Abstract
To determine the effects of a gradual temperature decrease on reactor performance and the microbial community, four fixed-bed reactors that were packed with a biofilm carrier were operated for 217 days. The temperature of the reactors was decreased from 30 °C to 3 °C. The reactors initially soured at 3 °C and recovered when they were returned to 4 °C, as indicated by the stabilization of biogas production, methane production, VFA concentration, pH, and the COD removal rate. Our results also revealed that methanomicrobiales were the dominant methanogen, the concentration of the 16S rRNA gene in the carbon-fiber carrier sludge exceeded the same gene concentration in the deposited sludge, and that the carbon-fiber carrier played an important role in methanomicrobiale colonization at low temperatures. We suggest that 4 °C is the low-temperature threshold for optimal reactor performance.
Highlights
Anaerobic digestion, which simultaneously produces biogas for use as fuel and reduces pollution, is an effective method for reducing biodegradable organic matter in wastewater [1].Compared with traditional wastewater treatment methods, anaerobic digestion has the advantages of higher organic load capacity, reduced reactor volume, significantly less sludge generation, and relatively low costs of operation and maintenance [2,3].Temperature has a strong effect on the efficiency of anaerobic digestion
The biogas production rate gradually decreased as the temperature was reduced, which indicated that the microbial community of the fixed-bed reactor was shocked or stressed by the decrease in temperature, and the community later adapted, after which the level of biogas production stabilized
The results showed that methanomicrobiales had a strong colony capacity under 10 °C and 4 °C, and it was confirmed that the peak biogas production of the fixed-bed carbon-fiber carrier rea fixed-bed anaerobic reactor was mainly due to the following: (1) methanomicrobiales could attach to the carbon-fiber carrier; (2) hydrogenotrophic methanogenic activity was elevated; and (3) a stabile microbial system was achieved [18,30]
Summary
Anaerobic digestion, which simultaneously produces biogas for use as fuel and reduces pollution, is an effective method for reducing biodegradable organic matter in wastewater [1].Compared with traditional wastewater treatment methods, anaerobic digestion has the advantages of higher organic load capacity, reduced reactor volume, significantly less sludge generation, and relatively low costs of operation and maintenance [2,3].Temperature has a strong effect on the efficiency of anaerobic digestion. Previous studies have demonstrated successful wastewater treatment via anaerobic digestion, the typical operation temperatures for full-scale anaerobic digesters are thermophilic (45–65 ◦ C) or mesophilic (20–45 ◦ C) [4,5]. The requirement of these relatively warm temperatures is significant because much of the industrial effluent from wastewater treatment plants is discharged at ≤10 ◦ C in the northern, colder regions of China, where the freezing period lasts for 3–6 months, and the average temperature of wastewater is 5–9 ◦ C [6]. Low-temperature bioreactors have reduced heating requirements and provide cost savings in comparison with more costly mesophilic and thermophilic bioreactors that are used for the treatment of sub-ambient waste streams
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