A Kinetic Model for Anaerobic Digestion and Biogas Production of Plant Biomass under High Salinity

Abstract

The aim of this study is to evaluate the anaerobic digestion and biogas production of plant biomass under high salinity by adopting a theoretical and technical approach for saline plant-biomass treatment. Two completely mixed lab-scale mesophilic reactors were operated for 480 days. In one of them, NaCl was added and the sodium ion concentration was maintained at 35.8 g-Na+·L−1, and the organic loading rate was 0.58-COD·L−1·d−1–1.5 g-COD·L−1·d−1; the other added Na2SO4–NaHCO3 and kept the sodium ion concentration at 27.6 g-Na+·L−1 and the organic loading rate at 0.2 g-COD·L−1·d−1–0.8 g-COD·L−1·d−1. The conversion efficiencies of the two systems (COD to methane) were 66% and 54%, respectively. Based on the sulfate-reduction reaction and the existing anaerobic digestion model, a kinetic model comprising 12 types of soluble substrates and 16 types of anaerobic microorganisms was developed. The model was used to simulate the process performance of a continuous anaerobic bioreactor with a mixed liquor suspended solids (MLSS) concentration of 10 g·L−1–40 g·L−1. The results showed that the NaCl system could receive the influent up to a loading rate of 0.16 kg-COD/kg-MLSS·d−1 without significant degradation of the methane conversion at 66%, while the Na2SO4–NaHCO3 system could receive more than 2 kg-COD·kg−1-MLSS·d−1, where 54% of the fed chemical oxygen demand (COD) was converted into methane and another 12% was observed to be sulfide.