Extraction and application of starch- based ...

Extraction and application of starchbased coagulants from sago trunk for semiaerobic landfill leachate treatment Hamidi Abdul Aziz & Nur Izzati Mohamad Sobri

Environmental Science and Pollution Research ISSN 0944-1344 Volume 22 Number 21 Environ Sci Pollut Res (2015) 22:16943-16950 DOI 10.1007/s11356-015-4895-7

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Author's personal copy Environ Sci Pollut Res (2015) 22:16943–16950 DOI 10.1007/s11356-015-4895-7

RESEARCH ARTICLE

Extraction and application of starch-based coagulants from sago trunk for semi-aerobic landfill leachate treatment Hamidi Abdul Aziz 1,2 & Nur Izzati Mohamad Sobri 1

Received: 9 March 2015 / Accepted: 15 June 2015 / Published online: 26 June 2015 # Springer-Verlag Berlin Heidelberg 2015

Abstract Malaysia is one of the highest starch producers. In this study, sago starch was utilized as a natural coagulant aid to reduce the dosage of aluminum-based coagulant in leachate treatment. The potential of native sago trunk starch (NSTS) and commercial sago starch (CSS) was evaluated as sole coagulant and coagulant aid in the presence of polyaluminum chloride (PACl) in the removal of color, suspended solids (SS), NH3-N, turbidity, chemical oxygen demand, organic UV254, Cd, and Ni. Leachate was sampled from Pulau Burung Landfill Site, one of the semi-aerobic landfills in Malaysia. The optimum dosage for PACl in the presence of NSTS or CSS as coagulant aid was reduced from 3100 to 2000 mg/L. In the presence of 2000 mg/L PACl with 6000 mg/L NSTS and 2000 mg/L PACl with 5000 mg/L CSS, the removal performance for color, SS, and turbidity are 94.7, 99.2, and 98.9 %, respectively. Similar results were obtained with the use of 3100 mg/L PACl alone. Therefore, CSS and NSTS can be used as coagulant aid.

Keywords Sago starch . Semi-aerobic leachate . Polyaluminum chloride

Responsible editor: Philippe Garrigues * Hamidi Abdul Aziz [email protected]; [email protected] 1

School of Civil Engineering, Engineering Campus, University Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia

2

Solid Waste Management Cluster, Engineering Campus, University Sains Malaysia, Gelugor, Malaysia

Introduction Landfill system is still the main method in Municipal Solid Waste (MSW) disposal in Malaysia. However, certain gases, liquids (leachate), and inert solids are produced from landfills (Bashir et al. 2009). Among the three products, landfill leachate remains the key pollution factor from municipal landfill sites (Gandhimathi et al. 2013). If not treated properly and disposed safely, then such leachate may percolate through soils and subsoils, producing widespread pollution to ground and surface waters (Tatsi et al. 2003). Leachate wastewater is difficult to treat because it contains various complex organic substances, heavy metals, and other pollutants. A number of methods in leachate treatment involve either physical, chemical, or biological processes. Coagulationflocculation is a relatively common chemical treatment for water, wastewater, and leachate. The commonly used coagulants are aluminum sulfate (alum), ferric chloride, and ferric sulfate (Zainol et al. 2011). Wang et al. (2009) found that coagulants from hydrolyzing metal salts, such as polyaluminum chloride (PACl), are commonly used because of their high efficiency and low cost. However, despite being an effective aluminum-based coagulant, PACl contributes in the development of Alzheimer disease. Aluminum-based coagulants also produce residual into the environment and give negative influence to living organisms. Higher level of aluminum in the water system will cause aluminum toxicity to fish (Muisa et al. 2011). Therefore, the use of a natural coagulant is considered environmentally essential to overcome the dilemma of landfill leachates. The abundance and availability of natural resources improve the coagulation-flocculation process, especially in the treatment of complex samples. Coagulation-flocculation processes using starch as a natural coagulant have been investigated by various workers, such as rice starch in palm oil mill

