Optimization of Biological ph Treatment for Acidic Palm Oil Mill Effluent

Transcription

1 Available online at GlobalIlluminators Full Paper Proceeding ITMAR -2014, Vol. 1, FULL PAPER PROCEEDING Multidisciplinary Studies ISBN: ITMAR-14 Optimization of Biological ph Treatment for Acidic Palm Oil Mill Effluent Norazwina Zainol 1*, Anis Sakinah Lokman Hakim 2 Universiti Malaysia Pahang Malaysia Abstract Palm oil mill effluent (POME) has been known as organic waste product from palm oil production which is featured by low ph of , high value of biological demand (BOD), chemical oxygen demand (COD) and suspended solids. It is mandatory for all palm oil mills to treat their wastewaters to an acceptable level before it is allowed to be discharged into the water courses. Biological treatment appears less cost than chemical and physical methods and have low environmental impact. The purpose of this study was to optimize the factors (temperature and agitation) which were influencing biological ph treatment of acidic POME. Acidic POME was collected from a nearby palm oil mill whereas soil mixed culture was obtained from soil near the plants root system. Soil mixed culture was acclimatized with POME as inoculum. Experimental design table was prepared based on Response Surface Method (RSM) and 13 experimental runs were conducted according to Center Composite Design (CCD) set up. The experimental results were optimized using Design Expert software (Version 6.0). The proposed model from the software showed proportional relationship between ph value and both studied factors. Temperature and agitation had individual significant influence on ph value. Based on the analysis, the suggested optimum conditions were at temperature of and agitation speed of 125 rpm. The expected ph value at these conditions was at Later, validation experiment was conducted at the suggested optimum conditions and the error between the actual and expected ph value was at 2.29%. Low errors from the validation experiments (<5%) proved that biological ph treatment for acidic POME could be represented by using the proposed model. This study showed that application of this biological process could be an effective solution for acidic POME treatment The Authors. Published by Global Illuminators. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the Scientific & Review committee of ITMAR Keywords: Agricultural Wastewater, Response Surface Method, Soil Mixed Culture, Biological Ph Treatment Introduction Palm oil industry is one of the contributors of environmental pollution due to its rapid expansion of the industry by year if their waste not being treated well. An increasingly stringent environmental regulations in view of the government s commitment to the conservation of the environment and increased public awareness of pollution problems caused the palm oil industries facing tremendous challenges as palm oil mill effluent (POME) is a highly pollutant effluent (Mustapa, 2008). POME has been known as organic waste product from palm oil production which is featured by low ph of , high value of biological demand (BOD), chemical oxygen demand (COD) and suspended solids. POME *All correspondence related to this article should be directed to Norazwina Zainol, Universiti Malaysia Pahang Malaysia azwinaz@gmail.com 2014 The Authors. Published by Global Illuminators. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the Scientific & Review committee of ITMAR-2014.

2 treatment requires an efficient system in facing the current challenges. There are many processing plants failed to achieve the standard discharge limits. It is mandatory for all palm oil mills to treat their wastewaters on site to an acceptable level before it is allowed to be discharged into the water courses (Wu et al., 2009). A new and improved palm oil mill effluent (POME) treatment would be required in order to meet the requirements of Department of Environment (DOE) discharge limits. Biological treatment have less cost than chemical and physical methods with faster natural degradation. Thus, the purpose of this research was to optimize biological ph treatment of acidic POME by using soil mixed culture as inoculum. Response surface methodology (RSM) was employed in this study. It is a mathematical and statistical technique for building models, evaluating relative significance of several independent variables (i.e., environmental factors), and determining optimum conditions for desirable responses (Rasdi et al., 2009). According to Zinatizadeh et al., (2006) application of RSM could be utilized to determine the most significant operating factors and optimum levels with minimum effort and time. Palm oil mill effluent (POME) Materials And Methods POME was obtained from a palm oil mill located in Maran, Pahang, Malaysia. The POME was collected in a container then brought to the laboratory and kept in a freezer at 4oC. The initial ph measured was Soil mixed culture and preparation of inoculum Soil sample was collected from a garden in Universiti Malaysia Pahang (UMP). It was taken near plant root area. The soil was transported to a laboratory and sealed in bags. Soil mixed culture was prepared by mixing the soil and distilled water at 1:1 ratio (100 ml soil and 100 ml water) (Miles and Moy, 1979). Then the soil mixed culture (SMC) was acclimatized with POME at 1:3 ratio (50 ml SMC to 150 ml POME). The culture then was agitated continuously at 150 rpm in the incubation shaker. The acclimatization period was for 10 days at 30oC and 150 rpm agitation (Lin et al., 2008). Later, the acclimatized soil mixed culture was used as inoculum in optimization set-up. Set-up for optimization process RSM with central composite design (CCD) set-up was used in optimization process. There were two factors involved in optimization process which were agitation and temperature. The ranges of these factors were rpm and 25oC 35oC for agitation and temperature respectively. Design Expert (DE) software was utilized to construct experimental design table. Experimental setup and procedure The experiments were conducted in batch tests. The batch tests were conducted in 250 ml shake flasks (200 ml working volume and 50 ml head space). Next, 50 ml of acclimatized inoculum was added to 150 ml of POME by 1:3 (inoculum: POME) for each shake flasks. Then the shake flasks were incubated anaerobically. 212

