ABSTRACT
Water
as a gift of nature is generally believed to have no enemy. Despite the
abundance of fresh water on the earth, many regions are in deep crisis of water
shortage due to there being polluted by human activities, or the ever
increasing demand by industrialization and high population growth. Thus,
groundwater is the alternative source of fresh water in areas where surface
water is polluted or particularly in arid and semi-arid region of the world. However,
the ground water that is presently rely on is generally been grossly polluted
by various sources e.g. solid waste
Waste is defined as any substance or object
discarded for any reason, whether part or all and such substance may be
recycled e.g. rubbish, trash, scraps, tiles, bottles, cans, papers, chemicals,
slugs, machine parts, scrap metals etc. Once waste is deposited at the landfill
(dumpsite) pollution can arise from the migration of both gas and leachate. There
are three broad types of contaminants present in leachates that can pollute
groundwater and subsequently affects public health. These are hazardous
chemicals, conventional and non-conventional contaminates. The cost of cleaning
up groundwater contaminated by Municipal Solid Waste landfill leachates require
large sum of money and technology, which are presently not available in our
society. Thus it is important that efforts are geared towards preventing pollution
that will arise from leachate.
INTRODUCTION
Water as a gift of nature is
generally believed to have no enemy. However, water is very essential to the
well being of man, animals and plants.
Of all the earth’s essential elements that support life water is the second
most important after air. Amazingly, a mere 3 per cent of the world’s water is
fresh, not salty. Out of this, 95% of the fresh water is locked up in glacier
and ice caps or in the underground aquifer thus leaving 1 percent that is
readily accessible to human kind. Basically, the total do not amount of water
on earth do not increases nor decreases, as the amount on earth now is all
there had been. This is because the water in and around the world endlessly
circulates from the oceans to the atmosphere, to the land; into the river and
back to the ocean again. Moreover, despite the abundance of fresh water on the
earth, many regions are in deep crisis of water shortage due to there being
polluted by human activities, or the ever increasing demand by
industrialization and high population growth. Thus, groundwater is the
alternative source of fresh water in areas where surface water is polluted or
particularly in arid and semi-arid region of the world.
GROUNDWATER
Groundwater is a resource of global
importance, particularly in areas where access to surface water is limited.
Groundwater resources include shallow and deep rechargeable aquifers that are
connected to rivers; streams or seas while non-renewable aquifers or fossil
water are those that may have been created by age. Groundwater makes up about
95 percent of the world’s supply of fresh water excluding fresh water in global
ice. Groundwater may in this case be directly fed through seepage from run off.
Furthermore, groundwater may be
fed from the soil surface by an impervious stratum but in general, the water is
deeper lying. However, alluvial groundwater presents a special case; where
ground water is located in alluvial soil close to a river. Thus, the quality of
the river water directly influences the quality of such ground water. Also, the
characteristics of groundwater depend on the geological nature of the terrain,
which in turn determine the composition of the water. This is constantly in
contact with the ground in which it stagnates or circulates leading to
equilibrium between the composition of the soil and that of the water.
Water that circulates in a sandy
organitic substratum is acidic and has few minerals. While water that
circulates in limestone contain bicarbonate thus making it alkaline. This water
is usually characterized by weak turbidity, constant temperature, chemical
composition, and an almost absence of oxygen.
However, confined groundwaters, especially one circulating in kast
terrain usually appear turbid with various pollutants. Generally, groundwaters
are often very poor microbiologically and also contain iron, manganese,
fluoride, sulphide, etc in concentrations that exceed the standards for
drinking water. This is due to the composition of the groundwater where the
water is store.
LAGOS GROUND WATER
Nigeria is subdivided into nine
different hydrogeological basins. Lagos is located within the Delta basin
within which water table aquifers are abundant. In Lagos, there is substantial
report of four aquifers horizon, which are made up of alternating sequence of
sands and clays. In some area, the medium is coarse sand layer, which occurs
below the superficial laterite. This contains high yielding aquifer with a free
water table within which predominantly lateral ground water movement occurs.
Also, there are reports that vertical groundwater flow appears to occur across
the clay in relatively small (aquifer). The upper and lower aquifer units have been
identified as local water sources. However, additional significant aquifers are
generally encountered between 80 and 100m and at about 600m below ground.
