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Comprehensive Evaluation of Integrated Energy Plantation Model of Palm Oil and Microalgae Based Biofuel for Sustainable Energy Production
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 68 (2015) 226 – 235
2nd International Conference on Sustainable Energy Engineering and Application, ICSEEA 2014
Comprehensive evaluation of integrated energy plantation model of palm oil and microalgae based biofuel for sustainable energy production Nugroho Adi Sasongkoa,b,* and Ryozo Noguchia a
Faculty of Life and Environmental Sciences, University of Tsukuba, 305-8577 Japan The Agency of Assessment and Application of Technology, Jakarta, 10340 Indonesia
b
Abstract Microalgae is a biofuel crop that needs large amounts of water and nutrients in cultivation stage and requires excessive energy at the downstream processes. 7his study presented an integrated plantation concept to accomplish these issues by material and energy balance optimization of microalgae based biodiesel production cycle. Significant potency of positive energy balance by utilizing agriculture waste water from Palm Oil Mill Effluent (POME) was comprehensively investigated. However, POME has rich nutrient compounds for microalgae growth and its utilization reduces energy penalty. The total energy balance indicated substantial figures, in range of 2.66 up to 3.05 or even higher following the system efficiency. Meanwhile, total energy output for 1 production cycle in 10 ha microalgae pond approximately 160 GJ and net energy produced reaches 100 GJ. Based on current best available methods or technologies, microalgae cultivation for biofuels by using wastewater provide a positive energy return and might be economically viable. © 2015 Published by Elsevier Ltd. B.V. This is an open access article under the CC BY-NC-ND license © 2015The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Scientific Committee of ICSEEA 2014. Peer-review under responsibility of Scientific Committee of ICSEEA 2014
Keywords: energy balance; integrated energy plantation;microalgae cultivation; palm oil mill effluent
* Corresponding author. Tel.: +81-90-2913-8129; fax: +81-29-853-4697 E-mail address: [email protected]
1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Scientific Committee of ICSEEA 2014 doi:10.1016/j.egypro.2015.03.251
Nugroho Adi Sasongko and Ryozo Noguchi / Energy Procedia 68 (2015) 226 – 235
227
1. Introduction 1.1. General To fulfill the target of national energy policy on biofuel energy roadmap, Indonesia government through the Ministry of Energy and Mineral Resources released a regulation on Biodiesel utilization (No. 25, August 29 th, 2013) and stated the minimum biodiesel blended is 10% for all sectors beginning from January 2014 [1]. Indonesia also plans to expand additional 6 million ha of palm oil plantation for biodiesel production (B100) since forecasted that in 2025, the total consumption of diesel as a fossil fuel will reach 30,668,976 kL [2]. In the meantime, based on comprehensive calculations and analysis, the vast required land can be minimized by selecting microalgae to produce biodiesel. Microalgae based biodiesel (30 g/m2/day and lipid content 30%) possible to produce 22.3 thousands L/ha/year of biodiesel. By this estimation, it only needs 1.4 million ha to meet national biodiesel target in 2025 by POME is selected as one of nutrient source for cultivation. This advantage can diminish land clearing for another 4.6 million ha, furthermore reducing deforestation in Indonesia. Compared to perennial crops such as palm oil, the ratio of microalgae biomass production rate is much higher. Microalgae lipid production can reach 10 times more than conventional biofuel crops [3]. The calculation of land required for each biodiesel crops is presented on Fig. 1.
Fig. 1. Estimated land required versus oil yield.
By total, there are 695 palm mills by average capacity 37.2 tones FFB/h across 9 million ha palm plantation in Indonesia [4]. In each mills, POME has a unique characteristic. The effluent is depended on characteristics of the Fresh Fruit Bunch (FFB), extraction and efficiency of the Crude Palm Oil (CPO) processes. The effluent treatment system is a multiple conventional anaerobic & aerobic lagoons. The typical land size required for POME treatment is about 5 – 10 ha with depth approximately 3 m, often up to 6 m. Waste water generation from the steam extraction process is about 0.5 m3 POME/t FFB or 2.5 m3 POME/t CPO [5]. In Indonesia, it is estimated 3.5 m3 POME/t CPO
