V. Fernández-Cegrí

Effect of hydrothermal pretreatment of sunflower oil cake on biomethane potential focusing on fibre composition

The aim of this study was to elucidate the effect of hydrothermal pretreatment at 25, 100, 150 and 200°C on fibre composition and the biomethane potential of sunflower oil cake (SuOC). An increase in pretreatment temperature from 25 to 200°C caused a decrease in hemicellulose content in the solid pretreated fraction from 13 to 6% while the lignin content increased by 16%. Soluble compounds also increased with temperature. Digestion of solid fractions from pretreatments at 25, 100, 150 and 200°C in batch assays at 35±1°C resulted in methane yields of 114±9, 105±7, 82±7 and 53±8mL CH(4) g(-1)COD(added), respectively. The corresponding methane yields for the liquid fractions were 276±6, 310±4, 220±15 and 247±10mL CH(4) g(-1)COD(added), respectively. Therefore the overall methane yield was highest for SuOC pretreated at 100°C; however, this value was only 6.5% higher than that achieved after pretreatment at 25°C.

Impact of ultrasonic pretreatment under different operational conditions on the mesophilic anaerobic digestion of sunflower oil cake in batch mode.

In this study ultrasonic (US) pretreatment was investigated with the aim of improving the anaerobic digestion of sunflower oil cake (SuOC), the solid waste derived from the extraction process of sunflower oil. Five ultrasonic pretreatment assays were conducted at specific energy (SE) and sonication times in a range from 24,000 kJ/kg TS and 16.6 min (assay 1: US1) to 597,600 kJ/kg TS and 331.2 min (assay 5: US5), respectively, all operating at a constant sonication frequency (20 kHz) and ultrasonic power (120 W). As regards ultrasonic pretreatment, the working conditions of the first assay (US1) using samples of SuOC at 2% (w/v) showed to be the most appropriate in terms of both lignin and hemicellulose degradation (57.7% and 66.7%, respectively) and cellulose increase (54% increase with respect to its initial concentration). The percentage of COD solubilization increased from only 14% to 21% when SE was 25 times higher. Results obtained in batch anaerobic digestion experiments (biochemical methane potential - BMP - tests) conducted at 35°C of the solid and liquid fractions released from the different ultrasonic conditions tested, indicated that for the first experiment (US1) the average ultimate methane yield obtained was 53.8% higher than that achieved for untreated SuOC. Finally, the kinetic constants of the anaerobic digestion of the solid and liquid fractions released after the ultrasonic pretreatment were virtually independent of the operation conditions assayed.

Feasibility of sunflower oil cake degradation with three different anaerobic consortia

Sunflower oil cake (SuOC) is the solid by-product from the sunflower oil extraction process and an important pollutant waste because of its high organic content. For the anaerobic digestion of SuOC three different industrial reactors were compared as inoculum sources. This was done using a biochemical methane production (BMP) test. Inoculum I was a granular biomass from an industrial reactor treating soft-drink wastewaters. Inoculum II was a flocculent biomass from a full-scale reactor treating biosolids generated in an urban wastewater treatment plant. Inoculum III was a granular biomass from an industrial reactor treating brewery wastes. The highest kinetic constant for methane production was achieved using inoculum II. The inoculum sources were analyzed through PCR amplification of 16S rRNA genes and fingerprinting before (t = 0) and after the BMP test (t = 12 days). No significant differences were found in the bacterial community fingerprints between the beginning and the end of the experiments. The bacterial and archaeal communities of inoculum II were further analyzed. The main bacteria found in this inoculum belong to Alphaproteobacteria and Chloroflexi. Of the Archaea detected, Methanomicrobiales and Methanosarcinales made up practically the whole archaeal community. The results showed the importance of selecting an appropriate inoculum in short term processes due to the fact that the major microbial constituents in the initial consortia remained stable throughout anaerobic digestion.

Anaerobic digestion of sunflower oil cake: a current overview

Due to the chemical and physical structure of a lignocellulosic biomass, its anaerobic digestion (AD) is a slow and difficult process. In this paper, the results obtained from a batch biochemical methane potential (BMP) test and fed-batch mesophilic AD assays of sunflower oil cake (SuOC) are presented. Taking into account the low digestibility shown during one-stage experiments the methane yield decreased considerably after increasing the organic loading rate (OLR) from 2 to 3 g VS L(-1) d(-1), SuOC was subjected to a two-stage AD process (hydrolytic-acidogenic and methanogenic stages), in two separate reactors operating in series where the methanogenic stage became acidified (with >1,600 mg acetic acid L(-1)) at an OLR as low as 2 g VS L(-1) d(-1). More recently, BMP assays were carried out after mechanical, thermal, and ultrasonic pre-treatments to determine the best option on the basis of the methane yield obtained.

Performance and kinetic evaluation of the semi-continuous anaerobic digestion of sunflower oil cake pretreated with ultrasound

A study of the semi-continuous anaerobic digestion of sunflower oil cake previously sonicated (at a specific energy of 24,000 kJ/kg TS, constant sonication frequency of 20 kHz and ultrasonic power of 120 W) was carried out in laboratory-scale completely stirred tank reactors at mesophilic temperature (35°C). Two anaerobic inocula were used: a mixture of flocculant biomass (I) from a full-scale anaerobic reactor treating waste activated sludge and a granular inoculum (II) from an industrial UASB reactor treating brewery wastewater. Soluble COD (CODs) removal efficiencies ranged between 67.7% and 70.1% and between 61.3% and 67.7% at hydraulic retention times (HRTs) of between 24–10 days for inoculum I and 24–8 days for inoculum II. However, for HRTs lower than 8 days and 6.7 days, equivalent to organic loading rates (OLRs) higher than 2.62 and 3.15 g COD/(L·d), respectively, a sudden decrease in the CODs removal efficiency was observed in both cases. In any case, inoculum II allowed for a more stable and efficient operation for a wider range of both OLRs and HRTs, permitting an appropriate and reliable operation for OLRs as high as 3.15 g COD/(L·d) and HRTs as low as 6.7 days. The methane production rates achieved with inoculum II were always higher than those reached with inoculum I. The overall methane yield obtained with inoculum II was 13% higher than that achieved with inoculum I. In addition, this value was 1.9 times higher than the methane yield obtained with untreated (non-sonicated) SuOC. A second-order kinetic model was found to be adequate to fit the experimental results obtained for the two inocula used. The kinetic constant obtained with inoculum I was 3.5 times higher than that achieved with inoculum II.