Effect of new palm oil mill processes on the EFB and POME utilisation

Transcription

1 Proceedings of Chemistry and Technology Conference PIPOC 2007, Kuala Lumpur, August C2 Effect of new processes on the EFB and POME utilisation F. Schuchardt 1, K. Wulfert 2, D. Darnoko 3, T. Herawan 3 ABSTRACT New processes are characterised by advanced oil separation technologies with zero dilution water (ECO-D System for example) and continuous sterilisation of the FFB. These processes have a deep impact on the amount and composition of waste water (POME). Compared to conventional s the total amount of POME can be reduced from 0.65 m³/ton FFB to 0.45 m³/ton (conventional sterilisation and zero dilution water) and 0.25 m³/ton (continuous sterilisation and zero dilution water). These changes influence the treatment processes and its cost significantly. One process for the EFB and POME utilisation which can fulfil the demand of a sustainable palm oil production is the combined composting of both of the materials. The composting process is used also for biological drying of the POME. The final product of the process is compost or mulch which unifies the nutrients of both in one product. The POME can be used also for biogas production (in fixed bed reactors for POME with low dry matter content and in totally mixed reactors for ECO-D biomass) before composting. The investment cost and profitability of the composting and fermentation process is calculated in detail based on data from practise in Indonesia. The new developments of processes in s can reduce the cost for the waste and waste water treatment up to 35 %. The benefits from biogas production and composting are the energy production, saved POME treatment cost in pond systems, total utilisation of the POME nutrients, reduced cost for the EFB transport and utilisation, higher FFB yields and from CDM. Abbreviations: POM, POME effluent, FFB fresh fruit bunch, EFB empty fruit bunch, CDM (clean development mechanism), DM dry matter, t ton INTRODUCTION Conventional s are considerable polluters of the environment and don t follow the principles of sustainability (Anonym Unilever 2003; Anonym RSPO 2005). In the RSPO principle 5 ( Environmental Responsibility and conservation of natural resources and biodiversity ) is written: Waste is reduced, recycled, and disposed of in an environmentally and socially responsible manner (criterion 5.3), Efficiency of energy use and use of renewable 1 Federal Agricultural Research Centre (FAL), Institute of Technology and Biosystems Engineering, Braunschweig, Germany 2 UTEC Consultant for Development and Application of Environmental friendly Technology GmbH, Bremen, Germany 3 Indonesian Oil Palm Research Institute, Medan (IOPRI), Indonesia 44

2 energy is maximised (criterion 5.4), and Plans to reduce pollution and emissions, including greenhouse gases, are developed, implemented and monitored. The main source of environment pollution in the oil mill is the pond system for the palm oil mill effluent (POME). The anaerobic ponds emit a huge amount of the strong green house gas methane with the biogas and the effluent of the ponds contains nutrients responsible for pollution of surface and ground water. Each ton of produced crude palm oil is responsible for the emission of 46 m³ (32.9 kg) of methane, corresponding 384 m³ (756 kg) CO 2 equivalent. Because climate protection becomes more and more important and especially methane emissions are in focus, it can be expected that the conventional waste water treatment in anaerobic ponds will be banned in the future. Furthermore the palm oil industry will come under pressure, if a huge amount of CPO (crude palm oil) or bio-diesel from CPO as renewable energy source will be exported to western countries. The requirement will arise, that the CPO production has to be sustainable less emissions, no pollution of the environment, implementation of recycling systems, utilization of energy sources, soil conservation by minimization of erosion, protection of rain forest and so on. Under these aspects the palm oil industry will be forced to implement new environmental friendly treatment technologies in their oil mills. Concepts, technical solution and practical experiences for new concepts as EFB composting in combination with POME and biogas production from POME/sludge are available since several years (Schuchardt et al. 1999, Schuchardt et al. 2002a, Schuchardt et al. 2002b, Wulfert et al. 2002; Schuchardt et al. 2006) Alternatives of POME, sludge and EFB treatment and utilization If the POME is not treated in an anaerobic-aerobic pond system, alternatives as follows can be discussed: Aerobic treatment in aerated ponds to avoid methane emissions is not suitable, because of o Enormous demand of current for aerators o Problems with de-sludging of ponds and handling of sludge o Biological problems (COD with 50,000 mg/l is too high for direct aerobic treatment) Anaerobic pre-treatment in a biogas plant and aerobic post-treatment in aerobic ponds is possible, but the aerobic post-treatment is not recommended, because o the aerobic post-treatment has still the problem of sludge sedimentation in the ponds (50 % of COD is suspended organic material, which are not degraded in a digester with relatively short retention time), sludge handling and o methane formation in sludge sediment can not be avoided. o Losses of all nutrients from POME and pollution of rivers and lakes. Technical drying of POME is not suitable, because of high invest- and running costs and high energy demand. Land application of the POME is not recommended, because of the high cost, if the application rate is in balance with nutrient uptake by the oil palm tree (Schuchardt et al., 2005). Furthermore the POME has to be pre-treated anaerobically to fulfil the application regulations (in Indonesia: BOD <5,000 mg O 2 /litre). One result of the anaerobic treatment is emission of methane. Utilization of POME for moistening in combination with EFB composting. This system is recommended, because: o the liquid of POME will be naturally evaporated without any additional energy input (except fuel demand of the turning machine), 45

