Effect of Modified Micro-Sand , Poly-Aluminium Chloride and Cationic Polymer on Coagulation-Flocculation Process of Landfill Leachate

Nur Hanani Thaldiri1, Marlia Mohd. Hanafiah1,2, Azhar Abdul Halim1,* 1School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia. 2International Water, Air & Soil Conservation Society, 59200 Kuala Lumpur, Malaysia *Corresponding author. Tel.: +60389214089; Fax.: +60389253357 E-mail address: azharhalim@ukm.edu.my


INTRODUCTION
Water pollution had been one of the major problems that need to be managed properly.Major problems such as diseases and death occurred due to uncontrolled water pollution, lack of clean drinking water and expensive water treatment due to high concentration of pollutants.One of the sources that cause water pollution is discharge of wastewater either from industrial or landfill into water system.The wastewater discharge from landfill known as leachate usually consists of high concentration of organic and inorganic matter such as chemical oxygen demand (COD), bio-chemical oxygen demand (BOD), suspended solid (SS), ammonia nitrogen (NH3-N) and heavy metals [1].The composition of the leachate depends on several factor such as moisture content, type of landfill, volume of waste produce, type of waste, age of the landfill and climate condition [2,3].Without any treatment, contamination of leachate into water system will not only cause water pollution, but also threaten the surrounding ecosystem [4].
Physical, biological treatment or physical-chemical treatment such as anaerobic and/or aerobic biological degradation, chemical oxidation, coagulation-precipitation, activated carbon adsorption, photooxidation and membrane process can be used to treat wastewater [5,2,6].Leachate from stabilized landfill involves more than ten years which has low biodegradability due to large amounts of non-biodegradable organic compounds with high molecular weight [1].These criteria lead to less effectiveness of biological treatment to treat stabilized landfill leachate.
To overcome this problem, physical-chemical water treatment has been applied to treat leachate from the stabilized landfill.One of the commonly used physical-chemical treatments applied in wastewater treatment is coagulation-flocculation.Coagulation process followed by flocculation process was said to be more effective in organic pollutant removal [6].The efficiency of coagulation-flocculation process depends on several factors such as type and dosage of coagulant/flocculant, pH, mixing speed and time, temperature and retention time [7,8,9,10].Coagulation-flocculation is a simple process that involves the use of inorganic metal salts such as aluminum sulfate (alum), ferric chloride (FeCl3) and poly-aluminum chloride (PAC) [11].Several studies have been done using alum and PAC as a coagulant in wastewater treatment by comparing their parameter such as COD, turbidity, color and SS.Overall, the result showed that PAC was very effective for the removal of physical parameters such as color, turbidity and SS but less effective in COD removal compared to alum [11].However, during coagulation-flocculation process, the settle down of the sludge or particle produced is rather slow.To enhance the settle down process, micro sand has been used to provide a surface area that enhances the flocculation and acts as a weight to settle down the sludge or particle [12].The aim of this study is to examine the effectiveness of coagulationflocculation process in landfill leachate treatment using combination of poly-aluminium chloride (PAC), cationic polymer and chemically modified micro-sand in term of chemical oxygen demand (COD), total suspended solid (TSS) and color removal.

2.
Materials & Method 2.1 Leachate Sampling and Characterization Samples of leachate were collected from leachate collection ponds at Pulau Burung Sanitary Landfill (PBSL).PBSL is situated within the Byram Forest Reserve in Penang, Malaysia and the total area of the landfill site is 23.7 hectares [13].PBSL has been operated semi-aerobically since year 1991 by employing a controlled tipping technique and has been upgraded to leachate circulation system in year 2001 [14].Leachate samples were collected in plastic container and transported to laboratory.The samples were stored at 4˚C and the characterization of the raw leachate samples from PBSL was carried out according to the Standard Method for the Examination of Water and Wastewater [15].The characteristic of raw leachate samples are shown in the Table 1.Parameters of leachate samples that were analyzed on site were pH, dissolved oxygen (DO), temperature, and conductivity; while measurement of color, chemical oxygen demand (COD), biochemical oxygen demand (BOD5), suspended solid (SS) and ammonia nitrogen (NH3-N) were performed immediately upon return to the laboratory.

Coagulation-Flocculation
Coagulation-flocculation experiment on leachate was carried out by using jar test equipment (VELP-Scientific, Model: JLT6, Italy) that consist of six paddle rotors (2.5 cm x 7.5 cm) and six beakers (500 mL).(PAC) and cationic polymer.Leachate samples were subjected to jar test after pH adjustment had been done by using sodium hydroxide (NaOH) and hydrochloric acid (HCl).This coagulation-flocculation process involves 3 distinct steps: (i) rapid mixing stage which aim to mix the coagulant with leachate to maximize the effectiveness of the destabilization of colloidal particles; (ii) slow mixing stage where the suspension is slowly stirred to increase contact or collision between coagulating particles to produce large flocs; (iii) settling time stage where the mixing is terminated and the flocs are allowed to settle down.The sample was immediately stirred at a constant speed of 200 rpm for 2 minutes followed by a slow stirring at 40 rpm for 10 minutes [16].Initial settling time in this experiment was 30 minutes.Later, by using the optimum condition gained, samples were observed at minute of 0, 0.5, 1, 5, 10, 15, 20, 30, 45 and 60 to compare settling time between coagulation-flocculation process with and without micro sand and modified micro sand.Modified micro sand used in this study was prepared by dissolving the sodium aluminium and sodium hydroxide in distilled water with micro sand.

