Feasibility of NaOH-treatment for improving biogas production of digested Spartina alterniflora

• Biogas residue of Spartina alterniflora was reused for biogas production.
• NaOH treatment was be used for improving biogas production of digested S. alterniflora.
• Biogas yield of digested S. alterniflora was increased by 15∼42% for 5% NaOH pretreated.

In order to improve the biotransformation rate of Spartina alterniflora (SA) and evaluate the feasibility of NaOH-treatment as a pretreatment of digested SA (DSA) for advanced anaerobic biogasification, two experiments were conducted under lab-scale conditions. First, SA was directly digested under 35 ± 1 °C with initial total solid (TS) loading of 20% (the first stage). After 90 day's reaction, cumulative biogas yield of SA and average methane content were 388 ± 22 ml g−1 TSadded and 59.62 ± 1.88%, respectively. Then the DSA was treated with 5% NaOH solution and was used for advanced biogasification (the second stage). The cumulative biogas yield of NaOH-treatment and control were 210 ± 11 ml g−1 TSadded and 103 ± 16 ml g−1 TSadded, respectively, with 70.78 ± 2.11% and 76.92 ± 1.94% of average methane content. The total cumulative biogas yield (sum of the first stage and the second stage of NaOH-treatment) and TS removal rate of SA were 495 ± 24 ml g−1 TSadded and 76.85 ± 1.94%. After NaOH treatment, surface lignin and some carbohydrate of DSA were destructed into lignin fragment, organic acids, and some other small molecular organic matter; while the skeleton structure of lignin and cellulose were not destructed significantly. The results of 13C NMR showed that methyl and carboxylic C groups of DSA were decomposed significantly. The results indicated that NaOH-treatment was a good pretreatment for DSA.