BIOGAS PRODUCTION FROM MAIZE STRAW AFTER PRETREATMENT WITH STEAM EXPLOSION

The production of bioenergy from agricultural residues does not compete with food or feed production and represents a largely unused resource. One of the most widely available lignocellulosic residue is maize straw, which is a very promising raw material for biofuel production. However, proper bioconversion of this biomass requires a pretreatment step. Steam explosion has proven to be an effective pretreatment method for refractory lignocellulosic biomass. The aim of this study was to (1) determine the optimum pretreatment conditions (temperature and time) of maize straw for biogas production, (2) optimize the utilization of the steam-exploded maize straw in continuous anaerobic digestion (AD) systems. Different steam explosion conditions were tested (temperature and pretreatment time). The effect of the pretreatment on the methane yield was analyzed in eudiometer batch digesters of 0.25 l capacity. The results of the batch tests showed that methane production raised with pretreatment at 160 degrees C for 30 min, obtaining an increase in the yields of around 33% in comparison to the untreated biomass. Methane yields decreased slightly with pretreatment intensities extending beyond this point. The continuous digestion tests were carried out in two fermenters with a capacity of 150 L at mesophilic temperature (40 degrees C). Two different organic loading rates (OLR) of 1 and 2.5 kg VS m(-3) d(-1) were tested and some parameters such as dry matter (DM), volatile solids (VS), pH, ammonium nitrogen (NH4-N), and residual methane potential were regularly measured. The results of the continuous tests showed that the utilization of steam exploded maize straw in a continuous system is feasible with an OLR of 2.5 kg VS m(-3) d(-1) with the use of no more additives than a nitrogen source (urea). The residual methane potential increased notably when the OLR was increased to 2.5 kg VS m(-3) d(-1) due to the decrease in the hydraulic retention time (HRT), entailed with an increment in the OLR.