An Investigation of Temperature Downshift Influences on Anaerobic Digestion in the Treatment of Municipal Wastewater Sludge

Abstract

Operating temperature significantly affects biogas output, process stability, and microbial communities involved in anaerobic digestion. There are several unanswered questions regarding how microbial communities adapt in correlation with biogas production performance, especially when a digester fails to maintain thermophilic conditions. In this study, long-term lab-scale anaerobic digestion was carried out using two fed-batch reactors at 55°C, with subsequent decreases in temperature to 48°C and 45°C. Within the first month of incubation, methane (CH 4 ) production increased by approximately 11.18% following a reduction in temperature from 55°C to 48°C. However, the methane production decreased by 33% after the temperature was downshifted to 45°C. Despite the difference in methane production, the thermophilic methanogen population in both reactors declined significantly in the first month with a temperature decrease. After two months of incubation, these methanogenic communities recovered faster at 48°C than at 45°C, which was highlighted by the rapid colonization of Methanosaeta, Methanobacterium, and Methanothermobacter. Notably, Methanosaeta was the most abundant methanogen under all temperature conditions, indicating its thermotolerance.

Effects of Temperature Shifts on Microbial Communities and Biogas Production: An In-Depth Comparison

“…Nevertheless, the biogas production decreased after the temperature was gradually downshifted and upshifted within 100 days of incubation for each temperature shift. These findings were supported by previous studies that showed a considerable decrease in biogas production (mainly CH 4 ) when the reactor was given a shock temperature raise [13,20,40] and a temperature decrease [8,41,42], despite the different thermal changing methods and source of inoculum and substrates used in these studies.…”

“…In the AD process, the temperature changes significantly influence the abundance and the species of microbial communities, which may also impact biogas production [7][8][9]. Previously, we attempted to investigate the effect of temperature upshifts [7] and downshifts [8] using a similar method as demonstrated in the present study. However, the microbiome analysis was briefly performed, and the intercorrelation between microbial communities during temperature shift conditions was not widely elucidated.…”

“…The microbial community is a complicated system in which numerous species constantly adapt their ecological features or interactions in response to perturbations or changes in the environment [33]. In the AD process, the temperature changes significantly influence the abundance and the species of microbial communities, which may also impact biogas production [7][8][9]. Previously, we attempted to investigate the effect of temperature upshifts [7] and downshifts [8] using a similar method as demonstrated in the present study.…”

“…Serum vials with a capacity of 160 mL and 72 mL of working volume were used in a fed-batch mode to produce methane [8]. First, 2 mL of substrate and 70 mL of sludge were added to the serum bottles.…”

“…The AD process is vulnerable to perturbation from variations in operational or environmental parameters, such as pH, temperature, organic loading rate (OLR), and hydraulic retention time (HRT), which could disturb the balance of interaction among AD microorganisms and lead to poor reactor performance [4,8]. Among those parameters, the temperature is an essential parameter that heavily influences the metabolic activity of the microbial community involved in methanogenesis and subsequently determines the stability of the community [9].…”