Study content: Leachate treatment by EC 1/ Experiments to study the effect of several parameters namely currentdensity, electrolysis time, pH, electrode distance on COD, ammonium, TSS an
Trang 1GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY
Trang 2- 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.
Trang 31. Rationale of the study:
Currently, along with the development of society, people lives aregradually improved and consume demand is increasing, leading to an increasingamount of waste, especially domestic waste (DW) The average annual increase
is approximately 12% The regular increase in domestic waste causes anincreasing amount of leachate Leachate is generated from both landfills andtransfer stations containing high polluted levels with Chemical OxygenDemand (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 3000mg/l,… Leachate with badly stink affects to surrounding areas and contaminatethe groundwater as well as pollute surface water sources Therefore,environmental pollution by leachate has always been a serious problem whichget special attention in environmental protection
Although, according to regulations, each landfill must have a leachatetreatment system, most of the current leachate treatment techniques in ourcountry still reveals many weaknesses neither the quality of treated water oftendoes not meet the effluent standards, especially the COD and nitrogenparameters (VN standards 25: 2009/MONRE column B), nor difficult operationand expensive cost The reason comes from the leachate characteristics with thecomplex 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 increasescontinuously Hence, it is necessary to find some appropriate technologieswhich are able to handle all the daily leachate, improve current leachatetreatment 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 leachatetreatment Unlike chemical coagulation, a large amount of coagulants must beused, thus consuming a lot of chemicals as well as creating a great amount ofgenerated sludge, the EC process has the ability to remove effectively heavymetals, phosphorus compounds, phenol compounds, hydrocarbons and severalpathogenic microorganisms, which are difficult to decompose by biologicalmethods In addition, this process is also easy to automate and minimize the use
of chemicals thus reducing the amount of generated sludge Meanwhile, the BFprocess has the high treatment performance of suspended compounds (TSS),total nitrogen (TN) and BOD5 In particular, the BF process on inexpensiveorganic substrates such as peat, wood bark, and plastic have a higher treatmentefficiency than conventional BF processes The reason is that the porousorganic substrates have a large specific surface area which is possible to absorb
a large amount of microorganisms, together with other physicochemicalprocesses, leading to very strong nitrate reduction Combining two above
Trang 4technologies allows optimization of leachate treatment process and treatment water can reach VN standards 25: 2009/MONRE column B2.
post-Facing this situation, successful research and application of EC technologycombined 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 colortreatment in leachate by EC
2/ Determine suitable conditions for COD, ammonium, TSS and colortreatment in leachate after EC treatment by BF
The task of the thesis is to study the EC process in combination with BFprocess to increase the effectiveness of leachate treatment, ensuringenvironmental 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 currentdensity, electrolysis time, pH, electrode distance on COD, ammonium, TSS andcolor 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 onCOD, 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 thatpermeates 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 thenew 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 beenmostly decomposed Meanwhile, the leachate in the new landfills usually has alow pH but very high content of COD, BOD5, nutrients, TDS and heavy metals Incontrast 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 andheavy metals decreases because most of the metals transfer to precipitate state as
pH increases In particular, leachate in long-term landfills contains many
Trang 5high-molecular compounds with many toxic chemicals that both cause dark color andunpleasant 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 canpermeate through the soil and contaminate the underground water sources aswell as surface water system Bad odor in leachate can pollute the airenvironment Therefore, when leachate is discharged into the environment, itwill 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 thenrelease coagulants (usually aluminum or iron ions) into the solution”
When metal electrolysis occurs, the following processes occur:
1.3.1 Mechanism of bio-filter process
BF is a technique that uses biofilms formed on a solid carrier The carriermay have a fixed position in a reaction device and the fluid flow forms a thinfilm that flows over the surface of the microbiological membrane in tricklingfiltration technology; microbiological membranes alternately intermittentlycontact with the gas and liquid phases through a rotating shaft such as in abiological rotating disc The carrier has a fixed position in a submerged layer andwater 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 secondstage 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 tomeet the effluent standards, several methods are needed to combine to treateffectively 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 acombination 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
Trang 6effectiveness of EC and BF combination in leachate treatment However, furtherstudies with other electrodes are needed to find the optimum conditions for leachatetreatment with high efficiency and low operating costs Therefore, the new directionthat the thesis focuses on is study on leachate treatment by the combination of ironelectrode EC and BF The dissertation also compares the effectiveness of leachatetreatment by iron electrode EC process with aluminum electrode EC process.
