Controlled carbon dioxide enrichment using beer fermentation off-gas results in 89% spinach yield increase

CO2 enrichment is a strategy commonly employed by indoor/vertical farms to
improve crop yields. Artificially elevating the CO2 concentration within
an enclosed growth space results in improved photosynthetic efficiency,
and therefore improved crop growth rates and flavor profiles. Alcohol
fermentation provides a steady stream of CO2 that is emitted to the
atmosphere as a by-product. To evaluate the feasibility of using
fermentation off-gas as a source for indoor carbon dioxide (CO2)
enrichment, spinach plants were randomly assigned to 2 growth chambers.
The control chamber was maintained under ambient CO2 concentrations, while
the treatment chamber was piped onto a flow control system capable of
delivering CO2 from a beer fermentation vessel to the growth chamber to
maintain CO2 levels at a setpoint of 1200 parts-per-million (ppm). CO2
flow was diverted to the growth chamber when levels were below 1200 ppm,
and to an external exhaust when chamber levels were above 1200 ppm, with
the flow control device measuring internal CO2 concentrations and
responding accordingly every 6 seconds. A standardized batch of beer was
used to replenish the fermentation source to maintain continuous
fermentation and CO2 off-gas production. The CO2 flow control device
successfully maintained a strong oscillation of CO2 around the 1200 ppm
setpoint within the treatment growth chamber for the duration of the
50-day growth period. Spinach plants grown in the treatment chamber
produced significantly more fresh biomass (5.456 g vs. 2.888 g, P <
0.0001), dry biomass (0.5711 g vs. 0.271 g, P = 0.0002), and significantly
longer leaf lengths (231.0 mm vs. 159.9 mm, P < 0.0001) than their
control chamber counterparts, respectively. This represents an 89%
increase in fresh spinach crop yield within a controlled indoor growth
environment.