Microwave and ultrasound pre-treatments influence microbial community structure and digester performance in anaerobic digestion of waste activated sludge

Abstract

Comparative analyses of bacterial and archaeal community structures and dynamics in three biogas digesters during start-up and subsequent operation using microwaved, ultrasonicated or untreated waste activated sludge were performed based on 454 pyrosequencing datasets of part of 16S ribosomal RNA sequences and quantitative PCR. The pre-treatment increased the solubility, and thus the availability of the substrate for microbial degradation and significantly affected the succession of the anaerobic community structure over the course of the digestion. Bacteroidetes, Proteobacteria and Firmicutes were the dominant phyla in all digesters throughout operation. Proteobacteria decreased in relative abundance from 23-26 % to 11-13 % in association with enhanced substrate availability. Negative correlations between relative abundance of Alpha-, Beta- and Gammaproteobacteria and the substrate availability and/or biogas production were disclosed in statistical analyses. Clostridiales was the dominant order in Firmicutes, and Clostridiales, Clostridia and Firmicutes relative abundance and richness were shown to positively correlate with substrate availability and biogas generation. Methanogenic communities had a fairly restricted structure, highly dominated by Methanosaeta and Methanobrevibacter phylotypes. A gradual decline in Methanobrevibacter and increased representation of Methanosaeta concilii over time were particularly apparent in the digester receiving untreated waste activated sludge, whereas more diversified archaeal communities were maintained in the pre-treatment digesters. The quantitative PCR analyses revealed a methanogenic community distribution that coincided with the 454 pyrosequencing data.

Comparative Analysis of Bacterial and Archaeal Community Structure in Microwave Pretreated Thermophilic and Mesophilic Anaerobic Digesters Utilizing Mixed Sludge under Organic Overloading

“…The relative abundance of Firmicutes increased from 14.8% ("M1-Control") to 21.6% and 28.4% in the digesters of "M2-80 • C" and "M3-160 • C", respectively. This increase is consistent with previous research conducted by Westerholm et al [18], which was related to a comparative analyses of bacterial and archaeal community dynamics in three mesophilic digesters during start-up and operation using non-irradiated and MW-irradiated WAS. Their results proposed that increased substrate availability induced by MW pretreatment stimulated growth of members within Firmicutes.…”

“…However, to our knowledge, a limited number of studies in the literature reported about the applications of Illumina sequencing technology in anaerobic sludge digestion [14,16,17]. Furthermore, there is very limited knowledge on bacterial and archaeal microbial community structures of anaerobic culture in AD utilizing MW-irradiated sludge [18,19], even though an extensive number of studies have examined the impact of MW pretreatment on sludge disintegration and many conventional operational parameters (e.g., solids destruction, biogas production, and digestate dewaterability) [3,10,13]. In this context, the objective of this study was to explore the impact of MW pretreatment on the relationship between process stability and microbial community structure in the mixed microbial culture samples from thermophilic and mesophilic anaerobic sludge digesters operated at high OLRs.…”

Pre-treatments to enhance the biodegradability of waste activated sludge: Elucidating the rate limiting step

“…For microwaves, applying 2.62 kJ/g TS at a temperature of 80°C and 10 min of application time, and US pretreatment, applying 2.37 kJ/g TS at a temperature < 35°C, it was found that microwaves caused a fourfold to fivefold greater cell death, but this did not result in significantly different biodegradation (Cella et al, 2015). Westerholm et al (2016) made a similar observation. This suggests that both microwave and ultrasonic pre-treatment result in comparable outcomes regarding biodegradation.…”

Genome-Centric Metagenomic Insights into the Impact of Alkaline/Acid and Thermal Sludge Pretreatment on the Microbiome in Digestion Sludge

“…Previous studies based on 16S rRNA gene amplicon sequencing showed that relative abundance of bacteria and archaea in digestion sludge microbiomes generally accounted for > 95% and < 5%, respectively [10,11], being further confirmed by recent metagenomics analyses [9,12]. In view of the bacterial community, Bacteroidetes, Proteobacteria, Spirochaetes and Firmicutes were generally the dominant phyla in sludge digesters, and most of them were fermentative bacteria with high compositional and functional redundancy [9,[13][14][15][16]. By contrast, the slow-growing acetogenic syntrophs and methanogenic archaea in digestion sludge were limited to several lineages [9,11].…”