TANDAN KOSONG SEBAGAI ALTERNATIF PEMENUHAN KEBUTUHAN UNSUR HARA TANAMAN KELAPA SAWIT

TANDAN KOSONG SEBAGAI ALTERNATIF PEMENUHAN KEBUTUHAN UNSUR HARA TANAMAN KELAPA SAWIT

By : Haris Sanjaya

Pendahuluan
Pabrik kelapa sawit menghasilkan limbah tandan kosong (tankos) 20 – 23 % dari jumlah tandan buah segar (TBS) yang diolah. Pada saat ini sebagian tankos masih dibakar pada incinerator di PKS sehingga tidak memberikan value added yang berarti. Tetapi proses tersebut kedepannya tidak akan ditolerir lagi karena pertimbangan isu sentral lingkungan hidup dengan klausal dampak global lingkungan yang ditimbulkannnya.

Menyikapi hal tersebut pemanfaatan tankos sebagai bahan alternatif untuk kesuburan tanah di perkebuan kelapa sawit merupakan salah satu solusi dalam penanganannya. Dari perspektif agronomi treatment mulsa tankos yang diaplikasi di kebun, selain menambah unsur hara juga akan meningkatkan kandungan bahan organik yang sangat diperlukan bagi perbaikan sifat fisik dan chemistry tanah. Dengan meningkatknya bahan organik tanah maka struktur tanah semakin mantap dan kemampuan tanah menahan air akan bertambah baik. Sehingga akan berdampak positip terhadap pertumbuhan akar tanaman dan penyerapan unsur hara di dalam tanah. Disamping itu pemberian tankos juga dimaksudkan untuk mencegah terjadinya erosi dan pencucian unsur hara (leaching).

Berdasarkan content hara, setiap ton tankos memiliki kandungan N,P,K dan Mg berturut-turut setara dengan 3 kg Urea, 0,6 kg CIRP, 12 kg MOP dan 2 kg Kieserit. Dengan demikian satu unit PKS kapasitas terpasang 30 ton tbs/jam atau 600 ton tbs/hari akan menghasilkan pupuk N,P,K dan Mg berturut-turut setara dengan 360 Kg urea, 72 Kg CIRP, 1.440 Kg MOP dan 240 Kg Kieserit.( Long, et.al in PL. Tobing 1998)

Sementara itu menurut kajian Tun Teja 1991 kandungan unsur hara yang terdapat dalam tankos adalah sebagai berikut: K = 2,13 % setara dengan 12,78 kg MOP; Ca = 0,18 %, Mg = 0,17 % setara dengan 0,46 kieserit ; Mn = 0,63 %, P205 = 0,14 % setara dengan 0,5 kg CIRP , Fe = 0,59 %, dan Na = 0,59 %.

Melalui kegiatan mikroorganisme tanah atau proses mineralisasi unsur hara yang terdapat pada tankos akan dikembalikan ke dalam tanah. Namun unsur tersebut tidak sepenuhnya dapat diabsorbsi /diserap oleh akar tanaman. Kondisi ini disebabkan oleh beberapa hal :

v Unsur N termobilisasi (digunakan oleh mikro organisme tanah untuk menunjang kelangsungan hidupnya), tercuci air perkolasi kelapisan tanah yang lebih dalam.

v Unsur P termobilisasi dan berubah menjadi senyawa yang sukar larut, sehingga lambat ketersediannya untuk diserap oleh tanaman. 

Persentasi hara yang termobilisasi mengendap dan tercuci dari masing-masing unsur yang berasal dari mineralisasi tankos belum diketahui secara tepat. Namun jumlah unsur hara Kalium dan Magnesium yang tersedia bagi tanaman cukup menunjang pertumbuhan dan produksi tanaman. Hal ini dapat dilihat pada result percobaan yang dilakukan Loong di Malaysia dan MM. Siahaan di Indonesia, dimana pupuk N dan P masih di aplikasikan sebagai pupuk tambahan sementara pupuk K dan Mg tidak diberikan lagi. Namun beberapa literatur mengatakan aplikasi ekstra hanya di berikan pada pupuk Urea saja.

Aplikasi tankos di lapangan
Aplikasi penebaran tankos diareal tanaman menghasilkan dilaksanakan dengan penebaran merata di gawangan hingga ke pinggir piringan pada jarak -+ 2 meter dari pangkal batang (agar tidak mengganggu aktivitas panen). Tankos disusun selapis untuk mencegah agar tidak menjadi sarang kumbang Oryctes. Hasil pengamatan menunjukan dalam waktu 7-10 bulan tankos sudah mengalami dekomposisi /pelapukan dan menyatu dengan tanah.

Kebutuhan tankos dalam setiap hektarnya adalah 65 ton atau rata- rata distribusi tankos sebanyak 500 kg/ pokok .Tofografi lahan sangat berpengaruh terhadap prestasi kerja penebar tankos. Norma rata-rata tenaga kerja dalam mengaplikasikan tankos dilapangan adalah 2.000 kg.

Komparasi kandungan hara & analisa biaya tankos vs pupuk compound
Dengan kaidah minimal kandungan hara tandan kosong tersebut diatas, apabila dikomparasikan dengan unsur hara pupuk NPK Compound (pupuk yang cenderung di aplikasikan dikebun) dan analisa biaya aplikasi dapat dilihat pada tabel berikut: 

1. Perbandingan kandungan hara

Uraian	Dosis	Kandungan Hara (gram)
		N	P	K	Mg
Tankos NPK	500 Kg/Pk 6.5 Kg/Pk	- 845 (13 %)	700 (0,14 %) 520 (8 %)	10.650(2,13 %) 1.755 (27 %)	850 (0,17 %) 260 (4 %)

2. Analisa biaya aplikasi tankos (Rp/ha/thn)

Uraian	Transport/Bahan	Aplikasi	Total
Tankos NPK Selisih	14 x 500 x 130 = 910.000 2.810 x 6.5 x 130 = 2.374.450 (1.464.450)	9 x 500 x 130 = 585.000 42.000 x 2 = 84.000 501.000	1.495.000 2.458.450 (963.450

Catt: Asumsi biaya transport = Rp.14/kg.
Nilai HOK/hari = Rp. 21000/kg Aplikasi Tankos Rp. 9/kg
Asumsi harga pupuk (thn 2007) = Rp. 2810/kg
Tankos hasil PKS kebun sendiri

Tabel 1. diatas menginformasikan, dengan dosis rekomendasi bahwa kandungan hara P, K dan Mg yang terdapat dalam tankos masih bisa memenuhi kebutuhan hara yang diperlukan oleh tanaman. Bahkan untuk unsur Kalium menampakkan content yang cukup tinggi.

Tabel 2. Menginformasikan, biaya yang dikeluarkan dalam pengaplikasian tankos masih lebih rendah dengan selisih harga Rp. 963.450. Dengan asumsi tersebut penambahan pupuk ekstra Urea sebanyak 1.877 kg/pk (hasil penyetaraan kandungan N pada pupuk compound) masih layak diaplikasikan. Dimana kalkulasi total selisih biaya setara dengan 3,8 kg Urea/pk.

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TANDAN KOSONG KELAPA SAWIT SEBAGAI PUPUK ORGANIK

TANDAN KOSONG KELAPA SAWIT SEBAGAI PUPUK ORGANIK

               Tandan kosong kelapa sawit (TKKS) dapat dimanfaatkan sebagai sumber pupuk organik yang memiliki kandungan unsur hara yang dibutuhkan oleh tanah dan tanaman.Tandan kosong kelapa sawit mencapai 23% dari jumlah pemanfaatan limbah kelapa sawit tersebut sebagai alternatif pupuk organik juga akan memberikan manfaat lain dari sisi ekonomi. bagi perkebunan kelapa sawit, dapat menghemat penggunaan pupuk sintesis sampai dengan 50%, pupuk organik yang dihasilkan dari TKKS dapat beupa pupuk kompos dan pupuk Kalium.

