Influence of temperature on kinetics and hydraulic retention time in discontinuous and continuous anaerobic systems

Abstract

Anaerobic digestion (AD) is a biological treatment susceptible to temperature variations. The Arrhenius model and the Van´t Hoff-Arrhenius relationship analyze the temperature effect in AD first-order kinetic constant (<i>k</i>). Kinetic data is relevant for estimating the hydraulic retention time (<i>HRT</i>) in continuous reactors. This research aimed to evaluate the behavior of kinetic constants concerning temperature using the Arrhenius model and Van´t Hoff-Arrhenius relationship and analyze the influence of kinetic constants as estimators of the <i>HRT</i>. The evaluation of the temperature effect in AD analyzed <i>k</i> fit to the Arrhenius model and Van’t Hoff-Arrhenius relationship. The research used data of AD methane yield (<i>B<sub>0</sub></i>) kinetics from the literature, corresponding to macroalgae (<i>MA</i>) (25, 35, 45<sup>o</sup>C), swine manure (<i>SM</i>) (25, 30, 35<sup>o</sup>C), and co-digestion of chicken manure with sawdust and miscanthus (<i>CM</i>) (35, 40, 42<sup>o</sup>C). The Arrhenius model and Van´t Hoff-Arrhenius relationship fitted the data with reduced temperature intervals (∆<i>T</i> = 5°C). The <i>HRT</i> analysis used a mass balance model considering 80% of the maximum <i>B<sub>0</sub></i> compared with the technical digestion time at 80 (<i>T<sub>80</sub></i>) and 90% (<i>T<sub>90</sub></i>) of the maximum <i>B<sub>0</sub></i>. The results indicate that the <i>HRT</i> calculation is sensitive for <i>k</i> below 0.13 d<sup>-1</sup>.