An International Journal

Transcription

1 Removal and Settling Velocity of POME Particles: P a g e 103 An International Journal J. Ind. Res. Tech. 1(2), , 2011 HATAM Publishers Journal of Industrial Research & Technology Journal homepage: Effect of Aluminium Sulfate Dosage and Mixing Ratio on Organic Loading Removal and Settling Velocity of Palm Oil Mill Effluent Particles Reem A. Alrawi a, Anees Ahmad b,*, Norli Ismail a and Mohd. Omar Ab. Kadir a a Division of Environmental Technology, School of Industrial Technology, Universiti Sains Malaysia, Penang, Malaysia b Division of Analytical and Environmental Chemistry, Department of Chemistry, Aligarh Muslim University, Aligarh , India *Corresponding author: aneesahmad.ch@amu.ac.in, Phone: ARTICLE INFORMATION Article history Received 10 March 2011 Revised 13 April 2011 Accepted 10 July 2011 Available online 30 August 2011 Keywords Palm oil mill effluent, Coagulation, Mixing ratio, Alum, Jar test, Removal efficiency ABSTRACT The palm oil mill effluent (POME) has high pollution level and needs vast area with long hydraulic retention time to treat it anaerobically. Coagulation process can be used prior the anaerobic treatment to reduce the pollution level of POME. In this work, six different doses of aluminium sulfate (alum) were used: 90, 180, 270, 360, 450 and 540 mg combined with four different mixing ratios of (water: POME): 0.5:1.0, 0.75:1.0, 1.0:1.0 and 1.25:1.0. The process performances have been evaluated through the (%) removal of total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD). The settling velocity of POME particles was determined by measuring the interface height during the settling process. The experiments were done in a batch coagulation system under original ph values The (%) removal of TSS, BOD and COD increased constantly with increase in alum dosages at 0.5:1.0 and 0.75:1.0 ratios. But the settling velocity was increased with the increase in alum dosages and mixing ratios HATAM: Publishers. All rights Reserved. 1. Introduction Oil palm industry is the largest agro-based industry in Malaysia. Malaysia is the second largest producer and exporter of palm oil after Indonesia in 2009 (WorldGrowth 2009). In Malaysia the wet process of palm oil milling is the most common and typical way of extracting the palm oil. It is estimated that for each ton of crude palm oil that is produced, ton of water is required, and more than 50% of this water ends up as palm oil mill effluent (POME) (Ahmad et al. 2003). The POME is acidic waste water ( ), with high organic load such as: BOD ( ) x10 4 mg/l, COD ( ) x10 4 mg/l, high oil and grease content ( ) x10 3 mg/l and high suspended solids ( ) x10 4 mg/l (Ahmed et al. 2011; Wong et al. 2009). This wastewater should be treated properly, otherwise it will pollute the surrounding environment (Othman et al. 2008). To solve this problem, many studies have been done and suggested various wastewater management approaches. Beside that in the recent years, the scarcity of freshwater supply and the increasing wastewater treatment cost due to stringent environmental standards became the major problem of mills (Chungsiriporn et al. 2006). The current treatment of POME depends upon biological approach which is based on anaerobic, facultative and aerobic digestion. The main system

2 Removal and Settling Velocity of POME Particles: P a g e 104 to treat POME is ponding and/or open digestion tank system. Although the ponding treatment system is considered as one of the major processes for the treatment of POME till today and its efficiency was evaluated by previous study (Chin et al. 1996), but it has particular disadvantages such as: long hydraulic retention time, bad odor, huge areas and difficulty to collect the emission biogases (CH 4 and CO 2 ) which could have detrimental effects on environment (Yacob et al. 2005). To reduce the strength of POME before entering the biological treatment, chemicals coagulation is being used to enhance the reduction of POME organic load to an acceptable and economical level. Up to 60% removal of BOD and COD with 90% removal of SS, can be done with proper selection of chemical