Short-term oxidative lime pretreatment of palm pruning waste for use as animal feedstuff

Abstract

Oxidative lime pretreatment (OLP) is an effective pretreatment for highly recalcitrant lignocellulosic materials. This experiment was conducted to investigate the effect of short-term OLP on fermentative gas production kinetics of date palm prunings. Rachis and petiole were pretreated with excess lime (0.5 g Ca(OH)2 g(-1) dry matter) in a reactor charged with 10 bar pure oxygen pressure at different times and temperatures. Lignin removal was greatly affected by OLP, whereas cellulose was well preserved even after severe pretreatment. After 72 h fermentation, the cumulative gas production was 321.2 mL gas g(-1) organic matter (OM) for the most severe pretreatment, compared to 73.6 mL g(-1) OM for the untreated rachis. For the petiole pretreated at 120 °C for 280 min, 268 mL gas was produced compared to 59 mL gas g(-1) OM for the untreated petiole. Scanning electron microscope images showed the formation of pores (average diameter of 10-12 µm) and carbonate calcium deposits on the surface of treated biomass. An increase in biomass crystallinity was observed in pretreated samples resulting from cellulose enrichment. The results suggest that OLP improves the ruminal digestibility of date palm prunings, which may have potential for inclusion in the ruminant diet at low cost.