CC BY
50
Van Huu Tap1, Nguyen Van Tuyen2, Nguyen Hoai Chau3 ©
:MSC. PhD student, Faculty of Environmental and Earth Sciences, Thainguyen University of Sciences, Thainguyen, Vietnam; 2PhD, Institute of Environmental Technology, Vietnam Academy of Science and Technology, Hanoi, Vietnam; 3Assoc Prof, PhD, Institute of Environmental Technology, Vietnam Academy of Science and Technology, Hanoi, Vietnam
DETERMINATION OF SEVERAL OPTIMAL CONDITIONS WITH TREATMENT OF ORGANIC COMPOUNDS OF LANDFILL LEACHATE IN VIETNAM BY
COAGULATION PROCESS
Summary
This paper presents some experimental results of removals of COD and color from landfill leachate by using coagulation to determine the optimal reaction conditions. Three coagulants were used for research are PAC (polyaluminium chloride), aluminum sulfate (Al2(SO4)3.18H2O), and ferric sulfate (Fe2(SO4)3. 7H2O). The results showed that the removals obtained from three types of coagulants showed a maximum of the concentration of coagulants are more than 3,000 mg l- under the pH region from 7 to 8. The results also indicated that the significant removals of COD and color were obtained at the concentration of 1,500 mg l- and that PAC was the most suitable coagulant for the treatment of landfill leachate in Vietnam. The removals of COD and color were approximately 30% and 70%, respectively.
Keywords : Landfill leachate, Coagulation, Coagulant, COD, Color.
INTRODUCTION
Currently, solid wastes generated in urban areas in Vietnam are not classified and treated thoroughly. Landfill leachate is a very complex wastewater in Vietnam. There are several toxic components of solid waste such as batteries, engine oil, chemicals, toxic waste in industry, commerce, hospital ...etc which can carry heavy metals and other toxic organic compounds out leachate.
Today, landfill sites in Vietnam have generated large amounts of leachate containing highly toxic and non-biodegradable organic chemicals due to sources of solide waste and high natural moisture, rain and biochemical processes [2]. If leachate is not properly treated, it will pollute surface and ground water, causing serious environmental contamination. It is a challenge to environmental scientists.
Coagulation can be used to remove suspended solids and organic matters in landfill leachate. This process reduces a part of the organic matter in the Persistent leachate. In Viet Nam, coagulation processes are used to reduce suspended solids, organic matters of wastewater through agglutination and settling out [2,3]. Chemical oxygen demand (COD) and color are the most difficult items for leachate treatment, in long time halogenated organic compounds with high molecular weight can be generated and endanged environment once they fall out surrounding soil and water [3].
The objective of this research investigate the application of coagulation to remove both COD and color from leachate of landfill sites in Vietnam. In this research, all effects of factors on coagulation process are considered to treat organic materials of leachate.
MATERIALS AND METHODS
Researching scale:
Landfill leachate was taken from Damai landfill site, Tancuong commune, Thainguyen city, Vietnam. Damai site have been operated since 1999 to treat solid waste for Thainguyen city and other towns. The source of landfill solid waste come from domestic and industrial activities, such as plastic bags, municipal waste, kitchen garbage, battery,.etc. So, the compound of leachate is very complex. In period of this research, leachate samples were taken from the pond between August and
© Van Huu Tap, Nguyen Van Tuyen, Nguyen Hoai Chau, 2013 r.
November 2010. It was kept in plastic cans and stored at 40C in the laboratory before analysing and treating. Table 1 shows the characteristics of landfill leachate from Damai site.
Table 1.
The characteristics of landfill leachate from Damai site
Parameters Unit Range
pH - 7.5 - 8.3
COD mg l-1 2,100 - 4,500
Color Pt-Co 1,450 - 4,400
Cl- mg l-1 916 - 2,280
Experiments:
Coagulation was used to treat leachate in experiments with flocculants: PAC, (Al2(SO4)3.18H2O, Fe2(SO4)3. 7H2O and H2SO4, NaOH.
Analytical methods: pH and COD were analyzed by Standard Methods (APHA, 1995). Color was analyzed by spectrum method with Pt-Co color at 420 nm (APHA, 1995).