coagulant and its optimum dosage (Nik Norulaini et al. 2001). The coagulation process consists of destabilizing colloids, aggregating them, and binding them together for ease sedimentation. The effectiveness of coagulation process depends on coagulant type, coagulant dosage, the ph of the solution, the concentration and nature of the organic compounds present in the wastewater (Bratby 2006; Duan and Gregory 2003; Lee and Westerhoff 2006). Aluminium and iron salts are widely used as coagulants in water and wastewater treatment and in some other applications. They are effective in removing a broad range of impurities from water, including colloidal particles and dissolved organic substances. Nearly all colloidal impurities in water are negatively charged and, hence, may be stable as a result of electrical repulsion (Duan and Gregory 2003). The mode of coagulant action is generally explained in terms of two distinct mechanisms: charge neutralization of negatively charged colloids by cationic hydrolysis products and incorporation of impurities in an amorphous hydroxide precipitate socalled sweep flocculation (Duan and Gregory 2003; Shammas 2005). Many researches used alum to treat different types of wastewaters like palm oil mill effluent (Ahmad et al. 2006), municipal wastewater (Guida et al. 2007), pharmaceutical wastewater (Saleem 2007), polluted cork processing wastewater (Gonzălez et al. 2007) and yeast wastewater after treated biologically, aluminum sulfate was used as an advanced treatment method to remove color and COD under different ph conditions and coagulant dosage (Zhou et al. 2008). The present work deals with the effect of two factors: different dosages of aluminium sulfate as coagulant and combined with the changing of POME strength. The coagulation considered as a POME pretreatment before biological treatment. This work reports the effect of these factors on removal of total suspended solids (TSS), biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of POME which are considered the most important parameters that used to evaluate the process performance. Furthermore, this work focuses about settling velocity of POME particles after end of coagulation process. The ph adjustment prior coagulation process had been omitted in an attempt to simulate the same ph as that of original site. 2. Materials and Method 2.1 Palm oil mill effluent (POME) The raw palm oil mill effluent (POME) was collected from palm oil mill factory (MALPOM) which is located at Nibong Tebal, Pulau Pinang-Malaysia. The samples were stored in a sealed plastic container and preserved at a temperature less than 4 o C but above the freezing point in order to prevent the wastewater from undergoing biodegradation due to microbial action (APHA 2005). The samples were analyzed for their characteristics and the average chemical properties of these samples are represented in Table 1. The portion of the sample to be analyzed was withdrawn in sufficient quantity from the preserved sample after it is allowed to reach to room temperature (27-30 o C) before the start of the experiments. Table 1 Chemical properties of raw Palm Oil Mill Effluent (POME) Parameters Concentration Standard deviation ph Biological oxygen demand (BOD) mg/l 8.28 x 10 3 Chemical oxygen demand (COD) mg/l 2.78 x 10 3 Total suspended solids (TSS) mg/l 2.05 x 10 3 Total Kjeldahl nitrogen (TKN) mg/l 1.41 x 10 3 Temperature 60 o C Analytical methods The ph, COD, BOD, and TSS were determined according to the APHA (2005). Total Kjeldahl nitrogen (TKN) was analyzed according to (HACH 1997). All tests were carried out at an ambient temperature in the range of (27-30 o C) and at original ph of POME ( ). The tests were run in triplicate and the average of each data was applied for further analysis. Aluminium sulfate (alum) [Al 2 (SO 4 ) 3.16H 2 O] was obtained from ChemAR and used for the preparation of the alum solution. The removal efficiency of TSS, BOD and COD were determined using the following equation: ( C ) rawpome C f Removal (%) = 100 (1) CrawPOME where; C raw POME is the concentration of raw POME and C f is the final concentration of TSS, BOD and COD separately.