A. Pupuk Kompos

                    Pupuk kompos adalah bahan organik yang telah mengalami fermentasi atau dekomposisi yang dilakukan oleh mikroorganisme. pada prinsipnya pengomposan TKKS untuk menurunkan nisbah C/N yang terkandung didalam tandan segar agar mendekati nisbah C/N tanah. C/N yang mendekati nisbah C/N tanah akan mudah diserap oleh tanaman. C/N kompos yang diinginkan adalah < 20

              Untuk membuat kompos tandan kosong dicacah terlebih dahulu menjadi serpihan-serpihan dengan memakai mesin pencacah. kemudian bahan yang telah dicacah ditumpuk memanjang dengan ukuran lebar sekita 2.5 m dan tinggi 1 m. Selama proses pengomposan tumpukan tersebut disiran oleh limbah cair yang berasal dari pabrik kelapa sawit. Tumpukan tersebut dibiarkan diatas lantai semen dan dibiarkan diudara terbuka selama enam minggu. Kompos dibolak-balik dengan mesin pembalik. Setelah itu, kompos siap dimanfaatkan. Pabrik kelapa sawit dengan kapasitas 30 ton tandan buah segar per jam dapat menghasilkan 60 ton kompos dari 100 ton tandan kosong yang dihasilkan.

            Kompos TKKS dapat dimanfaatkan untuk memupuk semua jenis tanaman. Kompos TKKS memiliki beberapa sifat yang menguntungkan antara lain sebagai berikut :

1. Memperbaiki struktur tanah berlempung menjadi ringan
2. membantu kelarutan unsur-unsur hara yang diperlukan bagi pertumbuhan tanaman.
3. bersifat homogen dan mengurangi resiko sebagai pembawa hama tanaman
4. merupakan pupuk yang tidak mudah tercuci oleh air yang meresap kedalam tanah.
5. dapat diaplikasikan pada sembarang musim.

               tandan kelapa sawit yang diubah menjadi kompos tidak hanya mengandung nutrisi tetapi juga mengandung bahan organik lain yang berguna bagi perbaikan struktur organik pada lapisan tanah, terutama pada kondisi tanah tropis. Kompos merupakan sumber Fosfor (P), Kalsium (ca), Magnesium (Mg), dan Karbon (C). Perlu diketahui bahwa pada proses pengomposan TKKS tidak menggunakan cairan asam dan bahan kimia lain sehingga tidak terdapat pencemaran atau polusi. Proses pengomposan pun tidak menghasilkan limbah. Dibawah ini ditampilkan beberapa gambar pengomposan.

B. Pupuk Kalium (Abu Janjangan)

                Tandan kosong kelapa sawit sebagai limbah padat dapat dibakar dan menghasilkan abu tandan. Abu tersebut ternyata mengandung 30 - 40% K2O, 7% P2O5, 9% CaO dan 3% MgO. Selain itu  juga mengandung unsur hara mikro yaitu 1.200 ppm Fe, 1.000 ppm Mn, 400 ppm Zn, dan 100 ppm Cu.

Sebagai Gambaran Umum bahwa pabrik yang mengolah kelapa sawit dengan 1.200 ton TBS/hari akan menghasilkan abu tandan sebesar 10.8% atau sekitar 129.6 ton abu/hari, setara dengan 5.8 ton KCL, 2.2 ton Kiserite dan 0.7 ton TSP. dengan penambahan polimer tertentu pada abu tandan dapat dibuat pupuk butiran berkadar K2O 30 - 38% dengan pH 8 - 9

          Kelangkaan pupuk KCL yang kerap kali dihadapi oleh perkebunan dapat diatasi dengan menggantinya menggunakan abu tandan. Biaya produksinya pun lebih rendah dibandingkan dengan harga pupuk KCL.

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Pemanfaatan Tandan Kosong Kelapa Sawit

Tandan kosong kelapa sawit merupakan limbah padat lignoselulosa yang dihasilkan oleh industri perkebunan kelapa sawit dan memiliki tingkat ketersediaan yang berlimpah setiap tahunnya, Upaya yang dilakukan untuk pengelolaan limbah adalah mengurangi daya cemar dan memanfaatkan limbah agar mendapatkan nilai tambah dari limbah tersebut. 

 

Penanganan limbah tandan kosong kelapa sawit saat ini belum optimal dan ekonomis, sehingga mendorong peneliti untuk mencari suatu metode alternatif untuk menfaatkan tandan kosong kelapa sawit sebagai bahan baku substitusi bagi beberapa industri di Indonesia. 

Sehubungan hal itu, maka penelitian ini dilakukan untuk mengetahui kadar dan kemurnian lignin yang dihasilkan pada kondisi optimum proses pada rentang penelitian yang dilakukan, serta mengetahui sejauh mana pengaruh suhu reaksi, waktu reaksi dan. konsentrasi basa (NaOH) yang digunakan terhadap persentase kadar lignin yang dihasilkan dari proses hidrolisis lignin dari tandan kosong kelapa sawit dengan metode ekstraksi pada interval penelitian yang ditentukan. 

 

Dari hasil penelitian menunjukkan bahwa kadar lignin maksimum yang dihasilkan dari proses ekstraksi tandan kosong kelapa sawit adalah 64,895 % dengan kemurnian 90 % pada kondisi suhu reaksi 160 °C, waktu reaksi 4 (empat) jam dan konsentrasi basa (NaOH) 20 %. Konsentrasi basa (NaOH) dan waktu reaksi merupakan faktor utama yang paling dominan dan sangat berpengaruh secara signifikan serta memberikan efek positif terhadap persentase kadar lignin yang dihasilkan dengan nilai probability P<0,05, sedangkan suhu reaksi memberikan efek negatif dan pengaruhnya cukup lemah terhadap peningkatan jumlah produk lignin dengan nilai P > 0,05

 

Interaksi yang terjadi antara konsentrasi basa (NaOH) dan waktu reaksi berpengaruh secara signifikan terhadap persentase kadar lignin yang dihasilkan dengan nilai probability P<0,05. Interaksi yang terjadi antara konsentrasi basa (NaOH) dan suhu reaksi serta interaksi antara suhu dan waktu reaksi sangat lemah dun tidak begitu signifikan namun memberikan efek positif terhadap terhadap persentase produk yang dihasilkan dengan nilai probability P>0.05. Interaksi yang terjadi antara konsentrasi basa (NaOH), waktu reaksi dan suhu reaksi pengaruhnya tidak begitu signifikan namun memberikan efek positif terhadap persentase kadar lignin yang dihasilkan dengan taraf kepercayaan 75,17 %. 

 

Oil Palm Empty fruit bunches is a lignocelulose solid waste produced by palm oil industry in a high volume in each year. Any efforts to treat the waste is to decrease the pollution potency and to reuse the waste for the added value of the waste. The treatment of empty bunches waste of oil palm has not yet optimal and economic that encourage the researcher to find out an alternativa mode to use empty bunches as substitution raw material for industries in Indonesia. Therefore, this study is hold to measure the content and pureness of lignin in optimum process condition during the study and to study how far the influence of temperature of reaction, time and base concentration (NaOH) use to percentage of lignin content produced by lignin hydrolysis process by extraction methode of oil palm empty fruit bunches in the study interval. Location of study is Indonesia Oil Palm Reascarch Institute (IOPRI) Laboratory Jalan Brigjend Kalamso Medan, North Sumalera. The Results of study indicates that the content of maximum lignin produced in extraction process of oil palm empty fruit bunches is 64,895% in the purncss 90% in condition of reaction temperature 160 °C, reaction time 4 (empat) hours and base concentration (NaOH) 20%. Base concentration (NaOH) and time reaction are dominant factors with significant influence and give a positive effect to lignin content percentage in the probability P0,05. Interaction that happened between base concentration (NaOH) and time of reaction having significant influence to the product percentage in the probability P 0,05. Interaction between base conccntration(NaOH), time of reaction and temperature of reaction did not significant but provide the positive effect to overage lignin content percentage in significant level 75,17%.

