Life Cycle Water Consumption and Withdrawal Requirements of Ethanol from Corn Grain and Residues

We assessed the water requirements of ethanol from corn grain and
crop residue. Estimates are explicit in terms of sourcesgreen
(GW) and blue (BW) water, consumptive and nonconsumptive requirements
across the lifecycle, including evapotranspiration, application and
conveyance losses, biorefinery uses, and water use of energy inputs,
and displaced requirements or credits due to coproducts. Ethanol consumes
50−146 L/vehicle kilometer traveled (VKT) of BW and 1−60
L/VKT of GW for irrigated corn and 0.6 L/VKT of BW and 70−137
L/VKT of GW for rain-fed corn after coproduct credits. Extending the
system boundary to consider application and conveyance losses and
the water requirements of embodied energy increases the total BW withdrawal
from 23% to 38% and BW + GW consumption from 5% to 16%. We estimate
that, in 2009, 15−19% of irrigation water is used to produce
the corn required for ethanol in Kansas and Nebraska without coproduct
credits and 8−10% after credits. Harvesting and converting
the cob to ethanol reduces both the BW and GW intensities by 13%.
It is worth noting that the use of GW is not without impacts, and
the water quantity and water quality impacts at the local/seasonal
scale can be significant for both fossil fuel and biofuel.

本研究评估了玉米谷物与作物残渣基乙醇的需水总量。本次估算明确按水源类型进行区分——绿水（Green Water, GW）与蓝水（Blue Water, BW），并覆盖全生命周期内的消耗性与非消耗性需水，包括蒸散发、灌溉施用与输送损失、生物炼制厂用水、能源投入的水耗，以及联产品带来的替代需水或信用抵扣。在扣除联产品信用后，灌溉玉米基乙醇的蓝水耗量为50~146升/车辆行驶公里数（Vehicle Kilometer Traveled, VKT），绿水耗量为1~60升/VKT；雨养玉米基乙醇的蓝水耗量为0.6升/VKT，绿水耗量为70~137升/VKT。将系统边界拓展至涵盖灌溉施用与输送损失，以及隐含能源的需水后，总蓝水取用量占比从23%提升至38%，蓝水与绿水总耗量占比从5%提升至16%。经估算，2009年美国堪萨斯州与内布拉斯加州，未扣除联产品信用时，用于乙醇生产所需玉米的灌溉用水占总灌溉用水的比例为15%~19%；扣除信用后该占比为8%~10%。将玉米芯回收并转化为乙醇，可使蓝水与绿水的水强度均降低13%。值得注意的是，绿水的使用并非全无环境影响，无论是化石燃料还是生物燃料，其在局地或季节尺度下的水量与水质影响均不容忽视。