Transition of microbial community structures after development of membrane fouling in membrane bioreactors (MBRs)

Yuya Sato,Tomoyuki Hori,Tomohiro Inaba,Tomo Aoyagi,Hiroshi Habe,Atsushi Ogata,Hidenobu Aizawa,Yan-Jie Zhao

doi:10.1186/s13568-020-0959-2

Yuya Sato, Tomoyuki Hori + Show 6 more

Open Access

https://doi.org/10.1186/s13568-020-0959-2

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Abstract

Although membrane fouling is a major issue when operating membrane bioreactors (MBRs), information regarding MBR performance and the sludge microbiome after the development of fouling remains limited. For the present study, two MBRs were operated for approximately 1 month under conditions of membrane fouling to investigate the effects of highly stressed environments on the sludge microbiome. After the development of fouling, a Collimonas-related operational taxonomic unit (OTU) was highly dominant in both reactors (relative abundances were ⁓ 63%) and this predomination caused a precipitous decline in the diversity indices of the sludge microbiomes. Because the excessive predomination by limited numbers of OTUs can lead to reductions in the adaptability to environmental changes, monitoring microbial diversity may be a valuable indicator for maintaining the robustness of a sludge microbiome. While, the decrease in the abundance of the Collimonas-related OTU resulted in the predomination of distinct microorganisms in each of the reactors despite being operated under the same conditions; this finding indicates existence of strong pressure to perturb the microbiomes. Detailed analyses suggested that the availability of terminal electron acceptors and competitive interactions between microbes via the secretion of extracellular proteins appeared to differentiate the structures of the respective microbial communities. During the extracellular proteins were secreted in the sludge, considerable portion of microbes were dead and large amounts of biomolecules seemed to be released; resultantly facilitated the predomination of fermentative anaerobes in one reactor as they use organic substances but not inorganic terminal electron acceptors to generate ATP under anaerobic conditions.

Highlights

Activated sludge has been used around the world for wastewater treatment for over 100 years and represents an important and familiar biotechnology in modern societies (Li et al 2015; Sheik et al 2014)
Under the high organic loading conditions after the development of membrane fouling, dissolved oxygen (DO) level in the sludge was low (Fig. 1f ), even though the activated sludge was continuously aerated throughout the operation
This indicates that there was a high demand for electron acceptors in the activated sludge under high organic loading conditions (Navarro et al 2016; Sato et al 2019), while electron donors were abundantly available

Summary

Introduction

Activated sludge has been used around the world for wastewater treatment for over 100 years and represents an important and familiar biotechnology in modern societies (Li et al 2015; Sheik et al 2014). It can be predicted that the activated sludge microorganisms would be highly stressed during the operation of an MBR with a fouled membrane because undegraded organic compounds in wastewater can remain inside the sludge for long periods due to a reduced effluent rate and increases in the organic loading rate within the system (Inaba et al 2018). Together, these factors may result in strong pressure that can perturb microbial populations in the activated sludge (Sato et al 2016b, c; Vuono et al 2015)

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