected at a depth of 35-50 cm depending with the location of the sampling areas. The soil samples were obtained below the aged ash layer of the dump from the five sampling sites. Aged ash and soil samples were collected in the same manner as the fresh ash. Soil samples from an uncontaminated area surrounding the dumpsite were collected as the control. Soil beneath waste dump and control were UZ red ferisialitic clay soils (Series 5E) (Nyamapfene, 1991).

3.2 Physical and chemical characterization

Soil samples were air-dried, ground and passed through a 2 µm sieve. Samples were subjected to Aqua Regia digestion followed by assaying for Zn, Cd, Mn, Pb, Fe, Cu and Ni. Aqua Regia solution was prepared using concentrated nitric acid and 6 M hydrochloric acid at a ratio of 1:3 respectively (Alloway, 1995). Aqua Regia was added to the solid media at a ratio of 1:5 and digested for an hour. Solutions were allowed to cool and made up to 50 ml with deionized water (Esakku et al., 2003). The solutions were filtered through a Whatman No. 45 filter paper. The filtrate was assayed for the heavy metals using a Varian Version 1.13 Atomic absorption spectrophotometer (Australia). Electrical conductivity of the filtrate was measured using an EC meter which uses a conductivity electrode (YSI 3200). pH of the different media was measured using a Eutech Instruments ION700 pH meter with an electrode that was immersed into each filtrate separately.

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3.3Batch experiments

Three leaching solutions were prepared using distilled water and pH regulated using nitric acid and sodium hydroxide to attain pHs of; 5, 7 and 9. The pH of leachate in solid waste dumps varies in the range of 4.5-9 (Christensen et al, 2001). 10 g of samples of ash and soil were weighed into plastic bottles and leaching solutions were added at a ratio of 1:20 (ASTM D3987, 1999). The samples were agitated for 18 hours at 25ºC at a shaking rate of 29 revolutions per minute (ASTM D3987, 1999). The samples were allowed to settle and filtered through a Whatman No. 45 filter paper. The control samples had to be subjected to centrifugation as filtrate was very cloudy. pH and electrical conductivity of filtrate were measured as previously described. The leachate solutions were assayed for the following heavy metals; Cd, Ni, Pb, and Zn.

10g soil/ash 200ml leaching solution shaking at 29revolutionsmin-1 filtration

Figure 3.3. Batch experimental setup.

3.4 Column Experiments

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Assaying for heavy metals with AAS and nitrate with Cd reduction method


Columns made of inert glass material with a volume of 1.61 m3, cross-sectional area of 8.04 cm2

were used and set up as illustrated in figure 3.4.1 below.

Figure 3.4.1. Column experimental set-up

Duplicate leaching columns were packed with untreated, air-dried and sieved solid material (< 2 mm) up to a height of approximately 18,5cm ±0.05. Estimated porosity of media was 0.43 and pore volume was approximately 63.98 cm3. To obtain uniform packing, the media was added to the columns in small portions with a spoon and pressed with a plunger under simultaneous gentle column vibration until the top of the soil column did not sink in further (OECD Method 312). The columns were packed at a uniform density of 1.5±0.1 gcm-3 (USEPA). After packing, the soil columns were pre-wetted with distilled water from bottom to top in order to displace the air in the soil pores by water (figure 3.4.2) Thereafter the soil columns were allowed to equilibrate and the excess water is drained off by gravity (Shackelford, 1991).

The surfaces of the soil columns were then covered by a glass wool to distribute the artificial rain evenly over the entire surface and to avoid disturbance of the soil surface by the rain drops. Then the artificial rainfall was added to the soil columns drop-wise with the aid of a dropping funnel (OECD Method 312). The leaching solutions of pH 5 and 7 were applied to the soil columns evenly at a rate of 0.3 ml/min (USEPA 2008: OPPTS 835.1240). Leachate collection for every 32±0.5 ml equivalent to 0.5 pore volumes and leachate assayed for heavy metals.

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Soil/ash from waste dump


Figure 3.4.2. Columns of soil and ash packed to uniform density and pre-wetted from bottom to top with distilled water in glass bottles.

