Jatropha curcas sludge valorization

Jatropha which grows in tropical and subtropical climates across the developing world, is a perennial species that received much attention for its ability to grow on 'marginal land and to produce seeds with high oil percentage. Among the different species of Jatropha, Jatropha curcas is suitable as ornamental plant, raw material for dye, potential feed stock, soil enrichment manure and more importantly for biodiesel production. The mechanical pressing of the Jatropha seeds for oil production results in large amounts of solid residue (seed cake) and sludge that contain oil, water, minerals, proteins, toxic compounds and anti-nutritional factors. The aim of our work was to screen the fertilizing power of Jatropha sludge and its oily and solid fractions for promoting biodiesel circular economy. Our results indicated that seeds of watercress had a better germination performance than lettuce with Jatropha sludge and its fractions. This could depend on the different sensitivity of the two species and/or also to the composition of the sludge and its fractions. The solid fraction had the greatest inhibitory effects on germination of both species. The oily fraction had the less phytotoxic effect on the germination process while only in presence of the total sludge at 25%, seeds of watercress and lettuce showed a germination percentage lower than 50%. Higher concentrations were completely inhibitory. The phytotoxic effects of the sludge and its fractions may be attributed to the combination of high EC and phenol contents. This study revealed that highly diluted Jatropha total sludge may be very useful as good source of nutrients for crop production, cutting short the use of chemical fertilizers. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.