Therefore, the study of leachate treatment by EC with BF is the directionchosen in this thesis
CHAPTER 2 STUDY OBJECT, SCOPE AND METHODS
Figure 2.1 Diagram of leachate treatment by EC combined with BF
2.1 Study object and scope
Trang 72.2.2 Experimental method of electrocoagulation.
Experiments were conducted to find suitable conditions of currentdensity, electrolysis time, pH, electrode distance for leachate treatment
2.2.3 Experimental methods of bio-filter
The experiments were conducted to find suitable conditions for aeration mode, input load for leachate treatment after EC treatment (assessed through COD, ammonium, nitrate, TSS, color)
CHAPTER 3 RESULTS AND DISCUSSIONS
3.1 Study on leachate treatment by electrocoagulation
Currently, EC is used to treat wastewater With leachate having highconcentration of COD, BOD, ammonium, TSS and color, EC is a new andeffective method
- For COD, TSS and pigments are basically treated according to theelectrocoagulation mechanism that flocculants are generated from electrolysis
- For ammonium treated basically by the mechanism of electrochemical,adsorption
In order to increase the of EC treatment efficiency, such as currentdensity, electrolysis time, electrode distance, electrode material and pH ofleachate need to be investigated and found the optimal condition
3.1.1 Effect of current density and electrolysis time to COD, ammonium, TSS and color treatment efficiency with iron electrodes.
Figure 3.1 Effect of current density and
electrolysis time on COD treatment
efficiency
Figure 3.2 Effect of current
density and electrolysis time onammonium treatment efficiency
Trang 8Figure 3.3 Effect of current density and
electrolysis time on TSS treatment
efficiency
Figure 3.4 Effect of current
density and electrolysis time oncolor treatment efficiencyThe variation of pH during EC process is shown in Figure 3.5:
Figure 3.5 The variation of pH in leachate during EC process by electrolysis time Table 3.1 Impact of electrolysis time on COD, ammonium, TSS and color
treatment efficiency (J= 3,896 mA/cm 2)
Reaction time (mins)
Impact of electrolysis time from 10 - 80 míns to pollutants treatment
efficiency with J= 3,896 mA/cm 2 was shown in Table 3.1
When J = 3,896 mA/cm2, according to Table 3.1 we can choose 60 minutes ofelectrolysis time for the next studies although the efficiency is not the highest athis time, treatment efficiency does not change much after 60 minutes
Thoi
Trang 9From Table 3.2 shows, as the current density increases, the powerconsumption increases At current density J = 1,298 mA/cm2 (I = 1A), theelectrical energy consumption is 1.05 KWh/m3 leachate As increasing to J =5,194 mA/cm2 (I = 4A), the power consumption increases to 24,67 KWh/m3
leachate At current density J = 3,896 mA/cm2 (I = 3A), power consumption is12,83 KWh/m3 leachate, when increasing current density to 4,545 and 5,194mA/cm2, power consumption increases considerably, respectively to 18.08 and24.67 KWh/m3 leachate The results from Table 3.2 also show that COD,ammonium, TSS and color performance at current density of J = 3,896 mA/cm2
does not change significantly compared to J = 4,545 and 5,194 mA/cm2 Theenergy consumed to treat 1 m3 of leachate at J = 5,194 mA/cm2 is almost doublethat of J = 3,896 mA/cm2 Therefore, selecting the current density of J = 3,896mA/cm2 is energy-efficient while the COD, ammonium, TSS and colorperformance are not much lower than J = 4,545 and 5,194 mA/cm2 Table 3.2show that if the current density is smaller than 3,896 mA/cm2, neither the powerconsumption is low nor COD, ammonium, TSS and color treatment efficienciesare small Therefore, current density of J = 3,896 mA/cm2 is applied to the nextstudies
Table 3.2 Power consumption and COD, ammonium, TSS and color
Power consumption (KWh/m 3 )
COD treatment efficiency (%)
Ammonium treatment efficiency (%)
TSS treatment efficiency (%)
Color treatment efficiency (%)
