2.1 DEFINITION
OF WASTE
Waste material in agriculture may be
defined as the undesirable products from biological, organic or industrial
sources. These wastes have been known to be of immense importance as potential
raw material in soil conservation and management for sustainable agriculture.
Soil organic waste is composed mainly of carbon, nitrogen, oxygen, hydrogen,
sulphur and phosphorus, but the most studies focus on carbon and nitrogen.
According to Williams (1988);
municipal waste is valuable in conditioning the soil, thereby enhancing crop
performance. Municipal waste forms which increases soil water holding capacity,
also helps to protect crop from drought and prevent the leaching of nutrients.
Municipal waste is measured by their
ability to supply essential plant nutrients and improve soil physical
properties (Wheel et al. 1988). The
agronomic potentials of municipal waste could also be assessed through the
physical observation of crop response and performance on soil due to the
amended material (Parret et al.
1989).
Many agriculturists in times past
have studied what effect municipal waste (solid waste) amended soil would have
on the soil’s eminent chemical properties. The cultivated plants take up these
material, metals and elements either as mobile ions present in the soil solution
through the roots or through foliar adsorption (Khaleel et al. 1988). This uptake of
the metal/element by plants results in the bioaccumulation of these elements in
the plant.
2.2 What
is Municipal waste (Solid Waste)
Municipal waste is the term used to
describe non-liquid waste materials arising from domestic, trade, commercial,
agricultural, industrial activities and from public service (Aibor and
Olurunad, 2006). The United State Environmental Protection Agency (USEPA)
defined municipal waste as any useless, unwanted or discarded materials with
insufficient liquid content to free flowing. According to the federal
environmental protection agency now the Federal Ministry of Environment (1995),
defines municipal waste are useless, unwanted or discarded materials that arise
from man’s activities within the environment and cannot be discarded through a
sewer pipe. The non-free flowing or sticky nature of municipal waste gives rise
to the accumulation of it on some habitable parts of the earth surface. History
has it that the manipulation of the environment that produced waste may have
begun with the domestication of fire (Encyclopedia Britannica, 1996).
The amount of waste produced by
human activities is increasing in most parts of the world, accompanied by the
problems of disposal which in turn affects the final disposal point which is
the soil (Microsoft Encarta 2010). The volume and types of municipal waste as a
result of continuous economic growth, urbanization and industrialization, is
experiencing a rapid increase all over the country. It is estimated that in
2006 the total amount of solid waste generated globally reached 202 billion
tones, representing 7% annual increase since 2003. It is further estimated that
between 2008 and 2011 the global generation of municipal waste will rise by
37.3%, equivalent to roughly 8% increase per year (Global Waste Management
Market Report, 2008). According to Salmon Chuck (2009), it is estimated that an
average Nigerian generates about 0.49kg of solid waste per day with households
and commercial centers contributing almost 90% of the total urban waste burden.
Until recently, Nigerians had not
been concerned with the amount of waste they generate. Their concern had not
gone beyond physical removal of waste from the streets. It has been common
practice to dispose off refuse by the expedite method. Such methods might be by
open dumping or the use of an open dump site, directly on the soil. But with an
increasing population and rapid urbanization, municipal waste is pilling up
faster than finding the appropriate place to put them (Sada and Odemerho,
1989).
A study in Nigeria showed that
municipal wastes are produced in the urban areas to a mean rate of 0.43kg per
individual a day (Sridhar et al.
1985). This is evident as it is not uncommon going through the length and
breath of the country without locating heaps of refuse littering the entire
landscape. This is a result of improper disposal and waste management plans.
The wastes of the early people were
mostly food stuffs and other less harmful substances that broke down easily by
natural decay processes. Pre-historic populations were also much smaller and
were spread over layer areas and as a result people were less concentrated in
one place and caused fewer problems (Sridhar et al.1984). Furthermore, most of the decayed wastes (Food stuff
etc) became compost, which then helps in making the soil more fertile. In
Nigeria, just like in the rest of the world rapid urbanization and population
growth have brought about a proportional increase in the amount of waste that
is generated. The inability to manage these wastes effectively in most
developing and some developed countries becomes an issue of great concern.