3 o all nutrients of POME are saved in the compost, o there is no waste water anymore, except leakage and rain water from the composting plant area, o pollution of surface water, ground water and atmosphere can be avoided. Since incineration of empty fruit bunches (EFB) is forbidden because of environment pollution by smoke, land application is the common accepted method of its sustainable utilisation. In praxis the oil mills use different procedures for handling, pre-treatment and distribution: untreated empty fruit bunch are distributed in plantation, negative aspects are: o EFB are still wet with high weight per bunch. o Distribution happens manually. o Danger of Ganoderma boninense and Oryctes rhinoceros (Rhinoceros beetle) if EFB are dumped in heaps. o Slow mineralisation of the nutrients, the fertilizer effect is difficult to calculate. Distribution of chopped fresh EFB, positive aspects are: o Easier to handle. o Distribution can be done manually or mechanised by spreader or blower. o Material has the function of mulch and soil conditioner. o Mineralisation is faster. Compost production from chopped EFB and distribution of compost, positive aspects are: o Less volume and tonnage, in consequence less afford for transport and distribution. o High content of mineralised nutrients, fertilizer effect can be quantified. In some cases s still dump the EFB somewhere in the plantation area (with methane emissions) or burn it in open heaps (with heavy smoke pollution) to get the ash as mineral fertilizer. Palm oil mills with new technologies The discussion about POME treatment is based on an "end of pipe strategy". An alternative is to modernize the production process itself. In s new technologies (so called "new s") had been developed and are in progress (Sivasothy et al. 2005; Sivasothy and Hwa 2006; Chungsiriporn and Prasertsan 2006; Westfalia Separator Industry 2006; Tornroth 2006). These technologies are particularly: New sterilisation processes without condensate instead of conventional autoclave sterilisation. The conventional sterilization creates a condensate flow of 0.20 m³/ton FFB. By modification to a new sterilization processes the condensate can be avoided almost totally. Zero dilution water for oil separation. The conventional oil recovery process as a combination of vertical clarifier and separators needs dilution water for good function. The process creates waste water: 0.45 m³/ton FFB. By using new oil recovery technology (for example "ECO-D" system by Westfalia Company) an addition of dilution water is not necessary anymore and the amount of effluent can be reduced up to 0.25 m³/ton FFB. The total amount of POME can be reduced step by step by implementation of new technologies (table 1). Because the loads of suspended solids, dissolved COD etc. are nearly unaffected by the reduction of water, the dry matter content will increase from 5 % in conventional POME up to 17 % in the biomass discharged from the ECO-D decanter system. 46