3.5 Laboratory analytical methods

The pH values of the solution were measured by a Eutech Instruments ION700 pH meter .The concentrations of heavy metals (Pb, Zn, Cr, Fe, Mn, Ni and Cu) in the solutions were analyzed using AAS (Varian Version 1.13 Atomic absorption spectrophotometer (Australia). Because the concentration of solutions and different metals varied substantially, the serial dilution method was needed in some solutions before analysis.

3.6 Data Analysis

Statistical tests were performed using Minitab version 16 at 95% confidence interval. ANOVA assumptions test first before data analysis. One- way Analysis of Variance (ANOVA) was used to test the significant difference of the means for pH and electrical conductivity for the solid media. Two- way ANOVA was used to test the significant effect of pH, material and their interactions on leaching of heavy metals from soil and ash from waste dump.

CHAPTER FOUR: RESULTS

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4.1 pH and electrical conductivity of soil and ash from waste dump

The pH varied significant (p<0.05) among the materials. Specifically, the pH values of the fresh ash (7.9±0.02) was significantly (p=0.02) higher than that of old ash (7.3±0.01), and soil from beneath the waste dump (7.2±0.01) were comparable. Both fresh and old ash and soil from beneath the dump had significantly higher pH than that of the control (6.9±0.02).

Electrical conductivity was significantly higher in soil and ash from solid waste dump than in the control (25.40±0.55 mS). Old ash had significantly higher electrical conductivity (64.70± 0.24mS) than fresh ash and soil beneath waste dump (28.7±0.24 mS and 43.10±0.26 mS respectively).

4.2 Total Aqua Regia extractable heavy metals

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The concentration of Cd and Ni was comparatively less than that of other heavy metals in the soil and ash samples. Descending order of heavy metal contents in solid waste was iron, manganese, zinc, copper, lead, nickel, cadmium. There were no significant differences between the treatment means (p>0.05).

Treatment Zn Cu Pb Cd Fe Mn Ni

Control 52.00 ± 0.50b

122.33 ± 0.88c

11.73 ±0.31b

0 3252.00 ± 0.58a

597.67 ± 0.88b

11.73 ± 0.07b

Fresh Ash 401.00 ± 0.55b

255.00 ± 0.58a

88.33 ± 0.87a

9.43 ± 0.11a

3031.00 ± 0.58b

355.33 ± 0.88bc

15.12 ± 0.1b

Old Ash 517.00 ± 0.40a

186.00 ± 0.58b

88.15 ± 0.08a

3.70 ± 0.12a

3176.70 ± 0.88a

487.70 ± 0.67b

20.16 ±0.05a

Soil 97.00 ± 0.50c

178.00 ± 0.58b

22.19 ± 0.07c

1.68 ± 0.07b

3227.70 ± 0.67b

797.00 ± 0.58a

19.50 ± 0.02a

Table 4.2. Total aqua regia extractable Zn, Cu, Pb, Cd, Ni, Mn and Fe in fresh ash, old ash, soil beneath the dump from waste dump and control. Data shown are concentration means in mgkg -1

± standard error of the mean. Different letters show significant differences amongst the treatments down a column.

4.3 Batch leaching

4.3.1Influence of pH on leaching of heavy metals

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Samples collected from dumpsite had a lower buffering capacity than the control samples. Buffering capacities were in ascending order Fresh ash< Soil beneath the dump< Old ash <Control. Final pH was predominantly above 7 as shown in figure 4.3.

Metal solubility generally decreased with increasing pH. This can be seen in figure 1 that amounts of Zn, Pb, Ni leached from soil and ash from the solid waste dump decreased significantly with increasing pH. Cd however showed a different trend in its leaching from old ash as it increased with increasing pH. Soil beneath waste dump leached the greatest amount of heavy metals, Zn and Pb in particular under acidic conditions (pH 5). (figure1).