3 Analytical method ph values in shake flasks was measured using ph meter (Model Mettler Toledo) every 24 hours for four days. Results And Discussion Effects of temperature and agitation speed on ph treatment Analysis of variance (ANOVA) was performed by using Design Expert 6.0 to obtain the result. The mathematical model relating the effects of independent variables of agitation speed and temperature on ph changes is given in the quadratic regression as follows: ph = A B A ( )B ( )AB eq. (1) where A and B were coded values of temperature and agitation respectively. R2 (0.8433) indicated that the models could fit satisfactorily the responses and only about 15.67% of the total variation could not be explained by this model. The P-values were used as a tool to check the significance of each coefficient; the smaller the value of P, the more significant was the corresponding coefficient (Feng et al., 2010). Moreover, the F-value for a term compares a term s variance with the residual variance. The probability > F of < means there was less than 0.01% chance that a model F-value could occur due to noise. Table 1 shows the model F-value of 7.53 implies the model is significant. There is only 0.97% chance that F-value could occur due to noise. Values of Prob > F less than 0.05 indicate model terms are significant. For any terms in the models, a large F-value and a small P-value would indicate a more significant effect on the respective response variables (Ahmad et al., 2010). The P-values for the linear, quadratic and interactive terms was also shown in Table 2. Apart from that, ANOVA analysis showed the significant terms (P < 0.05) which comprised of the second order effect of temperature (A2) and the second order effect of agitation (B2). Hence, the agitation (P = ) produce largest effect on ph changes followed by the temperature (P = ). Table 1 : Analysis of variance table (ANOVA) for biological ph treatment Source Sum of DF Mean Square F Value Prob>F Squares Model (significant) A B

