02:04:00
TASK: To
design an environmentally friendly flow sheet for biological/chemical
degradation of waste excluding combustion.
TYPES OF
SOLID WASTE
Solid waste can be classified into different types depending on their source:
— Municipal
waste.
— Industrial
waste.
— Hazardous
waste.
MUNICIPAL WASTE
This waste is generated mainly from residential and
commercial complexes. With rising urbanization and change in lifestyle and food
habits, the amount of municipal solid waste has been increasing rapidly and its
composition changing. Examples include: food waste, rubbish, agricultural
waste, construction and demolition waste, etc. (Howard, Donald, and
Tchobanglous, 1985).
SOLID WASTE MANAGEMENT
Management of solid waste reduces or eliminates adverse impacts on the
environment and human health and supports economic development and improved
quality of life. A number of processes are involved in effectively managing
waste for a municipality. These include monitoring, collection, transport,
processing, recycling and disposal.
In addition, an effective system of solid waste management
must be both environmentally and economically sustainable.
•Environmentally sustainable: It must reduce, as much as possible, the
environmental impacts of waste management.
•Economically sustainable: It must operate at a cost acceptable to
community.
An effective waste management system includes one or more of the
following options:
— Waste
collection and transportation.
— Resource recovery through sorting and recycling i.e. recovery of
materials (such as paper, glass, metals) etc. through separation.
— Resource recovery through waste processing i.e. recovery of materials
(such as compost) or recovery of energy through biological, thermal or other
processes.
— Waste
transformation (without recovery of resources) i.e. reduction of volume,
toxicity or other physical/chemical properties of waste to make it suitable for
final disposal.
— Disposal
on land i.e. environmentally safe and sustainable disposal in landfills.
CLASSIFICATION
OF SOLID WASTE
METHODS OF
SOLID WASTE DEGRADATION
— Biological
degradation
— Chemical
degradation
BIOLOGICAL
DEGRADATION
Biological degradation is the complete microbial
breakdown or mineralization of complex materials into simple inorganic
constituents such as CO2, water and mineral components. All biological waste
treatment processes involve the decomposition of biodegradable wastes by living
microbes.
(bacteria and fungi), which use biodegradable waste
materials as a food source for growth and proliferation. Microbes excrete
specialised enzymes that digest biodegradable waste constituents (e.g.
cellulose and other complex polysaccharides, proteins and fats) into simple
nutrients (e.g. sugars, amino acids, fatty acids).
These transformations may be achieved either
aerobically or anaerobically, depending on the availability of oxygen. Aerobic
conversion transforms waste to compost, while anaerobic conversion transforms
waste to CH4 and CO2 and resistant organic matter (Tchobanoglous et al., 1993).
COMPOSTING
Composting is aerobic decomposition of organic matter by the action of micro
organisms. It is the natural process of decomposition of organic waste that
yields manure or compost, which is very rich in nutrients. Composting is a
biological process in which micro-organisms, mainly fungi, and bacteria,
convert degradable organic waste into humus like substance. This finished
product, which looks like soil, is high in carbon and nitrogen and is an
excellent medium for growing plants.
ANAEROBIC DIGESTION
Anaerobic digestion is the bacterial
decomposition of organic waste in the absence of free oxygen The anaerobic
decomposition of organic materials yields principally methane (CH4),carbon
dioxide (CO2) and a solid compost material that can be used as soil
conditioner. It occurs in three stages, hydrolysis/liquefaction, acidogenesis
and methanogenesis. The first group of microorganism secretes enzymes, which
hydrolyses polymeric materials to monomers such as glucose and amino acids.
These are subsequently converted
by second group i.e. acetogenic bacteria to higher volatile fatty acids, H2
and acetic acid. Finally, the third group of bacteria, methanogenic bacteria,
convert H2, CO2, and acetate, to CH4.
LANDFILLING
Landfilling involves the controlled disposal
of solid waste on or in the upper layer of the earth’s mantel. Landfill has
been widely used for municipal solid waste (MSW) disposal all over the world.
Especially in developing countries, it is considered to be a reliable and cost
effective method if adequate land is available. Basic principle of conventional
landfill design is to contain or store the waste so that the exposure to human
and environment could be minimized. This is done by the prevention of gas
emission from landfill and infiltration of surface water.
Bioreactor landfill is an emerging
technology for solid waste management. The basic concept of bioreactor landfill
is to use specific design and operation practices to accelerate the
decomposition of organic wastes in a landfill by promoting optimum moisture
content and sufficient nutrients for the microorganisms to degrade the waste.
These enhanced microbial processes have the advantage of rapidly reducing the
volume of the waste creating more space for additional waste, they also
maximise the production and capture of methane for energy recovery systems and
they reduce the costs associated with leachate management.
CHEMICAL
DEGRADATION
This refers to processes that involve the use of chemical agents to process
waste.
Contact us for full project topic @
shadowfactonline@gmail.com
REFERENCES
EGSSAA
(2009). Solid Waste. Retrieved from www.encapafrica.org.
Howard, S.
P., Donald, R.R and Tchobanglous, G (1985). Environmental engineering.
McGraw-Hill International Press, Singapore. Pg 573-576.
Odocha JNK
(1994). Waste generation and management in a depressed economy. A lecture
delivered to student of the law and environmental faculties,UNEC, University of
Lagos.
Sabiiti EN
(2011). Utilizing Agricultural waste to conserve food security and conserve the
environment. Afr. J. Food, Agric. Nutr. Dev. 11:6.
Sani A,
Awe FA, Akinyanju JA (1992). Amylase synthesis in Aspergillusniger and
Aspergillusflavus grown on cassava peel. J. Ind. Microbiol. 10:55-59.
Sridhar
MKC (1996). “Women in waste management”. A seminar paper sponsored by LHHP and
the british council for the seminar on educating women for sustainable
environmental management. Owerri, Nigeria. March.
Tchobanoglous,
G., H. Theisen & S.A. Vigil (1993). Integrated Solid Waste Management.
McGraw-Hill International Press, Singapore. 957 p
Contact us for full project topic @
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