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.
Keywords: ADM1; high salinity; kinetics; methane fermentation; sulfate reduction.