The
first shallow aquifer sediment is used for very small private domestic
supplies, while the second and third aquifer (coastal plains sands) provides
substantial quantities of water for public water supply, industry and private
supplies. The fourth aquifer is the deep and highly productive Abeokuta
formation that is only accessable by selected few. The provision of water
supply relates differently to groundwater, since it is frequently an important
source for both the municipal water company, typically operating a few high
yielding wells or well fields and for the private individuals. However, the concern
of public and private water industries is the decreasing availability and
deteriorating quality and quantity of ground water. Today groundwaters are
polluted by various sources that include petroleum products , septic tanks,
landfill leachate etc.
Moreover,
the most significant impact on groundwater quality arises from the
contamination from landfill leachate. Landfill leachates are a more intractable
problem as, even if they can be collected effectively; sophisticated treatment
is needed before they can be discharged into the environment. However, landfill
leachates collection and treatment is not available in all landfills in Lagos.
Thus, leachates contamination is probably inevitable.
LANDFILL LEACHATES
Waste is defined as any substance or
object discarded for any reason, whether part or all and such substance may be
recycled e.g. rubbish, trash, scraps, tiles, bottles, cans, papers, chemicals,
slugs, machine parts, scrap metals etc. Once waste is deposited at the landfill
(dumpsite) pollution can arise from the migration of both gas and leachate.
However, gas problem have become increasingly high over the years. The
management of gases from landfill sites can be controlled through the
installation of engineered gas extraction system. This engineering control
system is not in use in any of the dumpsite (landfill) present in Lagos. Thus,
landfill gases still constitute a great problem.
On the other hand, landfill leachates are
a more intractable problem. Leachate is the name given to grossly polluted
liquid that can emerge from land filled decomposed waste mass. Also, it can be
said to be liquids that results from water collecting contaminates as it
trickles through agricultural, pesticides or fertilizers wastes. It is important
to recognize that the deposition of almost any waste to landfill (dumpsites)
will give rise to leachate whose chemistry is not in equilibrium with the
chemistry of the surrounding environment thus resulting in pollution.
Numerous physico-chemical and
biological processes govern the generation of leachates. The pioneer
investigation that provided the basis for a scientific understanding of these
processes was conducted in Manchester in 1931-34 by Jones and Owen and
subsequent studies by Farquahar et al.,(1972) and Rees (1980).The rate of
leachate generation is affected by various factors which include the age of the
refuse, waste density, water content, humidity, rainfall etc.Water acts as
transport medium for bacteria and for their nutrients and waste products. Thus,
the lack of moisture will reduce degradation rates and will result in a
landfill producing gas and leachate at a slower rate but over a much longer
period of time.
The decomposition of waste takes place by
the action of microbes within the waste mass. The decomposition of waste takes
place in three stages; thermal stage, acetogenic stage and methogenic stage. In
the first stage, aerobic organisms present in the waste attack the degradable
waste. In the presence of oxygen in entrapped air, to form more simple organic
compounds, carbon dioxide and water. Heat is then generated and aerobic
organisms multiply. The second stage commences when all the oxygen is consumed
or displaced by carbon dioxide. The degradation processes is then taken over by
organism that can thrive in either the presences or absent of oxygen. The
organisms brake down the large organic molecules present in food, paper and
similar waste into more simple compounds such as hydrogen, ammonia, water, carbon
dioxide and organic acid. During this acetogenic stage, carbon dioxide
concentration can reach a maximum of 90% but usually achieve about 50% of gas
generated.
In the third and final anaerobic or
methogenic stage, species of methane forming organisms multiply and brake down
organic acids to form methane gas and other products. The water-soluble
degradation products from these biological processes, together with other
soluble components in waste such as, the rusting of metals items will be present
in leachates. The composition of leachate varies from landfills to landfills.
However, based on the compilation of Lee and Jones (1993) who presented the
compilation of information from the literature on chemical composition of
municipal landfill leachate as detailed in Table 1 below:
PARAMETER TYPICAL CONCENTRATION AVERAGE RANGE
BOD
1,000-30,000
10,500
COD 1,000-50,000 15,500
TOC
700-10,000
3,500
Tva
(as acetic acid) 70
-28,000 NA
Total
Kjeldah N2(as N)
10-500 500
Nitrate
(as N)
0.1-10 4
Ammonia
(as N) 100-400 300
Total
Phosphate (Po4)
0.5-50
30
Orthophosphate
(Po4)
1.0-60
22
Total
alkalinity 500-10,000 3,600
Total
Hardness 500-10,000 4,200
Total
Solids 3,000-50,000
16,000
Total
Dissolved/Solids 1,000-20,000
11,000
Specific
Conductance 2,000-8,000 6,700
(Mhos/cm)
PH 5-7.5 6.3
Calcium 100-3,000 1,000
Magnesium 30-500 700
Sodium 200-1,500 700
Chloride 1,000-2,000 380
Sulphate 10-1,000 0.9
Chromium
(total) 0.05-2 0.05
Copper 0.02-1 0.5
Lead 0.1-1 0.5
Nickel 10-1,000 430
Zinc 0.5-30 21
Methane
gas 60%
Carbon
dioxide 40%
All
values are in mg/l except as noted NA-Not available.
