Anti-biofouling performance and microbial communities of an integrated fixed-film activated sludge membrane bioreactor with a fibrous carrier material: Pilot-scale demonstration.

Widespread use of membrane bioreactors for high-performance wastewater treatment depends on the prevention of biofouling during membrane filtration, which can reduce operating costs. Biofouling is usually prevented using mechanical and chemical membrane treatment methods, which can be time-consuming and expensive. In this study, we developed bio-capsules as a fluidizing carrier material in an integrated fixed-film activated sludge membrane bioreactor (IFAS-MBR). The bio-capsules were prepared from moniliform polyvinylidene chloride fibrous balls enclosed in a spherical plastic basket, and could harbor protozoa and metazoa. A pilot-scale anoxic-oxic IFAS-MBR system with a total volume of 132 m3 was operated to remove organic carbon and nitrogen from municipal wastewater at a high permeate flux (0.84 m3/m2/day). The efficacy of the bio-capsules and the prokaryotic/eukaryotic community structures in the system were investigated. After operation for 1 year, the system demonstrated stable removal of organic carbon (76.0 % ± 15.5 % as total organic carbon, 93.1 ± 5.3 % as BOD, and 88.5 ± 5.2 % as CODMn) and nitrogen (71.3 % ± 9.3 %) despite fluctuations in the influent concentrations. Increases in transmembrane pressure (TMP) were retarded from its increase rates from 0.56 kPa/day to 0.149-0.224 kPa/day by the bio-capsules, and the TMP was kept constant at around 20 kPa throughout the operational period. High-throughput sequencing of 16S rRNA gene amplicons showed that the prokaryotic family Pirellulaceae was metabolically active and correlated with the TMP. According to the 18S rRNA gene sequencing, the eukaryotic metazoan Bdelloidea was more abundant in the bio-capsules than in activated sludge, which was supported by microscopic observations. These results suggest that the application of bio-capsules prevents increases in the TMP by harboring the procaryotes and eukaryotes responsible for biofouling mitigation in the IFAS-MBR system.

Biofouling control of a forward osmosis membrane during single-pass pre-concentration of wastewater.

Pre-concentration of wastewater using a forward osmosis (FO) membrane prior to processing by an anaerobic digester can enhance biogas production. However, biofouling caused by microbes in wastewater remains a challenge. The study aimed to evaluate the efficacy of chloramination in mitigating the biofouling of an FO membrane during a single-pass concentration of primary wastewater effluent. Pre-disinfection at a chloramine dose of 22-121 mg/L successfully alleviated membrane fouling. Bacterial cell counts in the feed and concentrate showed that most of the bacterial cells in the wastewater were trapped on the membrane surface or spacer. The FO membrane surfaces in non-chloraminated/chloraminated systems were fully-covered by intact/damaged bacterial cells, respectively, indicating that chloramination effectively mitigated biofouling. However, due to high permeate-recovery and low cross-flow velocity in a single-pass concentration process, organic fouling on the membrane surface (and possibly on the interior wall of the membrane-pores) appeared to cause a gradual reduction in permeate-flux. This study demonstrated successful biofouling control using chloramination during a single-pass and high-recovery pre-concentration of primary wastewater effluent.

Irreversible membrane fouling during ultrafiltration of surface water.

For more efficient use of membranes, the control of irreversible membrane fouling, which can be defined as fouling requiring chemical reagents to be mitigated, is of importance. In this study, irreversible fouling caused by constituents in surface water was investigated, based on a long-term pilot scale study. The membrane employed was a low-pressure hydrophobic ultrafiltration (UF) membrane made of polysulfone and having a molecular weight cutoff of 750,000 Da. Various chemical reagents were examined to overcome the irreversible fouling that had developed through 5 months of continuous filtration. Among the tested cleaning reagents, alkaline (NaOH) and oxidizing reagent (NaClO) showed good performance in the restoration of membrane permeability, which implied that organic matter played an important role in the development of the irreversible fouling in this study. Chemical analysis, adsorptive fractionation methods, fluorescence excitation-emission matrix (EEM) and Fourie-transformed infra-red (FTIR) spectra analysis were applied to elucidate which fraction of organic matter caused the irreversible fouling. All of the analysis indicated that polysaccharide-like organic matter was responsible for the evolution of the irreversible fouling. In addition to organic matter, presumably iron and manganese also contributed to the irreversible fouling to some extent.