Table 1.

Comparison between operational challenges in continuous SCWG and SCWO reactors.

Challenge	Supercritical water gasification	Supercritical water oxidation
Destruction of refractory compounds	High reaction temperatures and long residence times needed, high potential to form char [7]	Oxygen free-radicals facilitate efficient destruction, less potential to polymerize molecules and form char [16]
Fuel value recovery	Reductive reactions allow for recovery of feedstock fuel value in gaseous form [1, 3, 6]	Oxidative reactions consume feedstock fuel value in favor of compound destruction [14, 16]
Reactor thermal management	Endothermic reactions necessitate additional heater(s) to maintain isothermal conditions	Cooling system or sand bath needed to prevent thermal runaway during exothermic reactions
Corrosion	Heteroatoms and salts are highly corrosive [13, 14]	Heteroatoms and salts are highly corrosive, oxide layer forms on metal reactor walls [13, 14]
Clogging	Char formation likely from complex organic feedstocks, salt precipitation and metal oxide formation commonly causes clogging [1, 7]	Salt precipitation and metal oxide formation commonly causes clogging [16]
Process economics	>20% solid content and efficient heat recovery needed for cost-effective fuel gas production [3, 11, 13]	Regenerative heating minimizes need for external energy input
Practical application	Fuel gas production from wet organic wastes (e.g. sewage, biomass) [3, 8, 9, 10, 11, 12]	Destruction and removal of toxic compounds (e.g. sewage, CWAs) [14]