Reclaimed water use in biofuel production

Abstract

Jatropha curcas L., a toxic species that does not interfere with the food chain, produces biodiesel of better environmental quality than mineral oils. However, in order to cultivate it sustainably, it is necessary to optimize the limited resources used, mainly water and soil. Therefore, in arid areas, it is necessary to cultivate under intensive conditions, irrigate with reclaimed water and cut production costs. To optimize water consumption, partial root-zone drying (PRD), which keeps a part of the root system dry, was used. This water management strategy, employed successfully in other oil crops, yielded less fruit per bunch, but more fruit bunches per plant. This fact will probably allow to establish higher planting density and, consequently, higher productivity per surface unit. This is one of the few available options for improving profitability as production per tree is stable (1.25 kg seed plant-1 year-1 for the most productive trees, with excellent climate and soil, and no limitations water use). A high percentage of fruit lying on the ground (24%) and non-uniform timing in fruit production (except some specimens) greatly hinder its mechanization. Although this crop's environmental and socio-economic benefits are not taken into account, it is very difficult, with only the calculated water consumption (15.5 m3 water per L of oil or 5.6 m3 water per L of oil according to our best estimations), to consider it a profitable option.