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or about 0.7 m3 POME/t FFB. If we assume POME is released by 18 m3/ha/year, then approximately 162 million m3/year of nutrients rich effluent release from 9 million ha palm plantation. Where water scarcity is an issue, this large volume of POME is prospective to be used as a nutrient for microalgae growth. A large fraction of the nutrients are recycled from the secondary treatment pond, thus resulting significant savings in makeup nutrient costs. It is a valuable resource to make a large scale cultivation and it can be considered in developing low cost microalgae production system. Further, commercial production of microalgae-based biofuels could be feasible. 1.2. Objective This research intentions to explore the possibility of utilizing of POME for microalgae cultivation. Material and energy balances of integrated energy system will be comprehensively analyzed in order to achieve technical feasibility and energy optimization. 2. Material and methodology 2.1. Existing POME treatment POME is considered as a polluting agro-industrial effluent due to its high values of COD and BOD concentrations, ranging from 50,000 to 90,000 mg/L [6]. However, Crude Palm Oil (CPO) which is extracted using steam and no the additional of chemicals, releases a homogeneous effluent and nutrient-rich (relatively clean and ease to control for further processing compared to municipal or industrial waste water). In order to use POME for microalgae growth, it is necessary to treat effluent, especially pH, COD, BOD, total nitrogen, total phosphorous, and ammonia composition. In addition, pH needs to be neutralized and it is required to shift other effluents composition meets the tolerable limit for microalgae growth. Palm Mill with capacity 45 ton FFB/h, and located in 20,000 ha plantation, has average POME almost 360,000 m3/year. Processing water in a particular site (PTPN V, Riau province, Indonesia) has average 21,454 m3/month. In this analysis, we used 66,666 L POME/d or 20,000 m 3/month or 240,000 m3/year which sufficient to run 10 ha of microalgae cultivation ponds. A previous study found that COD approximately 1000 mg/L affected the high consumption rate and growth of microalgae biomass [7]. It cultivated Chlorella pyrenoidosa in POME with different concentrations (0, 250, 500 and 1,000 mg COD/L).Meanwhile, a-5 year continuous field measurement from a particular POME treatment facility showed that COD has average 1,471.9 mg/L. Meanwhile, from a particular site was found that pH has average around 7.7 continuous in 5 years where NH3-Nhas average 125.1 mg/L. Some studies found that microalgae biomass and lipid productivities were highest at pH between 7.0 – 8.0 for Chlorella sp. [8]. Meanwhile, under different NH3-N concentration, biomass concentration of Chlorellavulgaris reaches optimum growth between 40 – 250 mg /L [9]. Certain level of nutrients concentration in the effluent can generally be controlled in several ways, for instance by utilizing aquatic plants. Aquatic plants are grown in the maturity pond found to be effectively balance the nutrient ratio in the waste water. If the nutrients are higher than ideal ratio, aquatic plants can be left to grow rapidly. While on the contrary, aquatic plants should be reduced, if the condition does not meet the nutrient ratio. At this time, utilization of aquatic plants is mostly done by the palm oil industry before releasing the waste into water bodies such as rivers, follow the requirements of environmental regulations. 2.2. Microalgae cultivation in POME The selection of strains which can grow and produce high quantities of lipids is a limitation in this phase. A study investigated Chlorella vulgaris for lipid production in a wastewater treatment and found that culture achieved the highest lipid content 42% of dry weight and average productivity was 147 mg/L/d [10]. Microalgae biomass production in digested POME was investigated and showed the possibility to use up to 75% concentration of POME to grow Chlorella sorokiniana C212 reached biomass productivity up to 97.14 ± 2.14 mg/L/d and lipid content approximately 20% [11]. Based on the research estimation, 30% of lipid content from Chlorella vulgaris in dry weight can be reachedby utilized POME [12]. A recent study showed Chlorella pyrenoidosa achieved the highest
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lipid content approximately 38.6% of dry biomass [13]. A study had been conducted to see the influence of different concentrations of filtered and centrifuged POME in sea water (1, 5, 10, 15 and 20%) as an alternative medium for microalgae cell growth and lipid yield [14]. Both Isochrysisgalbana and Pavlovalutheri had enhanced cell growth and lipid accumulation at 15% level with maximum specific growth rate (0.16 d-1 and 0.14 d-1) and lipid content (26.3 ± 0.31% and 34.5 ± 0.82%), respectively, after 16 days of cultivation. Scenedesmus sp. also found as a native wild microalgae in the existing POME treatment with vast biomass production but detailed studies have not been done. Furthermore, other researchers found Chlorella sp. in sewage can reach 30.0 - 40.0 g/m2/d of biomass productivity [15]. POME and serum latex from rubber effluent possible to be used as a base medium for cultivating four strains of oleaginous yeast, Y. lipolytica TISTR 5054, 5151, 5212 and 5621[16]. These yeasts grew well on POME and produced relatively high amount of lipid (1.6 – 1.7 g/L) corresponding to a high lipid content 48 – 61% based on their dry cell mass. Hence, in our proposed microalgae cultivation was assumed that 10 ha of integrated cultivation ponds with mixothropicmicroalgae (Chlorella sp. and Scenedesmus sp. and lipid content about 30% of dry weight) were cultivated in nearby the POME treatment. Mixothropic microalgae was chosen due to its excellent ability to live in the wastewater, rapid growth and vast biomass production.
Fig. 2. Microalgae cultivation in POME.