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Oil Palm Fibre

Oil Palm Fibre

100% Natural Palm Fibre

Palm Fibre is produced from oil palm's vascular bundles in the Empty Fruit Bunch (EFB). EFB is considered as waste products after the Fresh Fruit Bunch (FFB) have been processed. Palm fiber itself is 100% natural, non-hazardous, biodegradable and environmentally friendly.

HK is able to produce large quantities of oil palm EFB fibre, which are not only long, clean and fine, but also in uniformity through our self-designed and installed custom-built production lines.

Our Oil Palm Fibre :

• Low cost advantage

• Excellent year-round availability

• No species variations

• Very low moisture content

• Biodegradable and environmentally friendly

• No health hazards

• No traceable HCN compound

• Non-carcinogenic

• No toxic elements

• Contains lignin that acts as binder in compressed materials.

Oil Palm Fibre Specifications

Moisture Content	12-15%
Oil Content	<2%
Length	5-15cm
Impurities	<3%
Bale Size	L43’’x W43’’xH49’’
Packing	3mm Steel Wire
Weight	±450kg/bale
Loadability	40 bales per container (40‘HQ)
Container	±18MT (40'HQ)

Applications

Palm fibre is a superior substitute to coconut fibre due to its strong bond that are commonly used in making :

• Mattress and cushion production

• Erosion control mat/blanket for landscaping and horticulture

• Moulded wares and composite material production

• Medium density fiberboard manufacturing

• Paper and pulp production

• Acoustics control

• Compost and fertilizer

EFB Shredded Fiber Raw EFB shredded fibre can be use as solid fuel for steam boiler.
Low chlorine content, shredded fiber is a safe and sustainable bio-fuel resource to replace petroleum and coal to produce bio-fuel briquette.
Shredded fiber can be use to produce bio-oil through pyrolysis process.

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EFB Fibre ?

EFB Fibre Has Turn Useless to Useful

EFB (Empty Fruit Bunch) is the by-product from crude palm oil mill which having low economic value before more application being developed. Currently the major application of EFB is extract the fibre for others industry.

Before latest application being developed, converting EFB to compost is seems to be the only solution for most of the crude palm oil mill.  Those crude palm oil mills having their own estate will gather the EFB, expose to air to let it turn black and start fermentation.  After 120 days of fermentation, the EFB will be transferred back to oil palm estate for compost fertilizer.  Sometime we do see palm oil sludge being mixed in the EFB in order to expedite the fermentation process.

Now EFB has more other application other than compost.  The new application about EFB is using the fibre nature of the EFB.  There are researches about pressed and shredded the EFB to get fibre for biomass boiler; gone through further cleaning process and extracting long fibre for replacing coconut fibre for mattress; extracting Vitamin E from EFB Fibre.

Shredded EFB Fibre has become a major biomass media in this Malaysia.  Many steam provider companies have secure the EFB fibre supply chain from crude palm oil mill and selected biomass boiler for supplying steam to surrounding industry. There are estimated total 18million tons of EFB fibre available through out Malaysia for year 2010 and expected more for subsequence years.

EFB fibre as biomass has become one of the major converting application for EFB.  Apart there are also companies buying the EFB and recover the long fibre from the EFB.  The long EFB fibre has more economic value that could be used as fibre mattress.  Due to more profitable income, we also seeing many crude palm oil mills also start investing in this process to extract long fibre from EFB.

In bio-technology industry, there are also researches extracting Vitamin E from fibre or re-grinding the fibre in smaller grain size mixing in food chain.

We are seeing more and more application study in EFB fibre

EFB Fibre?

In Malaysia, more and more forest or estate are converting to oil palm estate, research has study and showed that using oil palm fibre as biomass for biomass power plant is not only feasible but also practically success.

In year 2009, Malaysia has produced 17.56 million tonnes of crude palm oil and this lead to almost 90 million tones of EFB that yet to further disposal. EFB will be shredded and become one of the major sources for biomass power plant in the country. Until EFB fibre can reach other economic value, we foresee there are still rooms for Malaysia company converting existing fossil fuel power plant to biomass power plant, however the transportation network need to further establish.

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Conversion of Oil Palm Empty Fruit Bunch to Biofuels

1. Introduction

Crude palm oil production is reaching 48.99 million metric tonnes per year globally in 2011 and Southeast Asia is the main contributor, with Indonesia accounting for 48.79%, Malaysia 36.75%, and Thailand 2.96% (Palm Oil Refiners Association of Malaysia, 2011). Oil palm is a multi-purpose plantation and it is also an intensive producer of biomass. Accompanying the production of one kg of palm oil, approximately 4 kg of dry biomass are produced. One third of the oil palm biomass is oil palm empty fruit bunch (OPEFB) and the other two thirds are oil palm trunks and fronds [1-3].

Figure 1.

Oil palm and oil palm empty fruit bunch.

The supply of oil palm biomass and its processing by-products are found to be seven times that of natural timber [4]. Besides producing oils and fats, there are continuous interests in using oil palm biomass as the source of renewable energy. Among the oil palm biomass, OPEFB is the most often investigated biomass for biofuel production. Traditionally, OPEFB is used for power and steam utilization in the palm oil mills, and is used for composting and soil mulch. Direct burning of OPEFB causes environmental problems due the incomplete combustion and the release of very fine particles of ash. The conversion of OPEFB to biofuels, such as syngas, ethanol, butanol, bio-oil, hydrogen and biogas etc., might be a good alternative and have less environmental footprint. The properties of OPEFB is listed in Table 1 [5].

	Literature values % (w/w)	Measured % (w/w)	Method
Components
Cellulose	59.7	na	na
Hemicellulose	22.1	na	na
Lignin	18.1	na	na
Eelemental analysis
Carbon	48.9	49.07	Combustion analysis
Hydrogen	6.3	6.48
Nitrogen	0.7	0.7
Sulphur	0.2	<0.10
Oxygen	36.7	38.29	By difference
K	2.24	2.00	Spectrometry
K2O	3.08–3.65	na	na
Proximate analysis
Moisture	na	7.95	ASTM E871
Volatiles	75.7	83.86	ASTM E872
Ash	4.3	5.36	NREL LAP005
Fixed carbon	17	10.78	By difference
HHV (MJ/kg)	19.0	19.35	Bomb calorimeter
LHV (MJ/kg)	17.2	na	na

Table 1.

Properties of oil palm empty fruit bunch

[i] - Notes: na - not available.

While all the OPEFB components can be converted to biofuels, such as bio-oil and syngas through thermo-chemical conversion, cellulose and hemicellulose can be hydrolysed to sugars and subsequently be fermented to biofuels such as ethanol, butanol, and biogas etc. Although many scientists around the world are developing technologies to generate biofuels from OPEFB, to-date, none of such technologies has been commercialized. This is largely due to the recalcitrance of the OPEFB and therefore the complexity of the conversion technologies making biofuels from OPEFB less competitive than the fossil-based fuels. Continual efforts in R&D are still necessary in order to bring such technology to commercialization. The aim of this paper is to review the progress and challenges of the OPEFB conversion technologies so as to help expedite the OPEFB conversion technology development.

2. Pretreatment

Similar to all other lignocellulosic biomass, OPEFB are composed of cellulose, hemicellulose and lignin. Among the three components, lignin has the most complex structure, making it recalcitrant to both chemical and biological conversion. Pretreatment of OPEFB is therefore necessary to open its structure and increase its digestibility and subsequently the degree of conversion. Pretreatment of OPEFB can be classified as biological pretreatment, physical pretreatment, chemical pretreatment, and physical-chemical pretreatment.

For biological pretreatment, oxidizing enzymes and white-rot fungi were used to degrade the lignin content in OPEFB. For example, enzymes such as lignin peroxidase (LiP) and manganese peroxidase (MnP) was used to pretreat OPEFB for fast pyrolysis and the bio-oil yield was improved from 20% to 30% [6]. Syafwina et al. used white-rot fungi to pretreat OPEFB and the saccharification efficiency was improved by 150% compared to that of the untreated OPEFB [7].

