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โครงการหนังสืออิเล็กทรอนิกส์ด้านการเกษตร เฉลิมพระเกียรติพระบาทสมเด็จพระเจ้าอยู่หัว

Monteith (Allen et al., 1998). The data used for calculation are mainly referred from the national
data obtained from the relevant government agencies such as the Office of Agricultural Economics

(OAE) (OAE, 2012), the Land Development Department (LDD) and especially the Royal Irrigation
Department (RID). As the planting period generally differs from region to region, the sugarcane and

cassava calendars of the OAE are referred to in the assessment.

8.2.2 Water requirements for feedstock processing

Sugar milling involves crushing cane to extract sugarcane juice. This juice is clarified to

remove any impurities and concentrated into syrup by boiling off excess water, seeded with raw
sugar crystals in a vacuum pan and boiled until sugar crystals have formed and grown

(Silalertruksa and Gheewala, 2009). The crystals are separated from the syrup by centrifugal
process before more crystals are grown in the syrup. Therefore, a variety of products and wastes

will be generated in the mills i.e. sugar is the main product; molasses, the syrup remaining after
the sugar has passed through the centrifuge for the last time in a mill or refinery, is a by-product as

well as bagasse which is generated after sugarcane crushing and it is used to produce steam and
electricity to supply for the mills and the surplus electricity is sold to the general grid-mix. The other

residues such as filter cake and wastewater effluents from the mills are considered as waste in the
study because generally they done not have an economic value and are hence, not traded.

To share the water use from sugarcane cultivation and sugar milling between the sugar

(main product) and the by-products i.e. molasses and bagasse, the energy-based allocation

techniques is applied in the study. In the mills, a ton of sugarcane processed will generate 109, 45,
and 287 kg of sugar, molasses, and bagasse, respectively. However, only the surplus bagasse
after internal use in the mills (for own energy requirements) i.e. about 131 kilogram per ton

sugarcane, is considered in the allocation calculation. Based on the average energy content of

sugar, molasses and bagasse of about 16.33, 11.43 and 7.53 MJ/kg respectively (Silalertruksa and
Gheewala, 2009), the allocation factors for sugar, molasses and the surplus bagasse are 0.54,
0.16 and 0.30, respectively. Thus, the factor 0.16 is used for determining the water use for

molasses production. Based on all processes including sugarcane washing, extraction, juice

treatment, juice concentration by condenser and evaporation (excluding ethanol production), the
3
water use is estimated to be around 1.23 m per ton of processed cane (Macedo, 2005; Gerbens-
Leenes and Hoekstra, 2009). The water use in sugar mills for molasses is estimated to be around

3
4.37 m /ton molasses.
The water use in the industrial processes i.e. feedstock processing and ethanol conversion

are considered to contribute to the blue WF. Effluents generated in this process contribute to water

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