Soluble Microbial Products In Membrane Bioreactor Research Articles

Characteristics of the sludge filterability and microbial composition in PAC hybrid MBR: Effect of PAC replenishment ratio

Periodic withdrawal and replenishment of powdered activated carbon (PAC) hybrid membrane bioreactor (MBR) is required for stable performance. The influence of the replenishment of powdered activated carbon (PAC) on sludge filterability and microbial community in hybrid MBRs was investigated. Results showed that the removal of organic matter and nitrogen were not significantly affected by the PAC refreshment, while soluble microbial products (SMP) concentration decreased and extracellular polymeric substance (EPS) increased with increasing PAC replacement ratio. MBR system with PAC replenishment exhibited low fouling propensity and prolonged filtration agreed well with fouling rate and resistance analysis. Molecular weight distribution of SMP in MBR confirmed the synergistic effects of PAC adsorption/biodegradation and membrane interception on organics removal. Microbial activity was positive associated with the PAC replenishment ratio. Moreover, the high-throughput sequencing indicated that due to fresh PAC added, the increased abundance of Proteobacteria, Bacteroidetes and Nitrospira guaranteed the pollutant removal, and the membrane fouling caused by Planctomycetes and Betaproteobacteria decreased. An optimal PAC replenishment ratio at 1.67% achieved the effective membrane fouling mitigation and enhanced dominant bacterial structure. PAC refreshment is considered to be a promising way to advance the application of MBR.

Effects of micro-organism growth phase on the accumulation and characteristics of soluble microbial products in MBR

AbstractSoluble microbial products (SMP) have been demonstrated as a primary obstacle for the widespread application of membrane bioreactor (MBR). This study has investigated the effects of micro-organism growth phase (MGPs) on the accumulation and characteristics of SMP in MBR. The results showed that there were three MGPs in the experiment, including exponential growth phase (EGP), deceleration growth phase (DGP), and stationary growth phase (SGP), respectively. Polysaccharides and proteins in SMP were steadily increased in the EGP. While in the DGP, the SMP were increased firstly and then decreased sharply. Finally, the concentrations of SMP maintained at a low steady level in the SGP. Furthermore, the biomass associated products (BAP) batch experiment showed that the production potential of SMP was the largest in the DGP. The percentage of SMP (>30 kDa) was remarkably increased, then dropped due to abruptly decreasing production potential of BAP and degradation by acclimated micro-organisms. The resul...

Changes in characteristics of soluble microbial products in membrane bioreactors associated with different solid retention times: Relation to membrane fouling

A membrane bioreactor (MBR) is a promising wastewater treatment technology, but there is a need for efficient control of membrane fouling, which increases operational and maintenance costs. Soluble microbial products (SMP) have been reported to act as major foulants in the operation of MBRs used for wastewater treatment. In this study, SMP in MBRs operated with different sludge retention times (SRTs) were investigated by means of various analytical techniques and their relations to the evolution of membrane fouling were considered. Bench-scale filtration experiments were carried out in a laboratory with synthetic wastewater to eliminate fluctuations that would occur with the use of real wastewater and that would lead to fluctuations in compositions of SMP. Three identical submerged MBRs were operated for about 50 days under the same conditions except for SRT (17, 51 and 102 days). Accumulation of SMP in the MBRs estimated by conventional analytical methods (i.e., the phenol–sulfuric acid method and the Lowry method) was significant in the cases of short SRTs. However, the degrees of membrane fouling in the MBRs were not directly related to the concentrations of SMP in the reactors estimated by the conventional analytical methods. Non-conventional analytical methods such as excitation-emission matrix (EEM) fluorescence spectroscopy revealed that characteristics of SMP in the three reactors considerably differed depending on SRT. Foulants were extracted from the fouled membranes at the end of the operation and were compared with SMP in each MBR. It was clearly shown that characteristics of the foulants were different depending on SRT, and similarities between SMP and the extracted foulants were recognized in each MBR on the basis of results of EEM measurements. However, such similarities were not found on the basis of results obtained by using the conventional methods for analysis of SMP. The results of this study suggest that the use of conventional methods for analysis of SMP is not appropriate for investigation of membrane fouling in MBRs.