Microalgae can grow optimum in POME by ideal nutrients ratio of C:N:P equal to 56:8:1 [17]. Meanwhile based on field measurement, the characteristic of C:N:P ratio in particular site of POME treatment in Indonesia has average values of 36:6:1. Thus, additional nutrients are necessary to balance the existing nutrients in POME. Therefore, additional nutrients such as synthetic fertilizers and flue (CO2&NOx) could reach the nutrient balance. In this analysis, the ideal nutrients ratio would be adjusted by additional CO2 and NOx from flue gas of biogas or biomass power plant. Growth rates for Chlorella sp. were shown to be higher on flue gases with a CO2 content of 11-13 % [20]. NOx in flue gases has been found to have slight adverse effect on microalgae and be able to afford a nitrogen source. In a study by MIT, microalgae were been found to be able to utilize not only the carbon dioxide from boiler emission, but also 85 % of NOx, potentially reducing nitrogen fertilizer demand [21]. In addition, the possibility of adding
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synthetic nutrients were not taken into account in this simulation since it was assumed that balance nutrients composition can be reached by considered flue gases from methane gas engine and biomass boiler or power plant inside the mill. 2.3. System boundary and model construction The integrated system was constructed as 3 main parts that couple each other as a linked system: The first part is the existing POME treatment system, the second part is the anaerobic digester systems which produce methane biogas and EFB biomass power plant to generate electricity, and the third part is the microalgae production pathway. Design of the proposed integrated energy system is presented on Fig. 3. Moreover, the microalgae-based biofuel production cycle was divided into 3 main phases; cultivation, harvesting and cell lysing, and lipid conversion process. There are a wide range of combinations of growth, harvesting and energy extraction unit operations that can form a microalgae biofuel production system. Cost-effective methods of cultivation, harvesting and dewatering microalgae biomass and lipid extraction, purification, and conversion to fuel are critical issues to effective commercial scale of biodiesel production.
Fig. 3. Concept of integrated energy plantation.
2.4. Energy flow calculation in each stage Energy Profit Ratio (EPR) is the ratio of the energy output compared to the amount of energy input in its production. This modest ratio can be useful in assessing the viability of fuels. A ratio of less than 1 indicates that more energy is used than produced, and value 3 of EPR has been suggested as the minimum that is sustainable [22]. POME treatment plant was assumed at the same efficiency all the time. The embodied energy within process equipment was not considered in the energy balances of this work. Nevertheless, this analysis excluded material and
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energy balances of some points from the boundary system, such as: inoculums facility, daily workers activities, construction of facility, cleaning and maintenance period and products transportation. The unit of balance in each stage is joule per liter of POME. Productivity (Palgae) [kg/L] calculated in grams per liter of growth volume per day, can be defined as, ݈ܲܽ݃ܽ݁ ൌ
݈݁ܽ݃ܽܯ
൘ܸ ܱܲܧܯ
(1)
where, M algae is the microalgae biomass production per crop cycle [kg], V POME is the volume of POME in the cultivation pond [L], and tc is the cultivation period [7 days]. Then, the energy production is formulated as: ݈݀݁݊݅ܽ݃ܽݐݐܧൌ ݈ܲܽ݃ܽ݁Ǥ H݈݅݀݅Ǥ MܩǤ MܪǤ MܴǤ ܩܣǤ MܣǤ ܦܤܥ
(2)
Hlipid is the percentage of lipid content in dry weight of algae biomass, MG,MH and MR are efficiency of cultivation, harvesting and processing phases, respectively. AG is the total area of raceway for algae cultivation (10,000 m2), and MA is a land covered efficiency (0.7), and CBD is the biodiesel energy content, 41 MJ/kg [24]. The energy required to produce biodiesel in MJ/L POME, can be defined as, ݀݁ݎ݅ݑݍ݁ݎ݈ܽݐݐܧൌ ݃ܧǤ M݃Ǥ ݄ܧǤ M݄Ǥ ݎܧǤ Mݎ
(3)
where, Eg,Eh and Er are the energy requirements for growth, harvesting and processing production steps in MJ/L POME, respectively. And Mg, Mh and Mr are the efficiencies of each phases, respectively. Energy balance of methane biogas production from POME was calculated based on the biogas plant common capacity from 45 ton FFB/hr of palm oil mill. Electric power generated from methane combustion can be calculated as: ܪܥܮܧͶሺݐሻ ൌ ሺܻܪܥͶሺݐሻǤ ܪܥܧͶǤ ݁ሻȀ͵ǡͲͲ
(4)
is the daily electric power generated from methane combustion [kWh/m2/d], is methane where, 3 production [m /d], is the higher calorific value for methane [39.18 MJ/m3], and is the power generating efficiency [30%][23]. 3. Result and discussion This analysis shows potential scale up from lab scale to 10 ha of outdoor cultivation pond. Material flow scheme of proposed integrated energy system is presented on Fig. 3. microalgae strain has daily productivity 118 mg/L/d or 30 gr/m2/din the POME. Average of efficiency from each phases is about 0.80. Current best available methods showed a good opportunity to increase net-EPR from 2.67 up to 3.05 by utilized wet extraction route, included POME for cultivation, auto-flocculation and controlled shock for cell disruption in harvesting, hydro-treatment or supercritical methanol process for lipid conversion. Fig. 4. shows the total energy required during cultivation is 297.41 MJ/ha/d. HROP paddlewheel took a significant portion, around 86.5% from total energy required. In order to achieve nutrient balance, required flue gases (CO2 and NOx) were calculated. The result shows approximately 320 Nm3/h or 26,730 - 38,400 m3/12h/10ha or 5,346 - 7,680 kg/10ha/d of flue gas stream was required. Flue gas utilization for microalgae growth is one of potential method of CO2 sequestration. Meanwhile, on harvesting stage, material and energy balance for a daily production can be shown on Fig. 5.