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effluent treatment, corn starch in dye wastewater treatment, tapioca starch in semiconductor wastewater treatment, and sago starch in synthetic wastewater (Teh et al. 2014; Louis and Sudha 2013; Fatehah et al. 2013 and Aziz et al. 2000). Common advantages of natural coagulants are cost-effectivity, biodegradability, and non-toxicity (Hasbi 2013). According to Yin (2010), most of the natural coagulants are polysaccharides or proteins. In the present study, sago starch, which is mainly composed of amylose and amylopectin (Chin et al. 2012), is used as a natural coagulant for leachate treatment. Given its composition, sago starch is expected to perform well as a natural coagulant or coagulant aid. This research evaluated the performance of NSTS and CSS as coagulant aid by reducing the dosage of PACl as a main coagulant in removing a few parameters from semi-aerobic landfill leachate. Madihah et al. (2001) found that starch is present in the form of water-soluble granules consisting of a mixture of two polymers; (1) amylose is a linear chain molecule, and (2) amylopectin is a branched polymer of glucose. Vijayaraghavan et al. (2011) stated that there may be interactions between the polymer and a solvent within a solution environment as the polymer may contain partially charged groups including –OH along its chain. Figure 1 shows the bonding of native sago starch. Hydroxyl group (−OH) of starch molecules will increase the flocculating efficiency through bridging (Awang and Aziz 2012).

Materials and methodology Leachate sampling and characterization Pulau Burung Landfill Site (PBLS), located within the Byram Forest Reserve in Penang, Malaysia (5″24′N, 100°24′E) at the southern district of Seberang Perai, was selected for the study. PBLS has been developed into a semi-aerobic sanitary landfill Level II with the institution of a controlled tipping technique in 1991. The site was improved to Level III Sanitary Landfill with the application of controlled tipping with leachate recirculation in 2001. PBLS has a 33-ha operational area and is equipped with a leachate collection pond (Al-Hamadani et al. 2011). On a daily basis, the landfill accepts 2200 t of solid wastes (Aziz et al. 2010). Plastic containers with sealed caps were used for the collection of leachate from PBLS aeration pond. The collected leachate was transported to the Environmental Engineering Campus within 25 min. Sampling was performed for five times within 5 months starting from January 6, 2014 to May 2, 2014. The samples were stored in a cold room maintained at 4 °C at the Environmental Laboratory 1 to minimize biological and chemical reactions in accordance with the Standard Method of Water and Wastewater (2005). The leachate was characterized immediately after sampling. The initial

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Fig. 1 Native sago starch bonding (Chin et al. 2012)

values of pH, color, suspended solids (SS), NH3-N, turbidity, chemical oxygen demand (COD), organic UV254, Cd, and Ni were determined. NSTS extraction NSTS was extracted according to the method described by Noor and Mehat (1999). This method is suitable for sago trunk (ST) extraction because it involves trunk components. ST was kept in a sealed container and stored in a cold room maintained at 4 °C until the extraction. The picture of ST is given in Fig. 2. ST was chipped manually into 1- to 2-cm cubes prior to extraction to ensure that the trunk was well mixed. Several batches of ST chips (300 g) were macerated for 60 s with 400 mL 0.5 % (w/v) sodium metabisulfite (Na2S2O5) aqueous solution. The mixture was transferred in a nylon bag and squeezed, and then the filtrate was collected in a plastic tray. The same process was employed to the residue for the extraction of residual starch. The final filtrate was sieved through a 212-μm filter to remove impurities and left to settle for 60 min. To ensure that the starch was not saturated with the supernatant, the supernatant was removed from the starch suspension using a syringe. The starch suspension was then mixed thoroughly with 1 L of 0.5 % (w/v) sodium metabisulfite aqueous solution and left to settle for 30 min. The supernatant was removed and distilled water (100 L) was added to the residue. The mixture was

Fig. 2 Sago trunk

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centrifuged twice for 5 min at 3000×g and filtered through a vacuum fitted with GF/C filter to wash and purify the starch extract. To remove the water, the purified starch was washed twice with 50 mL acetone and oven-dried overnight at 45 °C in an incubator shaker. The starch was lightly pounded into a fine powder and stored in a sealed container. The picture of NSTS is given in Fig. 3.

determined on a 2100 Q Hach turbidity meter using attenuate radiation method (Method 8237). Cd and Ni were determined through flame atomic absorption spectrophotometry with airacetylene flame (Perkin Elmer Analyst 800). The removal efficiency for parameter analysis was calculated using Eq. (1):   ðC i −C f Þ 100 ð1Þ Removalð%Þ ¼ Ci

Starch characterization

where Ci and Cf are the initial and final concentrations of the sample, respectively.