DUMPSITE
MANAGEMENT IN LAGOS.
In Lagos, the last decade have seen
considerable changes in the management of dumpsites. At the inception of Lagos
Waste Management Authority as Lagos State Refuse Disposal Board in 1977, there
were five existing dumpsites within Lagos metropolis namely; pelewura (Adeniji
Adele), Gbagada, Isolo, Achakpo and Ojota. These sites were open swamps that
are progressively reclaimed with refuse. The dumping of waste is done without
proper planning programme for leachate or landfill gas thus putting the
populace at the risk of environmental problem. In view of this, the state
government under the World Bank Assisted Project package of 1988 commissioned a
consultant for the development of landfill sites for the state. The project
gave rise to sites such as Olusosun, Abule-egba, and Solus.The Olusosun
landfill site is about 42 hectares in size with a life span of 35 years
receives an average of 1.2 million tones of waste annually. The Abule-Egba (Oke
-odo) landfill is about 3.0 hectares. While Solus is about 3.0 hectares. It
must be noted that Pelewura, Gbagada, Isolo, Achakpo and Ojota have been closed
down to waste disposal operations.
With
the existing landfills sites, the average tonnage of solid waste disposed
weekly in the state is estimated to be 17000 metric tones, while the recorded
dailywaste generation rate is about 0.5kg per capita. However, with the
composition of a still active landfill in Lagos and the climatic condition of
the state, the leachate generation is expected to be high. According to Ikem
(1996), table below represent the composition of an active landfill site in
Lagos.
Table
2: shows the composition of an active landfill site in Lagos.
Composition %
waste composition
Vegetation 59
Paper 17
Textiles 2
Plastic 12
Metals 8
Glass 2
Total 100
From
the above values it can be noted that the percentage of decomposable materials
is greater than the less decomposable materials. Moreover, it is worthy of note
that some other factors that contribute to the leachate generation include: the
mean annual rainfall in Lagos is 1620.59mm, which varies from place to place.
Generally, relative humidity is very high in Lagos being in a tropical region
with relative humidity ranges from76% to 80.5%.The morning hours recorded
annuals average of 90% while 01300hours has annual mean of 71%.the average
moisture content of Lagos waste is estimated to be 36.8%.(Lasisi K.S.A.,2001).
With this state of climatic condition leachate generation in Lagos
is expected to be high. Table below shows typical composition of leachate from
existing landfills in Lagos state.
PARAMETER OLUSHOSUN SOLUS ABULE-EGBA
Temperature
(oC) 34.20 37.40 31.20
PH 7.30 8.40 7.78
TS 17726 13252.20 12622.88
Chloride 1319 1389.00 1177.20
Sulphate 582 321 728
Nitrate 3.52 7.60 76.71
Phosphate 0.03 0.26 1.26
Lead 0.54 0.50 0.10
Magnesium 60.98 53.17 64.63
Iron 8.01 10.59 10.89
Copper 0.10 0.10 0.20
Calcium 13.59 14.75 11.69
Mercury 1.00 2.10 2.30
Cadmium 0.01 0.01 0.01
Arsenic 0.59 0.60 4.21
Nickel 0.04 0.02 0.31
Dissolved
Oxygen 2.34
2.33 3.15
*Mean
of five samples
All
results in mg/l except as noted
Source:
Lasisi K.S.A,(2001)
GROUNDWATER POLLUTION BY LEACHATE.
There is a common misconception that
since the materials placed in landfills are basically household wastes, they
are relatively ‘safe’ and are not likely to adversely affect public health and
groundwater quality. However, one need only to consider the proposition of
drinking the ooze that developed at the bottom of a garbage can or water used
to clean garbage disposal plastics to understand that it is not desirable to have
solid waste leachate in water considered desirable for potable use. Yet this is
what happens when leachate from municipal solid waste landfill is allowed to contaminate
water that is or could be used for domestic supply.