Apart from the destruction of the aesthetics
landscape by municipal waste dumped indiscriminately, some of the municipal
solid wastes contain both organic and inorganic toxic pollutants such as heavy
metal which threaten the productivity and stability of soil and also human health
and the entire ecosystem (Sridhar et al.
1985).
Composition of municipal wastes
provides a description of the constituents of the waste and it differs widely
from place to place. The most striking difference is the inorganic content
which is much higher in low income areas than the high income areas. This
reflects the difference in consumption pattern, cultural and educational
differences. In higher income areas, disposable materials and packaged food are
used at higher quantities. This results to the soil having a higher calorific
value, lower specific density and lower moisture content.
Municipal waste management according
to Ibrahim (2002) is the scientific way or established procedure and sanctioned
legislation for the collection, transportation and disposal of waste products
which is economically feasible and environmentally viable.
The biggest challenge with municipal
waste management in most Nigerian cities is not only the volume of the wastes,
but also the composition of the wastes. All categories of wastes including
toxic or non toxic, biodegradable or non-biodegradable, recyclable or
non-recyclable are dumped together making the management very difficult. The
reason(s) for this perturbing occurrence in developing countries may not be far
fetched, it could be as a result of lack of awareness, and poverty, population
growth, and high urbanization rate combined with the lack of government
policies on waste management and separation.
In places where there are government
policies, the agencies saddled with the mandate to enforce the policies are
either funded by the government or are not monitored for efficiency (Mato,
1999).
2.3 Characteristics of municipal waste
Municipal wastes have very unique
properties. They are known to mineralize and release available plant nutrient
as a result of microbial attack. It is also used particularly on soils that are
infertile (Kurl et. al, 1997). On the
other hand, marginal, erodible, sloppy and generally less productive soil would
benefit from the exposure to municipal waste material, especially waste material
having a high degree of microbial stability (parent et. al, 1999). Such material could release plant available nutrient
at a very high rate. Materials like undecomposed animal manure, green manures
and activated sewage sludge are subjected to rapid microbial decomposition, and
material such as municipal sewage sludge could be more resistant to microbial
attack and release their nutrients at a relative slower rate.
Municipal waste impaired a
beneficial and long term residual improvement on soil physical properties
because of its high level of municipal waste instability. Otori and Santana
1996 and Schleich 1986 noted that municipal sewage sludge material improves the
productivity of the soil more than inorganic fertilizers owing to its slow
release of nutrients. Most municipal sewage sludge and residue are low in their
content of macro and micro-nutrients compared with the chemical fertilizer
(Parr and Flornick, 1989).
2.4 Effect of municipal solid waste on
soil properties
According to Yondowei et al; (1986), the term refuse dump
means those materials that the primary generators or producers abandon within
the urban areas and which require decomposition upon abandonment.
Refuse are those materials, which
degenerates to organic material after which it has undergone decay and mix with
the soil, it replenishes one or more of the nutrients which plants needs to
grow property. Although plants will grow to some extent in almost all sandy
soil, refuse matter content is necessary to produce healthy plants in quantity.
Refuse dumps are manufactured from
the abandoned waste materials such as phosphate, potassium, potash gas and
petroleum phosphate. They are usually produced as solids in powder or granules
and as liquid. Plant cannot absorb nutrients that are free element, for this
reason refuse constitutes nutrient elements in order to be available to the
plant. The grade of such refuse is defined by its content of primary nutrients,
although other nutrients may be present in varying quantities (Ezedinma, 1997).
Refuse contains major elements in required quantity as the crop plant may need
for its growth. Nitrogen is obtained from the air and makes it into refuse form
by being combined with hydrogen from natural gas or petroleum distillate.
Phosphorus is applied to soil as ammonium phosphate or Super Di-Phosphate. The
basic materials for its manufacture are phosphate rock treated with sulphuric
acid. There are however, different types of refuse on the bases of nutrients they
supply. When a refuse is decayed and supply only a few nutrient to the soil it
should be seen as an incomplete refuse nutrient element.
Refuse has much effect in crop
yield. The rate of its application required will vary with the type of the
crop, the stage of growth, and the soil fertility. Mbagwu (1989) stated that
most crop grown in Nigeria
,
and the soil structure, particularly in the savannah area and as soil which shave
been exhausted by extensive cropping, responds well to refuse dump soil sites,
this response is because of the high nitrogen to moderate potassium content,
where as more positive results have been obtained from soil in the refuse dump
sites areas. Refuse dump matter content maintains correct soil consistency,
controls the soil acid content necessary to provide and maintain soil that will
produce high crop yield.
