The effect of substrate/inoculum ratio on the kinetics of methane production in swine wastewater anaerobic digestion

CÓRDOBA, VERÓNICA; FERNÁNDEZ, MÓNICA; SANTALLA, ESTELA

ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH

SPRINGER HEIDELBERG

Año: 2017

0944-1344

by using sewage sludge as inoculum in three substrateto inoculum ratios (SIRs) named A (1:1), B (3:1) and C(6:1), with the objective to identify the proportion that optimizesthe performance of the process. Duplicated batch bioreactorsof 1 L capacity under mesophilic conditions wereused to carry out the experiment. The highest biogas yieldwas observed in A treatment (554 ± 75 mL/g volatile solid(VS)). Cumulative methane production decreased from382 ± 22 to 232 ± 5 mL/g VS when SIR increased from 1:1to 6:1. The first-order model and the modified Gompertzequation were used to model the experimental cumulativemethane yield giving adjustments with coefficients of determinationof 96 and 99% respectively. The effect of the SIRwas analysed based on the kinetic parameters of the Gompertzequation, which are methane production potential, maximummethane production rate and lag-phase time. The best performancein terms of the kinetic parameters was obtained fortreatment A; however, treatment B could still ensure a stableprocess. The use of higher inoculum concentration generated463.1% higher methane production rate and required 77.3%shorter adaptation time (lag phase) in the SIR range studied.When higher SIR was used (e.g. 14:1, previous work), it couldbe observed that the Gompertz equation also adjusted adequatelythe experimental data (R2 > 0.99) although the lagphasetime did not remain in a linear relationship with SIR butexponentially above SIR = 6:1. These results demonstratedthat when a low amount of inoculum was used, the adaptationtime of microorganisms resulted much higher than expecteddelaying the methane production and extending the time neededto achieve adequate performance of the process.