3 Removal and Settling Velocity of POME Particles: P a g e Preparation of mixture ratios To enhance the aggregation of the suspended solids for their fast settling and removal, six dosages of alum: 90, 180, 270, 360, 450 and 540 mg were added to 1L of distilled water mixed with raw POME at 4 different ratios: 0.5:1.0, 0.75:1.0, 1.0:1.0 and 1.25:1.0 (these ratios will be called as mixing ratio in all subsequent paragraphs). A common Jar test stirring apparatus (Velp Scientifica type FC6S), manufactured in Italy, was used with six-spindle of stainless-steel paddles, operating at 120 rpm with stirring time range between 1 to 3 min at room temperature 28+2 o C. To carry out the sedimentation tests, graduated cylinder (34 cm height x 6.5 cm diameter) was used with working volume of 1000 ml. The determination of optimum coagulant dosage was carried out at ph and its performance was evaluated by determining the removal efficiency of TSS, BOD and COD of the upper layer. The interface height between the top and bottom layer at preset intervals of 30, 60, 90 and 120 min, the sludge volume after the end of settling process (120 min) and the settling velocity of POME particles all these parameters were measured during this study. Each set of these experiments were carried out in triplicate. 3. Results and Discussion In the current study, the performance of coagulation process is evaluated by the % reduction efficiency of COD, BOD and TSS of POME. The most suspended solids in POME were organic matter and its decrease enhances the reduction of COD and BOD (Chin et al. 1996). It is important to mention that the coagulation process in this study was done without ph adjustment because many previous studies showed that the effective coagulation process of POME can be done under original POME ph, (Ahmad et al. 2006; Nik Norulaini et al. 2001). One of the most important parameters used to evaluate coagulation process of POME is % TSS removal. The effect of different alum dosages (90, 180, 270, 360, 450 and 540 mg/l) on total suspended solids (TSS) removal (%) at different mixing ratios (0.5:1.0, 0.75:1.0, 1.0:1.0 and 1.25:1.0) are shown in Figure 1. Each point in this figure represented the TSS removal (%) after 120 min. It can be noticed from this figure that the TSS removal efficiency is depending on the coagulant doses, as well as on the POME concentration. The TSS removal % increased with the increase in alum dose due to the charge neutralization that caused settling of the positive charge metal with negative charge collide, but this efficiency can be changed with mixing ratio due to changing the ionic activities of the POME solution. It can be observed that the coagulant had a positive effect on TSS removal (%) at a mixing ratio of 0.5:1.0. The TSS removal (%) increased from 89.7% to 92.3% and it showed a constant increase. At 0.75:1.0, TSS removal (%) had slight increasing from 90.3 % to 91.0 %. At 1.0:1.0 mixing ratio, TSS removal (%) was almost constant ranging between (88.0 to 88.9 %) and the optimum dosage was mg/l which gave 90.6% removal. But at 1.25:1.0 mixing ratio, the addition of coagulant which exceeded the optimum dosage (275.5 mg), lead to a decrease in TSS removal efficiency from 90.6 to 82.9 % and this decrease was continuous. This reduction occurred probably because of restabilization due to excessive coagulant addition. Previous study had been proven this result and reported that many hydrolysis products are cationic and these can interact strongly with negative colloids, giving destabilisation and coagulation, under the correct conditions of dosage and ph, but excess dosage can produce charge reversal and restabilization of colloids (Duan and Gregory 2003). Stephenson and Sheldon (1996) showed that the addition of coagulants exceeding their optimum dosages gave no additional positive effect especially for iron salts, which reduces the separation process. This might be due to counter ion restabilization causing the dispersion of the flocks and subsequently affecting the settling of the particles (Shammas 2005; Stephenson and Duff 1996). POME is highly organic and its suspended solids are mainly associated with organic matter, alum can effectively remove most of the colloidal and suspended organic matter contents, but is less effective in removing of dissolve organic matter (Hassan and Puteh 2007). The relation between BOD and COD removal efficiencies with each dosage for each mixing ratio are shown in Figures 2 and 3. Figure 1 Total suspended solids (TSS) removal (%) as a function of aluminium sulfate dose (mg) at different mixing ratios. The trend of BOD and COD reduction efficiencies are the same as that of TSS removal efficiency that shown in Figure 1. It can be noticed from Figure 2 that when the coagulant dosage increases the BOD removal continuously increases