Fourier transform infrared (FTIR) spectroscopy (Perkin Elmer spectrometer) was employed to investigate the structure and analyze the functional groups of sago starch. An elemental analyzer (Perkin Elmer Series II 2400) was used to determine the elemental composition of the sago starch. The mechanism of coagulation can be identified based on the surface charge present in the sample using zeta potential. Particle size was examined in flocs. Leachate flocs were measured at wetdispersion condition using Mastersizer in volume-weighted mean gyration sizes. Jar test In this study, the rate of mixing was selected based on the method described by Al-Hamadani et al. (2011), in which PACl was used as coagulant. The following rates of mixing were employed: 80 rpm rapid mixing for 2 min, 30 rpm slow mixing for 30 min, and 120 min for settling time. For each experiment, each beaker was filled with 500 mL of sample. The pH value was adjusted using 3 M HCl and 3 M NaOH. Analytical procedure Supernatants were withdrawn 2 cm below liquid level for analysis (Zainol et al. 2011). DR6000 Hach spectrophotometer was used to determine color, SS, NH3-N, organic UV254, and COD, in accordance with the APHA PtCo standard method (Method 8025), photometric method (Method 8006), Nessler method (Method 8038), direct reading method (Method 10054), and Method 8000, respectively. Turbidity was

Fig. 3 Native sago trunk starch (NSTS)

Results and discussion Raw leachate characteristics The results of the characterization of raw leachate are given in Table 1. The leachate is classified as alkaline (pH 8.40) and it has a concentrated COD value of 3200 mg/L, which exceeds the 400 mg/L standard value. Stabilized leachate is usually considerably contaminated with non-biodegradable organic substances such as humic-like and fulvic substances that are measured in COD (Al-hamadani et al. 2011). The determined biological oxygen demand in a 5-day period (BOD5) is 448 mg/L, which is considerably high compared with the 20 mg/L standard value. These results indicate a high organic content of the sample. BOD5 determination involves the measurement of dissolved oxygen used up by microorganisms in 5 days (Aziz et al. 2010). The BOD5/COD for the leachate sample was 0.14. Bashir et al. (2009) indicated that PBLS produces stabilized leachate with high COD and ammonium concentrations and low BOD5/COD ratio. Aziz et al. (2010) reported that a 0.096 BOD5/COD falls within the range of stabilized leachate that varies from 0.06 to 0.15 BOD5/COD (Gandhimathi et al. 2013). Mahmud et al. (2012) concluded that low BOD5/COD ratio occurs when biodegradable organic fraction in leachates decreases as landfill age increases. Color concentration is high and blackish at 5206 PtCo. Aziz et al. (2007) reported that PBLS color ranges from 2480 to 8180 PtCo. The SS value at 290 mg/L exceeds the allowable standard in Malaysia. The measured turbidity is 263 NTU. Both Cd and Ni heavy metals also exceeded the standard limits. Thus, urgent treatment is needed because both metals are carcinogens. Organic UV254, which represents the natural organic matter (NOM), was also recorded high with a value of 12.6 cm−1. The average value obtained for NH3-N was 826 mg/L. Ammonia is mostly contributed by the decomposition of protein, and a level of 500 to 2000 mg/L NH3-N is common (Kjeldsen et al. 2002). Osada et al. (2011) found that ammonia contributes 58.7 % to the total toxicity of landfill leachate.

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Table 1 Characteristics of PBLS raw leachate (January 6, 2014– May 2, 2014)

Table 2

FTIR bandwidth and effective groups in CSS and NSTS

Vibration type

Range (cm−1) NSTS (cm−1) CSS (cm−1)

Hydroxyl (O–H stretching)

3200–3600

3301.73

3294.67

980–1200

995.69

997.56

1077.02

1077.23 1150.12

1550–1655

1641.98

1639.02

Parameter

Standard*

Average

Min

Max

pH

6.0–9.0

8.40

8.00

8.60

Zeta potential (mV)

–

−15.3

−11.2

−18.1

Amino (amines and amides) (N–H stretching)

Color (PtCO) Suspended solids (mg/L)

100 ADMI** 50

5206 290

4908 263

5800 320

Carboxyl (C=O stretching)

NH3-N (mg/L) Turbidity (NTU) COD (mg/L) Organic UV254 (cm−1)

5

826

810

838

– 400 –

263 3200 12.6

240 2800 11.9

285 3700 13.7

0.01 0.20 20 0.05

0.069 0.243 448 0.14

0.064 0.237 424 0.15

0.074 0.252 474 0.13

Cadmium (mg/L) Nickel (mg/L) BOD5 BOD5/COD

*Environmental Quality (Control of Pollution from Solid Waste Transfer Station and Landfill) Regulations 2009 **American Dye Manufacturers Institute