3.
Results & Discussion 3.1 Effect of pH pH is one of the important parameters in the coagulation-flocculation process since it controls hydrolysis species.Different pH values were applied to perform the coagulation-flocculation process.The ranges of pH examined were from 2 -10 as shown in the Fig. 1.From Fig. 1, coagulation-flocculation process was more efficient in removal of COD, TSS and color at the ranges of pH from 6 -7.The higher percentage removal for COD, SS and color were at 49.46%, 99.19% and 93.53%, respectively.After pH adjustment to pH 4 and 9, some flocs were already appeared even without coagulant.The color intensity gradually reduced as the pH approached the optimum pH which from dark brown to light yellow.Effect of Cationic Polymer Cationic polymer usually added in the coagulation-flocculation process to improve the settling characteristic.The different dose of cationic polymer was applied to determine the optimum dose of cationic polymer.Fig. 2 shows that the optimum dose of cationic was 8 mg/L with the higher percentage removal obtained for COD, TSS and color were 58.99%, 95.68% and 94.41%, respectively.There were a slightly increase and decrease in the percentage of removal for COD from 6 mg/L to 10 mg/L of cationic polymer.

3.3
Effect of PAC One of the commonly use coagulant in coagulation-flocculation process was PAC.Different doses of coagulant have been applied in this study.The ranges of coagulant dose examined were from 500 mg/L -2,500 mg/L.The percentages removal of COD, TSS and color are shown in the Fig. 3. Optimum doses of PAC observed in this study were ranges between 500 to 1,000 mg/L.The higher percentage removal of COD, TSS and color were obtained at 52.66%, 97.16% and 96.44%, respectively.Application of Modified Microsand Micro sand was used in the coagulation-flocculation process to enhance the flocculation process and settle down the sludge or particles that formed during the process.The dose of micro sand and modified micro sand used was 300 mg/L as optimum dose as shown in the Fig. 4. In this study, the settling time recorded to settle down the sludge and particle formed during coagulation-flocculation process were 1 minute with modified micro sand, 20 minutes with raw micro sand and 45 minutes without micro sand (Fig. 5).The results indicate that the settling time in coagulation-flocculation process of landfill leachate was accelerated by chemically modified microsand Fig. 4 Effect of modified micro sand dosage to COD removal in coagulationflocculation process

Conclusion
In the present study, the application of coagulation-flocculation process to treat landfill leachate collected from PBSL was examined.The efficiency of PAC and cationic polymer in removing COD, TSS and color as well as the use and efficiency of micro sand and modified micro sand to settle down sludge and particles formed during coagulation-flocculation process were also investigated.We found that the highest percentage removal of COD, TSS and color can be observed at pH 7 with the optimum dose of PAC was 1,000 mg/L and optimum dose of cationic polymer was 8 mg/L.Micro sand and modified micro sand were shown to be more efficient to settle down sludge and particles that formed in coagulation-flocculation process.With the addition of polymer, the removal process of COD, TSS and color can be improved.

Fig. 1
Fig. 1 Effect of pH toward percentage removal of COD, TSS and color 3.2Effect of Cationic Polymer Cationic polymer usually added in the coagulation-flocculation process to improve the settling characteristic.The different dose of cationic polymer was applied to determine the optimum dose of cationic polymer.Fig.2shows that the optimum dose of cationic was 8 mg/L with the higher percentage removal obtained for COD, TSS and color were 58.99%, 95.68% and 94.41%, respectively.There were a slightly increase and decrease in the percentage of removal for COD from 6 mg/L to 10 mg/L of cationic polymer.

Fig. 3
Fig. 3 Effect of PAC toward percentage removal of COD, TSS and color 3.4Application of Modified Microsand Micro sand was used in the coagulation-flocculation process to enhance the flocculation process and settle down the sludge or particles that formed during the process.The dose of micro sand and modified micro sand used was 300 mg/L as optimum dose as shown in the Fig.4.In this study, the settling time recorded to settle down the sludge and particle formed during coagulation-flocculation process were 1 minute with modified micro sand, 20 minutes with raw micro sand and 45 minutes without micro sand (Fig.5).The results indicate that the settling time in coagulation-flocculation process of landfill leachate was accelerated by chemically modified microsand