4 Interface Height (cm) BOD removal (%) COD removal (%) Removal and Settling Velocity of POME Particles: P a g e 106 with mixing ratios of 0.5:1.0 and 0.75:1.0 but rather gradually Aluminium Sulfate Dose (mg/l) Figure 2 Effect of aluminium sulfate dosage on BOD removal (%) at different mixing ratios. For the rest of the mixing ratios, the BOD removal efficiency was disturbed when the alum dosages become more than 450 mg/l, because the BOD removal efficiency at 1.0:1.0 mixing ratio decreased from 66 to 62%, and at 1.25:1.0 decreased from 66 to 60%. This might be due to the concentration of suspension at theses ratios was lower than 0.5:1.0 and 0.75:1.0 ratios and the overdosing of alum was beyond its optimum dosage and this get a surface charge reversal which led to restabilization of the collide complex and lower coagulation performance (Hassan and Puteh 2007). The COD removal (%) for all mixing ratios is almost identical, which means the increase of alum dosages leads to improve coagulation performance. At 0.5:1.0 and 0.75:1.0 mixing ratios the efficiencies were constantly increasing from 75.4 to 77.4% and from 75.1 to 78.6 % respectively. But it has been noticed with 1.0:1.0 and 1.25:1.0 mixing ratios that they were increasing but gradually. For 1.0:1.0 mixing ratio the increase was from 77.6 to 78.2%, and for 1.25:1.0 it increases from 76.4 to 77.1%. In general, COD is higher than BOD because more compounds can be oxidized chemically rather than biologically (Tchobanoglous and Burton 1991). These results were in agreement with Stephenson and Duff (1996) who found that the efficiency of the coagulation process was related to type and dosage of the coagulant as well as the concentration of wastewater used. This study focuses on the enhancement of POME settling velocity beside the treatment process. POME settling velocity was measured by determining the height of interface line between the supernatant POME (at the upper layer) and the sludge POME (at the bottom layer) were observed with respect to time. The relationships between the interface heights (cm) and aluminium sulfate dosages (mg/l) for different mixing ratios are shown in Figure 4. Each Aluminium Sulfate Dose (mg) Figure 3 Effect of aluminium sulfate dosage on COD removal (%) at different mixing ratios. point in this figure represents the interface height after (120 min) of settling time. It can be noticed from this figure that the interface heights increased continuously with increase in alum doses as well as mixing ratios which means the POME settling velocity increased with the POME dilution. This phenomena described by Richardson and Zaki (R & Z) and explained by pervious studies, who showed that the decrease in settling rate of interface line at high solid fraction is due to decreased permeability of the settling layer and an increase in the upward velocity of the displaced fluid (Heath et al. 2006; Richardson and Zaki 1954) Aluminium Sulfate Dose (mg/l) Figure 4 Interface heights as a function of aluminium sulfate dose after 120 min of settling time. Figure 4 shows that the lowest interface height between the upper and bottom layer of settling POME was at low mixing ratio 0.5:1.0 and this height was increasing with increase in mixing ratio. For 0.75:1.0 and 1.0:1.0 mixing ratios, the interface height was 16.0 cm and 19.0 cm respectively and the highest interface height was 22.8 cm for mixing ratio of 1.25:1.0. In the system that contains high concentration of suspended solids, both hindered or zone settling and compression settling usually occur in addition to discrete (free) and flocculent settling. Because of the high concentration of particles, the liquid tends to move up through the interstices of contacting particles. As a result, the contacting particles tend to

