Anaerobic treatment of post-hydrothermal liquefaction wastewater from >i<Spirulina>/i< associated with microaeration and photocatalysis
Author(s)
Date Issued
20 de diciembre de 2021
Type
Thesis
Abstract
Hydrothermal liquefaction is a thermochemical process that is being used for the conversion of wet feedstocks into bio-crude oil. During the hydrothermal conversion of microalgae, wastewater (PHWW) with an elevated organic and aromatic content is also produced. Although anaerobic digestion can be applied as a stage of energy recovery, the application of other methods that could enhance PHWW treatment is necessary. Firstly, the anaerobic treatment of PHWW was investigated in a sequencing batch process. The effect of increasing organic matter concentrations, measured as chemical oxygen demand (COD), was assessed (1.6, 2.4, 3.2, 4, and 4.8 gCOD.L -1 ). COD removal efficiencies and CH4 yields ranged from 53% to 49% and from 180 to 158 NmL.gCODadd -1 , respectively, for influent COD values up to 3.2 g.L -1 . Higher organic loads presented a drop in COD removal, CH4 yield, and a volatile fatty acids accumulation. Regarding the kinetic evaluation, the experimental data were adjusted to the modified Haldane model, observing a strong inhibition at COD concentrations above 3.7 gCOD.L -1 . Trichococcus, Aminobacteria, and Methanosarcina were the most representative microorganisms after biomass acclimation to PHWW. In second place, the effect of intermittent aeration in the anaerobic digestion of PHWW was assessed in two sequencing batch processes, R1 full anaerobic and R2 anaerobic-aerated. Three increasing organic matter were investigated (1.6, 3.2, and 4.8 gCOD.L -1 ). Results from R2 presented higher COD removal efficiencies for each condition evaluated. Moreover, metabolites accumulation observed in R1 was minimized in R2, and phenolic removal was also improved. On the other hand, CH4 production was reduced by 45% due to oxygen availability. Aerobic microorganisms capable of degrading aromatic compounds were enriched in R2. Finally, photocatalysis as a posttreatment of anaerobically digested PHWW was investigated. Removal efficiencies reached 50% for COD, 83% for phenolic compounds, and 95% for color, under optimum conditions of pH (9.6) and H2O2 addition (3.55g.L -1 ). Ecotoxicity assays with Daphnia similis and Eruca sativa Mill resulted in treated PHWW not negatively influenced by photocatalysis.
Subjects