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Figure 4.3. Comparison of leaching behavior of the different media under varied pH conditions error bars represent standard error of the heavy metal concentration means at sample size n=3

4.3.2Effect of heavy metal concentrations in soil and ash on leaching behavior

The leaching concentrations of heavy metals from the batch leaching test were rather low, and no significant correlation was found between the total contents of heavy metals in the soil and ash from waste dump and their leaching toxicity. Correlation analysis also showed the same result, since the correlation coefficients ranged from −0.15 to 0.18, indicating the minor influence of the existence of heavy metals in the bottom ash on their leachability.

The leaching behavior of the soil and ash proved to be relatively low, i.e., below the limit values for hazardous waste: 10 mg/l for Ni, 3 mg/l for Pb, and 50 mg/l for Zn with the exception of Cd, 0.3mg/l. All metal concentrations were less than 3 mg/l, and for Cd, no more than 0.5 mg/l was observed.

Percentage of total extractable heavy metals under batch experimental conditions and varied pH is rather low although there are significant differences between the four media. The behavior of the heavy metals under these leaching conditions suggests a low mobility under experimental conditions.

There was no significant effect on the leaching of heavy metals from soil and ash from waste dump by the interaction of the material and pH of leaching solution (p>0.05).

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TreatmentpH of leaching solution

% of heavy metal leached of total in soil and ash from waste dump

Cd Ni Pb Zn

Fresh Ash 5.03 2.12 1.32 0 0.17

7.10 2.12 1.32 0 0.20

8.99 13.79 1.32 0 0

Old Ash 5.03 5.41 4.61 0.76 0.22

7.10 5.41 1.98 0.23 0.10

8.99 12.70 0.99 0.37 0.08

Soil beneath dump 5.03 4.22 4.46 11.13 3.51

7.10 19.64 5.79 2.12 0.62

8.99 5.49 4.46 0 1.64

Control 5.03 0 5.12 7.42 1.79

7.10 0 9.12 12.53 1.40

8.99 0 4.52 2.30 1.67

Table 4.3.2. Percentage means of total extractable heavy metals leached during batch experiments at pH values 5.03, 7.10, and 8.99 (n=3)

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4.4 Column leaching

The cumulative concentrations of leached heavy metals from soil beneath waste dump, old ash and fresh ash was significantly (p=0.00) higher than that of the control. There were significant differences in the amounts of heavy metals leached from the ash and soil from the dump (p=0.03 and the control p=0.01). Fresh ash leached the highest amount of heavy metals (Zn, Pb, Ni and Cd) at both pH values 5 and 7. Area under the breakthrough curve is proportional to the mass of heavy metal leached. Since the pore volumes are a function of time, as time increased the release of heavy metals declined as expected.

The pH of leaching solution had a significant effect on the leaching of Pb (p=0.002), Zn (p=0.001) and Ni (p=0.001). There was no significant effect of pH of leaching solution on Cd leaching as p= 0.176. Interaction of pH of leaching solution and nature of material had a significant effect on heavy metal leaching from soil and ash from the waste dump (Cd; p=0.03, Zn and Pb; p=0.00, Ni; p=0.008).

Figure 4.4 shows a comparison of the heavy metals eluted from soil and ash samples from the dumpsite at intervals of 0.5 pore volume using leaching solutions of pH 5, 7 and 9 (figure 4.4).

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0

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(d) Ni

Figure 4.4. Comparison of heavy metals leached by the four media ( -old ash from waste dump, -control, - soil beneath waste dump, - fresh ash) using cumulative heavy metal concentrations from column experiments. Graphs (a), (b), (c) and (d) represent leaching from the four media of; Zn, Cd, Pb and Ni respectively at pH 5.05 and (e), (f), (g), (h) show leaching at pH 7.1

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(c)


CHAPTER FIVE: DISCUSSION

The current study investigated the leaching of heavy metals from an unsanitary solid waste dump at the University of Zimbabwe and its dependence on the pH of leaching solution. The key findings were; (1) heavy metal content in soil and ash from waste dump is significantly higher than that in uncontaminated soils ;( 2) the leaching behavior of heavy metals in soil and ash from waste dump is significantly dependent on pH of leaching solution and decreases as pH increased. The highest leaching was observed from soil beneath waste dump at pH 5; (3) fresh ash, old ash and soil beneath the waste dump have significantly higher concentrations of heavy metals leaching than the control indicating that they could be sources of ground water contamination. Here, we discuss the key findings of the effect of pH of leaching solution and type of solid material on the leaching of heavy metals (Zn, Pb, Cd, Ni) from soil and ash from the waste dump and their implications will be discussed.