According to Abdel-Aziz et al. (2011), coagulationflocculation effective groups are carboxyl, hydroxyl, and amino (amine and amide) groups, which were all detected in both NSTS and CSS. However, the frequency values of the same functional group differ between the starches. Awang and Aziz (2012) reported that hydroxyl (O–H) and carboxyl (C=O) groups help promote flocculating efficiency through bridging. However, other functional groups barely contribute to the coagulation-flocculation process. Elemental analysis

Characterization of coagulant Starch yield The starch yield was determined by weighing the starch produced after oven-drying in relation to the ST before blending. The NSTS yield is 6.48 % from ST. Noor and Mehat (1999) reported a 7.15 % yield of oil palm trunk starch (OPTS) using the same method. Sago starch quality is relatively high because it contains more amylose and amylopectin. Presently, common natural starches used as natural coagulants are corn, wheat, and tapioca. Sago starch has physico-chemical properties which are quite close to those of normally used starches (Ahmad et al. 1999). It has relatively great amylose content in the range 24–31 % and has a hot paste viscosity similar to potato (tuber) and tapioca (root) starches (Teng et al. 2011; and Ahmad et al. 1999). These provide sago starch the possibility of being used as a natural binder because fiber is not suitable as coagulant. As the mixture before centrifugation comes in milky color, it showed a lot of impurities. A centrifuge was used to remove fibers, fat, and other impurities. Repeated purification and centrifugation may reduce the impurity. Then the produced starch was lightly pounded into fine powder in white color. Functional group The functional groups of sago starch are given in Table 2. The FTIR spectrum of sago starch shows several effective groups for coagulation flocculation. The groups were detected at specific bandwidths, which were selected based on the values recommended by Yuen et al. (2005), Abdel-Aziz et al. (2011), Apopei et al. (2012), and Awang and Aziz (2012).

The elemental composition of sago starch is given in Table 3. Elemental analysis was used to determine the C, H, N, S, and O contents in the starch sample using the CHNS/O elemental analyzer (Perkin Elmer Series II 2400). The analyzer uses a combustion process to break down substances into simple compounds, which are then quantified by infrared spectroscopy. Such analysis instantaneously presents the weight percents of C, H, N, and S in the sample with the weight percent of O calculated by difference. The hydrogen composition of NSTS is higher than that of CSS. Alwi et al. (2013) reported that high value of hydrogen is due to moisture in the sample. These results are consistent with the FTIR analysis, in which high carbon and low nitrogen contents are found. Oxygen is the abundant element observed in the starch because of its rich carbohydrate composition. Moreover, plants break down carbohydrates into energy with the help of oxygen. Zeta potential The initial zeta potentials are given in Table 4. Zeta potential was used to determine the electrical charge of the sample and Table 3 Percentage elemental composition

Sample

NSTS

CSS

C (%) H (%) N (%) S (%) 0 (%)

38.94 9.77 0.00 0.88 50.41

33.39 8.44 0.00 0.56 57.61

Author's personal copy Environ Sci Pollut Res (2015) 22:16943–16950 Table 4 Initial zeta potential for samples and coagulants

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Sample and coagulant

Zeta potential (mV)

Leachate PACl

−15.3 15.7

NSTS

−22.2

CSS

−30.0

coagulant. During the test, both starches were diluted with deionized water to 1 % concentration. With the highly negative surface charge of leachate (−15.2 mV), coagulation activity of the coagulant alone may be slow. Xiao et al. (2008) stated that as zeta potential is increased, positively or negatively, stronger energy forces between particles exist, which lead to poor coagulation activity. A coagulant is necessary to stabilize the charges during coagulation process. Given that PACl gives cationic hydrolysis products, charge neutralization is a possible reason for the action of PACl as coagulant (Gregory and Duan 2001). Thus, zeta potential is reduced to neutralize the charge of negative particles in the leachate. Yang et al. (2010) found relatively higher zeta potentials of flocs formed after coagulation with PACl. The amount of coagulant added to the leachate depends on the electrical charge surrounding the colloidal particles. Alhamadani et al. (2011) stated that when negative zeta potential is large, more coagulant is required. The surface charge of NSTS (−22.2 mV) and CSS (−30.0 mV) indicate that the particles of sago starch are unstable and could not create flocs when used as primary coagulant because both coagulant and leachate carry almost the same charges. With similar electric charges, small particles in the water naturally repel each other, thereby keeping the small, colloidal particles separate and suspended (Ebeling et al. 2003). Therefore, NSTS and CSS are expected to be more suited as coagulant aid instead of sole coagulant.

