448

29 Zero-Waste Biorefineries for Circular Economy

both belowground and aboveground. For plywood and fuelwood manufacturing,

Populus and Eucalyptus are growing as a trend in Haryana and Punjab.

29.7

Methods for CO2 Capture

DAC is a physicochemical method, in which CO2 get directly captured and stored.

This involves sequestration of more CO2 per acre of land as compared to seques-

tration by trees in the same area of land. Streams of pure CO2 produced from air

capture have significant roles in various chemical industries and storage facilities

[46]. Methods like post-combustion, precombustion, and oxyfuel combustion have

been categorized which depends on the site of capture. After combustion, CO2 is

produced from flue gas and needs to be captured by the post-combustion system [45].

29.7.1

Scenario 1. Photosynthetic Bacterial Model for CO2

Sequestration

Adenosine triphosphate (ATP) is the energy source for photosynthetic bacteria,

which give biomass, biofuel, and bioproducts after converting from CO2 as an end

product. Photosynthetic bacteria (PB) followed a very unique and complex pathway

to fix CO2 via type I (Fe–S type in sulfur bacteria) reaction centers. Both photoau-

totrophs and chemoheterotrophs play a central role by glyceraldehyde-3-phosphate

(G3P) [44, 45]. It serves as a primary intermediate in pathways like homolactic, sol-

ventogenic, and ethanolic fermentation by chemoheterotrophic organisms. For CO2

sequestration, cyanobacteria from the photosynthetic phyla are considered to be

the key player. For H2 production, both enzymes, hydrogenase and nitrogenase, are

used by photosynthetic organisms [45, 46]. Using light energy, organic compounds

can produce hydrogen by anoxygenic photosynthetic bacteria.

29.7.2

Scenario 2. Biochar Model for CO2 Sequestration

Crop residues also contain plant nutrients such as carbon, nitrogen, phosphorus,

potassium, calcium, and magnesium. These nutrients are added to the soil by fertil-

izers. The crop residues are harvested every year and microbes also decompose these

plant residues to maintain the soil organic carbon levels [47]. Charcoal being incred-

ible adsorbent can enhance the capability of the soil to absorb nutrients and other

agricultural chemicals. As charcoal is relatively low in density, it decreases the den-

sity of high-clay soils. It increases the capability of sandy soil to hold water and nutri-

ents. Biomass pyrolysis is one of the methods to produce biochar by thermochemical

decomposition of biomass under 300–700 ^∘C of temperature with oxygen-limiting

conditions. Biomass pyrolysis and restrain of its products like biochar and bio-oil

could result in a viable solution to agricultural and forest slags. Biochar amendment

to the soil could result in improved fertility of the soil, and it can also mitigate the

GHG emission of the soils which will ultimately alleviate climate change.