Typical waste found at the waste dump were electronic and electrical waste, office waste papers, domestic waste from halls of residence and staff quarters, litter from university grounds, solid laboratory waste and demolition waste. Robinson (2009) found that electronic waste is a major source of heavy metals such as lead, nickel, zinc and cadmium from solid waste dumps. This agrees with the significantly higher heavy metal content in soil, fresh ash and old ash from waste dump than the control. Several field-based experiments have been conducted were the apparent migration of metals to depth has been found (Lund et al., 1976; Hinesly et al., 1979; Bell et al., 1991; McBride et al., 1997). In column leaching experiments, it has also been shown by several studies that heavy metals can leach through many tens of centimeters of soil (Giusquiani et al., 1992; Antoniadis and Alloway, 2002).

The differences in the heavy metal contents of soil and ash from waste dump are due to differences in the nature of the materials and age of material. Fresh ash was collected three weeks after burning and old ash had accumulated over 50years since the waste dump had been established. Soil beneath the dump has been in existence for a longer period of time and as a result could have accumulated HM leached from underlying materials. Therefore heavy metal contents are bound to differ as heavy metal solubility is affected by different mechanisms. (Figure 5.1).

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Figure 5.1. Sketch of mechanisms that may control heavy metal solubility (Johnson et al., 1996).

Leachability depends on the geochemical nature of the matrix in which the metal is bound and physical factors (Johnson et al., 1996). This study suggested that heavy metal leaching is dependent on the pH of leaching solution with the highest leaching under acidic conditions, as evidenced by results observed at pH 5. The residual metal content is strongly bound, probably confined within the matrix of an insoluble solid. Heavy metal leaching decreased with increasing pH probably due to formation of precipitates with leaching solution which cannot be leached from the solid material.

The high pH observed for fresh ash compared to old ash indicates that aging influences pH. The high pH for fresh ash relative to old ash could be attributed to formation of carbonates during waste combustion. Moreover, leaching of basic cations from old ash could also lead to low pH. However, the magnitude of pH differences between fresh and old ash was about two times lower than values reported in previous studies, probably due to differences in the chemical composition and age differences between the ash. The observed differences in pH could affect the leaching behavior of heavy metals under field conditions

The observed decrease in leaching of Zn, Pb and Ni with increasing pH of leaching solution could be attributed to decreased solubility of heavy metals with increasing pH. Solubility of Cd could be controlled by formation of CdCO3 (Johnson et al., 1996).Alloway et al., (1985) showed that pH, organic matter and hydrous oxide contents were the key factors controlling specific adsorption of Cd which in turn influence leaching. This may explain Cd leaching at pH 9 in old ash. The maximum concentrations of Ni, Pb, Cd and Zn represent 16, 12, 12 and 7%, respectively, of the total extractable heavy metal content of soil beneath waste dump ,old ash and fresh ash used in this experiment. It can be assumed that the remaining heavy metal cations are bound within matrices insoluble under the given experimental conditions.

Fresh ash showed the greatest buffering capacity as pH of media returned to almost near its initial state (pH 7.88) after pH had been altered by the three different leaching solutions in batch

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experiments. Buffering capacities were in descending order fresh ash, control, soil beneath the waste dump, old ash.

Zimbabwe’s Environmental Management Act (EMA) currently has no prescribed limits for hazardous waste thus World Health Organization (WHO) limits were used for comparison in the study. Heavy metals leached were below the WHO limit values for hazardous waste: 10 mg/l for Ni, 3 mg/l for Pb, and 50 mg/l for Zn with the exception of Cd, 0.3mg/l in fresh ash. Thus in environmental terms, leaching of Zn, Pb and Ni from soil, fresh and old ash from the waste dump seems rather insignificant constituting less than 20% of total aqua regia extractable concentrations. Cadmium leaching from fresh ash may exceed the limits may be a cause for concern as the Cd relatively mobile in soil and very bioavailable (European Commission DG ENV. E3, 2002).