4 A B AB Residual Lack of Fit < (significant) Interactive effect of the temperature and agitation speed on ph treatment of POME: The optimum level of each variable and the effect of their interactions on the Response 1 were studied by plotting three dimensional (3D) response surfaces and two dimensional (2D) contour lines (Figure 1). In the Figure 1 and 2 depicts the effects of temperature and agitation on the response (ph) while the reaction time was fixed at its optimal condition. The response surface of ph displayed a clear optimum point which fell inside of the boundary range. From the examination of contour plot, there was a slight elongation sloping downward. This result shows that agitation and temperature had an individual significant influence on ph. Yuan et al., (2011) has been observed that significant microbial activity increase when temperature was raised from 10 to 30. Lowering operational temperature usually contributes to a decrease in the maximum growth of microbial activity (Mu et al., 2006). Based on the Figure 2, the ph is increases during the temperature between to 30 and started decreases further increasing of temperature. The final ph from Wang and Wan (2008) study was starting to decrease sharply at 30 to 35. One possible reason for this may be that mixed culture used was responsible for fermentation, has a high conversion rate of carbohydrate to products and metabolites, and the high concentrations of metabolites may cause the ph to drop. Besides, the results obtained from Jamil et al. (2009) indicated that the microbial activity increases with gradually increasing value of agitation rate which is in adequate mixing condition. Agitation speed significantly affected the optimal ph condition (Chou et al., 2008). The purpose of mixing is to facilitate the distribution of the cells within the culture; aiding the homogenous exposure of the microorganisms to the light and substrate. Otherwise, the 2D presented a clear elongated running diagonally on plot, suggesting that agitation and temperature was interdependent, or that there was a significant interaction on ph treatment. Figure 2 shows the evidence that ph increased in the range between to 8.35 upon increasing of agitation between 125 to 175 rpm and temperature between 27.50oC to 30. For process at agitation of 125 rpm, the ph increased proportional to temperature but decreased a bit in the range between to However, at agitation of 175 rpm with the temperature range between 28.75oC to 30oC, ph value decreased with increasing temperature. According to Mu et al. (2006) ph and temperature were interdependent and their interactive effects were insignificant while agitation speed has individual influence to the process (Jamil et al., 2009). According to Yuan et al., 2011, higher temperature and more intense mixing (or increased contact opportunity) are necessary for completion of the biological process. Lack of mixing drastically reduced the amount of product generated due to the less microbial activity, particularly at low temperatures (Yuan et al., 2011). 214

5 Figure 1: The 3D-plot and 2D-projection (contour plot) showing the interaction between temperature and agitation on response 215

6 Figure 2: Interaction graph between the factors (agitation and temperature) and response Optimum conditions for ph treatment Table 2 shows the experimental runs to validate suggested optimum condition by DE software. The targeted ph for the experimental studies was 7.5. Within the temperature between 27.5 and 32.5 and agitation of 125 to 175, the ph was obtained in the range between 7.44 and The selected optimum condition for ph treatment was at temperature of 32.5 and agitation of 125 rpm. The expected ph value at this optimum condition was Better process stability could be achieved at mesophilic temperature (Poh & Chong, 2009). Ingesson et al. (2001) stated that adequate mixing is required to ensure sufficient contact between the substrate and microbes and to promote heat and mass transfer while excessive mixing can deactivate the microbes and reduce the conversion yields. Their result has showed that the high speed shaking produced the highest initial rate and final conversion yield. For the selection of agitation speed in Table 1 it clearly showed that agitation at 125 rpm having higher value of ph since it might increase microbial activity rapidly and having less reaction time to obtain targeted ph value. Meanwhile, Poh and Chong (2009) had stated that the optimum ph for microbial growth is between 6.8 and 7.2 while ph lower than 4 and higher than 9.5 are not tolerable. It is because the microbial community had their specific sensitivity on ph changes and generally on that ranges. Thus, their activity will decrease when ph is deviates from the optimum value. Table 2: The optimum condition for agitation and temperature suggested by DE software Solutions Agitation (rpm) Response number Temperature ( )

7 Validation experiment at optimum condition Experiment was conducted to validate the selected optimum condition. As shown in Table 3, the experimental response was very close to the predicted response at 2.29% error. Low errors from the validation experiments (<5%) proved that biological ph treatment for acidic POME could be represented by using the proposed model. Table 3: Data from validation experiment Temperature Agitation Speed Response (ph) Experimental Predicted Conclusion The purpose of this study was to optimize the factors that affecting biological ph treatment of acidic POME. In conclusion, the objective of this experiment was achieved. In this study, soil mixed culture was used to increase the ph of acidic POME. Optimization was done based on research surface methodology (RSM) with central composite design (CCD) using Design Expert software (Ver. 6.0). Experiments were conducted to determine the optimum condition for two selected factors which were agitation speed and temperature. Interaction plot for agitation speed and temperature showed that ph increased upon increasing of agitation and temperature. Both factors had individual significant influence on ph treatment. The optimum condition suggested by DE software was at temperature of and agitation speed of 125 rpm. The expected ph value at this condition was 8.03 and experimental ph obtained was Low errors from the validation experiments (<5%) proved that biological ph treatment for acidic POME could be represented by using the proposed model. This study showed that application of this biological process could be an effective solution for acidic POME treatment. 217

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