5 Sludge volume (ml) Settling Velocity (cm/min) Removal and Settling Velocity of POME Particles: P a g e 107 settle as a zone, or "blanket", maintaining the same relative position with respect to each other. The phenomenon is known as hindered settling. As the particles in this region settle, a relatively clear layer of water is produced above the particles in the settling region (Tchobanoglous and Burton 1991). The POME settling velocity in this study was measured by determining the settling distance (cm) that is shown in Figure 5 over settling time (min). Figure 5 Settling column details The value of POME settling velocity (cm/min) is obtained by the following equation: Interface height Settling Velocity, cm / min (2) Settling time Figure 6 shows the effect of different alum dosages on settling velocity (cm/min) during 120 min with different mixing ratios. It can be noticed that, when the mixing ratio increased the settling velocity increased which means the higher concentration gave lower rate of settling, this is caused because of the upward velocity of the displaced fluid is greater than the fall velocity (Coulson et al. 1996). It can be noticed from Figure 6 that the settling velocity increased continuously with increasing alum doses at mixing ratio 0.5:1.0 till it reaches 360 mg the settling velocity was increasing slightly. For the other mixing ratios and at different alum dosages, the settling velocity was constantly increasing with the same range (Ahmed et al. 2009). That means, at certain alum dosages in each mixing ratio, further dosage increases did not improve the settling rate (Bratby 2006). The mixing ratio and alum dose affect on the sludge production of POME after settling and this can be illustrated in Figure 7. This figure shows that at different alum dosage the higher sludge volume was obtained at low mixing ratio 0.5:1.0. The highest sludge volume was ranged between ml at 0.5:1.0 mixing ratio and the lowest sludge volume ranged between ml at 1.25:1.0. It can be concluded from this figure that the mixing ratios Aluminium Sulfate Dose (mg) Figure 6 Settling velocity as a function of aluminium sulfate dose at different mixing ratios. have more significant effect on sludge production than the alum dosage. There is no big difference between the sludge productions among all dosages at the same mixing ratio, but the difference is very obvious between the sludge productions among different ratios at the same dosage Aluminium sulfate dose (mg) Figure 7 Sludge volume as a function of aluminium sulfate dose at different mixing ratios 5. Conclusion This study was based on two main factors: different alum dosages and different mixing ratios at original ph of POME. This study revealed that the removal efficiency of TSS, BOD, and COD were constantly increasing with 0.5:1.0 and 0.75:1.0 mixing ratios even after adding a maximum dosage of aluminum sulfate (540 mg/l). But at 1.0:1.0 and 1.25:1.0 mixing ratios, these efficiencies were decreased after 450 mg/l of aluminium sulfate, this happened because of the overdosing of coagulant which may leads to the surface charge reversal of the particles and consequently restabilization of the collide complex. The study indicated that the strength of POME coupled with coagulant doses has significant effect on coagulation process. Furthermore, the settling velocity of POME particles was increased with both alum dosages and mixing ratio. But at certain alum dose the settling rate was slightly increased which means further increase in

6 Removal and Settling Velocity of POME Particles: P a g e 108 dosages does not improve the settling rate. This study also showed that the interface height between the supernatant and sludge POME was increasing with increased mixing ratio and consequently decreased the sludge production. Acknowledgements The financial assistance by Universiti Sains Malaysia (grant No: 1001/PTEKIND/842029) and the research facilities by School of Industrial Technology, USM are gratefully acknowledged. Special thanks for MALPOM Industries Sdn Bhd for providing the sample of POME throughout this research work. References Ahmad, A. L., Ismail, S., & Bhatia, S. (2003). "Water Recycling from Palm Oil Mill Effluent (POME) Using Membrane Technology." Desalination, 157, Ahmad, A. L., Sumathi, S., & Hameed, B. H. (2006). "Coagulation of residue oil and suspended solid in palm oil mill effluent by chitosan, alum and PAC." Chemical