3.1.2 Effects of initial pH in leachate on COD, ammonium, TSS and color treatment efficiencies with iron electrodes.
The pH value is one of the main factors affecting the treatment efficiency
of the EC process
The results also show that, in neutral environment (pH = 7-8), COD,ammonium, TSS and color removal efficiency are highest (specifically in Table 3.3)
Trang 10Figure 3.6 Effect of initial pH on
COD treatment efficiency
Figure 3.7 Effect of initial pH on
ammonium treatment efficiency
Figure 3.8 Effect of initial pH on
TSS treatment efficiency
Figure 3.9 Effect of initial pH on
color treatment efficiency
Table 3.3 The COD, ammonium, TSS and color
treatment efficiencies at different pH
(J = 3,896 mA/cm 2, 60 mins electrolysis, electrodes distance of 1 cm)
pH COD Ammonium Treatment efficiency (%) TSS Color
Trang 11treatment efficiency increases lightly or no increase On the other hand, the input
pH of Nam Son landfill leachate is around 8, then the input pH (about 7-8) ischosen for the further studies to save pH adjustment chemicals and cost
3.1.3 Effects of iron electrodes distance to COD, ammonium, TSS and color treatment efficiencies
Figure 3.10 Effect of electrodes
distance on COD treatment efficiency
Figure 3.11 Effect of electrodes distance
on ammonium treatment efficiency
Figure 3.12 Effect of electrodes
distance on TSS treatment efficiency
Figure 3.13 Effect of electrodes distance
on color treatment efficiency
Table 3.4 COD, ammonium, TSS and color treatment efficiencies at different electrodes distances (J = 3,896 mA/cm 2, electrolysis time of 60 mins)
Trang 12causing instability in the electrolysis process Therefore, the electrode gap of 1
cm is selected to apply for the study
The results of the study showed that in the current density of J = 3,896mA/ cm2, the input pH from 7 - 8 and the electrode gap of 1 cm are an optimumcondition for EC process
3.1.4 Comparison the COD, ammonium, TSS and color treatment efficiencies between iron and aluminum electrodes.
Comparison the COD, ammonium, TSS and color treatment efficiencies between iron and aluminum electrodes at different electrolysis times.
Figure 3.14 Effect of electrolysis time
on COD treatment efficiency by iron
electrodes in comparison with
aluminum electrodes
Figure 3.15 Effect of electrolysis time
on ammonium treatment efficiency byiron electrodes in comparison with
aluminum electrodes
Figure 3.16 Effect of electrolysis time
on TSS treatment efficiency by iron
electrodes in comparison with
aluminum electrodes
Figure 3.17 Effect of electrolysis time
on color treatment efficiency by ironelectrodes in comparison withaluminum electrodesElectrode material is one of the parameters that directly affects theelectrolysis reactions taking place inside the solution In each EC reaction, dissolvedanodes and flocculants play an important role to assess the method effectiveness
Trang 13The effect of electrolysis time on COD, ammonium, TSS and colortreatment efficiencies of iron and aluminum electrodes are shown in Table 3.5.
Table 3.5 shows that the COD, TSS and color treatment efficiencies ofiron electrodes are much higher than aluminum electrodes at all electrolysistime Whereas the ammonium removal efficiency of iron and aluminumelectrodes depends on the electrolysis time Thus, it is clearly to choose the ironelectrodes for research on leachate treatment by EC
Table 3.5 COD, ammonium, TSS and color treatment efficiencies with iron and
aluminum electrodes at different electrolysis time
(J = 3,896 mA/cm 2, electrodes distance of 1 cm)
Figure 3.18 Effect of pH on COD
treatment efficiency with iron and
aluminum electrodes
Figure 3.19 Effect of pH on
ammonium treatment efficiency withiron and aluminum electrodes