Upflow Anaerobic Sludge Blanket Reactor Codigestion of Algae and Acetate to Produce Methane

Abstract

Algae grown in wastewater treatment lagoons are a potentially important substrate for biofuel production. The feasibility of using upflow anaerobic sludge blanket (UASB) reactors in anaerobic digestion of algae to produce methane was investigated. A favorable carbon to nitrogen (C/N) weight ratio of 21/1 was determined in batch reactor experiments in which the ratio was adjusted by blending algal biomass with sodium acetate as a carbon source. This blend of algae and acetate was used in the feedstock applied to the UASB reactors. Duplicate, 34-L, UASB reactors initially received an organic loading rate (OLR) of 0.9 g chemical oxygen demand (COD)/L.d at a 7.2-day hydraulic retention time (HRT). The OLR was gradually increased to 5.4 g/L.d and the HRT was decreased to 5.5 days resulting in a methane production increase from 247 to 298 mL/g COD biodegraded. The COD removal efficiency was 80% with a biogas methane composition of 90%.

Qualitative Analysis of Microbial Dynamics during Anaerobic Digestion of Microalgal Biomass in a UASB Reactor

“…Results on utilization of a UASB reactor (Supplemental Figure 1) to digest a mixed feedstock of microalgae and sodium acetate are described in a recently published paper by two of this paper's authors [ 40 ] and this research is specifically aimed at results from analysis of microbial community that lead to the process of anaerobic digestion. Briefly, feedstock for the anaerobic digestion was combined with final C/N ratio of 21/1 and biogas production rate was 37 L/day during the last week of reactors operation (days 74–81, Figure 1 ).…”

“…Briefly, feedstock for the anaerobic digestion was combined with final C/N ratio of 21/1 and biogas production rate was 37 L/day during the last week of reactors operation (days 74–81, Figure 1 ). At organic loading rates corresponding to the initial COD of influent 6.25 g/L that was increased to 27.2 g/L, the UASB reactors demonstrated an average COD removal rate of 79% [ 40 ]. Utilization of microalgal biomass and sodium acetate as a feedstock for AD in UASB yielded, on average, 85% methane in the produced biogas [ 40 ].…”

“…At organic loading rates corresponding to the initial COD of influent 6.25 g/L that was increased to 27.2 g/L, the UASB reactors demonstrated an average COD removal rate of 79% [ 40 ]. Utilization of microalgal biomass and sodium acetate as a feedstock for AD in UASB yielded, on average, 85% methane in the produced biogas [ 40 ]. The fraction of methane gas that was produced explicitly from microalgal biomass was calculated from the mass balance of influent COD conversion including production of cell mass [ 41 ].…”

Augmentation of Granular Anaerobic Sludge with Algalytic Bacteria Enhances Methane Production from Microalgal Biomass

“…Bacterial enrichments to isolate potential algalytic bacteria to be used in bioaugmentation were performed on anaerobic sludge from up flow anaerobic sludge blanket (UASB) reactors seeded with anaerobic sediments from the Logan City Wastewater Lagoons (LCWL), Utah [11,12]. Microalgal biomass collected from the surface of the LCWL was supplied to the reactor as a substrate for microbial growth and biogas production.…”

Anaerobic Process

“…Food waste achieved a 73% of anaerobic biodegradability by co-digestion with waste water, and methane production was 2.9 times higher compared to wastewater only. Soboh et al (2016) co-digested algae with sodium acetate to produce methane via UASB reactor. Sodium acetate was used as a carbon source to adjust C/N ratio of substrate to 21/1.…”