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Fig. 4. Energy balance at cultivation stage.
Fig. 5. Energy balance at harvesting stage.
Approximately, 184.8 kg/ha/d of microalgae biomass can be harvested. Meanwhile, microalgae biomass needs to be dried, before continue to the lipid conversion stage. Dewatering process required huge amount of heat supply. At fresh harvest by using flocculation, the concentration of slurry contained of 10% biomass and 90% water. Almost 1,110 MJ/d of heat supply was required to reduce water content lower than 10%. The level of 10% was chosen as a target due to optimum or higher performance of biodiesel production of the wet lipid conversion process. In term of energy application, utilization the waste heat from biogas power plant, biomass power plant and supercritical process can increase system efficiency, to dry and reduce the water content during harvesting phase. Calculation as showed in Fig 6., removing up to 90% (or more) of moisture content from microalgae slurry was practically viable to fit the requirement of the lipid conversion process. Waste heat from flue gas, boiler, power plant and extraction phase possible to be used, up to 50% from their potential heat.
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Fig. 6. Energy required at dewatering process.
Fig 7. shows required energy input in wet lipid conversion of supercritical methanol where approximately 2.52 MJ/L biodiesel or about 6.15 GJ per one harvesting cycle for 10 ha cultivation ponds. Supercritical method was able to process microalgae slurry by 10% water content without reducing the biodiesel production efficiency [24]. The total fossil energy input (equivalent) in a daily microalgae cultivation reached 853.80 MJ/ha/d,by the share of cultivation, harvesting and lipid conversion stages were 35%, 27% and 38% respectively.
Fig. 7. Energy balance at lipid conversion process.
Meanwhile, total energy output of 1 production cycle (7 days) in 10 ha microalgae pond was approximately 160 GJ. Where energy required had total of 60 GJ and net-energy produce reached 100 GJ, as shown in Fig. 8. Based on current best available methods or technologies, microalgae cultivation by utilized wastewater (in this case is POME) provided a positive energy return and might be economically viable. In total, 674.5 ton of microalgae biomass or 223 kL/year of biodiesel was estimated possible to be produced. The biomass and lipid production even can be more or double by recycling water from cultivation ponds after harvesting and passed through some pre-treatment. This recycled nutrient rich water can be used to another new microalgae ponds. If 2.5 kWh electric heater was utilized, EPR of 2.66 can be gained. Meanwhile, 3.05 of EPR were able to be achieved if electric heater was replaced to biogas dryer. Based on current progress of microalgae-based biodiesel researches, the average EPR is around 2.10 for open pond cultivation. Therefore, utilization of agricultural waste water in an integrated energy plantation for microalgae cultivation is a promising research in the future.
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Fig. 8. Share of fossil energy input in daily microalgae-base biodiesel production system.
4. Conclusions Microalgae cultivation-based biofuel is a promise for the future bioenergy resource, compared to other edible oil crops in terms of land use. On the other hand, utilization of agricultural waste water, such as POME, possible to increase cultivation viability and reduces required energy. Moreover, integrated energy plantation showed a positive energy balance which provides the opportunity for sustainable energy production. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
The ministry of energy and mineral resources Republic of Indonesia. Regulation No. 25, August 29 th2013, about Biofuel utilization. BPPT. 2013. Indonesia energy outlook 2013: Energy development in supporting transportation sector and mineral processing industry. Chisti Y. 2007. Biodiesel from microalgae. Biotechnology Advances 25 (3), pp. 294-306. The ministry of agriculture of Republic of Indonesia. 2013. Annual report. Schmidt, J. 2007. Life cycle assessment of rapeseed oil and palm oil: Part 3: Life cycle inventory of rapeseed oil and palm oil. Doctoral thesis. Alborg University. Denmark. Harsono, et al. 2014. Anaerobic treatment of palm oil mill effluents: Potential contribution to net energy yield and reduction of greenhouse gas emissions from biodiesel production. Journal of Cleaner Production 64, pp. 619 - 627. Kamyab H., et al. 2014. Lipid production using Chlorella pyrenoidosa cultivated in Palm Oil Mill Effluent (POME). Proceeding of International Science Postgraduate Conference (ISPC2014). Moheimani, N. R. 2012. Inorganic carbon and pH effect on growth and lipid productivity of Tetraselmis suecica and Chlorella sp. (Chlorophyta) grown outdoors in bag photobioreactors. Journal of Applied Phycology 25 (2), pp. 167-176. Selmani N., et al. 2013. Study the growth of microalgae in palm oil mill effluent waste water. 4thInternational Conference on Energy and Environment (ICEE). Feng Y., et al. 2011. Lipid production of Chlorella vulgaris cultured in artificial wastewater medium. Bioresource Technology 102, pp. 101–105. Nwuche, C.O., et al. 2014.Use of palm oil mill effluent as medium for cultivation of Chlorella sorokiniana. British Biotechnology Journal, Vol. 4, Issue: 3 (May - June). Hadiyanto, et al. 2013. Phytoremediations of Palm Oil Mill Effluent (POME) by using aquatic plants and microalgae for biomass production. Journal of Environmental Science and Technology 6 (2), pp. 79 - 90. Kamyab H., et al. 2013. A review on microalgae as potential lipid container with wastewater treating functions. Journal of Environmental Treatment Techniques, Volume 1, Issue 2, pp. 76 - 80. Shah S., et al. 2014. Enhancement of lipid content in Isochrysis galbana and Pavlova lutheri using palm oil mill effluent as an alternative medium. Chemical Engineering Transactions37, pp. 733-738. Edward, P. 1980. The production of microalgae on human wastes and their harvest by herbivorous fish. In Algae Biomass: Production and Use, ed. Shelef, G. & Soeder, C.J. pp. 191 – 203. Amsterdam: Elsevier North Holland. Cheirsilp B., Louhasakul Y. 2013. Industrial wastes as a promising renewable source for production of microbial lipid and direct transesterification of the lipid into biodiesel. Bioresource Technology 142, pp. 329 - 337. Phang, S.M., Ong K.C. 1988. Algal biomass production in digested palm oil mill effluent. Biological Wastes 25, pp. 177 – 191. Vairappan, C.S., Yen, AM. 2007. Palm Oil Mill Effluent (POME) cultured marine microalgae as supplementary diet for rotifer culture. Journal of Applied Phycology, Vol. 20, No 5, pp. 153 – 158. Putri E.V. et al. 2011. Investigation of microalgae for high lipid content using Palm Oil Mill Effluent (POME) as carbon source. International Conference on Environment and Industrial Innovation.
