MINISTRY
OF EDUCATION AND TRAINING
VIETNAM ACADEMY OF SCIENCE AND
TECHNOLOGY
GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY
-----------------------------
Le Cao Khai
RESEARCH ON THE LEACHATE TREATMENT BY
ELECTROCOAGULATION METHOD COMBINED WITH
BIOLOGICAL FILTRATION
Major: Environmental Engineering
Code: 9.52.03.20
SUMMARY OF ENVIRONMENTAL ENGINEERING
DOCTORAL THESIS
Hanoi - 2019
This thesis was done at:
- Institute of Environmental Technology, Vietnam Academy of Science and Technology
- Graduate University of Science and Technology - Vietnam Academy of Science and
Technology.
Supervisor 1: Assoc.Prof., Dr. Trinh Van Tuyen
Supervisor 2: Dr. Le Thanh Sơn
The dissertation will be defended at Graduate University of Science and Technology
- Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet street, Hanoi.
Time: .............,.............., 2019
This thesis could be found at:
- National Library of Vietnam
- Library of Graduate University of Science and Technology.
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INTTRODUCTION
1. Rationale of the study:
Currently, along with the development of society, people lives are
gradually improved and consume demand is increasing, leading to an increasing
amount of waste, especially domestic waste (DW). The average annual increase
is approximately 12%. The regular increase in domestic waste causes an
increasing amount of leachate. Leachate is generated from both landfills and
transfer stations containing high polluted levels with Chemical Oxygen
Demand (COD) up to 70000 mg/l, Dissolved Solids (DS) up to 50000 mg/l,
Total Suspended Solids (TSS) to 2000 mg/l and nitrogen content up to 3000
mg/l,… Leachate with badly stink affects to surrounding areas and contaminate
the groundwater as well as pollute surface water sources. Therefore,
environmental pollution by leachate has always been a serious problem which
get special attention in environmental protection.
Although, according to regulations, each landfill must have a leachate
treatment system, most of the current leachate treatment techniques in our
country still reveals many weaknesses neither the quality of treated water often
does not meet the effluent standards, especially the COD and nitrogen
parameters (VN standards 25: 2009/MONRE column B), nor difficult operation
and expensive cost. The reason comes from the leachate characteristics with the
complex composition and the continuous change by the landfill operating time.
The selection of inappropriate treatment technologies has resulted in non-
responding to discharge standards, while the leachate in landfills increases
continuously. Hence, it is necessary to find some appropriate technologies
which are able to handle all the daily leachate, improve current leachate
treatment systems and equip for the new landfills.
The option of combining electro-coagulation (EC) with biological filtration
(BF) is one of the promising solutions to increase the effectiveness of leachate
treatment. Unlike chemical coagulation, a large amount of coagulants must be
used, thus consuming a lot of chemicals as well as creating a great amount of
generated sludge, the EC process has the ability to remove effectively heavy
metals, phosphorus compounds, phenol compounds, hydrocarbons and several
pathogenic microorganisms, which are difficult to decompose by biological
methods. In addition, this process is also easy to automate and minimize the use
of chemicals thus reducing the amount of generated sludge. Meanwhile, the BF
process has the high treatment performance of suspended compounds (TSS),
total nitrogen (TN) and BOD5. In particular, the BF process on inexpensive
organic substrates such as peat, wood bark, and plastic have a higher treatment
efficiency than conventional BF processes. The reason is that the porous
organic substrates have a large specific surface area which is possible to absorb
a large amount of microorganisms, together with other physicochemical
processes, leading to very strong nitrate reduction. Combining two above
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technologies allows optimization of leachate treatment process and post-
treatment water can reach VN standards 25: 2009/MONRE column B2.
Facing this situation, successful research and application of EC technology
combined with bio-filter is essential for leachate treatment. Because of this
reason, the topic “Research on the leachate treatment by electrocoagulation
method combined with biological filtration” is chosen.
2. Study object:
This thesis aims to investigate advance techniques for leachate treatment,
especially electrocoagulation, biological filtration, and their combination.
Through research, the thesis wishes to achieve the following objectives:
1/ Determine suitable conditions for COD, ammonium, TSS and color
treatment in leachate by EC.