4 Table 1 POME and sludge from conventional and new s POM Conventional POM "New POM" Parameter Conventional sterilisation Convent. sterilis., new oil recovery New sterilisation, new oil recovery A B C sterilizer condensate m³/t FFB clarification sludge m³/t FFB sum POME m³/t FFB dilution water m³/t FFB POME % DM POME m³/t EFB POME water m³/t EFB In view to the combined treatment of POME/sludge and EFB in table 1 the specific amount of water per ton EFB are also given. It is obvious, that the amount of water related on EFB is strongly influenced by using new technologies. The modernisation of the production process in s has a significant impact on the absolute and related amount of POME and water in POME (m³/ton FFB), the composition (dry matter content, concentration of nutrients, liquid or sludge), the utilisation (type of biogas plant, size of composting plant), and the treatment cost of the POME. RESULTS Concept and further strategy The proposed concept of a sustainable POME and EFB treatment can fulfil the following aspects: Alternative to common procedures as pond system and dumping of EFB. Minimization of pollutions of surface water, ground water and atmosphere (realisation of zero-waste-concept). Minimization of nutrient losses and concentration of all nutrients from POME and EFB in one product. Possibility of biogas production by demand. Creation of CO 2 -certificates. Flexible application for conventional and new s. Acceptable technical and financial afford. The basic lines of the concept are shown in figure 1. The key-process in the concept is the composting of EFB. The chopped EFB are transported to a composting plant and set up to windrows. The heaps can evaporate 70 kg water/(ton EFB*day) because of the high self heating temperature as result of the intensive rotting process (Schuchardt et al.1998; Schuchardt et al. 2002) and would fall dry, if the heaps are not irrigated regularly. Effluents of the POM are used to keep the humidity in the rotting material. The rotting material is mixed and turned by windrow turning machines to optimise the biological process and to maximise water evaporation. The size and costs of a composting plant depends on the amount of water, which have to be evaporated. Under this aspect it is important how much POME accumulate in the 47

5 oil mill. Therefore three alternatives will be considered: A: conventional POM with 0.65 m³ POME/ton FFB, B: new POM with new oil recovery process with 0.45 m³ POME/ton FFB and C: new POM with new technology for sterilization and new oil recovery processes with 0.25 m³ POME/ton FFB. If the POM has a demand or a market for biogas/energy, the POME can be treated in a biogas plant. The produced biogas is used as energy source. Different types of biogas plants are necessary, depending on the kind of effluent. For POME with low dry matter content fixed bed digesters are favoured, for POME with high dry matter content totally mixed digesters are absolutely necessary. After anaerobic pre-treatment the effluent of a biogas plant is used for moistening of the compost heaps. A Conventional B New C conventional autoclave sterilizer, conventional oil recovery conventional autoclave sterilizer, new oil recovery (ECO-D System) new sterilizer, new oil recovery (ECO-D System) POME [m³/t FFB] fixed bed fermenter composting plant totally mixed fermenter alternative compost, mulch Figure 1: Alternative use of POME and ECO-D biomass from conventional and from new s. Process design of anaerobic POME treatment After POME passed the de-oiling (de-oiling pond, oil skimmer) the hot POME is cooled down by a cooler (figure 2). As cooling medium cold process water and/or air is used. The water is pumped via pipe to the waste water treatment plant, where it passes a screen, which separates all solid with a size >0.75 mm (minimization of risk of plugging the fixed bed). The effluent of the screen flows directly into the pre-storage to enable a continuously feeding of the digester 24 hours a day at 7 days a week. For anaerobic treatment a fixed bed digester is chosen, because of its high process stability in view of shock load, variation of feeding rate and COD-concentration (Wulfert et al. 2002). The inflow is fed at the bottom of the digester, pass in up flow mode the support material and flows out on top level. A part of the effluent is used as circulation water and is mixed with the 48

6 fresh waste water coming from pre-storage tank. The circulation flow is necessary to dilute the high polluted waste water to lift the low ph and decrease the acid concentration. The anaerobic bacteria degrade the dissolved organic components of POME during passing the fixed bed and transform them to biogas. The biogas is collected and used as energy source. The effluent of the digester flows by gravity into a post-storage, where a part of the suspended solids settles down. The circulation water to dilute the inflow of the digester is taken out in the upper part of the post-storage. The discharged water is taken out in the bottom part and is pumped to final storage in composting area. The post-storage is constructed as closed tank to collect the biogas, which is produced there still. POME de-oiling cooler biogas biogas waste water treatment plant screen pre-store fixed bed digester recirculation post-store waste water to composting plant Figure 2: Process design of anaerobic treatment of POME with low dry matter content The totally mixed digester is the most common type of type of digesters in biogas plant to treat sludge world wide. The digester is a cylindrical closed steel or concrete tank, equipped with a mixing device, which guarantees a well mixing of the content to avoid the formation of sediment and swimming scum and to ensure a good distribution of fed substrate. For dimensioning of the biogas plant only few parameters are relevant: 1. The hydraulic retention time has to be more than 15 days to ensure that the bacteria grows is higher than the bacteria losses by effluent 2. The loading rate (kg degradable organic matter per m³ digester volume and day) ranges between 2 and 4 kg/(m³ *d) otherwise the risk of overloading increase. 3. The digestion temperature should be kept on constant level; a drop of more than 1 K within short time has an negative impact to the performance of methanogenic bacteria. 4. The composition and characteristics of the sludge, which shall be treated Results of digestion tests with biomass from ECO-D System The digestion test of ECO-D-biomass was done in the laboratory of UTEC. The biomass sample was taken from an ECO-D decanter running in a POM in Malaysia. The digestion tests were done in lab-scale digesters with semi continuous mixing (digestion temp. 38 C). Results of the digestion test: The organic substance can be degraded almost up to 100 %. Within 8 days almost all of organic components can be hydrolysed and transformed to biogas. The specific gas yield is around 112 and 120 m³/ton biomass with a methane content of 60 %. The gas yield reaches the theoretical maximum. 49