Optimal performance of NSTS and CSS as coagulant at pH 4

Parameter

Raw leachate without coagulant (%)

NSTS at 7000 mg/L dosage (%)

CSS at 6000 mg/L dosage (%)

Color (PtCo)

11.5

13.1

15.1

SS (mg/L)

32.5

27.9

29.5

NH3-N (mg/L)

1.7

8.2

10.7

COD (mg/L) Turbidity (NTU) Organic UV254 (cm−1)

0.0 1.0 5.6

1.7 0.0 43.8

28.0 0.0 51.6

Cd (mg/L) Ni (mg/L)

0.0 0.0

25.5 44.1

16.3 33.2

This mechanism requires absorption of the polymer chains (amylose or amylopectin) by surface particles through few points of attachment, whereas the bulk of the chains projecting into the surrounding solution are for contact and adherence of other pollutant particles (Nasser and James 2006). However, further increase from the optimal dosage may lead to the destabilization of the particles. The performance of CSS as sole coagulant is much better than NSTS in most of the parameters. However, heavy metals are better removed by NSTS with 44.1 % (Ni) and 25.5 % (Cd) removal rates. Sago starches are also ineffective in removing NH3-N, which is mainly because sago starches are organic compounds, which contain portions of protein. NH3N is usually formed from the degradation of proteinaceous organic materials during methanogenesis (Sung and Liu 2003). In terms of COD, the removal with CSS is 28 % as compared with almost no reduction (1.7 %) with NSTS. Nevertheless, no turbidity reduction was achieved from both starches.

Starch as coagulant aid Comparisons between CSS and NSTS as coagulant The optimal performances of CSS and NSTS as sole coagulants are given in Table 5 and compared with raw leachate (without coagulant). The values obtained for raw leachate were used to assess the change in percentage removal with the addition of coagulant. The values selected for comparison is based on the optimal performance obtained from each experiment. Destabilization of leachate particles by NSTS and CSS was mainly through bridging flocculation mechanism because of the high molecular weight and non-ionic to weakly ionic nature of starch (Teh et al. 2014). Gao et al. (2002) stated that coagulants with high molecular weights are more effective in improving the bridge-formation ability of colloidal impurities, causing rapid size development of flocs.

CSS and NSTS were used as natural coagulant aids to reduce PACl consumptions. Alwi et al. (2013) stated that various weaknesses have been reported on the use of chemical-based coagulants, among which are relatively high procurement costs and effects on human health and environment. In this study, PACl dosage was reduced to four smaller dosages of 500, 1000, 2000, and 3000 mg/L from the 3100 mg/L optimum value. The sharp reduction of PACl dosage to 500 and 1000 mg/L was considered inefficient in improving leachate removal, as opposed to the 3100 mg/L PACl optimal value. Leachate removal can be improved at both concentrations, but a significant amount of coagulant aid is required. Therefore, further investigations on sago starches as coagulant aid are focused on the use of 2000 and 3000 mg/L PACl.

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Comparisons between NSTS and CSS as coagulant aids are shown in Fig. 4. More than 90 % reduction in color, SS, and turbidity was observed in the presence of sago starch as coagulant aid. Aziz et al. (2007) suggested that landfill leachate color is mostly contributed by organic matter and some insoluble substances, which also contribute to turbidity and SS readings. A number of substances such as fine organic and inorganic matter, as well as algae (phytoplankton) and other microscopic organisms, such as bacteria (Zemmouri et al. 2012), also cause turbidity. With the addition of more coagulant, electrostatic forces decrease and more flocs are formed, thereby reducing turbidity. With the use of 2000 mg/L PACl with 6000 mg/L NSTS and 5000 mg/L CSS as coagulant aid, the color, SS, and turbidity reductions are higher compared with the use of 3100 mg/L PACl alone. However, the reductions observed for the other parameters are not as significant as with the use of 3100 mg/L PACl as sole coagulant.