Among all the pretreatment methods, chemical pretreatment is most often reported for OPEFB. Two-stage dilute acid hydrolysis [8], alkali pretreatment [9], sequential dilute acid and alkali pretreatment [10], alkali and hydrogen peroxide pretreatment [11], sequential alkali and phosphoric acid pretreatment [10], aqueous ammonia [12], and solvent digestion [5] were used to increase the digestibility of OPEFB. Among all the chemical methods investigated, alkali pretreatment seemed to be the most effective. Umikalsom et al. autoclaved the milled OPEFB in the presence of 2% NaOH and 85% hydrolysis yield was obtained [13]. Han and his colleagues investigated NaOH pretreatment of OPEFB for bioethanol production [9]. The optimal conditions were found to be 127.64°C, 22.08 min, and 2.89 mol/L NaOH. With a cellulase loading of 50 FPU /g cellulose a total glucose conversion rate (TGCR) of 86.37% was obtained using the Changhae Ethanol Multi Explosion (CHEMEX) facility. The effectiveness of alkali pretreatment might be attributed to its capability in lignin degradation. Mission et al. investigated the alkali treatment followed H₂O₂ treatment and found that almost 100% lignin degradation was obtained when OPEFB was firstly treated with dilute NaOH and subsequently with H₂O₂ [11]. This confirmed the lignin degradation by NaOH and its enhancement by the addition of H₂O₂.

Besides alkali pretreatment, physical-chemical pretreatment such as ammonium fibre explosion (AFEX) [14] and superheated steam [15] were also shown to be effective in the increase of OPEFB digestibility. Hydrolysis efficiency of 90% and 66% were obtained, respectively.

3. Thermo-chemical conversion

Thermo-chemical conversion is one of the important routes to obtain fuels from lignocellulosic biomass. Thermo-chemical conversion of biomass involves heating the biomass materials in the absence of oxygen to produce a mixture of gas, liquid and solid. Such products can be used as fuels after further conversion or upgrading. Generally, thermo-chemical processes have lower reaction time required (a few seconds or minutes) and the superior ability to destroy most of the organic compounds. These mainly include biomass pyrolysis and biomass gasification. Recently, thermo-chemical pretreatment of biomass, such as torrefaction was introduced to upgrade biomass for more efficient biofuel production [16-17].

3.1. OPEFB pyrolysis

Pyrolysis is defined as the thermal degradation of the biomass materials in the absence of oxygen. It is normally conducted at moderate temperature (400 – 600°C) over a short period of retention time. Its products comprise of liquids (water, oil/tars), solids (charcoal) and gases (methane, hydrogen, carbon monoxide and carbon dioxide). The efficiency of pyrolysis and the amount of solid, liquid, and gaseous fractions formed largely depend on the process parameters such as pretreatment condition, temperature, retention time and type of reactors.

Misson et al investigated the effects of alkaline pretreatment using NaOH, Ca(OH)₂, in conjunction with H₂O₂, on the catalytic pyrolysis of OPEFB [11]. They proved that consecutive addition of NaOH and H₂O₂ decomposed almost 100% of OPEFB lignin compared to 44% for the Ca(OH)₂ and H₂O₂ system, while the exclusive use of NaOH and Ca(OH)₂ could not alter lignin composition much. In addition, the pretreated OPEFB was catalytically pyrolysed more efficiently than the untreated OPEFB samples under the same conditions.

Fast pyrolysis represents a potential route to upgrade the OPEFB waste to value-added fuels and renewable chemicals. For woody feedstock, temperatures around 400-600°C together with short vapour residence times (0.5-2 s) are used to obtain bio-oil yields of around 70%, along with char and gas yields of around 15% each. Sulaiman and Abdullah investigated fast pyrolysis of OPEFB using and bench top fluidized bed reactor with a nominal capacity of 150 g/L [18]. After extensive feeding trials, it was found that only particles between 250 and 355 m were easily fed. The maximum liquid and organics yields (55% total liquids) were obtained at 450°C. Higher temperature was more favourable for gas production and water content was almost constant in the range of temperature investigated. The maximum liquids yield and the minimum char yield were obtained at a residence time of 1.03 s. The pyrolysis liquids produced separated into two phases; a phase predominated by tarry organic compounds (60%) and an aqueous phase (40%). The phase separated liquid product would represent a challenging fuel for boilers and engines, due to the high viscosity of the organics phase and the high water content of the aqueous phase. These could be overcome by upgrading. However, the by-product, charcoal, has been commercialized for quite some time. It is worth noting that the first pilot bio-oil plant by Genting Bio-oil has already started operation in Malaysia [19].

3.2. OPEFB gasification

Gasification process is an extension of the pyrolysis process except that it is conducted at elevated temperature range of 800–1300 °C so that it is more favourable for gas production [20]. The gas stream is mainly composed of methane, hydrogen, carbon monoxide, and carbon dioxide. Biomass gasification offers several advantages, such as reduced CO₂ emissions, compact equipment requirements with a relatively small footprint, accurate combustion control, and high thermal efficiency. The main challenge in gasification is enabling the pyrolysis and gas reforming reactions to take place using the minimum amount of energy and gasifier design is therefore important [21].

Ogi et al. used an entrained-flow gasifier for OPEFB gasification at 900°C [22]. During gasification with H₂O alone, the carbon conversion rate was greater than 95% (C-equivalent), and hydrogen-rich gas with a composition suitable for liquid fuel synthesis ([H₂]/[CO] = 1.8–3.9) was obtained. The gasification rate was improved to be greater than 99% when O₂ was added to H₂O; however, under these conditions, the gas composition was less suitable for liquid fuel synthesis due to the increase of CO₂ amount. Thermogravimetric (TG) analysis suggested that OPEFB decomposed easily, especially in the presence of H₂O and/or O₂, suggesting that OPEFB is an ideal candidate for biomass gasification. Lahijani and Zainal investigated OPEFB gasification in a pilot-scale air-blown fluidized bed reactor [23]. The effect of bed temperature (650–1050°C) on gasification performance was studied and the gasification results were compared to that of sawdust. Results showed that at 1050°C, OPEFB had almost equivalent gas yield and cold gas efficiency compared with saw dust, however, with low maximal heating values and higher carbon conversion. In addition, it was realized that agglomeration was the major issue in OPEFB gasification at high temperatures. This can be overcome by lowering the temperature to 770 ± 20 °C. Mohammed et al. studied OPEFB gasification in a bench scale fluidized-bed reactor for hydrogen-rich gas production [24]. The total gas yield was enhanced greatly with the increase of temperature and it reached the maximum value (~92 wt.%) at 1000 °C with big portions of H₂ (38.02 vol.%) and CO (36.36 vol.%). The feedstock particle size of 0.3–0.5 mm, was found to obtain a higher H₂ yield (33.93 vol.%), and higher LHV of gas product (15.26 MJ/m³). The optimum equivalence ratio (ER) (0.25) was found to attain a higher H₂ yield (27.31 vol.%) at 850 °C. Due to the low efficiency of bench scale gasification unit the system needs to be scaling-up. The cost analysis for scale-up EFB gasification unit showed that the hydrogen supply cost is $2.11/kg OPEFB. Recently, a characterization and kinetic analysis was done by Mohammed et al. and it was found that a high content of volatiles (>82%) increased the reactivity of OPEFB, and more than 90% decomposed at 700 °C; however, a high content of moisture (>50%) and oxygen (>45%) resulted in a low calorific value [25]. The fuel characteristics of OPEFB are comparable to those of other biomasses and it can be considered a good candidate for gasification.

3.3. OPEFB torrefaction

Torrefaction is a thermal conversion method of biomass in the low temperature range of 200-300 °C. Biomass is pretreated to produce a high quality solid biofuel that can be used for combustion and gasification [16-17]. It is based on the removal of oxygen from biomass to produce a fuel with increased energy density. Different reaction conditions (temperature, inert gas, reaction time) and biomass resources lead to the differences in solid, liquid and gaseous products.