7 As consequence of the high content of protein it might happen that the ammonia/ammoniac concentration reaches a level, which caused an inhibition of anaerobic bacteria. This problem can be solved by addition of dilution water (c-nhx-max = 5200 mg/l; c-nhx-limit = 4500 mg/l; dilution water 0.16 m³ per ton sludge) Resume: Eco-D biomass is a very good substrate for bio-methanisation. The characteristic of digestion is comparable with other substrates from food industry which are digested successfully in full scale plants already. Process design of anaerobic sludge treatment The biomass from the ECO-D System or the mixture of biomass and condensate is pumped to the biogas plant, where the suspension is stored in a tank (figure 3). The tank is equipped with mixing device to ensure a homogeneous composition. The feeding of the digester happens continuously out of the pre-storage via pump. The mixing device in the digester ensures a good distribution of the substrate. The control of digestion temperature happens via internal or external cooling device. The adjusted temperature level can range between 28 and 40 C. In view to the high ammonia concentration a temperature of 30 to 35 C is proposed. The effluent flows out via overflow by gravity into the closed post-storage, from where it is pumped to composting plant. POME (ECO-D biomass) pump biogas biogas waste water treatment plant pre-store tot. mixed digester cooler post-store waste water to composting plant Figure 3: Process design of anaerobic treatment of POME with high dry matter content Process design of composting plant After chopping the EFB they are formed to heaps for composting. (figure 4). The size of the heaps depends on the size of the turning machine. The selfheating process of the EFB, initiated by the microorganims in the substrate, starts within very short time and water is evaporated to the atmosphere. POME (with or without anaerobic pre-treatment) will be added step by step to the rotting EFB, depending on the water evaporation. The composting process can go on until the substrate is totally stabilized as compost (C/N ratio <15) or it can be stopped at a stabilisation level of mulch (C/N ratio >15); it depends on the further use of the substrate. If compost should be produced as a market product it is necessary to screen it before packaging to have a product with a homogenous structure. The mixture of leakage water and rain water from the composting area is collected in a pond and will be used for irrigation of the heaps (or in plantation area). The floor of the composting area is made by concrete or asphalt, to protect the environment by uncontrolled run-off of the leakage water (with nutrients) and to ensure a controlled turning of the heaps and high compost quality. A protection of the heaps with a geo-textile is not necessary. 50

8 water to the atmosphere EFB chopping composting compost or mulch for plantation POME screening packaging compost for market Figure 4: Process design combined EFB/POME composting Conclusions and consequences for the composting of EFB POME The composting process can be divided into two process stages: Stage 1: o addition of POME o evaporation of the water o biological drying o final product: mulch Stage 2: o stabilisation of the compost o drying period (for screening as market product) o final product: compost At the end of the stage 1 (after 12, 24 and 37 day resp., table 2) the EFB are like wet mulch and not stabilized as compost. The mulch can be used in plantation area for palm oil trees (or other plants) but not in a nursery. The biological degradation of the EFB/POME mixture will go on under the natural soil and climate conditions. If mature compost should be produced, the rotting time should be prolonged for about 30 days more. To produce dry compost for screening and packaging the retention/drying time depends on the climate conditions. The retention time of the EFB in the composting plant is relevant for the cost of the composting process. A reduction of the specific POME amount will reduce the time necessary to evaporate the water. The figures 5 to 9 show the flow sheets and the equipment for the biological drying/composting of EFB and POME. Table 2: Time for biological drying and stabilisation of EFB and POME composting Type of No. biol. drying stabilisation total time product d d d A POM with conventional sterilisation, with dilution water; mulch for composting fresh POME or after fermentation compost B POM with conventional sterilis., new oil recovery, mulch fresh POME for composting compost POM with conventional sterilis., new oil recovery, mulch POME after fermentation for composting compost C POM with new sterilisation, new oil recovery, mulch fresh POME for composting compost POM with new sterilisation, new oil recovery, mulch POME after fermentation for composting compost 51