Experimental equipment: Coagulation experiments were performed in the Jar-test aparatus (model: JLT6 Jar test/Flocclulator, made in Italy) equipped with 6 backers.
Experimental methods:
Experiments of leachate were carried out with three types of coagulants: PAC (polyaluminium chloride), aluminum sulfate (Al2(SO4)3.18H2O), and ferric sulfate (Fe2(SO4)3.7H2O). 5 mg l-1 of flocculant auxiliary A110 (sodium acrylates Acrylamic copolime) was added to increase flocculation process.
The experiments were investigated the effects of concentration of coagulants and leachate pH on treatment efficiency, flowed by the concentration of which will be suitably determined for flocculation process.
The experiments were conducted at room temperature (20 ± 4°C). In each of the tests, flocculants (with calculated ratio) were added into a reaction beaker containing 500 ml of leachate. Sodium hydroxide (NaOH 4M) or sulfuric acid (H2SO4 2.5M) were used to adjust pH of leachate. pH of leachate was varied from 3, 4, 5, 6, 7, 8, 9 to 10. The concentration of coagulants were varied from 500; 1,000; 1,500; 2,000; 3,000; 4,000 to 5,000 mg l-1. Quick phases took place in 3 min at a speed of 150 revolutions per minute and then added flocculants auxiliary (A110) at the last minute of rapid stirring time. After that, stirring speed was reduced to 50 revolutions per min for 10 min. After slow stirring process, samples were settled out from 30 to 60 min.
RESULTS AND DISCUSSIONS
Determination of suitable pH:
The pH value was selected between 3 and 10 for experiments.
*. Effects of pH on COD removal:
The effects of pH value on COD removal efficiency by coagulation process shows in Fig. 1.
Raw landfill leachate with high COD concentration is difficult to treat due to it contains high persistent organic compound. However, the concentration of COD was changed after flocculation process with pH range from 3 to 10.
3000
1000
500 -
0 -I-,-т-т-т-
5 е 7 8 Э 10
pH
—»— Raw COD —ш-РАС —*—AI2(SOt)3.18Н,0 —•—Fe2(S04b.7H20
Fig. 1. The effect of pH on COD removal by coagulation
Fig.1 indicated that COD concentration of raw leachate was 2,798 mg l-1, but the results of flocculation with three coagulants (PAC, Ab(SO4>.18H2O and Fe2(SO4)3.7H2O) showed that COD removal efficiency decreased with increasing pH. For Al2(SO4)3.18H2O, the lowest concentration of COD was 1,389 mg l-1 at pH = 3 and 4, reduced 47%. For PAC and Fe2(SO4)3.7H2O, the concentration of COD reduced to 1,075 mg l-1 at pH = 4 and achieved efficiency of 59%, and 60% respectively. The efficiency of COD removal of leachate by PAC and Fe2(SO4)3.8H2O is the same and higher than that of Ab(SO4)3.18H2O at all pH values.
*. Effects of pH on color removal:
Effects of pH of landfill leachate on the change of color in coagulation process were showed in Figures 2:
The efficiency of color removal decreased with increasing pH value of leachate. Overall performance of color removal of three coagulants was similar, but the efficiency of color removal of PAC was slightly higher. The most effective treatment was achieved at pH value around 4 (with PAC: about 85%, Ab(SO4>.18H2O: 84% and Fe2(SO4>.7H2O: around 78%).
Fig. 2. Effect of pH on color removal by coagulation
The efficiency was higher at low pH value than that compare to high pH value. COD concentration and color removal efficiency decreased with increasing pH. The COD concentration and color removal efficiencies were equivalent at pH values of 6-7, the COD concentration and color then increased with pH of leachate from 8 - 10. This proved that coagulants were good dissolved at alkaline condition. We found that COD concentration and color removal efficiency was the highest with PAC and Fe2(SO4>.8H2O.
Because pH of raw leachate is approximately 7.5 to 8.3, when the coagulants were added to leachate, pH will be decreased. The leachate was treated effectively in alkaline condition by ozone process, so pH between 7 and 8 was chosen for further experiments to reduce the cost on chemicals for pH adjustment.
Determination of suitable concentration of coagulants
pH range was determined between 7 and 8. The next experiments were conducted in this pH range with change of concentrations of coagulant of 500 mg l-1 to 5,000 mg l-1.