Uemura et al. [16] studied the effect of torrefaction on the basic characteristics of oil palm empty fruit bunches (EFB), mesocarp fibre and kernel shell as a potential source of solid fuel. It was found that mesocarp fibre and kernel shell exhibited excellent energy yield values higher than 95%, whereas OPEFB, on the other hand, exhibited a rather poor yield of 56%. Torrefaction can also be done in the presence of oxygen. Uemura and his colleagues [17] carried out OPEFB torrefaction in a fixed-bed tubular reactor in the presence of oxygen at varied oxygen concentration. The mass yield decreased with increasing temperature and oxygen concentration, but was unaffected by biomass particle size. The energy yield decreased with increasing oxygen concentrations, however, was still between 85% and 95%. It was found that the oxidative torrefaction process occurred in two successive steps or via two parallel reactions, where one reaction is ordinary torrefaction, and the other is oxidation.

3.4. Summary

The analysis of thermo-chemical conversion of OPEFB suggests that gasification is the most suitable thermo-chemical route for OPEFB conversion to biofuels. It has the highest carbon conversion (>90%) and biofuel yield. Due to the high viscosity and high water content of pyrolysis products, application of bio-oil as a biofuel is still very challenging. Compared to other oil palm residues, such as oil palm kernel, due to its high water content, OPEFB may not be a good candidate for solid fuels even after torrefaction pretreatment.

4. Bioconversion

Bioconversion of lignocellulosic biomass to fuels involves three major steps: 1) pretreatment- to effectively broken the biomass structure and release the biomass components i.e. cellulose, hemicellulose, and lignin, and therefore increase the digestibility of the biomass; 2) enzymatic hydrolysis – to hydrolyse cellulose and hemicellulose and produce fermentable sugar, such as glucose, xylose etc.; 3) fermentation – to convert the biomass hydrolysate sugars to the desired products. OPEFB was intensively investigated as a potential substrate for the production of biofuels, such as ethanol, butanol, and biogas etc. Among the biofuels produced through bioconversion of OPEFB, cellulosic ethanol is the most intensively studied.

Two stage dilute acid hydrolysis was applied for OPEFB bioconversion to ethanol, 135.94 g xylose/kg OPEFB and 62.70 g glucose/kg OPEFB were produced in the first stage and 2nd stage, respectively [8]. They were then fermented to ethanol using Mucor indicus and Saccharomyces cerevisiae, respectively, and the corresponding ethanol yields were 0.45 and 0.46 g ethanol/g sugar.

Alkali is the most often used pretreatment chemical for cellulosic ethanol production from OPEFB. Kassim et al. pretreated OPEFB using 1% NaOH followed by mild acid (0.7% H₂SO₄) hydrolysis and enzymatic saccharification [26]. A total of 16.4 g/L of glucose and 3.85 g/L of xylose were obtained during enzymatic saccharification. The OPEFB hydrolysate was fermented with Saccharomyces cerevisiae and an ethanol yield of 0.51 g/g yield was obtained, suggesting that OPEFB is a potential substrate for cellulosic ethanol production. Han and his colleagues investigated ethanol production through pilot scale alkali pretreatment and fermentation [9]. The best pretreatment condition was 127.64 °C, 22.08 min, and 2.89 mol/L NaOH. Enzyme loading of 50 FPU/g cellulose resulted in 86.37% glucose conversion in their Changhae Ethanol Multi Explosion (CHEMEX) facility. An ethanol concentration of 48.54 g/L was obtained at 20% (w/v) pretreated biomass loading, along with simultaneous saccharification and fermentation (SSF) processes. This is so far the highest reported ethanol titre from OPEFB. Overall, 410.48 g of ethanol were produced from 3 kg of raw OPEFB in a single run, using the CHEMEX 50 L reactor.

Jung and his colleagues tried aqueous ammonia soaking for the pretreatment of OPEFB and its conversion to ethanol [12]. Pretreated OPEFB at 60°C, 12 h, and 21% (w/w) aqueous ammonia, showed 19.5% and 41.4% glucose yields after 96h enzymatic hydrolysis using 15 and 60 FPU of cellulase per gram of OPEFB, respectively. An ethanol concentration of 18.6 g/L and a productivity of 0.11 g/L/h were obtained with the ethanol yield of 0.33 g ethanol/glucose.

Lau et al. successfully applied ammonia fibre expansion (AFEX) pretreatment for cellulosic ethanol production from OPEFB [14]. The sugar yield was close to 90% after enzyme formulation optimization. Post-AFEX size reduction is required to enhance the sugar yield possibly due to the high tensile strength (248 MPa) and toughness (2,000 MPa) of palm fibre compared to most cellulosic feedstock. Interestingly, the water extract from AFEX-pretreated OPEFB at 9% solids loading is highly fermentable and up to 65 g/L glucose can be fermented to ethanol within 24 h without the supplement of nutrients.

OPEFB was also used for butanol production. Noomtim and Cheirsilp (2011) studied butanol production from OPEFB using Clostridium acetobutylicum [27]. Again, the pretreatment by alkali was found to be the most suitable method to prepare OPEFB for enzymatic hydrolysis. 1.262 g/L ABE (acetone, butanol and ethanol) was obtained in RCM medium containing 20 g/L sugar obtained from cellulase hydrolysed OPEFB. Ibrahim et al also investigated OPEFB as the potential substrate for ABE production [28]. Higher ABE yield was obtained from treated OPEFB when compared to using a glucose-based medium using Clostridium butyricum EB6. A higher ABE level was obtained at pH 6.0 with a concentration of 3.47 g/L. The accumulated acid (5 to 13 g/L) had inhibitory effects on cell growth.

Nieves et al. investigated biogas production using OPEFB. OPEFB was pre-treated using NaOH and phosphoric acid [29]. When 8% NaOH (60 min) was used for the pretreatment, 100% improvement in the yield of methane production was observed and 97% of the theoretical value of methane production was achieved under such pretreatment condition. The results showed that the carbohydrate content of OPEFB could be efficiently converted to methane under the anaerobic digestion process. O-Thong et al. investigated the effect of pretreatment methods for improved biodegradability and biogas production of oil palm empty fruit bunches (EFB) and its co-digestion with palm oil mill effluent (POME) [30]. The maximum methane potential of OPEFB was 202 mL CH₄/g VS-added corresponding to 79.1 m³ CH₄/ton OPEFB with 38% biodegradability. Co-digestion of treated OPEFB by NaOH presoaking and hydrothermal treatment with POME resulted in 98% improvement in methane yield comparing with co-digesting untreated OPEFB. The maximum methane production of co-digestion treated OPEFB with POME was 82.7 m³ CH₄/ton of mixed treated OPEFB and POME (6.8:1), corresponding to methane yield of 392 mL CH₄/g VS-added. The study showed that there was a great potential to co-digestion treated OPEFB with POME for bioenergy production.

In summary, OPEFB has been frequently investigated as a substrate for biofuel production through bioconversion. Cellulosic ethanol production was most intensively investigated and the highest ethanol titre of 48.54 g/L was obtained through alkali pretreatment in a pilot scale reactor [9]. Although not much research has been done for ABE and biogas production, the few reports summarized in this paper suggest that OPEFB is also potential substrate for butanol and biogas production. Throughout the reports reviewed, alkali-based pretreatment methods, such as NaOH alone, NaOH followed by acid, and ammonium fibre expansion (AFEX) pretreatment are the most effective in enhancing OPEFB digestibility.

5. Conclusion

In conclusion, OPEFB is the most potential renewable resource for biofuel production in Southeast Asia. It can be converted to biofuels through thermo-chemical or biological conversion. Pretreatment of OPEFB is necessary for both routes of conversion and alkali pretreatment is the most effective. A summary of OPEFB conversion technology is shown in Fig. 2.

Figure 2.

Biofuel production from OPEFB.

