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Utilisation of Date Palm by products I :
Potential Technological and Economic Utilization of the OASIS
by products
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| Introduction |
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| Date palm trees yield various quantities of cellulosic by-products during the year's seasons. The weight and composition of these by-products depend on the nature of the date pal part from which those by-products come from. The typical by-products include leaves, leaf bases (Karab with connecting fibers), fruit bunches, inflorescent shields (male and female spathe) and trunks of old and dead trees. The average annual quantity (dry) of these by-products (except trunks) is 10-14 kg per trees which are 10 years old and it is about 20 kg in older trees. However, unlike most of other agricultural models, the contribution of these by-products to the economics of date palm farming and date palm industry in general is marginal. The lack of modern technology in the utilization of these farm by-products is the most important cause of this low economic value. The existing practices are rather primitive with very limited scope of applications such as: |
- Composting for on farm organic fertilizer
- Traditional furniture and crates
- Hand made ropes
- Crushing and direct mixing with ruminants feed
Oasis LTD integrated agro-industrial model for modernization of the whole date palm sector gave careful consideration to the economic utilization of these valuable "by-products" in order to improve date palm farm revenues and broaden the scope of date palm based products (through single and multiple transformations). Thus, this paper presents an attempt to explore the most feasible options to achieve efficient economic utilization of date palm cellulosic by-products. |
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| Composition of Date Palm By-Products |
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Although the annual amounts of cellulosic by-products depend on date palm gender, cultivar and age, the average amounts for a `10 years old tree are presented in table (1). More than 50% of these by-products are leaves (the whole leaves which include fronds and leaflets) which are cut in the pruning process (yellowish to dry) and along with leaf bases and fruit bunches (after harvest) comprise about 90% of cellulosic by-products. Seasonality is one of the most important factors to be considered in the utilization process designs since it will dictate the availability of these materials. The accumulation of these by-products minimizes overall farm revenues and represent a potential hazard through harboring a variety of insects and rodents in addition to fire hazards. |
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| By-Product |
Average Weight (kg) |
Palm Productivity (pieces/year) |
Annual Amount (kg/year) |
Relative Weight (%) |
| Leaves |
0.8 |
10 |
8 |
55.5 |
| Leaf Bases |
0.3 |
8 |
2.4 |
16.7 |
| Fruit Bunches |
0.25 |
10 |
2.5 |
17.4 |
| Spathe |
0.1 |
15 |
1.5 |
10.4 |
| Total |
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43 |
14.4 |
100 |
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| Table (1). The average annual amounts of date palm cellulosic by-products |
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| Table (2) presents the average content of major components of date palm by-products. The ash content represents the minerals content in the various parts and it should considered as an important source for animal feed and organic fertilizers production (composting). The main structural difference between cellulose and hemicellulose is the latter content of pentoses (or pentosans which are five-carbon sugars). The high content of this polysaccharide (~50% of by-products composition) could be considered as major obstacle in the bioconversion processes of date palm by-products. The relatively high lignin content (~23%) contributes negatively to the efficiency of bioconversion in spite of its industrial and economic significance. Lignin is not a carbohydrate (i.e. unlike cellulose, hemicellulose and starch) but it is a high molecular weight polymer of phenolic monomers. |
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| Table (2). The major components of date palm cellulosic by-products. |
| Component / Content (%)* |
Frond bases |
Frond (midrib) |
Leaflets |
Fruit Bunch |
Spathe |
| Ash |
10.5 |
9.3 |
11.0 |
7.3 |
6.0 |
| Hemicellulose |
54.5 |
55.6 |
48 |
60.4 |
64.45 |
| Cellulose |
22.5 |
33.5 |
28 |
30 |
37 |
| Lignin |
27 |
21.5 |
28.1 |
21 |
19.4 |
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| * On dry weight basis |
| The potentially high economic value of by-products is confirmed by detailed analyses as shown in table (3). The high organic matter content is an important indicator for the bioconversions of by-products into feed and organic fertilizers. However, lowering the high carbon : nitrogen ratio is the major target in all bioconversion processes. The crude protein content of whole dry leaves is about 4.9% (conversion of nitrogen by the factor of 6.25) and should be increased via fermentation processes which are used in the feed and compost production in order to achieve the acceptable levels. |
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| Table (3). Typical analysis of date palm cellulosic by-products. |
| Components |
Leaves
(Whole) |
Leaf Bases |
Fruit Bunches |
Spathe |
| Moisture (%) |
5.41 |
7.30 |
5.35 |
6.17 |
| Organic Matter (%) |
92.30 |
90.87 |
95.46 |
95.17 |
| Carbon/Nitrogen Ratio |
59.8 |
87.4 |
73.4 |
31.7 |
| Nitrogen (%) |
0.78 |
0.52 |
0.65 |
1.50 |
| Phosphorous (%) |
0.02 |
0.01 |
0.02 |
0.07 |
| Potassium (%) |
0.32 |
0.24 |
1.06 |
0.69 |
| Calcium (%) |
0.23 |
0.56 |
0.06 |
0.11 |
| Magnesium (%) |
0.17 |
0.26 |
0.05 |
0.09 |
| ٍSulfur |
0.06 |
0.08 |
0.04 |
0.11 |
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| Organic Fertilizer Production (Composting) |
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| Although composting could be carried out either under aerobic or anaerobic conditions, preparation procedures of by-products are identical since they involve size reduction (crushing) to small particles (≤ 5 mm)followed by wetting with water and thorough mixing. The aerobic process requires timed agitation (twice a week) along with water wetting and will take 8-10 weeks to be completed. This type of composting involves variety of aerobic microorganisms including fungi, streptomycetes and bacteria in addition to worms. The compost temperature increased naturally to around 65◦C during the first three weeks killing insects (eggs, larvae and adults) and weed seeds. The bioconversions in this stage are carried out by thermophilic microorganisms which cause rapid degradation of cellulosic structures and yielding various sugars. Compost temperature decreased gradually to maintain about 30◦C allowing the mesophiles and worms to complete the degradation processes. |
