A photobioreactor for production of algae biomass from gaseous emissions of an animal house

Abstract

Sustainable approaches to circular economy in animal agriculture are still poorly developed. Here, we report an approach to reduce gaseous emissions of CO₂ and NH₃ from animal housing while simultaneously using them to produce value-added biomass. To this end, a cone-shaped, helical photobioreactor was developed that can be integrated into animal housing by being freely suspended, thereby combining a small footprint with a physically robust design. The photobioreactor was coupled with the exhaust air of a chicken house to allow continuous cultivation of a mixed culture of Arthrospira spec. (Spirulina). Continuous quantification of CO₂ and NH₃ concentration showed that the coupled algae reactor effectively purifies the exhaust air from the chicken house while producing algal biomass. Typical production rates of greater than 0.3 g/l*day dry mass were obtained, and continuous operation was possible for several weeks. Morphological, biochemical, and genomic characterization of Spirulina cultures yielded insights into the dynamics and metabolic processes of the microbial community. We anticipate that further optimization of this approach will provide new opportunities for the generation of value-added products from gaseous CO₂ and NH₃ waste emissions, linking resource-efficient production of microalgae with simultaneous sequestration of animal emissions. KEY POINTS: • Coupling a bioreactor with exhaust gases of chicken coop for production of biomass. • Spirulina mixed culture removes CO₂ and NH₃ from chicken house emissions. • High growth rates and biodiversity adaptation for nitrogen metabolism. Towards a sustainable circular economy in livestock farming. The functional coupling of a helical tube photobioreactor with exhaust air from a chicken house enabled the efficient cultivation of Spirulina microalgae while simultaneously sequestering the animals' CO₂ and NH₃ emissions.

Keywords: Ammonium sequestration; Animal agriculture; Photobioreactor; Spirulina.

Fig. 1

Details of the photobioreactor setup. A Schematic flow diagram and illustration of the coupling of the chicken coop with the photobioreactor. The exhaust air from the coop is taken by an air pump via a CO₂ “input” sensor and blown into the bioreactor via the air inlet at the bottom, rises into the reservoir via the helical tube, and escapes via the gas outlet and the CO₂ “output” sensor. The buoyancy of the rising air transports the medium through the helix into the reservoir, and then flows back from there through a central return tube into the lower part of the helix. B Technical drawing and C photographic image of the helical tube photobioreactor. Note that the reservoir in the prototype shown is located inside the helical tube and is therefore not visible. The LED light bars located inside the helix can be seen in pink. Scale bar is 500 mm

Fig. 2

Cultivation of Arthrospira sp. microalgae with exhaust air from chicken coop. A Representative plot of CO₂ concentration in the daily cycle of the chicken house (CO₂ input, red graph) fed into the algae reactor. The blue graph shows the CO₂ concentration of the exhaust air after passage through the algae reactor (CO₂ output). The colored bars show the daytime phases with active chickens when the outer flap is open (yellow), sleeping chickens when the flap is closed (black), and in the morning when the outer flap is closed and the chickens are awake in the coop (blue). The dashed green line represents the algae biomass in the reactor, and the harvest is marked by a green asterisk. B Representative data on CO₂ turnover and biomass production in the reactor over a 16-day period. Data were collected in mid-November when the barn had a daylight cycle from 5 AM to 6 PM due to artificial lighting. Same color coding for the graphs as in (A). Note that in the course of this experimental series, varying amounts of biomass were removed on the days indicated by green asterisks

Fig. 3

Light microscopy images of the Arthrospira sp. microalgae culture used in this study. A Overview image of cell culture suspension, revealing primarily helical and straight Arthrospira as well as small microorganism, e.g., B ciliates. C, D Cell aggregates from various microbes revealing phytoplankton such as diatoms and Nannochloropsis. Scale bars are 20 µm

Fig. 4

Taxonomic distribution of the algae suspension samples before and 22 days after the algae culture was aerated with exhaust air from the chicken coop. The taxonomic classification was calculated based on rRNA, single-copy marker genes and total proteins, respectively. The results were visualized based on their taxonomy using KronaTools