9 A POM with conventional sterilisation and conventional oil recovery with or without biogas POME EFB oil mill cooler chopping mill belt conveyor channel wheel loader truck composting plant tank pump station piping system composting area turning machine pond leachate no part of compost or mulch cost calculation Figure 5: Equipment of a composting plant for EFB with addition of POME (POM type A) B POM with conventional sterilisation and new oil recovery process (ECO-D System) without biogas B POM with conventional sterilisation and new oil recovery process (ECO-D System) with biogas condensate ECO-D biomass EFB water condensate ECO-D biomass EFB oil mill cooler screw conveyor chopping mill press belt conveyor oil oil mill cooler biogas plant chopping mill belt conveyor mixer channel wheel loader truck pipe wheel loader truck composting plant tank pump station piping system composting area turning machine pond leachate composting plant tank pump station piping system composting area turning machine pond leachate compost or mulch no part of cost calculation Figure 6: Equipment of a composting plant for EFB with addition of POME without biogas production (POM type B) compost or mulch no part of cost calculation Figure 7: Equipment of a composting plant for EFB with addition of POME with biogas production (POM type B) 52

10 C POM with new sterilisation process and new oil recovery process (ECO-D System) without biogas C POM with new sterilisation process and new oil recovery process (ECO-D System) with biogas cleaning water ECO-D biomass EFB water cleaning water ECO-D biomass EFB oil mill channel screw conveyor mixer wheel loader chopping mill press belt conveyor oil oil mill biogas plant pipe chopping mill belt conveyor wheel loader truck composting plant pump station piping system truck composting area turning machine pond compost or mulch leachate no part of cost calculation Figure 8: Equipment of a composting plant for EFB with addition of POME without biogas production (POM type C) composting plant pump station piping system composting area turning machine pond compost or mulch leachate no part of cost calculation Figure 9: Equipment of a composting plant for EFB with addition of POME with biogas production (POM type C) Cost calculation To compare the anaerobic treatment alternatives for the POME the cost calculation based on a biogas production rate of 1,000 m³ methane per day (1,000 l Diesel fuel equivalent or 10,000 kwh). The composting plant is calculated for a 30 t mill with 153,000 tons FFB per year and the full rate of POME/sludge. All prices based on market prices in Indonesia in the years 2006/2007. The data for the cost calculation are given in tables 3 to 8. Table 3: Basic data for cost calculation for anaerobic treatment and composting Maintenance % of investment 2 to 5 Depreciation years 10 Currency 1 EUR 11,000 IDR Capital cost Credit % 70 Equity % 30 Interest % 16 Pay back time years 5 Energy Diesel fuel EUR/l

11 Table 4: Cost calculation for biogas plant with fixed bed digester (1000 l diesel fuel equivalent); POM type A Investment cost 1) EUR 486,560 Capital costs EUR/a 148,599 Production cost EUR/a 72,784 Total annual costs EUR/a 221,383 Benefit 2) EUR/a 219,000 Profit calculation Pay back period, year (annuity-method) Actuarial return with reference to total investment Actuarial return with reference to equity a % % ) Components: Preparation work, cooling, pre-storage, digester incl. support material, security device, post-storage, gasholder, de-sulphurication, biogas flare + blower, process measurement and control, switch board room, pipes for water, gas pipes, cable/power supply, traffic area, planning cost 2) Energy-production (Diesel fuel equivalent) Table 5: Cost calculation for biogas plant with totally mixed digester (1000 l diesel fuel equivalent) POM type B/C Investment cost 1) EUR 424,200 Capital costs EUR/a 129,555 Production cost EUR/a 63,298 Total annual costs EUR/a 192,853 Benefit 2) EUR/a 219,000 Profit calculation Pay back period, year (annuity-method) Actuarial return with reference to total investment Actuarial return with reference to equity a % % ,7 1) Components: Preparation work, cooling, pre-storage, digester, mixer, security device, post-storage, gasholder, de-sulphurisation, biogas flare + blower, process measurement and control, switch board room, pipes for water, gas pipes, cable/power supply, traffic area, planning cost 2) Energy-production (Diesel fuel equivalent) Table 7: Overview about cost calculation for the mulch and compost production from EFB and POME without anaerobic pre-treatment of the POME investment difference pay back actuarial return [%] POM No. EUR % EUR a total investm. ref. to equity Only mulch production (biological drying) A 1 749, B 3 680, , C 7 592, , Only compost production A 2 1,158, B 4 871, , C 8 782, ,

