Table 2.

Comparison of integration of hydrothermal treatment and gas biofuels production in the literature and this study

Feedstock	Products	HTL process	Conditions	Fermentation process	HRT (day)	Gas yield	COD removal (%)	Reference
Algae	Methane	Batch (stainless steel cylinder), 100 °mL	0–1.5 h, 260–320 °C	Batch, 37 °C, Liquid products	62	–	44–61	Tommaso et al. [35]
Swine manure	Methane	–	–	Batch, 37 °C, Liquid products	65	~150–175 mL/g COD	45–55	Zhou et al. [58]
Sunflower stalks	Methane	Batch	30 min, 160 °C H2SO4	Batch, 37 °C, Mixture	45	278 mL/g VS		Hesami et al. [19]
Sugar beet pulp	Methane	Batch (thermostatic reactor), 600 mL	20 min, 160 °C	Batch, 37 °C, Mixture	25	502.5 mL/g VS		Ziemin´ski et al. [17]
Wheat straw	Methane	Batch (cylindrical steel tank), 6.2 L	1 h, 160 °C, NaOH	Batch, 35 °C, Mixture	31	224 mL/g TS		Sambusiti et al. [15]
Rice straw	Methane	Batch (hydrothermal reactor), 131 mL	10 min, 200 °C,	Batch, 35 °C, Mixture	60	132.7 mL/g VS		Chandra et al. [18]
Beech wood	Methane	Batch (Inconel-625 vessel), 5 mL	7–240 s, 380 °C	Batch, 50 °C, Liquid products	35	–	–	Yoshida et al. [28]
Laminaria japonica	Hydrogen	Batch (stainless steel vessel), 5 L	20 min, 170 °C	Batch, 35 °C, Mixture	3.5	109.6 mL/g COD		Jung et al. [38]
Wheat straw	Hydrogen	–	15 min, 180 °C	Continuous (CSTR, UASB AF), 70 °C, Liquid products	1–3	212 mL/g sugar		Kongjan et al. [39]
Sunflower stalks	Hydrogen	Batch (Stainless autoclave), 1 L	1 h, 170 °C, HCl	Batch, 35 °C, Liquid products	30	0	–	Monlau et al. [33]
Gelidium amansii	Hydrogen	Batch (high-pressure reactor) 30 L	15 min, 150 °C H2SO4	Batch, 35 °C, Liquid products	1.25	0	–	Parka et al. [36]
Switchgrass	Hydrogen	Batch (steam explosion reactor), 4 L	10 min, 190 °C	Continuous (UASB), 37 °C, Liquid products	0.42	288 mL/g COD	–	Veeravalli et al. [37]
Cornstalk	Hythane	Batch (High-pressure reactor), 1.8 L	0 min, 260 °C	Continuous(UASB, PBR), 37 °C, Liquid products	Hydrogen, 0.5 Methane, 0.5	H2, 0–146 mL/g COD CH4, 158–302  mL/g COD	H2, 19 − 2 CH4, 93 − 67	This study