# A Cyanobacteria-Based Biofilm System for Advanced Brewery Wastewater Treatment
## 4 Conclusions  
A novel biofilm photob bioreactor was introduced for brewery wastewater post-treatment. By semi-immersing the biomass within the liquid medium, the flat-plate bioreactor design enabled efficient gas transfer and light transmission that enhanced pollutant removal and biomass production. Both growth surface materials tested (glass/polyurethane) managed to achieve complete biomass attachment (>99%); however, the hydrophilic material (glass) performed better at the initial stages of microbial adhesion. This finding suggests that for mature cyanobacterial biofilms, the effect of the EPSs produced prevails over the supporting surface hydrophobicity. Biomass harvesting and dewatering are considered the bottleneck that hinders wastewater treatment using algae/cyanobacteria in full-scale applications. The reactor design suggested by the present study successfully addresses these issues without sacrificing water treatment performance or produced biomass quality. Namely, d-COD removal exceeded 70% for both materials tested, a significant increase compared to suspended cyanobacteria-based systems for brewery wastewater post-treatment. Moreover, due to extensive nitrogen limitation, EPSs retention and efficient irradiation, the harvested biomass accumulated a remarkable carbohydrate content of 61%. The carbohydrate-enriched biofilm could be utilized as a substrate for high yield bioethanol production as well as EPSs extraction. Overall, the results suggest that a flat-plate photob bioreactor design using a hydrophilic supporting material could be a simplistic yet efficient approach for sustainable, low-cost, brewery wastewater post-treatment.  
Conceptualization, K.P.P., C.N.E., and D.V.V.; methodology, K.P.P., C.N.E., and A.G.T.; software, K.P.P. and C.N.E.; validation, K.P.P. and C.N.E.; investigation, K.P.P. and C.N.E.; resources, A.G.T. and D.V.V.; data curation, K.P.P. and C.N.E.; writing--original draft preparation, K.P.P. and C.N.E.; writing--review and editing, K.P.P., C.N.E., A.G.T., and D.V.V.; visualization, K.P.P. and C.N.E.; supervision, D.V.V.; project administration, D.V.V.; funding acquisition, K.P.P., C.N.E., A.G.T., and D.V.V. All authors have read and agreed to the published version of the manuscript.  
This study was financially supported by \"INVALOR: Research Infrastructure for Waste Vaporization and Sustainable Management\" (MIS 5002495) which is implemented under the Action \"Reinforcement of the Research and Innovation Infrastructure\", funded by the Operational Program \"Competitiveness, Entrepreneurship and Innovation\" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund).  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.  
**Acknowledgments:** The authors gratefully acknowledge [PERSON] for identifying the microbial community.  
**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.