It is noteworthy that this is a short-term study. Cumulative effects could be significant; hence remedial or preventive measures are needed. Heavy metals were not easily leached probably due to high adsorption capacity, CEC of the soil, or the presence of organic matter. Although the concentration of organic matter were not measured, it is also possible that organic carbon from waste could account for high heavy metal retention. It is thus important to put remedial measures such as lining of the waste dump to reduce leaching of heavy metals from waste. Groundwater processes are rather slow and eventually after long periods of time, heavy metals in leachate may exceed limits and result in groundwater pollution.

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CHAPTER SIX: CONCLUSION AND FUTRURE RESEARCH

This study was conducted to assess heavy metal leaching from an unsanitary waste dump by investigating the leaching of heavy metals from unsanitary solid waste dumps and its dependence on pH of leaching solution using column and batch experiment. The key findings of the study were:

1. Heavy metal content in soil and ash from waste dump is significantly higher than that in uncontaminated soils posing the risk of soil and groundwater contamination

2. The leaching behavior of heavy metals in soil and ash from waste dump is significantly dependent on pH of leaching solution and decreases as pH increased. The highest leaching was observed from soil beneath waste dump at pH 5

3. Fresh ash, old ash and soil beneath the waste dump have significantly higher concentrations of heavy metals leaching than the control indicating that they could be sources of ground water contamination.

The high leaching at acidic pH suggest that acid rain may enhance heavy metal mobility in soil and ash in the waste dump. Results showed that pH varied significantly among materials, which could in turn affect heavy metal leaching. The high pH observed for fresh ash compared to other materials could be attributed to the presence of carbonates from waste combustion. The results on ash could provide some indications on what could happen if solid waste is subjected incineration and the ash subsequently disposed of in unlined waste dumps. Also the fresh and old ash could be sources of heavy metals observed in soil below.

Current study only investigated pH, therefore there is need for a more detailed study of factors influencing retention and mobility of heavy metals in ash and soil beneath the waste dump. Moreover, current study used laboratory batch and column experiments. Therefore, there is need for field measurements of heavy metal leaching from an unsanitary waste dump using lysimeters. Long-term assessments of waste material, the total heavy metal content should be considered when conducted long term studies, since the metal speciation may change as a function of time (Johnson et al, 1996).

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REFERENCES

Aderemi A.O., Falade T.C., (2012), Environmental and Health Concerns Associated with the Open Dumping of Municipal Solid Waste: A Lagos, Nigeria Experience, and American Journal of Environmental Engineering, Volume 2, pp.160-165

Alloway B.J., et al (1985), Trace substances, Journal of Environmental Health, Volume 18, pp.187-201

Alloway B.J., (1995), Heavy metals in soils, Springer Science and Business Media, pp.72-75

Antoniadis V., Alloway B.J., (2002), Leaching of cadmium, nickel and zinc down the profile of sewage sludge-treated soil, Communications in Soil Science and Plant Analysis, Volume 33, pp.273–286

Ashworth D.J. and Alloway B.J.,(2004), Soil mobility of sewage sludge-derived dissolved organic matter, copper, nickel and zinc, Journal of Environmental Pollution, Volume 127, pp.134-144

ASTM International, (1999), Standard test method for shake extraction of solid waste with water D 3987

Bandara N.J.G.J and Hettiarachchi P.J., (2003), Environmental Impacts Associated with Current Waste Disposal Practices in a Municipality in Sri Lanka – A Case Study, Workshop on Sustainable Landfill Management, Chennai, India, pp.19-26

Batchelor B., (1999), Inorganic Leaching Science in EPA Leaching Meeting Proceedings, Texas A and M University, Accessed from: http:// www.epa.gov/osw/hazard/testmethods/pdfs/i leaching .pdf