Among the studies on OPEFB thermo-chemical conversion, it seems that gasification is the most suitable approach to obtain bioenergy from OPEFB and has potential in commercialization. Pyrolysis, on the other hand, produced very complex bio-oil with high viscosity and water content, making it challenging for commercialization. However, charcoal from OPEFB pyrolysis can be a potential commercial product. Compared to other palm oil residues, such as oil palm kernel, OPEFB may not be a good candidate for solid fuel production, even after torrefaction pretreatment due to its high water content and low energy capacity.

Biological conversion of OPEFB is another route to obtain biofuels from OPEFB. Cellulosic ethanol production was most intensively studied and around 50 g/L titre was obtained with 20% (w/v) biomass loading through NaOH pretreatment. AFEX also showed potential in OPEFB pretreatment and a glucose yield of 90% was obtained with 9% biomass loading. The water extract of the AFEX pretreated OPEFB was highly fermentable. OPEFB also showed some promising preliminary results in ABE (acetone, butanol and ethanol) and biogas production; however, further investigation is necessary to enhance OPEFB conversion potentials in these areas.

For both thermo-chemical and biological conversion of OPEFB, pretreatment technology is the key for the process cost. Although alkali pretreatment is effective, scaling-up the process requires huge amount of acid to neutralize the base in the pretreatment solution. In addition, before alkali pretreatment, OPEFB should be milled to reduce its size, which is energy-consuming. Steam explosion is effective for a lot of lignocellulosic biomass, however not much research was found on its pretreatment of OPEFB. A cost-effective pretreatment is the key for the successful commercialization of OPEFB conversion technologies for biofuel production.

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Energy Potential of Empty Fruit Bunches

Energy Potential of Empty Fruit Bunches

A palm oil plantation yields huge amount of biomass wastes in the form of empty fruit bunches (EFB), palm oil mill effluent (POME) and palm kernel shell (PKS). In a typical palm oil mill, empty fruit bunches are available in abundance as fibrous material of purely biological origin. EFB contains neither chemical nor mineral additives, and depending on proper handling operations at the mill, it is free from foreign elements such as gravel, nails, wood residues, waste etc. However, it is saturated with water due to the biological growth combined with the steam sterilization at the mill. Since the moisture content in EFB is around 67%, pre-processing is necessary before EFB can be considered as a good fuel.

Unprocessed EFB is available as very wet whole empty fruit bunches each weighing several kilograms while processed EFB is a fibrous material with fiber length of 10-20 cm and reduced moisture content of 30-50%. Additional processing steps can reduce fiber length to around 5 cm and the material can also be processed into bales, pellets or pulverized form after drying.

There is a large potential of transforming EFB into renewable energy resource that could meet the existing energy demand of palm oil mills or other industries. Pre-treatment steps such as shredding/chipping and dewatering (screw pressing or drying) are necessary in order to improve the fuel property of EFB. Pre-processing of EFB will greatly improve its handling properties and reduce the transportation cost to the end user i.e. power plant. Under such scenario, kernel shells and mesocarp fibres which are currently utilized for providing heat for mills can be relieved for other uses off-site with higher economic returns for palm oil millers.

The fuel could either be prepared by the mills before sell to the power plants, or handled by the end users based on their own requirements.  Besides, centralized EFB collection and pre-processing system could be considered as a component in EFB supply chain. It is evident that the mapping of available EFB resources would be useful for EFB resource supply chain improvement. This is particular important as there are many different competitive usages. With proper mapping, assessment of better logistics and EFB resource planning can lead to better cost effectiveness for both supplier and user of the EFB.

A covered yard is necessary to supply a constant amount of this biomass resource to the energy sector. Storage time should however be short, e.g. 5 days, as the product; even with 45% moisture is vulnerable to natural decay through fungi or bacterial processes. This gives handling and health problems due to fungi spores, but it also contributes through a loss of dry matter trough biological degradation. Transportation of EFB is recommended in open trucks with high sides which can be capable of carrying an acceptable tonnage of this low-density biomass waste.

For EFB utilization in power stations, the supply chain is characterized by size reduction, drying and pressing into bales. This may result in significantly higher processing costs but transport costs are reduced. For use in co-firing in power plants this would be the best solution, as equipment for fuel handling in the power plant could operate with very high reliability having eliminated all problems associated with the handling of a moist, fibrous fuel in bulk.

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Janjangan sawit sebagai BAHAN BAKAR BOILER

Pemanfaatan Produk Samping Kelapa Sawit Sebagai Sumber Energi Alternatif Terbarukan

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PENDAHULUAN
Sebagai bangsa yang besar dengan jumlah penduduk sekitar 220 juta jiwa, Indonesia menghadapi masalah energi yang cukup mendasar. Sumber energi yang tidak terbarukan (non-renewable) tingkat ketersediaannya semakin berkurang. Sebagai contoh, produksi minyak bumi Indonesia yang telah mencapai puncaknya pada tahun 1977 yaitu sebesar 1.7 juta barel per hari terus menurun hingga tinggal 1.125 juta barel per hari tahun 2004. Di sisi lain konsumsi minyak bumi terus meningkat dan tercatat 0.95 juta barel per hari tahun 2000, menjadi 1.05 juta barel per hari tahun 2003 dan sedikit menurun menjadi 1.04 juta barel per hari tahun 2004 (Tabel 1).

Tabel 1. Produksi dan Konsumsi Minyak Bumi Indonesia

Tahun	Produksi (juta barel/hari)	Konsumsi (juta barel/hari)
2000	1.4	0.9446
2001	1.3	0.9632
2002	1.2	0.9959
2003	1.1	1.0516
2004	1.125	1.0362

Sumber: Media Indonesia, 8 September 2004 dan Kompas, 27 Mei 2004.

Indonesia yang semula adalah tergolong net-exporter di bidang bahan bakar minyak (BBM), sejak tahun 2000 telah menjadi net importer jika produksi minyak mentah Indonesia dikurangi dengan bagian kontraktor asing sebesar 35% produksi. Pada tahun 2003, impor bersih BBM Indonesia mencapai 0.336 juta barel per hari atau sedikit lebih kecil dari produksi bagian kontraktor asing. Impor bersih ini diperkirakan akan terus meningkat dengan semakin menurunnya produksi ladang-ladang minyak Indonesia dan meningkatnya konsumsi minyak penduduk Indonesia.Dalam upaya mengatasi masalah defisit energi tersebut, pengembangan sumber energi terbarukan merupakan suatu keharusan. Terhadap tuntutan ini, industri kelapa sawit mempunyai potensi kontribusi yang sangat besar. Produk utama kelapa sawit yaitu minyak sawit (CPO) kini sudah mulai dikembangkan sebagai sumber energi terbarukan dengan memprosesnya menjadi biodiesel, seperti yang sudah dikembangkan di Malaysia. Produk samping kelapa sawit seperti cangkang dan limbah pabrik CPO juga potensial sebagai sumber biomassa yang dapat dikonversi menjadi energi terbarukan. Alternatif ini memiliki beberapa kelebihan. Pertama, sumber energi tersebut merupakan sumber energi yang bersifat renewable sehingga bisa menjamin kesinambungan produksi. Kedua, Indonesia merupakan produsen utama minyak sawit sehingga ketersediaan bahan baku akan terjamin dan industri ini berbasis produksi dalam negeri. Ketiga, pengembangan alternatif tersebut merupakan proses produksi yang ramah lingkungan. Keempat, upaya tersebut juga merupakan salah satu bentuk optimasi pemanfaatan sumberdaya untuk meningkatkan nilai tambah.Sejalan dengan hal tersebut, maka dalam tulisan ini akan dibahas mengenai pemanfaatan produk samping sawit (PSS) sebagai sumber energi terbarukan. Pembahasan difokuskan pada potensi secara empiris produk samping kelapa sawit sebagai sumber energi terbarukan. Di samping itu, teknologi yang sudah berkembang serta status penguasaan teknologi Indonesia dalam hal produk samping kelapa sawit sebagai sumber energi dibahas secara ringkas di bagian akhir tulisan ini.