The USEPA estimates that there are about
55,000 landfills in the United State with 75% of which are polluting
groundwater. If this is happing in the US where there is a groundwater-monitoring
programme, then only God knows the quantity of leachates that are presently
polluting groundwater in Lagos with high water table. As reported, there are
three broad types of contaminants present in leachates that can pollute
groundwater and subsequently affects public health. These are hazardous
chemicals, conventional and non-conventional contaminates. Gintautass et. al,
(1992) reported the present of Phenoxyalkanoic acid herbicide in leachate,
which had not been previously reported. In a study trip to the existing
landfills in Lagos, it is not surprising to note the present of cans and
container of herbicides, germicides and other materials in the landfills. Belevi
and Baccini (1989) estimated that unlined landfills in a fairly wet climate
will hazardous chemical, such as, lead at concentration above drinking water
standards for several thousands years.
Presently,
automobile waste oil with its elevated heavy metals and hydrocarbons are
routinely thrown into household trash. Also, various types of batteries, such
as, mercury, nickel and cadmium based are presently been disposed off in
landfill in Lagos. Also, the disposal of burned out fluorescent tubes used for
home or commercial lighting also eventually finds its way to the groundwater.
HOW YOU CAN HELP
·
Minimizing
the type of materials disposed into landfills helps in the reduction of the
types of contaminants presents in the leachates.
·
The
removal of materials, such as, battries, and other heavy metal based products from
waste.
·
The use
of degradable waste as a source of filling materials for old wells should be
discourage.
·
Industrialist that generates hazardous waste should
make effort to develop their own landfill.
·
Organized
household hazardous material collection programs are introduced to reduce the
amount of hazardous chemicals discarded from homes.
·
Education of waste operators on hazardous
materials should be organized.
·
Introduction
of waste checking/tracking programme be established.
·
Compulsory
development of a groundwater-monitoring programme put in place.
·
Development
of criteria for proper landfill disposal facility.
·
Introduction
of a waste reduction programme.
CONCLUSION
The removal of contaminants from
contaminated landfill is generally difficult. It involves the use of many
methods, such as, air stripping, bioremediation, ion exchange demineralization
or reverse osmosis, activated carbon colums etc. This means that the cost of cleaning up
groundwater contaminated by municipal solid waste landfill leachates require
large sum of money and technology, which are presently not available in our
society. Even if they are cleaned up they cannot be relied upon to provide safe
drinking water supply. In this view, the US EPA in 1999 concluded that once a
water supply well has been contaminated by MSW
leachates, the well has to be abandoned as source of potable water supply.
Thus, there is need for the development of a leachate-monitoring program, which
must include routine measurement of a wide variety of chemicals that are known
or suspected to be present in the landfill that can be measured at very low
concentration.
More than 90% of the contaminates present
in landfill leachate are not identified or quantified; their public health
implication are unknown. The efficacy of groundwater “remediation”-treatment
methods in removing such contaminants to “safe” levels cannot be determined.
Thus, prevention and monitoring is the only option. We must be wise,
groundwater resources is becoming the only available sources of water supply.
REFERENCES
1. Adesina O. G (2000):
Sustainable Management of Municipal Solid Waste. Lagos State Experience. “Paper
Presented at a 4-day International Conference/Exhibition ENVIRON-NIGERIA 2000.
2. Belevi,H., and Baccini,
P.,(1989): “Long-Term Behavior Of Municipal Solid Waste. Landfills Waste
Mgt.&Res.7:43-56.
3
Coe J. J.(1970):Effects of Solid
Waste on Groundwater Quality.
J American Water Works Assoc., 22,776.
4
Federal Ministry Of Housing and
Environment (1982): The State of the Environment in Nigeria. Monograph Series
No 2: Solid Waste Management in Fifteen Cities and Urban areas in Nigeria. FHE.
Lagos.
5
Lasisi, K.S.A (2001): Composition
Of Landfill Leachates from existing Landfills in Lagos state.
6
Lavalin International (1992):
Design &Operation Report for the Oregun Landfill Site.
7
Lindorff D.E (1979): Groundwater
Pollution-a Status Report. Groundwater, 17,9-17.
8
Mather J. D. (1994): Preventing
Groundwater Pollution From Landfilled Waste-is Engineered Containment an Acceptable
Solution-in Groundwater Quality Edited by H.Nash and G.J. H McCall Chapman
&Hall. London.
9
Oladele Osibajo, Sunday Ajayi,
Folashade Adebiyi and Popo Akinyanju (2000): Public Analyst’s Reporting System
as Applied to Environmental Issues. Institute Of Public Analyst of Nigeria News
Vol.2.No 4 pg. 7-10.
10 . Raven A and Avnimelech .Y (1979): Leaching of Pollutants
Sanitary Landfill Models. Water Pollution Control, 51, 2705-2716.
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