サトウキビ畑の廃水灌漑　Irrigation of sugar cane field by waste waters

Eiji Matsumoto, on July 21, 2007, said:

Two sorts of waste waters are discharged from ethanol refineries, water used for washing sugar cane and waste fluid (vinhoto) occurred in the process of ethanol production. Now many refineries utilize these wastes to irrigate the sugar cane fields. I’m afraid of the injury to soils by appling such a strong acid fluid as vinhoto onto the ground.

バイオエタノール工場からは２種類の廃水が出る。一つはサトウキビの洗浄水、もう一つはエタノールを造る時に出る廃液でヴィニョートVinhotoと呼ばれるもの。エタノール生産量の10倍以上も出るヴィニョートは強酸性で強い悪臭を放つ。かつて、これらの廃水が川にたれ流しされ、著しい河川汚染を起こした。それが禁じられた現在、多くの工場はヴィニョートをサトウキビ洗浄水で薄めた上、水路（写真左）でサトウキビ畑に導きスプリンクラーで散布している。ヴィニョートはカリ（K）分に富んでいるので肥料の節約にもなり、一石二鳥というのだが．．．。人工的に酸性雨を降らせて、土壌を痛めないか心配である。2004年8月8日撮影。

marc boncz, on May 7, 2008, said:

Applying this vinhoto to the fields has both advantages and disadvantages. Advantages are that water body pollution is reduced, and that nutrients are recycled to the cane fields, thus greatly eliminating the need to apply fertilizers for the cultivation. The problem is that the vinhoto also contains organic residuals (amongst others organic acids indeed) causing soil pollution. Research is being carried out to try to make biodigestion of the liquid, before its application on the fields, a viable option. This would remove the organic contamination from the liquid, producing biogas (a 70/30 mixture of natural gas and CO2), which can be used for electricity generation. This way, pollution would be almost eliminated and the whole cycle of bioenergy production from sugar cane obtain an even higher EROEI (energy returned on energy invested) ratio than it already has (now around 8.7, compare that to the 1.3 obtained in the US with corn-based ethanol).

bentir, on January 27, 2009, said:

organic acids present in the vinhoto are not entirely bad. research shows that as they are negatively charged (i.e. anions) they bind with the positively charged soil matrix and thus reducing phospate fixation. as the soils on which the sugarcane are generally deep, well drained, high clay content soils, and the organic compounds present in the vinhoto are low weight, they tend to reside briefly in the soil. The microbiota brake them down very quickly, in a matter of days.

of course even those deep, high iron tropical soils are not immune to pollutants leaching into the ground water.