Impact of Organic Loading Rate on Performance and Methanogenic Microbial Communities of a Fixed-Bed Anaerobic Reactor at 4 °C

Abstract

We investigated the feasibility of producing biogas in a fixed-bed anaerobic reactor at 4 °C with a gradual increase in organic loading rate (OLR). Reactor efficiency was highest when OLR was 4.33 kg/m3·d, whereas the reactor acidification occurred when OLR was 4.67 kg/m3·d. The values of methane content, biogas production, chemical oxygen demand (COD) removal rate, biogas production rate, acetic acid content, and propionic acid content were 69.3%, 5.33 L, 59.8%, 1.03 L/OLR, 0.17 g/L, and 1.15 g/L, respectively. The pH was stable and ranged from 7.2 to 6.8 when the reactor was operating at 4 °C during OLR increase. The 16S rRNA gene analysis revealed that the dominant archaea were Methanosaetaceae at 30 °C. At 4 °C, the dominant archaea were Methanomicrobiales, which were more abundant in adhering sludge compared to settled sludge. In conclusion, operating a fixed-bed anaerobic reactor at psychrophilic temperatures is more suitable.

Impact of Temperature on the Performance and Character of the Methanogenic Community of a Fixed-Bed Anaerobic Reactor at Psychrophilic Temperature

“…Therefore, compared with other wastewaters (e.g., trichloroethylene wastewater and synthetic wastewater), molasses wastewater is more difficult to treat and causes operational issues for reactors performing anaerobic biological treatment. In previous research, we confirmed that fixed-bed anaerobic reactors had impact resistance and high methane content when used to treat molasses wastewater at low temperatures [14,18,22]. However, no study has evaluated fix-bed reactor operation at decreasing temperatures in order to assess the microbial community for molasses wastewater treatment at low temperatures.…”

“…The experiments were divided into three operation phases (Table 1), which were characterized by changes in temperature and COD. In order to verify the operating temperature threshold and the methanomicrobiale colonization of the carbon-fiber carrier fixed-bed reactor operating at low temperatures, we confirmed that the fixed-bed reactor could be operated at the low temperatures of 5 • C and 4 • C [14,18], but whether this is the temperature threshold for low-temperature operation has not been confirmed. Therefore, we selected 4 reactors with exactly the same specifications and types for this study.…”

“…Domestic wastewater in Europe and the USA has an annual mean temperature of approximately 18 • C on average, and the common occurrence of domestic wastewater temperatures below 20 • C, which may occur in winter months, has greatly increased the interest in psychrophilic anaerobic treatment of cold wastewater [7][8][9]. Previous research confirmed that it is feasible to treat wastewater at low temperatures, and the anaerobic digester energy input and associated operating costs can be significantly reduced by treating wastewater at the discharge temperature [10][11][12][13][14]. Low-temperature bioreactors have reduced heating requirements and thus provide cost savings in comparison with more costly mesophilic and thermophilic bioreactors that are used for the treatment of sub-ambient waste streams.…”

“…Molasses is commonly used to produce amino acids, ethanol, and enzymes. The COD concentration of molasses is high (50,000-100,000 mg COD/L), and it has a low pH value (4-5) [14]. Therefore, compared with other wastewaters (e.g., trichloroethylene wastewater and synthetic wastewater), molasses wastewater is more difficult to treat and causes operational issues for reactors performing anaerobic biological treatment.…”

High-Solid Anaerobic Digestion: Reviewing Strategies for Increasing Reactor Performance

“…This is probably explained by the well-established consortium attained after an extended operation time in industrial operating reactors [147]. Zhao et al [148] studied digestion performance at 4 • C, indicating that the maximum treatment capacity was set at 4.33 g VS/Lr d of OLR. Therefore, low-temperature operating digestion systems may become a low-cost solution for the operation of decentralized reactors with a treatment capacity equivalent to that of more complex mesophilic and thermophilic reactors.…”