Mixed cultures of cyanobacteria and bacteria for simultaneous brewery wastewater treatment and CO2 fixation
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Date
2026-07-09
Authors
Κοτρέτσου, Νεφέλη
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Abstract
Motivated by the modern issue of climate change and the need for environmentally friendly and ef-ficient carbon capture methods, the topic of this research was selected. Simultaneously, an environ-mentally friendly and energy efficient method for wastewater treatment was tested. More specifically, the effect of CO2 concentration and N:P nutrient ratio on the CO2 fixation ability, wastewater treat-ment, biomass growth and metabolite production was examined.
The experiments were conducted on a laboratory scale using 10 L systems with continuous CO2-rich air flow. The aim was to gradually increase the CO2 concentration between experiments to reach industrial emissions levels. This increase is gradual, so as to study the response and viability of the cul-ture in each set of experimental conditions. Before the start of each experiment, raw brewery wastewater was electrocoagulated in a pre-treatment step. Four experiments were conducted, two with a 1% CO2 inlet and two with 2.5% CO2. Within each set, different nitrogen and phosphorus nutri-ent ratios were tested, more specifically ratios of N:P=16:1 and 10:1. Throughout the duration of each experiment, samples were taken to determine d-COD reduction, biomass growth, and the biochemical composition of biomass (protein and carbohydrate content as well as a-chlorophyll and c-phycocyanin pigment production).
The results of each experiment were evaluated based on the culture’s CO2 biofixation ability, the wastewater treatment efficiency and the quality of the produced biomass. It was found that the 2.5% CO2 systems reached fixation percentages of up to 76%, with the 1% CO2 systems not falling far behind with a maximum of 70%. In terms of fixation rate, the higher CO2 systems fared better, with the N:P=16:1 ratio reaching 32 mg L-1 CO2 d-1.
Biomass productivity was similar across all experiments, between 2-3 g L-1, with the 2.5% CO2 and N:P=16:1 system reaching the highest final biomass. Regarding the wastewater treatment, all experi-ments managed to reduce d-COD below the legislation limit of 125 mg L-1 for disposal with HRT of be-tween 5 and 11 days.
Additionally, a-chlorophyll, c-phycocyanin, protein and carbohydrate contents were analyzed. At 1% CO2 and N:P=16:1, the largest pigment production was recorded, with a-chlorophyll reaching 19 mg/(g DW). The increased CO2 concentration lead to suppressed pigment production, albeit with a small in-crease in c-phycocyanin production peaking at 28 mg/(g DW) (at N:P=10:1) compared to 17 mg/(g DW) reached at 1% CO2 and N:P=16:1. Regarding the nutrient ratios, the higher nutrient ratio favored pig-ment production at 1% CO2, while the reverse effect was observed at 2.5% CO2. Protein content showed no significant advantage between experiments, with small fluctuations within each experi-ment. Carbohydrate content reflects culture stress and was higher at lower N (N:P=10:1) when 2.5% CO2 was provided, most likely due to nutrient limitation. In 1% CO2, available carbon is reduced so overall carbohydrate content was lower, generally remaining below 15% mg (w/w).
Overall, the findings of this work highlight the efficiency of the proposed cyanobacteria-bacteria consortium in CO2 biofixation and simultaneous wastewater treatment in an environmentally friendly manner. While both CO2 concentrations tested were capable of reaching effective carbon fixation lev-els and wastewater remediation, the systems supplied with 2.5% CO2 showed better overall perfor-mance in both N:P ratios, offering higher CO2 fixation rates while also reducing d-COD below the legis-lation limit of 125 mg L-1. Simultaneously, the high biomass productivity rich in proteins, lipids, and car-bohydrates, allows for its use in applications such as biofuels, animal feed and various added value bi-oproducts. These findings support the feasibility of integrating cyanobacteria-based cultivation systems into industrial wastewater treatment units to sustainably perform wastewater treatment alongside efficient carbon capture and biomass utilization.
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Keywords
Wastewater treatment, Brewery wastewater, Cyanobacteria-bacteria culture