Bell P.F., James B.R., Chaney R.L., (1991), Heavy metal extractability in long-term sewage sludge and metal salt-amended soils, Journal of Environmental Quality, Volume 20, pp.481–486

Bosshard P.P., Bachofen R. and Brandl H., (1996), Metal Leaching of Fly Ash from Municipal Waste Incineration by Aspergillus niger, Environmental Science and Technology, Volume 30, pp.3066-3070

Christensen T.H., (2001), Biogeochemistry of landfill leachate plumes; Applied Geochemistry, Volume 16#78, pp. 659-718

Page | 27


Environmental Management Act (EMA), (2007) Environmental Management (Effluent and Solid Waste Disposal) Regulations 2007. Statutory Instrument 6: 2007, Chapter 20:27. Government Printer, Harare, pp. 38

Environmental Management Act (EMA), (2007) Environmental Management (Hazardous Waste Management) Regulations 2007. Statutory Instrument 10: 2007, Chapter 20:27. Government Printer, Harare, pp150

Environmental Protection Agency (EPA), (2004) OECD Guidelines for the Testing of Chemicals: Leaching in Soil Columns, Accessed from: http://www.epa.gov/scipoly/sap/meetings/2008/october/312_soil_column_leaching.pdf

Esakku S., Palanveuk., Joseph K.,(2003), Assessment of heavy metals n municipal solid waste dumpsite n : Proceedings f workshop in sustainable landfill management, Chenna, India, pp. 139-145

European Commission DG ENV. E3, (2002), Heavy Metals in Waste Final Report, Accessed from: C:\temp\IECache\OLK29\Heavy metals in waste1.doc

Fatta D., Papadopoulos A., Loizidou M, (1999), A study on the landfill leachate and its impact on the groundwater quality of the greater area, Journal of Environmental Geochemistry and Health, Volume 21(2), pp175–190

Giusquiani P.L., Gigliotti G., Businelli D., (1992), Mobility of heavy metals in urban waste-amended soils, Journal of Environmental Quality , Volume 21, pp.330–335

Hageman P.L., Leaching Studies, USGS Billing Symposium / ASMR Annual Meeting, Assessing the Toxicity Potential of Mine Waste Piles Workshop, pages 2-5 http://www.reopure.com/nitratinfo.html

Hesbach P., and Lamey S., (2001). Accessed from: http://www.mcrcc.osmre.gov/PDF/Forums/CCB3/4.2pdf.

Hinesly T.D., Ziegler E.L., Barrett G.L., (1979), Residual effect of irrigating corn with digested sewage sludge, Journal of Environmental Quality, Volume 8, pp.35–38

Hjelmar O., (1990), Leachate from land disposal of coal fly ash: Waste Management and Research, Volume 8, pp.429-449

Johnson E.A., et al (1996), Leaching behavior and solubility controlling solid phases of heavy metals in municipal solid waste incineration ash, Journal of Waste Management, Volume 16#1-3, pp.129-134

Kim A.G., (2002), Fluid extraction of heavy metals from coal ash. Accessed from; http ://WWW.mcrcc.osmre.gov/PDF/Forums/CCB3/4.2pdf

Page | 28


LaGrega M.D., et al (2001), Hazardous waste management, 2nd edition, McGraw Hill, pp.149-197

Lund L.J., Page A.L., Nelson C.O., (1976), Movement of heavy metals below sewage disposal ponds, Journal of Environmental Quality, Volume 5, pp.330–334

Masocha M., (2004), Solid Waste Disposal in Victoria Falls Town: Spatial Dynamics, Environmental Impacts, Health Threats and Socio-economic Benefits, University of Zimbabwe, Faculty of Arts e-thesis Collection, Accessed from : http://ir.uz.ac.zw/jspui/handle/10646/819?mode=full

McBride M.B., et al (1997), Mobility and solubility of toxic metals and nutrients in soil fifteen years after sludge application, Journal of Soil Science, Volume 162, pp.487–500