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[21] [22] [23] [24]
Istiyanie, D. 2011. Utilization of CO2emission from coal power plant in domestic wastewater treatment with microalgae based (Study of CO2emissions flow rate effect against microalgae growth which potentially as raw material of biofuel and domestic wastewater quality). Master Thesis. University of Indonesia, Indonesia. Milledge, JJ. 2013. Energy balance and techno-economic assessment of algal biofuel production systems. Doctoral Thesis. The University of Southampton, UK. Sander K., Murthy G.S. 2010. Life cycle analysis of algae biodiesel. International Journal of Life Cycle Assessment 15, pp. 704 – 714. Beal C.M., et al.2012. Energy return on investment for algal biofuel production coupled with wastewater treatment. Water Environment Research; Volume 84, Number 9. Takisawa, K. 2014. Biodiesel production from wet microalgae using acid. Doctoral Thesis, University of Tsukuba, Japan.
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ScienceDirect Energy Procedia 68 (2015) 226 – 235
2nd International Conference on Sustainable Energy Engineering and Application, ICSEEA 2014
Comprehensive evaluation of integrated energy plantation model of palm oil and microalgae based biofuel for sustainable energy production Nugroho Adi Sasongkoa,b,* and Ryozo Noguchia a
Faculty of Life and Environmental Sciences, University of Tsukuba, 305-8577 Japan The Agency of Assessment and Application of Technology, Jakarta, 10340 Indonesia
b
Abstract Microalgae is a biofuel crop that needs large amounts of water and nutrients in cultivation stage and requires excessive energy at the downstream processes. 7his study presented an integrated plantation concept to accomplish these issues by material and energy balance optimization of microalgae based biodiesel production cycle. Significant potency of positive energy balance by utilizing agriculture waste water from Palm Oil Mill Effluent (POME) was comprehensively investigated. However, POME has rich nutrient compounds for microalgae growth and its utilization reduces energy penalty. The total energy balance indicated substantial figures, in range of 2.66 up to 3.05 or even higher following the system efficiency. Meanwhile, total energy output for 1 production cycle in 10 ha microalgae pond approximately 160 GJ and net energy produced reaches 100 GJ. Based on current best available methods or technologies, microalgae cultivation for biofuels by using wastewater provide a positive energy return and might be economically viable. © 2015 Published by Elsevier Ltd. B.V. This is an open access article under the CC BY-NC-ND license © 2015The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Scientific Committee of ICSEEA 2014. Peer-review under responsibility of Scientific Committee of ICSEEA 2014
Keywords: energy balance; integrated energy plantation;microalgae cultivation; palm oil mill effluent
* Corresponding author. Tel.: +81-90-2913-8129; fax: +81-29-853-4697 E-mail address: [email protected]
1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Scientific Committee of ICSEEA 2014 doi:10.1016/j.egypro.2015.03.251
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1. Introduction 1.1. General To fulfill the target of national energy policy on biofuel energy roadmap, Indonesia government through the Ministry of Energy and Mineral Resources released a regulation on Biodiesel utilization (No. 25, August 29 th, 2013) and stated the minimum biodiesel blended is 10% for all sectors beginning from January 2014 [1]. Indonesia also plans to expand additional 6 million ha of palm oil plantation for biodiesel production (B100) since forecasted that in 2025, the total consumption of diesel as a fossil fuel will reach 30,668,976 kL [2]. In the meantime, based on comprehensive calculations and analysis, the vast required land can be minimized by selecting microalgae to produce biodiesel. Microalgae based biodiesel (30 g/m2/day and lipid content 30%) possible to produce 22.3 thousands L/ha/year of biodiesel. By this estimation, it only needs 1.4 million ha to meet national biodiesel target in 2025 by POME is selected as one of nutrient source for cultivation. This advantage can diminish land clearing for another 4.6 million ha, furthermore reducing deforestation in Indonesia. Compared to perennial crops such as palm oil, the ratio of microalgae biomass production rate is much higher. Microalgae lipid production can reach 10 times more than conventional biofuel crops [3]. The calculation of land required for each biodiesel crops is presented on Fig. 1.
