Succession of biofilm communities responsible for biofouling of membrane bioreactors (MBRs)

© 2017 Luo et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Biofilm formation is one of the main factors associated with membrane biofouling in membrane bioreactors (MBRs). As such, it is important to identify the responsible organisms to develop targeted strategies to control biofouling. This study investigated the composition and changes in the microbial communities fouling MBR membranes over time and correlated those changes with an increase in transmembrane pressure (TMP). Based on qPCR data, bacteria were the dominant taxa of the biofilm (92.9–98.4%) relative to fungi (1.5–6.9%) and archaea (0.03–0.07%). NMDS analysis indicated that during the initial stages of operation, the biofilm communities were indistinguishable from those found in the sludge. However, the biofilm community significantly diverged from the sludge over time and ultimately showed a unique biofilm profile. This suggested that there was strong selection for a group of organisms that were biofilm specialists. This pattern of succession and selection was correlated with the rapid increase in TMP, where bacteria including Rhodospirillales, Sphingomonadales and Rhizobiales dominated the biofilm at this time. While most of the identified fungal OTUs matched Candida sp., the majority of fungal communities were unclassified by 18S rRNA gene sequencing. Collectively, the data suggests that bacteria, primarily, along with fungi may play an important role in the rapid TMP increase and loss of system performance

A conceptual design of spacers with hairy structures for membrane processes

The development of membrane technology requires spacers that can significantly enhance the mass-transfer rate while avoiding a severe pressure drop across the membrane module. A potential solution to this challenge is to introduce some flexible and dynamic structures into the spacer mesh. The current work was motivated to explore a conceptual design of spacers with hairy structures. The hairy structures were simulated using highly flexible nylon fibers that were fixed on a well-designed framework. The effects of fiber asymmetry and spacing on the vibrations were discussed in terms of the observations via a high speed camera. A variety of spacer prototypes were employed in a forward osmosis process to examine the performance of the hairy structures. The experimental results indicate that fiber vibrations could have a great impact on the mass transfer in the vicinity of the membrane surface and enhance the filtration flux (up to ~20%). This fundamental study not only provides insight into the mechanisms underlying the complex fiber-flow interactions but also charts the direction for future hairy spacer design

The application of nitric oxide to control biofouling of membrane bioreactors

© 2015 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology. A novel strategy to control membrane bioreactor (MBR) biofouling using the nitric oxide (NO) donor compound PROLI NONOate was examined. When the biofilm was pre-established on membranes at transmembrane pressure (TMP) of 88-90kPa, backwashing of the membrane module with 80μM PROLI NONOate for 45min once daily for 37 days reduced the fouling resistance (Rf) by 56%. Similarly, a daily, 1h exposure of the membrane to 80μM PROLI NONOate from the commencement of MBR operation for 85 days resulted in reduction of the TMP and Rf by 32.3% and 28.2%. The microbial community in the control MBR was observed to change from days 71 to 85, which correlates with the rapid TMP increase. Interestingly, NO-treated biofilms at 85 days had a higher similarity with the control biofilms at 71 days relative to the control biofilms at 85 days, indicating that the NO treatment delayed the development of biofilm bacterial community. Despite this difference, sequence analysis indicated that NO treatment did not result in a significant shift in the dominant fouling species. Confocal microscopy revealed that the biomass of biopolymers and microorganisms in biofilms were all reduced on the PROLI NONOate-treated membranes, where there were reductions of 37.7% for proteins and 66.7% for microbial cells, which correlates with the reduction in TMP. These results suggest that NO treatment could be a promising strategy to control biofouling in MBRs

The role of membrane technology in sustainable decentralized wastewater systems

Decentralized wastewater treatment has the potential to provide sanitation that meets criteria for sustainable urban water management in a manner that is less resource intensive and more cost effective than centralized approaches. It can facilitate water reuse and nutrient recovery and can potentially reduce the ecological risks of wastewater system failure and the community health risk in a wastewater reuse scheme. This paper examines the potential role of membrane technology in sustainable decentralized sanitation. It is argued that the combination of membrane technology within decentralized systems can satisfy many of the criteria for sustainable urban water management. In particular, the role of membranes as a dependable barrier in the wastewater treatment process can increase system reliability as well as lowering the latent risks due to wastewater reuse. The modular nature of membranes will allow plant size to range from single dwellings, through clusters to suburb size. It is concluded that realization of the potential for membrane-based technologies in decentralized wastewater treatment will require some progress both technically and institutionally. The areas where advances are necessary are outlined. © IWA Publishing 2005

Production of sinterable uranium dioxide from ammonium diuranate, Part 1 - a review of gas/solid contractors.

This report reviews the performance characteristics of a variety of contactors used for gas/solid reactions. A critical assessment is made of their suitability for the conversion of ammonium diuranate to sinterable uranium dioxide in terms of their heat transfer and powder handling characteristics, and the capability of obtaining a high conversion efficiency consistent with continuous operation. The pulsed fluidised bed is judged to be particularly promising for future development

Production of sinterable uranium dioxide from ammonium diuranate in a pulsed fluidised bed reactor - interim report.