2/ Determine suitable conditions for COD, ammonium, TSS and color
treatment in leachate after EC treatment by BF.
The task of the thesis is to study the EC process in combination with BF
process to increase the effectiveness of leachate treatment, ensuring
environmental standards VN standards 25: 2009/MONRE column B2.
3. Study content:
Leachate treatment by EC
1/ Experiments to study the effect of several parameters namely current
density, electrolysis time, pH, electrode distance on COD, ammonium, TSS and
color treatment in leachate by iron and aluminum electrodes.
Leachate treatment by BF after EC process
2/ Experiments to study the effect of aeration modes and input loads on
COD, ammonium, TSS and color treatment in leachate after EC treatment by BF.
CHAPTER 1. OVERVIEW
1.1 Leachate
1.1.1. Leachate characteristics and composition
Leachate is defined as any type of polluted liquid in the rubbish that
permeates through the garbage layers in landfills and entitles suspended solids,
dissolved colloids from solid wastes discharged into or outside the landfills.
The composition of the leachate varies widely depending on the composition
of the landfill waste and the landfill time. The pollutant content in leachate of the
new solid waste landfill is much higher than the old solid waste landfill. Because
in the old landfills, the content of easily biodegradable organic matter has been
mostly decomposed. Meanwhile, the leachate in the new landfills usually has a
low pH but very high content of COD, BOD5, nutrients, TDS and heavy metals. In
contrast to the new landfills, leachate in long-term landfills often has high pH (due
to increased methaneization) and the content of COD, BOD5, nutrients, TDS and
heavy metals decreases because most of the metals transfer to precipitate state as
pH increases. In particular, leachate in long-term landfills contains many high-
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molecular compounds with many toxic chemicals that both cause dark color and
unpleasant odor, which are difficult to decompose by biological methods.
1.1.2. Impact of leachate on the environment and people
Leachate has high concentrations of pollutants such as: COD = 2000 -
70000 mg/l, BOD = 1200 - 27000 mg/l and many other toxics which can
permeate through the soil and contaminate the underground water sources as
well as surface water system. Bad odor in leachate can pollute the air
environment. Therefore, when leachate is discharged into the environment, it
will cause severe environmental pollution and affect public health.
1.2. Electrocoagulation overview
Mechanism of electrocoagulation process
“Electrocoagulation is an electrolysis method to treat contaminated water,
using direct current (DC) to corrode anode (usually aluminum or iron) and then
release coagulants (usually aluminum or iron ions) into the solution”.
When metal electrolysis occurs, the following processes occur:
M → Mn+ + ne-
These metal cations combine with the OH- ions (present in the water) to
form metal hydroxides according to the following reaction equations:
Mn+ + nOH- → M(OH)n
1.3. Bio-filter overview
1.3.1. Mechanism of bio-filter process
BF is a technique that uses biofilms formed on a solid carrier. The carrier
may have a fixed position in a reaction device and the fluid flow forms a thin
film that flows over the surface of the microbiological membrane in trickling
filtration technology; microbiological membranes alternately intermittently
contact with the gas and liquid phases through a rotating shaft such as in a
biological rotating disc. The carrier has a fixed position in a submerged layer and
water containing impurities flows through the material layer in the BF column.
1.3.2. Theoretical basis of nitrogen treatment in wastewater by biological processes
Nitrogen treatment in wastewater is usually carried out in two stages. Stage
1 is the process of converting ammonium to nitrate (nitrification). The second
stage is the process of nitrate denitrifying to evaporate (de-nitrification).
1.3.3. Combining methods in leachate treatment
Wiszniowski et al. (2006) have shown that in order to treat the leachate to
meet the effluent standards, several methods are needed to combine to treat
effectively the leachate. The primary is a combination of 3 methods: physics,
chemistry and biology. There have been many studies showing the effectiveness
of a combination of methods in leachate treatment. The following is just a
combination of EC and BF in leachate treatment.
Currently, there are only 2 studies combining EC with BF in leachate treatment.
One is to combine BF first, then magnesium - electrode EC. Other is the combination
of aluminum electrodes EC before BF process. Both of these results show the