Fig. 1. Estimated land required versus oil yield.
By total, there are 695 palm mills by average capacity 37.2 tones FFB/h across 9 million ha palm plantation in Indonesia [4]. In each mills, POME has a unique characteristic. The effluent is depended on characteristics of the Fresh Fruit Bunch (FFB), extraction and efficiency of the Crude Palm Oil (CPO) processes. The effluent treatment system is a multiple conventional anaerobic & aerobic lagoons. The typical land size required for POME treatment is about 5 – 10 ha with depth approximately 3 m, often up to 6 m. Waste water generation from the steam extraction process is about 0.5 m3 POME/t FFB or 2.5 m3 POME/t CPO [5]. In Indonesia, it is estimated 3.5 m3 POME/t CPO
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or about 0.7 m3 POME/t FFB. If we assume POME is released by 18 m3/ha/year, then approximately 162 million m3/year of nutrients rich effluent release from 9 million ha palm plantation. Where water scarcity is an issue, this large volume of POME is prospective to be used as a nutrient for microalgae growth. A large fraction of the nutrients are recycled from the secondary treatment pond, thus resulting significant savings in makeup nutrient costs. It is a valuable resource to make a large scale cultivation and it can be considered in developing low cost microalgae production system. Further, commercial production of microalgae-based biofuels could be feasible. 1.2. Objective This research intentions to explore the possibility of utilizing of POME for microalgae cultivation. Material and energy balances of integrated energy system will be comprehensively analyzed in order to achieve technical feasibility and energy optimization. 2. Material and methodology 2.1. Existing POME treatment POME is considered as a polluting agro-industrial effluent due to its high values of COD and BOD concentrations, ranging from 50,000 to 90,000 mg/L [6]. However, Crude Palm Oil (CPO) which is extracted using steam and no the additional of chemicals, releases a homogeneous effluent and nutrient-rich (relatively clean and ease to control for further processing compared to municipal or industrial waste water). In order to use POME for microalgae growth, it is necessary to treat effluent, especially pH, COD, BOD, total nitrogen, total phosphorous, and ammonia composition. In addition, pH needs to be neutralized and it is required to shift other effluents composition meets the tolerable limit for microalgae growth. Palm Mill with capacity 45 ton FFB/h, and located in 20,000 ha plantation, has average POME almost 360,000 m3/year. Processing water in a particular site (PTPN V, Riau province, Indonesia) has average 21,454 m3/month. In this analysis, we used 66,666 L POME/d or 20,000 m 3/month or 240,000 m3/year which sufficient to run 10 ha of microalgae cultivation ponds. A previous study found that COD approximately 1000 mg/L affected the high consumption rate and growth of microalgae biomass [7]. It cultivated Chlorella pyrenoidosa in POME with different concentrations (0, 250, 500 and 1,000 mg COD/L).Meanwhile, a-5 year continuous field measurement from a particular POME treatment facility showed that COD has average 1,471.9 mg/L. Meanwhile, from a particular site was found that pH has average around 7.7 continuous in 5 years where NH3-Nhas average 125.1 mg/L. Some studies found that microalgae biomass and lipid productivities were highest at pH between 7.0 – 8.0 for Chlorella sp. [8]. Meanwhile, under different NH3-N concentration, biomass concentration of Chlorellavulgaris reaches optimum growth between 40 – 250 mg /L [9]. Certain level of nutrients concentration in the effluent can generally be controlled in several ways, for instance by utilizing aquatic plants. Aquatic plants are grown in the maturity pond found to be effectively balance the nutrient ratio in the waste water. If the nutrients are higher than ideal ratio, aquatic plants can be left to grow rapidly. While on the contrary, aquatic plants should be reduced, if the condition does not meet the nutrient ratio. At this time, utilization of aquatic plants is mostly done by the palm oil industry before releasing the waste into water bodies such as rivers, follow the requirements of environmental regulations. 2.2. Microalgae cultivation in POME The selection of strains which can grow and produce high quantities of lipids is a limitation in this phase. A study investigated Chlorella vulgaris for lipid production in a wastewater treatment and found that culture achieved the highest lipid content 42% of dry weight and average productivity was 147 mg/L/d [10]. Microalgae biomass production in digested POME was investigated and showed the possibility to use up to 75% concentration of POME to grow Chlorella sorokiniana C212 reached biomass productivity up to 97.14 ± 2.14 mg/L/d and lipid content approximately 20% [11]. Based on the research estimation, 30% of lipid content from Chlorella vulgaris in dry weight can be reachedby utilized POME [12]. A recent study showed Chlorella pyrenoidosa achieved the highest
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lipid content approximately 38.6% of dry biomass [13]. A study had been conducted to see the influence of different concentrations of filtered and centrifuged POME in sea water (1, 5, 10, 15 and 20%) as an alternative medium for microalgae cell growth and lipid yield [14]. Both Isochrysisgalbana and Pavlovalutheri had enhanced cell growth and lipid accumulation at 15% level with maximum specific growth rate (0.16 d-1 and 0.14 d-1) and lipid content (26.3 ± 0.31% and 34.5 ± 0.82%), respectively, after 16 days of cultivation. Scenedesmus sp. also found as a native wild microalgae in the existing POME treatment with vast biomass production but detailed studies have not been done. Furthermore, other researchers found Chlorella sp. in sewage can reach 30.0 - 40.0 g/m2/d of biomass productivity [15]. POME and serum latex from rubber effluent possible to be used as a base medium for cultivating four strains of oleaginous yeast, Y. lipolytica TISTR 5054, 5151, 5212 and 5621[16]. These yeasts grew well on POME and produced relatively high amount of lipid (1.6 – 1.7 g/L) corresponding to a high lipid content 48 – 61% based on their dry cell mass. Hence, in our proposed microalgae cultivation was assumed that 10 ha of integrated cultivation ponds with mixothropicmicroalgae (Chlorella sp. and Scenedesmus sp. and lipid content about 30% of dry weight) were cultivated in nearby the POME treatment. Mixothropic microalgae was chosen due to its excellent ability to live in the wastewater, rapid growth and vast biomass production.
