Impact of microwave pre-treatment on the batch anaerobic digestion of two-phase olive mill solid residue: a kinetic approach

Abstract

SUMMARY:The effect of a microwave (MW) pre-treatment on two-phase olive mill solid residue (OMSR) or alperujo with a view to enhancing its anaerobic digestibility was studied. The MW pre-treatment was carried out at a power of 800 W and at a targeted temperature of 50 °C using different heating rates and holding times. The following specific energies were applied: 4377 kJ·kg TS −1 (MW1), 4830 kJ·kg TS −1 (MW2), 7170 kJ·kg TS −1 (MW3) and 7660 kJ·kg TS −1 (MW4). The maximum methane yield, 395±1 mL CH 4 ·g VS added −1 , was obtained for MW4. The effect of the pre-treatment on the kinetics of the process was also studied. The methane production curves generated during the batch tests showed a first exponential stage and a second sigmoidal stage for all the cases studied. In the first stage, the kinetic constant for the pre-treatment MW1 was 54.8% higher than that obtained for untreated OMSR.KEYWORDS: Alperujo; Anaerobic digestion; Batch; Kinetics; Microwave RESUMEN: Impacto del pretratamiento con microondas sobre la digestión anaerobia en régimen discontinuo de residuos sólidos de almazaras de dos fases: un enfoque cinético. El efecto del pretratamiento con microondas (MW) sobre el residuo semisólido procedente de la elaboración del aceite de oliva por el sistema de dos fases o alperujo fue estudiado con el objeto de aumentar su digestibilidad anaerobia. El pretratamiento fue llevado a cabo a una potencia de 800W y a una temperatura de 50 °C empleándose distintas velocidades de calentamiento así como diferentes tiempos de espera para obtener dichas condiciones. Las siguientes energías específicas fueron aplicadas: 4377 kJ·kg TS −1 (MW1), 4830 kJ·kg TS −1 (MW2), 7170 kJ·kg TS −1 (MW3) y 7660 kJ·kg TS −1 (MW4). El máximo rendimiento 395±1 mL CH 4 ·g SV añadidos −1 se obtuvo para MW4. El efecto del pretratamiento en la cinética del proceso también fue estudiado. Las curvas de producción de metano durante los ensayos mostraron una etapa exponencial y una sigmoidal en todos los casos. En la primera etapa, la constante cinética para MW1 fue 54.8% mayor que la obtenida para el alperujo sin pretratar.

Evolution of control parameters in biochemical methane potential tests of olive mill solid waste (OMSW), thermal pre-treated OMSW, and its co-digestion with Dunaliella salina

“…The AD of OMSW is a widely studied process (Borja et al, 2002;Rincón et al, 2007;Christoforou and Fokaides, 2016). There is also information about the use of different pre-treatments on OMSW or lignocellulosic wastes before AD where methane production has been improved: thermal pre-treatments on OMSW (Rincón et al, 2013), ultrasound pre-treatments (Rincón et al, 2014), microwave pretreatments (Rincón et al, 2016) and hydrothermal carbonization (Volpe et al, 2016;Codignole et al, 2018). Another widely studied alternative to improve methane yield during the AD of OMSW is the codigestion of this substrate with microalgae.…”

Evolution of the Olive Oil Industry along the Entire Production Chain and Related Waste Management

“…Waste from oil mills can be treated with this technology only if added in a limited percentage (10-20%) to different substrates for which AD is the preferred solution [102,103]. Alternatively, they re-quire previous pretreatments to eliminate or transform bactericidal substances [94,[104][105][106][107]. Further alternatives are the adoption of technology solutions that allow reducing the feed flow rate of the incoming biomass and its stratification, considering that the total input solids are variable during the processing time [108] and the hybridization of AD with pyrolysis [109].…”