DAC with biointegration (hybrid bio-DAC)

Classical direct air capture (Climeworks solid amine sorbents, Carbon Engineering liquid potassium-hydroxide solvent) strips CO2 from ambient air (~420 ppm) but needs high-temperature regeneration — roughly 100 C for solid systems and up to 900 C for liquid ones — which keeps removal cost in the hundreds of dollars per tonne. Hybrid bio-DAC integrates biology to lower that energy barrier along two routes. Enzymatic DAC immobilizes carbonic anhydrase (CA) — the fastest known enzyme, turning over around one million reactions per second — onto sorbents and membranes so CO2 is captured rapidly and regenerated at mild ~45-50 C, cutting regeneration heat substantially. PBR-DAC runs atmospheric air through closed photobioreactors of engineered microalgae (enhanced RuBisCO / carboxysomes) that fix CO2 into biomass, later converted to biochar or biocrude. The lower regeneration temperature lets bio-DAC run on waste heat, geothermal or heat-pump energy. Projects are environmentally regulated and MRV-audited by the EPA (US), with CDR credits governed by the EU Carbon Removals and Carbon Farming (CRCF) Regulation, the DOE DAC Hubs programme and ISO 14064. The five organizations in this projection span mineral-bio loops (Heirloom), electric bio-sorbents (Sustaera), the leading DAC operator (Climeworks), enzyme engineering (Fraunhofer IGB) and engineered microalgae (Institute of Microbiology, CAS).

Key directions of hybrid bio-DAC:

1. Carbonic-anhydrase enzymatic DAC: CA-functionalized sorbents capture CO2 ~10^6-fold faster and regenerate at low temperature.
2. Electrically-heated bio-sorbents: cheap sorbents plus direct electric heating target removal below USD 100 per tonne (Sustaera).
3. Mineral carbonation with bio-enhancement: a CaO/CaCO3 lime loop with enzymatic humidification that accelerates the carbonation cycle (Heirloom).
4. Microalgae PBR-DAC: engineered RuBisCO strains fix air CO2 into biomass routed to biochar or hydrothermal-liquefaction biocrude.

Sectoral value chain#

[biomaterial production] ──> [sorbent functionalization] ──> [air contactor capture]
                                                                       │
                                                             (low-temperature regeneration)
                                                                       │
                                                                       ▼
[MRV & CDR credits] <─── [CO2 recovery & storage] <─────┘

Value chain levels#

Cross-cutting technologies of the sector:

• carbonic-anhydrase: the zinc enzyme catalysing CO2 hydration at ~10^6 reactions per second.
• dac-sorbents: amine and solid sorbents functionalized with CA for a low-temperature swing.
• microalgae-photobioreactors: engineered RuBisCO strains fixing atmospheric CO2 into biomass.

The stack combines enzyme biochemistry, protein immobilization and low- temperature process engineering.

1. Carbonic anhydrase catalysis:
   • CA’s active site holds a zinc ion coordinated by three histidine residues; it activates water to a zinc-hydroxide that performs a nucleophilic attack on CO2, forming bicarbonate, with a turnover of around 10^6 per second — the fastest known enzyme and the basis of low-temperature capture.
2. Enzyme immobilization and stabilization:
   • free enzyme denatures and leaches, so CA is covalently bound to mesoporous silica or polymer fibers (APTES amination plus glutaraldehyde crosslinking), giving thermostable sorbents that tolerate mild regeneration for many cycles.
3. Low-temperature desorption:
   • because the CA-catalysed bicarbonate pool releases gaseous CO2 on a mild temperature or pressure swing (~45-50 C), regeneration can run on waste heat from data centres or geothermal energy instead of the 100-900 C swing of classical DAC.