Fig. 2. Microalgae cultivation in POME.
Microalgae can grow optimum in POME by ideal nutrients ratio of C:N:P equal to 56:8:1 [17]. Meanwhile based on field measurement, the characteristic of C:N:P ratio in particular site of POME treatment in Indonesia has average values of 36:6:1. Thus, additional nutrients are necessary to balance the existing nutrients in POME. Therefore, additional nutrients such as synthetic fertilizers and flue (CO2&NOx) could reach the nutrient balance. In this analysis, the ideal nutrients ratio would be adjusted by additional CO2 and NOx from flue gas of biogas or biomass power plant. Growth rates for Chlorella sp. were shown to be higher on flue gases with a CO2 content of 11-13 % [20]. NOx in flue gases has been found to have slight adverse effect on microalgae and be able to afford a nitrogen source. In a study by MIT, microalgae were been found to be able to utilize not only the carbon dioxide from boiler emission, but also 85 % of NOx, potentially reducing nitrogen fertilizer demand [21]. In addition, the possibility of adding
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synthetic nutrients were not taken into account in this simulation since it was assumed that balance nutrients composition can be reached by considered flue gases from methane gas engine and biomass boiler or power plant inside the mill. 2.3. System boundary and model construction The integrated system was constructed as 3 main parts that couple each other as a linked system: The first part is the existing POME treatment system, the second part is the anaerobic digester systems which produce methane biogas and EFB biomass power plant to generate electricity, and the third part is the microalgae production pathway. Design of the proposed integrated energy system is presented on Fig. 3. Moreover, the microalgae-based biofuel production cycle was divided into 3 main phases; cultivation, harvesting and cell lysing, and lipid conversion process. There are a wide range of combinations of growth, harvesting and energy extraction unit operations that can form a microalgae biofuel production system. Cost-effective methods of cultivation, harvesting and dewatering microalgae biomass and lipid extraction, purification, and conversion to fuel are critical issues to effective commercial scale of biodiesel production.
Fig. 3. Concept of integrated energy plantation.
2.4. Energy flow calculation in each stage Energy Profit Ratio (EPR) is the ratio of the energy output compared to the amount of energy input in its production. This modest ratio can be useful in assessing the viability of fuels. A ratio of less than 1 indicates that more energy is used than produced, and value 3 of EPR has been suggested as the minimum that is sustainable [22]. POME treatment plant was assumed at the same efficiency all the time. The embodied energy within process equipment was not considered in the energy balances of this work. Nevertheless, this analysis excluded material and
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energy balances of some points from the boundary system, such as: inoculums facility, daily workers activities, construction of facility, cleaning and maintenance period and products transportation. The unit of balance in each stage is joule per liter of POME. Productivity (Palgae) [kg/L] calculated in grams per liter of growth volume per day, can be defined as, ݈ܲܽ݃ܽ݁ ൌ
݈݁ܽ݃ܽܯ
൘ܸ ܱܲܧܯ
(1)
where, M algae is the microalgae biomass production per crop cycle [kg], V POME is the volume of POME in the cultivation pond [L], and tc is the cultivation period [7 days]. Then, the energy production is formulated as: ݈݀݁݊݅ܽ݃ܽݐݐܧൌ ݈ܲܽ݃ܽ݁Ǥ H݈݅݀݅Ǥ MܩǤ MܪǤ MܴǤ ܩܣǤ MܣǤ ܦܤܥ
(2)
Hlipid is the percentage of lipid content in dry weight of algae biomass, MG,MH and MR are efficiency of cultivation, harvesting and processing phases, respectively. AG is the total area of raceway for algae cultivation (10,000 m2), and MA is a land covered efficiency (0.7), and CBD is the biodiesel energy content, 41 MJ/kg [24]. The energy required to produce biodiesel in MJ/L POME, can be defined as, ݀݁ݎ݅ݑݍ݁ݎ݈ܽݐݐܧൌ ݃ܧǤ M݃Ǥ ݄ܧǤ M݄Ǥ ݎܧǤ Mݎ
(3)
where, Eg,Eh and Er are the energy requirements for growth, harvesting and processing production steps in MJ/L POME, respectively. And Mg, Mh and Mr are the efficiencies of each phases, respectively. Energy balance of methane biogas production from POME was calculated based on the biogas plant common capacity from 45 ton FFB/hr of palm oil mill. Electric power generated from methane combustion can be calculated as: ܪܥܮܧͶሺݐሻ ൌ ሺܻܪܥͶሺݐሻǤ ܪܥܧͶǤ ݁ሻȀ͵ǡͲͲ
(4)
