Effect of pretreatment and total solid content on thermophilic dry anaerobic digestion of Spartina alterniflora

• Biogas production rate but not biogas yield for thermo-lime pretreated sample was improved.
• Hot-water pretreated sample has higher biogas yield and k value than thermo-lime.
• High TS content led to metabolite accumulation due to mass transfer limitations.
• A decrease in TS content from 20.8% to 17.9% increased 29.6% of biogas yield.

The effect of pretreatment [thermo-lime with 0.09 g Ca(OH)2/g total solid (TS) of biomass at 120 °C for 4 h and hot water at 120 °C for 4 h] and TS content on the thermophilic anaerobic digestion of Spartina alterniflora was assessed in six batch reactors and three leaching bed reactors. The componential change in solid biomass was analyzed to understand the changes in biogas production. The biogas production rate but not the biogas yield of the sample pretreated with thermo-lime was improved compared with that of raw and hot-water pretreated samples. The biogas yield (206.8 mL/g TS) and production rate constant (k; 0.052 d−1) of the hot–water pretreated sample were obviously higher than those of the thermo-lime-pretreated sample (168.3 mL/g TS and 0.028 d−1) because more biodegradable matter were preserved in the former sample. Dry anaerobic digestion at high TS content caused a high componential reduction. However, the digestion also led to organic metabolite accumulation because of mass transfer limitations, which decreased biogas yield and production rate. A decrease in TS content from 20.8% to 17.9% increased 29.6% of biogas yield and 67.9% of k values. Process stability was enhanced with decreasing TS content.