(i) Does not produce any process inhibitors (ii) Increased methane (5%–25%)
(i) High energy requirements (ii) High maintenance cost
2
Feedstock extrusion
(i) Extrusion increases the surface area to volume ratio
(i) Leads to increased energy consumption (ii) Increases equipment maintenance cost
3
Steam pretreatment/steam explosion
(i) Increased cellulose fiber reactivity (ii) Can make use of process energy/biogas
(i) Risk of producing inhibitors (e.g., furfural and HMF) (ii) Reduces digestible biomass due to lignin condensation (iii) More process energy input and reduced net energy output (iv) Precipitation phenomena
4
Hot water treatment
(i) Solubilized hemicellulose and lignin products are present in lower concentrations (ii) Reduced risk of producing inhibitors like furfural and HMF (iii) Increased enzyme accessibility
(i) High heat demand and hence energy consumption (ii) Not effective at all temperature ranges
5
Microwave
(i) Leads to more biogas production by 4%–7%
(i) Increased process energy input (ii) Increases labor and maintenance cost
6
Diluted or strong acid pretreatment
(i) Used to solubilize hemicellulose component (ii) Methanogens can adapt to inhibiting compounds
(i) Acids are expensive (ii) Can form inhibiting compounds (iii) Causes corrosion problems
7
Alkaline pretreatment
(i) Used to solubilize hemicellulose and some lignin (ii) Increased methane production
(i) Can produce inhibitors (ii) Can cause high alkali concentration in the reactor
