Photosynthesis and High Energy Crops

Carbon dioxide emission in the biosphere is attributed to two sources, one biological and the other industrial. Industrial carbon dioxide emission is mainly from the exhaust gases of industrial processes. Where carbon dioxide occurs in high concentration in such processes, the carbon dioxide in the exhaust gas can be trapped and then recovered for uses as a raw material. However, carbon dioxide released from automobiles, for example, is too diluted to be trapped for recovery. Photosynthesis is the most successful means for the trapping and recovery of car­bon dioxide released to the air from diluted emission sources. A counter-measure against the elevation of carbon dioxide in the atmosphere is to strengthen the path of carbon dioxide recycling through photosynthesis and then efficiently utilize the plant biomass formed as a result.

2-1 Oil Palm

In terms of photosynthesis, tropical areas offer great advantages over tem­perate zones due to high solar radiation. High energy crops native to South East Asia (and Africa and South America) are therefore desirable tools for the counter­measure to carbon dioxide elevation.

Year Atm Oil Preaa fibre Effluent

million ha million ton million ton million kl

(ai fuel 15 t)

Energy recovery 6% 0.8 fbel t/h у

Fig.2. Total biomass production and waste materials in palm oil industry.

Oil palm is one crop which has a very high energy fixation per land area, i. e. 5 t/ha year of oil (4.5xl07 kcal/ha year of energy) can be harvested. However, as shown in Fig.2, oil is only 1/3 of the total biomass of the tree. Hence the total en­ergy fixed by biomass is estimated to be 13.5×107 kcal/ha year, this being equiva­lent to 15 tons of fuel. In the world as a whole, the plantation area for oil palm trees is estimated to be about 4,000,000 ha (equivalent to 12,000,0001 oil/year). Thus, the total biomass fixed in oil palm trees is equivalent to about 30,000,0001 of fuel. As shown in Fig. 2,2/3 of the biomass in the oil palm indus­try is agricultural waste. A number of valuable resources are wasted and dumped in the plantation and oil mills. Among them, potential resources are press fiber and waste liquor. The chemical composition of the carbohydrate component of delignified palm fiber is 56.4% glucose, 36.0% xylose, 5.9% arabinose, and 1.7% mannose (1). Our experiments showed that delignified palm fiber can be digested to form glucose and xylose by commercial cellulases such as Meicellase and Onozuka and the hydrolysate can be subjected to fermentation to produce biofuel and chemicals (1). Our study estimates that 3,000,0001 of glucose and 2,000,000 t of xylose could be recovered from this waste per year.

Another big resource in the palm oil industry is the waste liquor from the oil mill. Two kinds of waste from the crude oil separation process are discharged, sterilized condensate and separator sludge. The mixture contains about 30,000 ppm of BOD and it is very hard to reduce BOD to the regulation limits. Our tech­nology proved that the waste which digested by commercial cellulase can be fer­mented well by CL saccharoperbutylacetonicum N1-4 to produce acetone, bu­tanol and ethanol without any additional medium supplementation (2-3). Extrac­tion of butanol by fatty acid methylester stimulated fermentation rates by release of end product inhibition (4) and the extract was similar to diesel fuel. We are confident that a process using crude palm oil (CPO, the product from the oil mill) methylester will stimulate the fermentation rate to produce biodiesel efficiently. Thus, about 200,0001 of biodiesel could be recovered from the waste by this process (Fig.3).

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