Table 2.

Different mechanical pretreatment applied to the biogas production and yield

S/N	Biomass	Pretreatment	Anaerobic digestion condition	YBP	YAP	Refs
1	Water hyacinth	0.05 mm	Digester 0.45 L		Increase by 16%	[107]
2	Water hyacinth	1.0 mm	Digester 0.45 L		Increase by 10%	[107]
3	Meadow grass	200 mm	Bottle 0.5 L	297 mL/g VS	376 mL/g VS	[111]
4	Rice straw	0.3 mm	Glass reactor 2 L	58.1 mL/g VS	62.7 mL/g VS	[109]
5	Wheat straw	0.3 mm	Reactor 2 L	167.8 mL/g VS	245.6 mL/g VS	[108]
6	Wheat straw	1.2 mm	Reactor 2 L	167.8 mL/g VS	264.7 mL/g VS	[108]
7	Barley Straw	5 mm	Glass reactor 2 L	240 mL/g VS	370 mL/g VS	[112]
8	Waste activated sludge	Ultrasonic pretreatment	Semi-continuous reactors (15 days)		49% increase	[113]
9	Wheat straw	High hydrostatic pressure		31.8 mL	77.9 mL	[110]
10	Hyacinthus spp.	Microwave		137.18 mL/g-sub	221 mL/g-sub	[114]
11	Groundnut shell	2 mm	Batch		147.6 lN/kgFM	[28]
12	Groundnut shell	4 mm	Batch		180.7 lN/kgFM	[28]
13	Groundnut shell	6 mm	Batch		177.3 lN/kgFM	[28]

Y_BP = Yield before pretreatment and Y_AP = Yield after pretreatment