Engineering Journal 118, Ahmed, M., Nik Norulaini, N. A., Aliyu-Paiko, M., Hashim, R., Mohd Omar, A. K., & Anees, A. (2011). "Solid POME sludge as a new source of fish feed ingredient Nile tilapia (Oreochromis niloticus) " Journal of Industrial Research & Technology, 1(1), Ahmed, R. A., Ahmad, A., Ismail, N., & Kadir, M. O. A. "Effect of Aluminium Sulfate on TSS Removal and Settling Velocity Of Palm Oil Mill Effluent (POME) Particles " Proceedings of Symposium of USM Fellowship Holders 2009 Penang, Malaysia. APHA. (2005). "Standard methods for the examination of water and wastewater." American Public Health Association, Washington, D.C. Bratby, J. (2006). "Coagulation and Flocculation in Water and Wastewater Treatment." IWA Publishing LONDON.SEATTLE. Chin, K. K., Lee, S. W., & Mohammad, H. H. (1996). "A Study of Palm Oil Mill Effluent Treatment Using A Pond System " Water Science & Technology, 34(11), Chungsiriporn, J., Prasertsan, S., & Bunyakan, C. (2006). "Minimization of water consumption and process optimization of palm oil mills." Clean Techn Environ Policy, 8, Coulson, J. M., Richardson, J. F., Backhurst, J. R., & Harker, J. H. (1996). Particle Technology and Separation Processes, Butterworth-Heinemann. Duan, J., & Gregory, J. (2003). "Coagulation by hydrolysing metal salts." Advances in Colloid and Interface Science, , Gonzălez, T., Domĭnguez, J. R., Beltrăn-Heredia, J., Garcĭa, H. M., & Sanchez-Lavado, F. (2007). "Aluminium sulfate as coagulant for highly polluted cork processing wastewater: Evaluation of settleability parameters and design of a clarifier-thickener unit." Journal of Hazardous Materials, 148, Guida, M., Mattei, M., Roccab, C. D., Melluso, G., & Meriç, S. (2007). "Optimization of alumcoagulation/flocculation for COD and TSS removal from five municipal wastewater." Desalination 211, HACH. (1997). "Water Analysis Handbook." HACH Company, USA. Hassan, M. A. A., & Puteh, M. H. (2007). "Pretreatment of palm oil mill effluent (POME): A comparison study using chitosan and alum." Malaysian Journal of Civil Engineering, 19(2), Heath, A. R., Bahri, P. A., Fawell, P. D., & Farrow, J. B. (2006). "Polymer Flocculation of Calcite: Relating the Aggregate Size to the Settling Rate." American Institute of Chemical Engineers AIChE Journal, 52(6), Lee, W., & Westerhoff, P. (2006). "Dissolved organic nitrogen removal during water treatment by aluminum sulfate and cationic polymer coagulation." Water Research, Nik Norulaini, N. A., Ahmad Zuhairi, A., Muhamad Hakimi, I., & Mohd Omar, A. K. (2001). "Chemical Coagulation of Settleable Soils-Free Palm Oil Mill Effluent (POME) for Organic Load Reduction." Journal of Industrial Technology, 10(1), Othman, Z., Bhatia, S., & Ahmad, A. L. (2008). "Influence of the Settleability Parameters for Palm oil Mill Effluent (POME) Pretreatment by Using Moringa Oleifera Seeds as an Environmental Friendly Coagulant " International Conference on Environment 2008 (ICENV 2008). Richardson, J. F., & Zaki, W. N. (1954). "Sedimentation and fluidisation. Part 1." Trans. Inst. Chem. Eng., 32, Saleem, M. (2007). "Pharmaceutical Wastewater treatment: A Physicochemical Study." Journal of Research (Science), 18(2), Shammas, N. K. (2005). "Coagulation and Flocculation." Physicochemical Treatment Processes, L. K. Wang, Y.-T. Hung, & N. K. Shammas, eds., Humana Press Inc., Stephenson, R. J., & Duff, S. J. B. (1996). "Coagulation and Precipitation of a Mechanical Pulping Effluent-I. Removal pf Carbon, Colour and Turbidity " Water Research, 30(4), Tchobanoglous, G., & Burton, F. (1991). "Wastewater Engineering: Treatment, Disposal, Reuse. Metcalf and Eddy, INC.", McGraw-Hill, Inc.

7 Removal and Settling Velocity of POME Particles: P a g e 109 Wong, Y. S., Kadir, M. O. A. B., & Teng, T. T. (2009). "Biological kinetics evaluation of anaerobic stabilization pond treatment of palm oil mill effluent." Bioresource Technology, 100(21), WorldGrowth. (2009). "Palm Oil The Sustainable Oil." World Growth - Palm Oil Green Development Campaign. Yacob, S., Hassan, M. A., Shirai, Y., Wakisaka, M., & Subash, S. (2005). "Baseline study of methane emission from open digesting tanks of palm oil mill effluent treatment." Chemosphere, 59, Zhou, Y., Liang, Z., & Wang, Y. (2008). "Decolorization and COD removal of secondary yeast wastewater effluents by coagulation using aluminum sulfate." Desalination, 225,