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| Anaerobic composting is carried out in the absence of air (e.g. air exclusion by plastic covers) and methanogenic bacteria represent the main microbial population where methane gas is one of the most important by-product. Both types of composting require large amounts of water when they are carried out under open systems (e.g. farms and classic organic fertilizer factories). However, conducting these processes in closed systems (i.e. solid state fermentation lines) lowers water consumption and production time to the minimum allowing highly accurate control on the process. |
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| Animal Feed Production |
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| Crushed date palm leaves were used in ruminants feed during the last two decades of the past century in some date producing countries. The process is strictly physical (size reduction) without any chemical or biological alterations. However, biological modification is required to increase crude protein content, breakdown of the complex lingo-cellulosic structure and improve overall digestability. To achieve these targets, there are two major options as summarized below: |
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| 1. Supplementation with chemical nitrogen source |
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| In this approach, urea solution is mixed with crushed cellulosic parts (≤ 1 cm), covered with thick plastic sheets and left for several weeks after which the fermented product is agitated thoroughly for aeration and removal of residual ammonia gas. The presence of urea is essential for raising the pH of cellulosic parts (from ~5.5 to alkaline values) and promoting mixed bacterial cultures growth (nitrogen source) which hydrolyze the cellulose and hemicellulose and increase the overall crude protein to 13-15%. This fermentation is not only a mixed culture but also involves aerobic (starting phase) and anaerobic microorganisms (intermediate and final phases). |
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| 2. Biodegradation by fungal cultures |
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| This approach is based totally on biological transformations and excluding chemical supplements. Cellulase(s) hyperproducing fungal strains (naturally selected or genetically engineered) are the most important microorganisms in this process where they secrete extracellular enzymes into the crushed cellulosic by-products causing massive hydrolysis to simple sugars (e.g. glucose and cellobiose). However, lignin remains intact since it requires special enzyme systems which are present in certain microbial strains (e.g. specific strictly anaerobic bacteria). |
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| Oasis LTD. has focused on this approach in order to maintain adoption of all possible environment friendly technologies and practices. In order to achieve a dual output fermentation process, the crushed by-products are steam sterilized, wetted by a dilute slurry containing cull dates (~1%), water and fungal spores (of the selected strain) in a solid state fermenter with timed agitation for several days at a constant temperature (usually 45◦C for thermophilic strains). The simple sugars content of the thin dates slurry promotes spores germination and heavy fungal growth (high and active fungal biomass) during the first 48 hours. After depletion of dates sugars the fungal cells start massive secretion of their extracellular hydrolytic enzymes to maintain growth and avoid starvation. The downstream process involves enzymes extraction, liquid/solid separation and further processing of the extracted cellulases as required. The solid by-product of this process includes hydrolyzed cellulosic solids and a rich fungal biomass (high quality protein and vitamins) which is suitable for feed production for a wide range of animals. |
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| Date Palm By-Products as Bioethanol Feedstock |
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The utilization of various agricultural by-products (e.g. straw and corn stover) and wood waste as feedstock in bioethanol production has created new considerations about the possibility of using date palm by-products in bioethanol production.
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| Feedstock |
Ethanol Conversion Factor (gallons/ton) |
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| Sugar Cane |
19.50 |
| Sugar Beets |
24.80 |
| Molasses |
69.40 |
| Corn |
98.21 |
| Wheat |
87.50 |
| Straw |
45.75 |
| Corn Stover |
36.35 |
| Wood |
37.45 |
| Dates |
90 |
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| Table (4). Bioethanol conversion ratios of selected feedstocks. |
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Table (4) shows a concise comparison of ethanol conversion ratios for various feedstocks. Date palm by-products are the closest to corn stover and wood where the potential yield is about 37 gallons/ton. The process techno-economic feasibility is based on the following main features:
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1. The main by-product is lignin has a similar heat content to coal (~85%) which is usually used for electricity generation.
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2. The process contribute positively to the economics of bioethanol production
from dates
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3. The yeast biomass (from ethanol fermentation) represents additional important concentrated protein source for feed production.
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However, cost reduction of enzymatic hydrolysis of by-products and pentose fermentation (from hemicellulose hydrolysis) represent the most significant challenges facing the enhancement of process economics. |
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“ Inquiries about references and further technical details should be forwarded to OASIS Ltd”
Email::info@oasisnakhoil.com |