Matt (1970) reported that soil that
is low in organic matter content level could not be expected to sustain it’s
imposed family system, but with the application of refuse on the soil will
increase the soil micro-organism, with the needed organic matter contained in
the non-refuse dump soil.
Epstein
et al. (1976) reported that refuse
enhances the physical, biological and chemical properties of the soil. Hall
(1983) added that refuse matter diminishes the hazards of erosion and land
slide by returning completely the crop nutrients that help in soil particles
aggregation. Also refuse releases deposits of nutrients which increases soil
aggregation, structural stability, water holding capacity, infiltration rate
and reduces the power of erosive agent.
Allison (1973) noted that the
decrease in the refuse use on soil results to degradation of soil structure,
low infiltration rate, poor aeration, water logging of soil, low cation exchange
capacity and acceleration of runoff and erosion, which leads to the loss of
natures resource base.
Wahab (1980) disclosed that refuse
that was not controlled will lead to an increase of soil pH. Hence refuse
improves soil nutrition status and aids in crop productivity and yield. Since
refuse usually contain the entire major plant nutrient in the right
proportions, while the physical properties of the soil such as depth, texture
and structure contributes to its productivity, the use of refuse for cropping
or agricultural activities is profitable, Conazi (1986).
Refuse soil and non-refuse soil
structure are different as a result of the nutrient content value of each.
Alexander (1977) revealed that refuse site has more organic matter which was
induced by the presence of refuse matter. A variety of products are formed from
the original refuse. As the organic material undergoes further decomposition,
they are converted to brown and black organic complex which is generally known
as humus. Conclusively for effective long term sustainability, the question of
how fertile is soil, is crucial, for their ability to supply essential plant
nutrients, improve soil physical properties, increase crop yield, and maintain
durable soil productively. A research on this, laid on the agronomic potential
of refuse matter and the decomposition of the original material on the soil
properties can not be over emphasized.
2.5 REFUSE DUMP SITE
Refuse site is a land disposal area
at which solid wastes are disposed of in a manner that does not protect the
enviroment. Refuse site is susceptible to open burning, and is exposed to
elements, diseases, vectors and scavengers. These planned heaps of uncovered
waste, often burned and surrounded by a pool of stagnated polluted water, rat,
flies and domestic animal roaming freely and families of scavengers picking
through the waste is not only an eyesore but a great environmental hazard (Christian
Zurbrugg, 1999).
Scavenging is disruptive to good
dump site operation. It presents safety hazards to both scavengers themselves
and dump site employees. It reduces productivity by delaying waste compaction
and removal. In addition the fire set on the waste to facilitate scavenging is
a great environmental hazard (Defteris, 1998).
2.6 AGRONOMIC BENEFITS OF MUNICIPAL
WASTE.
The agronomic value of municipals waste is measured by
their ability to supply the plant essential nutrients, and improve soil
physical properties, (Khaled et. al,
1981). On marginal soil, it improves the structure and water retention capacity
which may be all that is needed to ensure a better soil enviroment for root
development and nutrient uptake. Soil with good structure improves physical
properties which is secondary to enhance the fertility status associated with
waste application.
The agronomic benefit of municipal waste could also be
assessed through the physical observation of crop response and performance due
to the amendment (Parr et. al, 1986).
Crop yield response to addition of municipal waste material are highly variable
and is dependent upon soil type, the crop, climatic condition, management
systems and types of municipal waste material used. Therefore productivity is a
determining factor in discovering if a particular waste material is suitable as
a soil amendment relative to another waste material (Parr et. al, 1986). The poor physical condition of the tropical soil
could be attributed to cultivators, erosion and intensive weathering.
Mbagwu (1992) reported that the major physical
constraint to high level of crop production oN degraded soil was high bulk density
resulting from confined cultivation. Highly weathered alfisol, exisols and
utisols have inherent low waste retention capacity due to low content of
colloidal materials, and the resulting consequence of this is reduced porosity.
Infiltration rate and saturated hydraulic conductivity and low available water
capacity.