PRODUK SAMPING KELAPA SAWIT SEBAGAI SUMBER ENERGI TERBARUKAN 

Potensi Produk Samping Sawit sebagai Sumber Energi Terbarukan

Kebun dan pabrik kelapa sawit menghasilkan limbah padat dan cair dalam jumlah besar yang belum dimanfaatkan secara optimal. Serat dan sebagian cangkang sawit biasanya terpakai untuk bahan bakar boiler di pabrik, sedangkan tandan kosong kelapa sawit (TKKS) yang jumlahnya sekitar 23% dari tandan buah segar yang diolah, biasanya hanya dimanfaatkan sebagai mulsa atau kompos untuk tanaman kelapa sawit (Goenadi et al., 1998). Pemanfaatan dengan cara tersebut hanya menghasilkan nilai tambah yang terendah di dalam rangkaian proses pemanfaatannya.

Gambar 1. Kesetaraan biomassa dan energi dalam proses pengolahan sawit di pabrik kelapa sawit

Proses pengolahan Tandan Buah Segar (TBS) kelapa sawit menjadi Crude Palm Oil (CPO) secara sederhana dapat dilihat pada Gambar 1. Dari 1 ton TBS yang diolah dapat diperoleh CPO sebanyak 140 – 220 kg. Proses ini membutuhkan energi sebanyak 20–25 kWh/t dan 0.73 ton steam (uap panas). Proses pengolahan ini akan menghasilkan limbah padat, limbah cair dan gas. Limbah cair yang dihasilkan sebanyak 600–700 kg POME (Palm Oil Mill Effluent). Limbah padat yang dihasilkan adalah serat dan cangkang sebanyak 190 kg dan 230 kg TKKS segar (kadar air 65%). Selain itu juga dihasilkan limbah emisi gas dari boiler dan incenerator (Lacrosse, 2004).

Potensi energi yang dapat dihasilkan dari produk samping sawit dapat dilihat dari nilai energi panas (calorific value). Nilai energi panas (calorific value) dari beberapa produk samping sawit ditunjukkan pada Tabel 2. Produk samping yang memiliki nilai energi panas tinggi adalah cangkang dan serat. Cangkang dan serat (fibre) dimanfaatkan sebagian besar atau seluruhnya sebagai bahan bakar boiler PKS. Produk samping yang lain belum banyak dimanfaatkan sebagai sumber energi. TKKS yang juga memiliki nilai energi panas cukup tinggi saat ini banyak dimanfaatkan sebagai mulsa atau diolah menjadi kompos. Sebagian PKS masih membakar TKKS dalam incinerator untuk mengurangi volume limbah TKKS, walaupun sudah dilarang sejak tahun 1996.

Tabel 2. Nilai energi panas (calorific value) dari beberapa produk samping sawit (berdasarkan berat kering).

	Rata-rata calorific value (kJ/kg)	Kisaran (kJ/kg)
TKKS	18 795	18 000 – 19 920
Serat	19 055	18 800 – 19 580
Cangkang	20 093	19 500 – 20 750
Batang	17 471	17 000 – 17 800
Pelepah	15 719	15 400 – 15 680

Sumber: Ma et.al. (2004)

TKKS adalah limbah biomassa yang potensial sebagai sumber energi terbarukan. TKKS dapat digunakan sebagai bahan bakar generator listrik. Sebuah PKS dengan kapasitas pengolahan 200_000 ton TBS/tahun akan menghasilkan seba-nyak 44_000 ton TKKS (kadar air 65%)/tahun. Nilai kalor (heating value) TKKS kering adalah 18.8 MJ/kg, dengan efisiensi konversi energi sebesar 25%, dari energi tersebut ekuivalen dengan 2.3 MWe (megawatt-electric). TKKS dapat juga dimanfaatkan untuk menghasilkan biogas walaupun proses pengolahannya lebih sulit daripada biogas dari limbah cair.

Di samping itu, limbah padat dapat juga diproses menjadi briket arang sebagai sumber energi terbarukan. Dengan teknologi yang relatif sederhana, pemanfaatan limbah padat menjadi briket arang merupakan suatu pilihan yang sangat realistis dan prospektif.

Menurut Loebis dan Tobing (1989), limbah cair PKS berasal dari air kondensat rebusan (150–175 kg/ton TBS), air drab (lumpur) klarifikasi (350–450 kg/ton TBS) dan air hidroksiklon (100-150 kg/ton TBS). PKS dengan kapasitas olah 30 ton TBS/jam menghasilkan limbah cair sebanyak 360–480 m3 per hari dengan konsentrasi BOD rata-rata sebesar 25_000 mg/l. Limbah cair tidak dapat dibuang langsung ke perairan, karena akan sangat berbahaya bagi lingkungan. Saat ini umumnya PKS menampung limbah cair tersebut di dalam kolam-kolam terbuka (lagoon) dalam beberapa tahap sebelum dibuang ke perairan. Secara alami limbah cair di dalam kolam akan melepaskan emisi gas rumah kaca yang berbahaya bagi lingkungan. Gas-gas tersebut antara lain adalah campuran dari gas methan (CH4) dan karbon dioksida (CO2). Kedua gas ini sebenarnya adalah biogas yang dapat dimanfaatkan sebagai sumber energi. Potensi biogas yang dapat dihasilkan dari 600–700 kg POME kurang lebih mencapai 20 m3 biogas (Lacrosse, 2004). Penelitian pemaanfaatan POME untuk menghasilkan biogas saat ini menjadi perhatian banyak pihak. Selain sebagai sumber energi, teknologi biogas ini juga dapat mengurangi dampak emisi gas rumah kaca yang berbahaya bagi lingkungan.

Potensi Indonesia untuk Memanfaatkan Produk Samping Sawit untuk Energi

Indonesia memiliki potensi yang sangat besar dalam memanfaatkan produk samping sawit sebagai sumber energi. Seperti diketahui, kelapa sawit Indonesia merupakan salah satu komoditi yang mengalami perkembangan yang terpesat. Pada era tahun 1980-an sampai dengan pertengahan tahun 1990-an, industri kelapa sawit berkembang sangat pesat. Pada periode tersebut, areal meningkat dengan laju sekitar 11% per tahun. Sejalan dengan perluasan areal, produksi juga meningkat dengan laju 9.4% per tahun. Konsumsi domestik dan ekspor juga meningkat pesat dengan laju masing-masing 10% dan 13% per tahun. Pada awal tahun 2001–2004, luas areal kelapa sawit dan produksi masing-masing tumbuh dengan laju 3.97% dan 7.25% per tahun, sedangkan ekspor meningkat 13.05% per tahun (Direktorat Jenderal Bina Produksi Perkebunan, 2005). Sampai dengan tahun 2020, industri kelapa sawit Indonesia diperkirakan akan terus tumbuh, walau dengan laju pertumbuhan yang lebih rendah apabila dibandingkan dengan periode sebelum tahun 2000. Sampai dengan tahun 2010, produksi CPO diperkirakan akan meningkat antara 5%–6%, sedangkan untuk periode 2010–2020, pertumbuhan produksi diperkirakan berkisar antara 2%–4% (Susila, 2004).

Pertumbuhan produksi CPO berarti pula peningkatan ketersediaan produk samping sawit yang antara lain bersumber dari TBS. Seperti terlihat pada Gambar 2, produksi TBS diperkirakan akan terus meningkat dan mencapai sekitar 83 juta ton pada tahun 2020, sehingga dapat dihasilkan 17 ton CPO. Volume tersebut merupakan sumber produk samping yang sangat besar untuk menghasilkan energi.

Gambar 2. Grafik Perkembangan dan Proyeksi Produksi CPO Indonesia 2000/2010.