Fig. 4 Comparison of percentage removal using different parameters

Environ Sci Pollut Res (2015) 22:16943–16950 Table 6 Summary of optimal removal using 2000 mg/L PACl as coagulant and 6000 mg/ L NSTS as coagulant aid at pH 6

Parameter

Removal efficiency (%)

Color (PtCo)

94.7

SS (mg/L) NH3-N (mg/L) Turbidity (NTU) COD (mg/L) Organic UV254 (cm−1)

99.2 2.4

Cd (mg/L) Ni (mg/L)

53.8 0.0

98.9 35.5 69.5

Based on the experiment, NH3-N reduction did not reach more than 10 %. The coagulation-flocculation process is generally ineffective in eliminating ammonia nitrogen because it prevents attraction between the coagulant and ammonia nitrogen in a sample (Al-Hamadani et al. 2011). Sago starches are

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Fig. 5 Particle size distribution of NSTS as coagulant aid in varying dosages

also ineffective in removing NH3-N, which is mainly because sago starches are organic compounds, which contain portions of protein. NH3-N is usually formed from the degradation of proteinaceous organic materials during methanogenesis (Sung and Liu 2003). The efficiency of wastewater decolorization depends on the removal of organic colorants, such as pigments and NOM (Zhou et al. 2008). NOM content was determined using organic UV254. Highest removal of organic UV254 at 77.8 % was observed using 3000 mg/L PACl with 6000 mg/L NSTS. With the use of 2000 mg/L PACl with 6000 mg/L NSTS, organic UV254 reduction was recorded at 69.5 % after passing through a 0.45-μm-size membrane. Bolto and Gregory (2007) stated that dissolved organic compounds (DOCs) are compounds that can pass through a membrane with 0.45 μm size. DOCs pose aesthetic problems for water treatment in terms of color, taste, and odor; DOCs also cause health hazards. DOCs are one of the constituents of NOM. With the use of 2000 mg/L PACl with 6000 mg/L NSTS coagulant aid, the color, SS, and turbidity are reduced by 94.7, 99.2, and 98.9 %, respectively. By comparison, the COD and organic UV254 are optimally reduced by 40.5 and 77.8 %, respectively, with the use of 3000 mg/L PACl with 6000 mg/L NSTS as coagulant aid. Both Ni and Cd achieved 77.5 and 14.7 % reductions, respectively, using 3000 mg/L PACl with 3000 mg/L CSS as a coagulant aid. In general, 2000 mg/L PACl with 6000 mg/L NSTS as coagulant aid is the optimal combination for reducing the values of all of the parameters considered. The optimal performance of NSTS as coagulant aid is given in Table 6.

Floc size The particle size distribution of flocs obtained with the use of NSTS as a coagulant aid is given in Fig. 5. Results indicate that particle size increased after the addition of NSTS as coagulant aid. The increase in particle size could be a proof of the increased polymer chain through bridging. Zhu et al. (2009) stated that bridging-flocculation produces relatively

large and strong flocs because of the reduced repulsion between the flocs (using metal salts) compared with those produced by destabilization. The highest particle size was obtained with the use of 2000 mg/L PACl with 6000 mg/L NSTS as a coagulant aid.

Conclusion The optimal dosage for NSTS as sole coagulant is 7000 mg/L at pH 4. At this condition, color, SS, turbidity, NH3-N, COD, organic UV254, Cd, and Ni are reduced by 13.1, 27.9, 0.0, 8.2, 1.7, 43.8, 25.5, and 44.1 %, respectively. With CSS alone, optimal dosage and pH are 6000 mg/L at pH 4, respectively, and the associated reductions of color, SS, NH3-N, turbidity, COD, organic UV254, Ni, and Cd are at 15.1, 29.5, 10.7, 0.0, 28.0, 51.6, 33.2, and 16.3 %, respectively. The optimal dosage for PACl in the presence of NSTS or CSS as coagulant aid was reduced from 3100 to 2000 mg/L. Using 2000 mg/L PACl with 6000 mg/L NSTS or with 5000 mg/L CSS, the removal performance for color, SS, and turbidity are 94.7, 99.2, and 98.9 %, respectively. Similar results were obtained with the use of 3100 mg/L PACl alone. The optimal condition for PACl was obtained at pH 6, with or without the addition of coagulant starch as coagulant aid. The results indicate that CSS and NSTS are more suited as coagulant aids than as main coagulants. Acknowledgments This work is supported by Universiti Sains Malaysia under RU-Team grant scheme RUT-1001/PAWAM/854005. The authors also wish to acknowledge Majlis Perbandaran Seberang Perai for their assistance during the sampling process.

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