Mor S., et al (2006), Leachate Characterization And Assessment Of Groundwater Pollution Near Municipal Solid Waste Landfill Site , Environmental Monitoring and Assessment, Volume 118, pp.435–456

Norvell W.A., (1984), Comparison of chelating agents for metals in diverse soil materials, Soil Science Society of America Journal, Volume 48, pp.1285 – 1292

Nyamapfene K., (1991), The Soils of Zimbabwe, Nehanda Publishers, Harare, Zimbabwe, pp.179

OECD/OCDE 312, (2004), Leaching in soil columns, OECD Guidelines for the testing of chemicals

Eludoyin A.O and Oyeku O.T., (2010),Heavy Metal Contamination of Groundwater Resources in a Nigeria Urban Settlement, African Journal of Environmental Science and Technology, Volume 4, pp.201-214

Practical Action (2007), Community Based Waste Management in Urban Areas, Practical Action Publications

Pruduent P., Domeizer M., and Massiani, (1996), Chemical Sequential Extraction as decision making tool, Application to Municipal Solid Waste

Scott J. et al., (1990), Management, leachate generation and leach testing of solid wastes in Australia and overseas, Critical reviews in Environmental Science, USEPA

Shackelford C. D., (1991), Laboratory diffusion testing for waste disposal: A review, Journal of Contamination Hydrology, Volume 7, pp.177-217

Sharma D., (1994), Waste Contaminant Systems, Waste Stabilization and Landfills: Design and Evaluation, John Wiley &Sons, pp.284-287

Page | 29


Speir T.W., (2002), Heavy metals in soil, plants and groundwater following high-rate sewage sludge application to land, accessed from: http://download.springer.com/static/pdf/606/art%253A10.1023%252FA%253A1026101419961.pdf?auth66=1394719859_72705bd6baa3b66f980e01533516ce4d&ext=.pdf

Sutherson S.S., (1996), Remediation Engineering: Design Concepts, CRC Press, pp.306

Robbins N., Davies J. and Farr J., (2013), Groundwater supply and demand from southern Africa’s crystalline basement aquifer: evidence from Malawi, Hydrogeology Journal , Volume 21, Issue 4, pp. 905-917

Robinson B.H., (2009), An Assessment of Global Production and Environmental Impacts, Sci Total Environ, Volume 20, pp.183-91

Training and Research Support Centre (TARSC), Civic Forum on Housing (CFH) (2010) Assessment of solid waste management in three local authority areas of Zimbabwe, Report of a Community Based Assessment: Discussion paper TARSC Harare

Tessier, Campbell P.D.G., and Bisson M., (1979), Sequential U.S. EPA (1986), Multiple Extraction Procedure (MEP) test method and structural test methods for evaluation of solid waste

United States Environmental Protection Agency (US EPA), publication SW- 846, 1320, Extraction Procedure for the speciation of particulate trace metals. Analytical Chemistry, Volume 51, pp.844-851

United States Environmental Protection Agency (US EPA), (2008), Fate, Transport and Transformation Test Guidelines, OPPTS 835.1240 Leaching Studies, Prevention, Pesticides and Toxic Substances (7101)

United States Environmental Protection Agency (US EPA), (1984), Office of Drinking Water, A Ground Water Protection Strategy for the Environmental Protection Agency, pp. 11.

United States Environmental Protection Agency (USEPA), (2014), Student’s site: Acid Rain Accessed from: http://www.epa.gov/acidrain/education/site_students/phscale.html

Ure A.M.,(1995), In Methods of Analysis for heavy metals in soils, Alloway B.J, Springer, 2nd Edition, Blackie Academic and Professional

Wilson D.J., (1993), Hazardous Waste Site Soil Remediation: Theory and Application of Innovative, CRC Press, pp.148-149

Wasay S.A.,(1992), Leaching behavior of trace toxic metals from fly ash, their seepage control to ground water and utilization of fly ash, Journal of Environmental Science and Health Part-A ,pp.25-39

Page | 30


Zimbabwe National Statistics Agency, (2010-11), Zimbabwe Demographic and Health Survey, Harare, Zimbabwe

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