Volume produksi CPO tersebut dihasilkan dari 205 pabrik kelapa sawit yang sebagian besar berlokasi di Sumatera (177 pabrik), dan lainnya di Kalimantan, Sulawesi dan Jawa. Sebagai ilustrasi, produksi TBS Indonesia pada tahun 2004 diperkirakan sebesar 53_762 juta ton TBS. Produksi ini akan terus meningkat dan pada tahun 2010 diperkirakan mencapai 64_000 juta ton TBS. Dari produksi TBS tahun 2004 dapat diperkirakan produksi POME sebanyak 32_257 – 37_633 juta ton dan TKKS sebanyak 12_365 juta ton. Jumlah ini sangat melimpah dan berpotensi besar sebagai sumber energi terbarukan.

Potensi produksi biogas dari seluruh limbah cair tersebut kurang lebih adalah sebesar 1075 juta m3. Nilai kalor (heating value) biogas rata-rata berkisar antara 4700–6000 kkal/m3 (20–24 MJ/m3) (CTL, 2004). Dengan nilai kalor tersebut 1075 juta m3 biogas akan setara dengan 516_000 ton gas LPG, 559 juta liter solar, 666.5 juta liter minyak tanah, dan 5052.5 MWh listrik. TKKS juga memiliki potensi energi yang besar sebagai bahan bakar generator listrik. TKKS sebanyak 12_365 juta ton berpotensi menghasilkan energi sebesar 23_463.5 juta MWe.

Alternatif lain pemanfaatan limbah padat kelapa sawit yang paling sederhana untuk Indonesia adalah menjadikannya briket arang. Hal ini dapat dilakukan dengan memperbaiki sifat tersebut dengan cara pemadatan melalui pembriketan, pengeringan dan pengarangan. Pusat Penelitian Kelapa Sawit (PPKS) telah merancang bangun paket teknologi untuk produksi briket arang dari limbah sawit, baik tandan kosong maupun cangkang sawit.

Pada dasarnya ada dua metode pembuatan briket arang, yaitu (i) bahan baku-penggilingan-pengayakan-pembriketan-pengarangan, dan (ii) bahan baku-pengarangan-penggilingan-pengayakan-pembriketan. Untuk limbah sawit ternyata metode kedua lebih sesuai untuk menghasilkan briket arang yang bermutu tinggi.

TKKS dan cangkang sawit memiliki karakteristik yang berbeda, sehingga untuk proses pengarangannya juga memerlukan tungku yang berbeda. Untuk TKKS, proses pengarangan lebih sesuai dilakukan dalam tungku vertikal, sedangkan untuk cangkang sawit lebih baik dilakukan proses pengarangan pada tungku horisontal. Rendemen yang dihasilkan dari proses pengarangan tersebut adalah 25–30%.

Proses pembriketan limbah sawit dapat dilakukan dengan mesin pembriket tipe ulir dengan kapasitas 1 ton per hari. Mesin ini menghasilkan briket arang berbentuk silinder dengan diameter 5 cm dan panjang 10–30 cm. ukuran ini sesuai dengan briket arang komersial yang dibuat dari serbuk gergaji. Briket arang sawit memiliki keunggulan yaitu permukaannya halus dan tidak meninggalkan warna hitam apabila dipegang.

Karakteristik briket arang yang terbuat dari TKKS dan cangkang sawit sangat berbeda, seperti yang terlihat pada Tabel 3. Briket arang TKKS memiliki kadar abu yang lebih tinggi, sedangkan kadar kalor dan karbon terikatnya lebih rendah. Ditinjau dari segi kalor, kedua briket arang tersebut telah memenuhi Standar Nasional Indonesia (SNI) untuk briket arang kayu yaitu minimal 5000 kalori/gram.

Tabel 3. Karakteristik Briket Arang dari TKKS dan Cangkang Sawit

No	Karakteristik	Briket arang tandan kosong sawit	Briket arang cangkang sawit
1	Kadar air, %	9.77	8.47
2	Kadar abu, %	17.15	9.65
3	Kadar zat terbang, % (volatile matter)	29.03	21.10
4	Kadar karbon terikat, % (fixed carbon)	53.82	69.25
5	Keteguhan tekan, kg/cm2	2.10	7.82
6	Nilai kalor, kal/g	5_578.00	6_600.00

Perkembangan Teknologi Energi Terbarukan dari Produk Samping Sawit

Potensi biomassa dari produk samping sawit sebagai sumber energi terbarukan mulai dikembangkan di beberapa negera produsen sawit utama. Malaysia sebagai salah satu negera produsen CPO utama telah mengembangkan teknologi produksi biogas dari POME. Dari sisi teknologi Malaysia lebih maju daripada Indonesia dalam mengembangkan teknologi ini. Sejak tahun 2001 Malaysia melaksanakan program pengembangan energi terbarukan yang disebut dengan Small Renewable Energy Programe (SREP) (Yeoh, 2004). Salah satu energi terbarukan yang dikembangkan dalam program ini adalah pengembangan biogas dari POME (Ma et al, 2003). Saat ini mereka telah berhasil mengembangkan bioreaktor untuk produksi biogas dari POME. Bumibiopower (Pantai Remis) Sdn. Bhd. adalah salah satu perusahaan di Malaysia yang melaksanakan proyek untuk mengembangkan pabrik produksi biogas dari POME (Mitsubishi Securities, 2004). Pabrik ini direncanakan akan mengolah POME dari salah satu pabrik kelapa sawit yaitu Pantai Remis Paml Oil Mill. Biogas yang dihasilkan juga akan digunakan untuk generator listrik dengan kapasitas 1 MW – 1.5 MW.

COGEN bekerjasama dengan ASEAN melaksanakan proyek pengembangan energi terbarukan dari limbah biomassa sebanyak 8 proyek ( 3 proyek di Thailand, 3 proyek di Malaysia, dan 2 proyek di Singapura). Proyek ini memanfaatkan limbah biomassa, salah satunya adalah TKKS, sebagai bahan bakar generator listrik. Proyek pemanfaatan TKKS sebagai bahan bakar listrik dilaksanakan oleh TSH Bio Energy Sdn Bhn di Sabah, Malaysia. Kapasitas listrik yang dihasilkan adalah sebesar 14 MW (Lacrosse, 2004).

Pengembangan produk samping sawit sebagai sumber energi terbarukan masih tertinggal dibandingkan negera-negara lain. Menurut Abdullah (2004) dari total potensi biomassa (TKKS termasuk di dalamnya) sebesar 178 MWe baru sekitar 0.36% yang dimanfaatkan. Melalui Kep.Men. No. 1122 K/30/MEM/2002 tentang Distribusi Pembangkit Listrik Skala Kecil, Indonesia mulai mengembangkan energi terbarukan. Tahun 2005 Indonesia mendapatkan bantuan sebesar $ US 500.000 dollar dari ADB (Bank Pembangunan Asia) untuk mengembangkan energi terbarukan dari limbah cair kelapa sawit (Kompas, 27 Desember 2004).

Dalam waktu yang tidak terlalu lama, Indonesia diperkirakan akan mengalami defisit energi dengan volume defisit semakin meningkat. Hal ini terjadi karena sementara konsumsi energi terus meningkat, sumber energi, khususnya yang tidak terbarukan, semakin menurun. Untuk mengatasi hal ini, pengembangan sumber energi yang terbarukan merupakan pilihan yang strategis. Dalam konteks ini, pemanfaatan produk samping sawit dan limbahnya mempunyai potensi besar untuk dimanfaatkan. Produk samping sawit dan limbahnya mempunyai potensi besar sebagai sumber energi yang terbarukan. Dengan perkembangan industri kelapa sawit yang masih relatif pesat, upaya untuk mewujudkan hal tersebut perlu mendapat prioritas. Indonesia perlu segera memacu diri untuk mewujudkan hal tersebut sehingga ketertinggalan dengan negara lain dalam hal teknologi dan implementasi dapat terus diperkecil. Hal ini memerlukan dukungan semua pihak, khususnya pelaku bisnis, lembaga riset, dan pemerintah. Kebijakan Pemerintah perlu diarahkan pada pemberian insentif finansial kepada industri yang merintis kegiatan pengembangan energi terbarukan seperti ini, misalnya dengan memanfaatkan sebagian dana kompensasi pencabutan subsidi BBM.

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