Abstract
We examined the effect of ammonium and temperature on methane production in high rate upflow anaerobic sludge bed reactors treating pig manure supernatant. We operated four reactors at two ammonium concentrations (‘low’ at 1.9, ‘high’ at 3.7 g L−1, termed LA and HA reactors, respectively) and at variable temperatures over 358 days. Archaeal and bacterial communities were characterized by Illumina sequencing of 16S rRNA amplicons. Ammonium was a major selective factor for bacterial and archaeal community structure. After ~200 days of adaptation to high ammonium levels, acetate and propionate removal and methane production improved substantially in HA reactors. Aceticlastic Methanosaeta was abundant and positively correlated to methane yield in the HA reactors, whereas Methanosarcina was more abundant in LA reactors. Furthermore, a group of monophyletic OTUs that was related to Thaumarchaeota in phylogenetic analysis was highly abundant in the archaeal communities, particularly in the HA reactors. The most abundant bacterial OTU in LA reactors, representing Syntrophomonadaceae, was also positively correlated to methane yield in the HA reactors, indicating its importance in methane production under ammonia stress. In conclusion, efficient methane production, involving aceticlastic methanogenesis by Methanosaeta took place in the reactors at free ammonia concentrations as high as 1 g L−1.
Highlights
On-farm anaerobic digestion has been suggested as an attractive option for manure treatment, as it reduces greenhouse gas emissions from the agricultural sector, it produces high quality biogas and reduces other environmental impacts such as water pollution and odour emissions[1]
We examined how temperature and ammonia concentrations affected the performance of high rate upflow anaerobic sludge bed (UASB) reactors treating pig manure slurry supernatant
Addition of urea to the feed for the HA reactors from day 69 resulted in a 2-fold increase in total ammonia nitrogen (TAN) and 20-fold increase in the free ammonia nitrogen (FAN) concentrations into the HA reactors compared to the LA reactors (Table 1)
Summary
On-farm anaerobic digestion has been suggested as an attractive option for manure treatment, as it reduces greenhouse gas emissions from the agricultural sector, it produces high quality biogas and reduces other environmental impacts such as water pollution and odour emissions[1]. A few SAOBs have been isolated and characterized so far, including two mesophilic bacteria (Clostridium ultunense[12] and Syntrophaceticus schinkii13), the thermotolerant Tepidanaerobacter acetatoxydans[14] and three thermophilic SAOBs (strain AOR15, Thermacetogenium phaeum[16,17] and Thermotoga lettingae[18]) The significance of these strains in methane producing anaerobic communities is not well described, and characterization of microbial communities by metagenomic approaches has suggested that other SAOBs may exist in anaerobic biogas reactors[19,20]. We examined how temperature and ammonia concentrations affected the performance of high rate upflow anaerobic sludge bed (UASB) reactors treating pig manure slurry supernatant. We characterized the bacterial and archaeal communities using Illumina sequencing of 16S rDNA amplicons, and aimed at identifying key players in methanogenesis at high ammonia concentrations
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