31.4 Technological Trends and Challenges in the Anaerobic Biorefinery

477

Pharmaceuticals, cosmetics

Pharma

Volume

Value

Food and feed

Bioplastics

and polymers

Bulk chemicals

and fuels

Heat and power

Functional foods, nutritional

supplements, health foods

Fine chemical, commodity

chemicals, bioplastics

Fertilizers, biogas, biodiesel,

biohydrogen

Electricity, heat

Figure 31.4

Valorization process in biorefineries.

The valorization of raw material into products is a well-established procedure in

the current fossil fuel processing industry (Figure 31.4). Along with the same prin-

ciple, biorefinery incorporates biomass as input material leading to a wide variety

of bioproducts and bioenergy. The biosolids can be applied to crops and the liquid

used for fertigation. The digestate can be further processed to a plethora of biobased

products and chemicals. However, an alternative approach is to use nutrients in the

liquid fraction for the cultivation of protein- and lipid-rich algae.

31.4

Technological Trends and Challenges in the

Anaerobic Biorefinery

31.4.1

Pretreatment

Currently, biorefineries are attempting to produce additional bioenergy by integrat-

ing AD from organic waste because of the importance of future direction. Lignocel-

lulosic feedstocks have high methane potential in anaerobic digestion. However, it

is not widely applied due to its complex, recalcitrance structure that decreases the

stability of the AD process. Research efforts on the biowaste treatment increased dur-

ing the last decade, and several reports were published recently, aiming at challenges

and opportunities during pretreatment [9].

The complex structure of the feedstock is a major challenge, which can be over-

come by pretreatment. Pretreatment can enhance the digestibility of high-content

lignocellulose feedstock by increasing the substrate porosity, reducing cellulose

crystallinity, increasing the surface area for enzymes to attack, and solubilizing

cellulose, hemicellulose, and/or lignin. The conversion of cellulose and hemicel-

lulose into more accessible substrates for the extracellular enzymes improves the

AD of lignocellulosic feedstocks [17]. Various methods for pretreatment including

chemical, physical, biological, and physicochemical processes have been suggested

to improve the hydrolysis of cellulose and hemicellulose in biomass [18]. A selection

of these methods together with their advantages and disadvantages are presented

in Figure 31.5.