Densification of Synechococcus subsalsus biomass by chitosan coagulation for biogas production.

TL;DR: This study evaluates chitosan coagulation for concentrating Synechococcus subsalsus biomass, achieving 30-fold densification, and enabling biogas production with a methane yield of 207 NmL CH4/g CODi, compared to 270 NmL CH4/g CODi from non-densified biomass.

Abstract: ABSTRACTThis study evaluated the coagulation/flocculation process using chitosan as a natural coagulant to concentrate suspensions of the cyanobacterium Synechococcus subsalsus and enable biogas production from concentrated biomass. The chitosan performance was tested and compared with the inorganic ferric chloride (FeCl3) coagulant. Using the liquid fraction of the coagulation/flocculation process in subsequent biomass cultivations proved viable, with similar growths in culture media with up to 80% of the liquid fraction. At pH 6 and 400 mg/L FeCl3, the biomass concentrated almost seven times, increasing the total suspended solids (TSS) of the suspension from 0.4–0.6 g/L to 2.6–4.0 g/L. With 80 mg/L chitosan and pH 7, the TSS concentration attained values in the range of 7.0–9.7 g/L, an increase of more than 30 times, clearly showing that chitosan has a much higher capacity for biomass concentration at a lower concentration. A ratio of 0.3 g chitosan/g dry mass of the biomass was established to reach the maximum densification. The production of methane from chitosan-densified biomass proved to be feasible. Chitosan-densified biomass showed a two-phase cumulative methane production when digested, with slower methane production and 23% lower methane yield after 30 days of digestion (207 NmL CH4/g CODi) compared to the biomass from cultivation (non-densified, 270 NmL CH4/g CODi). However, optimizing the digestion conditions of the densified biomass should increase the methane yield and reduce process time.KEYWORDS: BiogaschitosandensificationharvestingSynechococcus subsalsus AcknowledgmentsThe authors express their gratitude to the National Council for Scientific and Technological Development [grant number 303406/2017-8] and the Carlos Chagas Filho Foundation for Research Support in the State of Rio de Janeiro [grants number E-26/203.010/2018, E-26/210.390/2018] for the financial support. M. C. de Oliveira thanks the financial support of the Human Resources Program in Environmental Engineering from the National Petroleum and Biofuels Agency.Data availability statementThe authors confirm that the data supporting the findings of this study are available within the article.Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico [Grant Number 303406/2017-8]; Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro : [Grant Number E-26/203.010/2018,E-26/210.390/2018].