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FMTLxLyLz DIMENSIONAL EQUATION
FOR SLUDGE DRYING BED.
EZE BRENDAN IFEANYI
A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE
REQUIREMENT FORTHE AWARD OF MASTER OF ENGINEERING
(M.ENGR. IN WATER RESOURCES AND ENVIROMENTAL ENGINEERING).
DEPARTMENT OF CIVIL ENGINEERING,
FACULTY OF ENGINEERING,
UNIVERSITY OF NIGERIA, NSUKKA.
Waste generation, a growing problem facing the world is as a result of rapid
industrialization, urbanization and increase in population growth. Emphasis on
agriculture for more food production to take care of the expansion in population
has generated increased volume of domestic, industrial as well as agricultural
Owing to health and other environmental hazards (like ,water, air and soil
pollution) industrial and domestic wastewaters pose to the existence of man and
the entire ecosystem there is therefore, every need to treat wastewater properly
before discharging to receiving streams , water bodies or agricultural lands.
Sludge, a term used to designate the solid that settles when sewage is passed
through a settling tank is a serious problem for all wastewater treatment plants
all over the world in terms of disposal and handling. Industrial as well as
domestic wastewater processing in an effort to meet more stringent discharge
measures and limitations led to increased sludge production.
Sludge which is produced as a by-product of all treatment processes have
considerable application potentials (such as fertilizer and soil conditioners).The
liquid sludge contains about 90-98% water and sometimes it is transported long
distance for ultimate disposal. Economically, it is very important to reduce the
sludge volume by removing as much water as possible to ease the transportation,
handling and disposal cost.
Dewatering and disposal of sludge is a major economical factor in the
operation of wastewater treatment plant. MIKKELSEN, (2002) reported that 30-
50% of the annual operating costs of treatment plants are related to sludge
Sludge dewatering can be done through a natural means- drying bed. Drying
beds are mostly used in small industries as well as small community with a
population of over 100,000 people, (Echenfelder and Santhanam, 1981).The
assumptions in designing drying beds are mainly based on the solid content as
well as the sludge volume. Sludge drying beds are often open to the air and the
performance or efficiency is dependent on weather and climatic conditions. It
equally depends on the nature of the sludge, the height of the sludge applied on
the drying bed and this is usually between 150mm- 350mm and the dry initial
solid content of the sludge. Solar intensity, wind velocity and temperature also
play important role in the efficient performance of drying beds though they are
often neglected. Moisture reduction on the drying bed is lost through percolation
Dispersed particles in sludge had often been observed to have a negative effects
on filtration rate and the increase in resistance experienced using drying bed is
due to the blinding of the filter medium of sludge cake with small particle.
(Mehrdadi, et al,2006).
FMTL (Force, Mass, Time and Length) dimensional analysis is a
mathematical technique used in checking derived equations according to Rajput,
(1998). It is used in solving several engineering problems. Since no chemical
reaction is assumed to take place during sludge filtration, dimensional analysis
can be used in deriving an equation to describe the system.
1.02 Research Aims and Objectives.
(1) To use dimensional analysis approach of FMTLxLyLz to develop sludge
filtration equation for sand drying bed without the compressibility attribute.
(2) To examine the effect of chemical conditioning on specific resistance using
sand drying bed.
(3) To demonstrate or investigate the performance of sand drying bed as sludge
1.03 Research Problems.
Since mechanical method of dewatering sludge is very expensive in terms of
operation, as well as equipment and maintenance cost. The research work is to
develop a dewatering option that will be more economical to maintain and
1.04 Significance of Study.
To maintain a healthy environment is a goal worthwhile, and hence the great
need to treat properly our waste water before they find their way into our water
bodies or agricultural lands and other possible reuse. Over the years mechanical
method of dewatering have proved very expensive both in maintenance and cost
of equipment. As a result, researchers in this field are concerned with
developing a dewatering technique like the natural drying bed to reduce the high
maintenance and equipment costs of dewatering sludge.
This work highlights the use of dimensional analysis approach to derive sludge
filtration equation which can be found useful in the design and operation of sand
1.05 Scope and Limitation of the Research.
The scope is limited to the treatment of sewage sludge from the waste water
treatment plant at the University Of Nigeria, Nsukka. Owing to the weather and
climatic condition at the time the research was carried out, sludge treatment was
adversely affected as longer time was needed to attain the optimum temperature
needed to intensify dewatering.
2.01 LITERATURE REVIEW.
Sludge disposal is a growing challenge all over the world as most waste
water treatment plants in an effort to meet or adhere to the recommended
discharge limits lead to more waste generation.
Reduction in sludge volume by dewatering before drying and subsequent
disposal is very important; as the water content of the sludge is reduced it
enhances the cost of handling, disposal as well as transportation cost. Most often
than not, to utilize this sludge for different applications such as fertilizer and soil
conditioners it is sometimes transported over a long distance.
Economically, sludge volume reduction will significantly reduce the cost of
transportation, barging trips and time (in a situation where sludge is to be
deposited in a river, sea or ocean.) handling and disposal of the waste.
Ademiluyi, et al, (1983), reported that because of the high water content in
sludge which is about 97.5%, sludge generated is difficult to handle.
According to Agunwamba, (2001), dewatering process increases solid contents
of the sludge between 20-35%. In the same way, Grag (,2008) agreed that
dewatering of sewage sludge does not only remove the high water content, but
also produce sludge that is non putrescible and odourless.
2.02 Sludge Treatment Processes.
Sludge treatment processes are aimed at achieving a low sludge mass for
disposal i.e a low solid mass and a high dry matter content of the dewatered
sludge cake, and destruction or stabilization of sludge solids. While digestion,
accomplish solid destruction and stabilization, sludge volume reduction is
achieved by both concentration and dewatering. Both volume reduction and
solid destruction are also possible via heat drying and
Several techniques exist to dewater sludge. Most of them are mechanically
done using a filter press (employing pressure or vacuum) or a centrifuge .The
other methods are based on natural phenomenon such as evaporation ,
percolation, temperature, wind velocity, precipitation or rainfall to achieve
sludge volume reduction. These include the natural drying bed, lagoons,
oxidation ponds, bio-filters, oxidation ditch etc. All these technologies
especially drying beds and oxidation ponds require large areas of land and with
the current increase in industrialization and urbanisation to acquire such area of
land is a scarce resource.
2.03 Sludge Digestion
Sludge digestion is a decomposition process which can either be aerobically (in
the presence of oxygen) or anaerobically (absent of oxygen). Anaerobic
digestion is usually mesophylic at a temperature of 35. The major thing in
sludge digestion is that living organisms eat up or consume the organic matters
in the sludge and the fermentation process that result from the sludge
decomposition reduces the pollution that comes from the sludge.
This process is accompanied by liquefaction, production of gas (methane gas)
and stabilization of organic matter. The gas so produced can be useful in
producing heat or electrical energy. The digested sludge can be used as soil
conditioner for agricultural purposes and can also be incinerated. (Fair, et al,
1971) developed an equation, a relationship for sludge digestion as,
Bacteria + Organic matter = Bacteria + CH4 + CO2 + H2O + Residue.