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.
Highlights
Anaerobic digestion, an effective treatment for wastewater containing biodegradable organic matter, reduces pollution and produces biogas for use as fuel [1,2]
To establish a high organic loading treatment system for industrial molasses wastewater [19,20], we reported the operating parameters and methanogenic community of a fixed-bed reactor at a low temperature of 5–18 ◦ C in a previous study [21]; previous studies have not explored the temperature threshold and the ability of fixed-bed reactors to resist organic loading rate (OLR) under the temperature threshold
Changes in biogas production can reflect altered microbial activity and disorder caused by temperature shock [24]
Summary
An effective treatment for wastewater containing biodegradable organic matter, reduces pollution and produces biogas for use as fuel [1,2]. Many countries have reported using anaerobic digestion for wastewater treatment, including China, the USA, Germany, Austria, Tunisia, Denmark, Italy, Spain, South Africa, and the Netherlands [3,4,5,6,7]. The capacity for wastewater treatment in China lags behind other countries, especially when it comes to energy recovery [8]. Despite this shortfall, clean energy production via anaerobic digestion of treated wastewater has significant potential in China. Mesophilic anaerobic digestion has a higher performance and methane content, but lower pathogen sterilization efficiency. Thermophilic anaerobic digestion has a higher organic loading rate (OLR) and an increased ability to kill pathogens; the methane content is lower even though energy consumption is higher. The energy input required for anaerobic digestion at psychrophilic temperatures is markedly reduced due to the decreased energy needed for heating the bioreactor; the operating costs for anaerobic digestion at psychrophilic temperatures are considerably reduced [2,13]
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