Results and operational experience are reported for the batchwise production of uranium dioxide for ammonium diuranate in a pulsed fluidised bed reactor. Alternative proposals for batch/continuous operation are assessed and compared with continuous operation. The future development programme is outlined

Production of sinterable uranium dioxide from ammonium diuranate, Part 3 - continuous production in a pulsed fluidised bed reactor.

The development of a 0.13 m diameter pulsed fluidised bed reactor for the continuous production of sinterable uranium dioxide from ammonium diuranate is described. Calcination-reduction at 670 to 680 ºC produced powders with surface areas of 4 to 6 m2 g-1 giving pellet densities in excess of 10.6 g cm-3. Sinterability was relatively insensitive to changes in operating conditions, provided the availability of hydrogen was adequate, for gas flow rates in the range 0.95 to 1.4 ℓ s-1, pulse frequencies of 0.5 and 0.75 Hz and mean residence times of the solids from 0.6 to 1.4 hours. Sinterability was shown to be improved either by use of higher input concentrations, or by use of a secondary flow of hydrogen (about 5 per cent of input) fed into the powder collection system and flowing countercurrent to the U02 product. The maximum throughput of 17 kg U02 h-1 (0.6 hours mean residence time) required only 120 per cent of the stoichiometric requirement at an input concentration of 50 vol.% with secondary hydrogen flow. Results are given for studies of the kinetics of reduction of calcined ammonium diuranate in hydrogen and the residence time distribution of solids in a pulsed fluidised bed. Estimates based on these data suggested that the overall conversion of ammonium diuranate to uranium dioxide in the continuously operated pulsed fluidised bed reactor was in excess of 99 per cent. Continuous stabilisation of the U02 product was demonstrated at 12 kg h-1 of U02, in a 0.15 m diameter glass stabiliser, using 10 vol.% air in nitrogen and a temperature of about 50ºC

Production of sinterable uranium dioxide from ammonium diuranate, Part 2 - batch production in a pulsed fluidised bed reactor - interim report

Results and operational experience are reported for the batchwise production of uranium dioxide from amanium diuranate in a pulsed fluidised bed reactor. Alternative proposals for the batch/continous operation are assessed and compared with continuous operation. The future development programme is outlined

Honeycomb structured porous films prepared from carbohydrate based polymers synthesized via the RAFT process

Carbohydrate based polystyrene was synthesized via RAFT polymerization. The RAFT agents were based on alpha-D-glucose, beta-cyclodextrin and modified cellulose to obtain polystyrene with a polar head or polystyrene with a star or comb structure, respectively. The polymerizations were carried out in different solvents. The molecular weight of the linear polymer was found to develop according to the expected values, but the synthesis of the carbohydrate based polymers was influenced by other parameters. The molecular weight for the star polymer synthesis showed a pronounced deviation due to the reduced accessibility of the RAFT group at higher conversions of the polymerization. Films of these carbohydrate containing polystyrenes were cast from carbon disulfide and dichloromethane producing highly regular honeycomb structured films with pore diameters between 0.5 and 4 mum. The pore size was influenced by the polymers used as well as by the casting conditions

Colloidal interactions and fouling of NF and RO membranes: A review

Colloids are fine particles whose characteristic size falls within the rough size range of 1-1000 nm. In pressure-driven membrane systems, these fine particles have a strong tendency to foul the membranes, causing a significant loss in water permeability and often a deteriorated product water quality. There have been a large number of systematic studies on colloidal fouling of reverse osmosis (RO) and nanofiltration (NF) membranes in the last three decades, and the understanding of colloidal fouling has been significantly advanced. The current paper reviews the mechanisms and factors controlling colloidal fouling of both RO and NF membranes. Major colloidal foulants (including both rigid inorganic colloids and organic macromolecules) and their properties are summarized. The deposition of such colloidal particles on an RO or NF membrane forms a cake layer, which can adversely affect the membrane flux due to 1) the cake layer hydraulic resistance and/or 2) the cake-enhanced osmotic pressure. The effects of feedwater compositions, membrane properties, and hydrodynamic conditions are discussed in detail for inorganic colloids, natural organic matter, polysaccharides, and proteins. In general, these effects can be readily explained by considering the mass transfer near the membrane surface and the colloid-membrane (or colloid-colloid) interaction. The critical flux and limiting flux concepts, originally developed for colloidal fouling of porous membranes, are also applicable to RO and NF membranes. For small colloids (diameter ≪ 100 nm), the limiting flux can result from two different mechanisms: 1) the diffusion-solubility (gel formation) controlled mechanism and 2) the surface interaction controlled mechanism. The former mechanism probably dominates for concentrated solutions, while the latter mechanism may be more important for dilute solutions. Future research needs on RO and NF colloidal fouling are also identified in the current paper. © 2010 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex