Effect of wet air oxidation on the composition and biomethanation of water hyacinth

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Water hyacinth (Pontederia crassipes) is a potential feedstock for biorefinery due to its rapid growth and phytoremediation properties when cultivated in wastewaters. The effects of wet air oxidation (WAO) and alkaline wet air oxidation (AWAO) on the structure and biomethanation kinetics of water hyacinth were studied. Water hyacinth (50 g/L) was pretreated using WAO and AWAO (0.15 g Na2CO3/g feed), at 170 °C under 0.4 MPa air for 30 min. After WAO and AWAO, the fixed carbon (% w/w) of water hyacinth (25.9 ± 0.8) was reduced to an average of 21.4 ± 1.6. The volatiles (% w/w) in the WAO solid residue were higher (69.0 ± 0.7) than in the AWAO (60.5 ± 1.2) and unpretreated biomass (62.9 ± 0.2), but the soluble COD [mg/g feed] of WAO (153.5 ± 4.1) was half that of AWAO (310.3 ± 4.1). The AWAO biomass showed higher cellulose deconstruction and lignin and extractives removal compared with WAO and unpretreated biomass. The methane production rate [N. mL CH4/g feed day] during the biomethanation of water hyacinth (4.1 ± 0.2) increased 63% after WAO (6.7 ± 1.5) and 117% after AWAO (8.9 ± 0.7). AWAO increased the methane potential [N. mL CH4/g feed] of water hyacinth by 24%, from 153.7 ± 1.9 to 191 ± 4.1. The estimated energy production from the biomethanation of AWAO water hyacinth was 30 times above that of unpretreated biomass. The biomethanation of water hyacinth after AWAO was better than WAO and unpretreated biomass.