*. The effect of coagulants' concentration on COD removal:
The effects of coagulants' concentration on treatment efficiency are showed in Fig. 3.
Raw COD -^PAC A12(S04)3.1SH20 Fe2(S04)3.7H20
Fig. 3. Effect of flocculants concentration on COD removal
Figures 4 showed that performance of COD concentration removal increased with increasing concentration of coagulants (performance with PAC: 17 - 38%, Al2(SO4)3.18H2O: 14 -34% and Fe2(SO4)3.7H2O: 3 - 30%). The COD concentration decreased significantly after coagulation at concentrations from 1,500 mg l-1. The COD concentration decreased from 2,798 mg l-1 to 1,740 mg l-1 when flocculants reached from 3,000 mg l-1 or higher. Reaction might be saturated. The PAC was found to give higher efficiency of removal of organic matters than others with its concentration from 500 to 3,000 mg l-1. After that, it was not increased even with increasing concentration of coagulant. However, COD removal reduced when increasing concentration of ferric sulfate.
*. Effect of concentration on color removal:
Fig. 4. Effect of coagulants concentration on color removal
Performance of color removal by using coagulation process increased quickly with increasing their concentrations from 500 to 2,000 mgl-1. It was increased mostly in amounts of 1,000 to 2,000 mg l-1, and then remains constant. PAC was one of the three chemicals that had the highest performance of coagulation for these experiments. The efficiency of color removal by Al2(SO4)3.18H2O is similar to Fe2(SO4>.7H2O. Color went down quickly from 1,512 to 280 (81%) at PAC concentration of 2,000 mg l-1 it then is not significantly reduced. It decreased down to 480 and 360 (68% and 76% respectively) at 3,000 mg l-1 of Ak(SO4)3.18H2O and Fe2(SO4)3.7H2O, respectively. However, it was still high after coagulation. Because persistent organics of leachate, such as humic, benzen and phenol affect highly on pretipication and adsorption of coagulants, their concentrations were required higher than other that of wastewater. The pH of leachate samples had decreased after treatment by coagulation because cations of Al3+ and Fe3+ have acidic characters.
Coagulation - flocculation was applied for treating non-biodegradable organic matters from hazardous landfill leachate [1]. The coagulation efficiency of ferric chloride was higher for removing organic compounds (55%) than that of alum (42%), with an initial COD concentration of 4,100 mg l-1 and the doses of Fe or Al were 0.035 mol l-1. According to Tatsi et al (2003), the treatment of stabilized leachate from the Thssaloniki landfill (Greece) by application of coagulation- flocculation for the treatment was performed without pH adjustment, the COD removal rate was achieved at 80% when the addition of 1.5g l-1 of FeCU while it increased to 38% with 1.5 g l-1 of Al ions [4]. These results were slighly difference with our findings because landfill leachate in Vietnam is more complex than that of previous studies. Landfill sites consist of municipal and industrial solid waste as well as hospital solid waste without classifying from sources. So leachate characteristics are very complex, including high organic compounds (such as humic and fulvic acid, lignin, phenol and macromolecular compound...etc) and high toxic compounds from solid waste of industry and hospital.
CONLCUSION
From this study pH values and concentration of coagulants were identified for leachate treatment with the highest effective occurs in an acidic environment (pH 3 and 4). Optimal concentration of coagulant is 3000 mg l-1. In addition, the effective of leachate treatment is similar with PAC and Fe2(SO4)3.7H2O.
References
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2. Khanh, N.H. Report of the project: Research and Comparison of Landfill Leachate Treatment Systems in Viet Nam and the World to Choose Suitable one to Meet Level B of TCVN for Landfill Sites of Hanoi city / Institute of Environmental Technology, Vietnam Academy of Science and Technology. 2007. -36p.
3. Phuoc, N.V. and Phuong, N.T.T. Textbook of Treatment Techniques of Industrial Waste // Publisher of Construction. -2006. -p.136-140.
4. Tatsi, A.A., Zouboulis, A.I, Matis, K.A, and Samaras, P. Coagulation-locculation pretreatment of sanitary leachates // Chemosphere. -2003. No 53. -p.737-744.