is the daily electric power generated from methane combustion [kWh/m2/d], is methane where, 3 production [m /d], is the higher calorific value for methane [39.18 MJ/m3], and is the power generating efficiency [30%][23]. 3. Result and discussion This analysis shows potential scale up from lab scale to 10 ha of outdoor cultivation pond. Material flow scheme of proposed integrated energy system is presented on Fig. 3. microalgae strain has daily productivity 118 mg/L/d or 30 gr/m2/din the POME. Average of efficiency from each phases is about 0.80. Current best available methods showed a good opportunity to increase net-EPR from 2.67 up to 3.05 by utilized wet extraction route, included POME for cultivation, auto-flocculation and controlled shock for cell disruption in harvesting, hydro-treatment or supercritical methanol process for lipid conversion. Fig. 4. shows the total energy required during cultivation is 297.41 MJ/ha/d. HROP paddlewheel took a significant portion, around 86.5% from total energy required. In order to achieve nutrient balance, required flue gases (CO2 and NOx) were calculated. The result shows approximately 320 Nm3/h or 26,730 - 38,400 m3/12h/10ha or 5,346 - 7,680 kg/10ha/d of flue gas stream was required. Flue gas utilization for microalgae growth is one of potential method of CO2 sequestration. Meanwhile, on harvesting stage, material and energy balance for a daily production can be shown on Fig. 5.
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Fig. 4. Energy balance at cultivation stage.
Fig. 5. Energy balance at harvesting stage.
Approximately, 184.8 kg/ha/d of microalgae biomass can be harvested. Meanwhile, microalgae biomass needs to be dried, before continue to the lipid conversion stage. Dewatering process required huge amount of heat supply. At fresh harvest by using flocculation, the concentration of slurry contained of 10% biomass and 90% water. Almost 1,110 MJ/d of heat supply was required to reduce water content lower than 10%. The level of 10% was chosen as a target due to optimum or higher performance of biodiesel production of the wet lipid conversion process. In term of energy application, utilization the waste heat from biogas power plant, biomass power plant and supercritical process can increase system efficiency, to dry and reduce the water content during harvesting phase. Calculation as showed in Fig 6., removing up to 90% (or more) of moisture content from microalgae slurry was practically viable to fit the requirement of the lipid conversion process. Waste heat from flue gas, boiler, power plant and extraction phase possible to be used, up to 50% from their potential heat.
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Fig. 6. Energy required at dewatering process.
Fig 7. shows required energy input in wet lipid conversion of supercritical methanol where approximately 2.52 MJ/L biodiesel or about 6.15 GJ per one harvesting cycle for 10 ha cultivation ponds. Supercritical method was able to process microalgae slurry by 10% water content without reducing the biodiesel production efficiency [24]. The total fossil energy input (equivalent) in a daily microalgae cultivation reached 853.80 MJ/ha/d,by the share of cultivation, harvesting and lipid conversion stages were 35%, 27% and 38% respectively.
Fig. 7. Energy balance at lipid conversion process.
Meanwhile, total energy output of 1 production cycle (7 days) in 10 ha microalgae pond was approximately 160 GJ. Where energy required had total of 60 GJ and net-energy produce reached 100 GJ, as shown in Fig. 8. Based on current best available methods or technologies, microalgae cultivation by utilized wastewater (in this case is POME) provided a positive energy return and might be economically viable. In total, 674.5 ton of microalgae biomass or 223 kL/year of biodiesel was estimated possible to be produced. The biomass and lipid production even can be more or double by recycling water from cultivation ponds after harvesting and passed through some pre-treatment. This recycled nutrient rich water can be used to another new microalgae ponds. If 2.5 kWh electric heater was utilized, EPR of 2.66 can be gained. Meanwhile, 3.05 of EPR were able to be achieved if electric heater was replaced to biogas dryer. Based on current progress of microalgae-based biodiesel researches, the average EPR is around 2.10 for open pond cultivation. Therefore, utilization of agricultural waste water in an integrated energy plantation for microalgae cultivation is a promising research in the future.
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Fig. 8. Share of fossil energy input in daily microalgae-base biodiesel production system.
4. Conclusions Microalgae cultivation-based biofuel is a promise for the future bioenergy resource, compared to other edible oil crops in terms of land use. On the other hand, utilization of agricultural waste water, such as POME, possible to increase cultivation viability and reduces required energy. Moreover, integrated energy plantation showed a positive energy balance which provides the opportunity for sustainable energy production. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
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