Effects of Organic-Loading-Rate Reduction on Sludge Biomass and Microbial Community in a Deteriorated Pilot-Scale Membrane Bioreactor

Abstract

The effects of a precipitous decrease in the inlet organic loading rate on sludge reductions and the microbial community in a membrane bioreactor were investigated. The sludge biomass was markedly reduced to 47.4% of the initial concentration (approximately 15,000 mg L−1) within 7 d after the organic loading rate was decreased by half (450 to 225 mg chemical oxygen demand L−1 d−1). An analysis of the microbial community structure using high-throughput sequencing revealed an increase in the abundance of facultative predatory bacteria-related operational taxonomic units as well as microorganisms tolerant to environmental stress belonging to the classes Deinococci and Betaproteobacteria.

A novel culture-independent method to search unknown dominant bacterial groups and its application to microbial analysis of membrane bioreactors

“…2). Our other results, that the composition of overall classes was not changed between sampling periods, was also consistent with those by the other conventional techniques (29, 30) (Fig. 2).…”

“…As a new finding through our method, which has not been reported by the other conventional techniques (23, 26-30, 32), the present results indicated that different homogeneous bacteria were numerically dominant in all three MBRs individually, whose numbers were high enough to affect the performance of the reactor as a single strain. The numerically dominant bacteria in A farm were the homogeneous Arthrobacter genotype and the homogeneous Burkholderi a genotype (AB299593) (Table 1a, 1b), while those in B had the homogeneous Alphaproteobacteria genotype (Table 2a, 2b), and those in C had the homogeneous Betaproteobacteria genotype (Table 3), which occupied a higher ratio among the detected bacteria (Table 6).…”

“…As for conventional activated sludge (CAS) equipped with final settling tanks for solid-liquid separation, the culture independent methods such as clone library sequencing (18), denaturing gradient gel electrophoresis (DGGE) (19, 20), terminal restriction fragment polymorphisms analysis (21-23), fluorescence in situ hybridization (FISH) (24, 25), microarray-based genomics (26), and NGS (27-32) have been used to clarify bacterial relation to their performance. These methods have also been used for membrane bioreactor (MBR), by which solids and liquids could be completely separated through a membrane, was an increasingly implemented technology because of advantages such as reduced excess sludge, higher effluent quality and operation under higher biomass concentrations over CAS (23, 24, 30).…”

“…Most reports have focused mainly on the comparative study of overall microbial composition (23, 26-28, 32), and their changes in the reactor (29, 30). With respect to the well-known specific gene, or bacteria, their numbers were estimated by using real-time PCR (33-35), or by FISH (24, 25).…”

“…There have been few reports to show whether numerically dominant specific microorganisms, which might affect the performance of the reactor, existed in the reactor or not until now (1, 2). Higher biomass in effluent, and higher performance of the reactors (16, 20, 22-24, 27, 28, 30, 31) implied that the unculturability of microorganisms in the reactor might mainly be cased from unknown growth condition, and not by low-abundance and slow growing microorganisms, nor by dormant cell.…”