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

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. •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.