12 Table 6: Cost calculation for alternative composting plants in a 30 t oil mill (153,000 t/a) for POM type A, B and C with mulch production and compost production (see table 2) Type of oil mill 1) A A B B B B C C C C Alternative Investment cost 2) EUR 749,705 1,158, , , , , , , , ,972 Capital costs EUR/a 228, , , , , , , , , ,186 Production cost 3) EUR/a 189, , , , , , , , , ,218 Total annual costs EUR/a 418, , , , , , , , , ,404 Benefit 4) EUR/a 607, , , , , , , , , ,774 Profit calculation Pay back period, year (annuity-method) Actuarial return with reference to total investment Actuarial return with reference to equity a % % , ) A: Conventional with conventional autoclave sterilizer and oil recovery B: "New " with conventional autoclave sterilizer and new oil recovery process (ECO-D System) C: "New " with new sterilizer process and new oil recovery process (ECO-D System) 2) components: POME/sludge tank, chopping mill, belt conveyor, screw conveyor, mixer, turning machine, concrete floor 15 cm, dump truck, wheel loader, pond for leakage water, piping system, pump stations, mechanical work, electrical work, planning cost 3) fuel, electricity, labour, maintenance, depreciation, general cost 4) Cost saved for POME treatment in ponds, Value of the nutrients in POME, Reduced cost for compost transport + distribution, Increased FFB production of 2 %, CO 2 -certificate only for POME ,

13 Table 8: Overview about cost calculation for the mulch and compost production from EFB and POME with anaerobic pre-treatment of the POME investment difference pay back actuarial return [%] POM No. EUR % EUR a total investm. ref. to equity Mulch production (biological drying) and biogas production A 1 749, B 5 654, , C 9 566, , Compost production and biogas production A 2 1,158, B 6 845, , C , , CONCLUSIONS New s (Type B with conventional autoclave sterilizer and new oil recovery process and type C with new sterilizer process and new oil recovery process) produce a sludge with high dry matter and COD content ( ECO-D biomass ). The sludge can be used for biogas production in a totally mixed reactor. Compared to conventional s (type A) which should use a fixed bed fermenter for the POME treatment, the investment cost can reduced up to 13 % and the pay back time can reduced from 2.96 to 2.5 years. The biogas production from POME or ECO-D biomass is profitable (calculated on the Diesel fuel energy equivalent and a price of 0.60 EUR/litre) when the gas can be used. The mulch or compost production from EFB with addition of POME/Eco-D biomass is profitable with pay back times between 1.1 and 2.4 years. Compared to conventional palm oil mills (type A) the investment cost can be reduced up to 35 %. With the process of mulch or compost production from EFB in combination with POME or ECO-D biomass (with or without anaerobic fermentation with biogas production before) it is possible to realize a sustainable process in s with zero waste. ACKNOWLEDGEMENT The international research project between Indonesia and Germany was supported by the German Federal Ministry of Education and Research and the Indonesian Oil Palm Research Institute (IOPRI), Medan. REFERENCES Anonym (RSPO) (2005) RSPO principles and criteria for sustainable palm oil production. In: Anon. Anonym (Unilever) (2003) Sustainable Palm Oil - Good agricultural practice guidelines. In: Anon. Chungsiriporn J, Prasertsan S, Bunyakan C (2006) Minimization of water consumption and process optimization of s. Clean Technologies and Environmental Policy 8(3):

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