Soil erosion is also a factor responsible for the
rapid degradation and breakdown of good structure exhibited in tropical forest
soil as manifested in low bulk density and high infiltration rate and hydraulic
conductivity. Generally, some of these physical properties includes; water
holding capacity, water retention bulk density, particle size density, micro
and macro porosity, saturated hydraulic conductivity, water infiltration, total
and available water capacity, aggregate stability, plastic limit, soil structure
and electrical conductivity.
2.7 CHEMICAL QUALITIES OF THE SOIL
Some
chemical qualities of the soil are discussed below:
Cation
Exchange capacity (CEC)/Effective cation Exchange capacity (ECEC)
Cation
exchange capacity is defined as the total sum of exchangeable cations that can be
absorbed by 1g of the soil. It is measured in miliequivalent. It is the
capacity of the soil colloids to absorb nutrients. Using ammonium acetate (NH2OAC)
method (Jackson 1958). The cation exchange capacity of soil varies with;
1. The kind of clay
2. The percent of clay and
3. The percent of organic matter
It should be pointed out that the
cation exchange capacity (CEC) in most soils increases with pH value, only the
so-called permanent charges of clay and a small portion of the charges or
organic colloids held ions that can be replaced by cation exchange.
As the pH is raised, the hydrogen
held by the remainder of the organic and inorganic colloids becomes ionized and
is replaceable. Also this absorbed aluminum hydroxyl ions are removed forming
AI(OH)3 thereby releasing additional exchange sites on the mineral `colloids.
The net result is an increase in the cation exchange capacity. In most cases
the cation exchange capacity is determined at a pH of 7.0 or above. These means
that it includes most of those charges depended of pH as well as the more or
less permanent ones. The cation exchange capacity as mentioned above is
expressed in terms of equivalents, or more specifically as milliequivalents per
100 grams.
ECEC
The effective cation Exchange
capacity (ECEC) is used for soils which are not base saturated, that is pH less
than 7. The effective cation exchange capacity gives rise to the cation
exchange capacity of the soil near its neutral pH. Methods such as NH4
acetate or barium chloride extractions determine the ECEC of the soil
particularly those dominated by variable charged clay. The effective cation
exchange capacity (ECEC) is calculated by summing the exchangeable acidity.
Aluminum saturation is the percentage of ECEC occupied by the exchangeable
aluminum and is written as ECEC =meq/1000g=exchangeable k+ exchangeable Ca +
exchangeable acidity.
While
aluminum saturation = Exchangeable A13 x
100
ECEC 1
BASE SATURATION
Two groups of absorbed cations tend
to have opposing effects on soil acidity and alkalinity. Hydrogen and aluminum
tend to dominate acid soils, both contributing to the concentration of H+
ions in the soil solution. Absorbed hydrogen contributes directly to the H+
ion concentration in the soil solution.
A13+ ions do so
indirectly through hydrolysis. Most of the other cations called exchangeable
bases change the soil towards alkalinity. The proportion of the cation exchange
capacity occupied by these bases is called the percentage base saturation. Colloid
complexes in arid-region soils are practically saturated with base. As the base
saturation is reduced, due to the loss in drainage of lime and other metallic
constitutes, the pH also is lowered to a definite proportion. This is in line
with the common knowledge that leaching tends ordinarily to increase the
acidity of humid-region soils (Bates et,
al.). This is calculated as:
Base
saturation = Total Exchangeable bases x 100
Cation
exchange capacity 1
OR
Percentage base saturation = Meg
exchange bases
(PBS) X100
CEC
pH (Power
of Hydrogen)
The ph value of a solution is the
logarithm to base 10 of the reciprocal of the +I ion concentration it may be
state conveniently as follows;
pH = log10 1
This can be determined by electric method
H+
The concentration of the H ion (and
consequently the pH) is related mathematically to the concentration of the OH
ion: this determines the percentage of H+ in the soil. If there is
preponderance of H+ in the soil the soil will be acidic and alkaline.
And if the proportion of H+ and OH is equal the soil is neutral.
This pH determines the acidity or alkalinity of soil.
Mineral content
This
is the amount of mineral nutrient that is contained in the soil. The percentage
mineral composition of plants varies considerably according to soil, climate
and crop variety. The essential elements other than the CHO are generally
regarded as the mineral nutrients. The mineral elements are all obtained from
the soil.