Potential of mechanical cleaning of membranes from a mebrane bioreactor
Brink, P. van den; Vergeldt, F.J. ; As, H. van; Zwijnenburg, A. ; Temmink, H. - \ 2013
Journal of Membrane Science 429 (2013). - ISSN 0376-7388 - p. 259 - 267.
drinking-water - biofilm reactor - critical flux - waste-water - exopolysaccharides - denitrification - precipitation - communities - limitation - bacteria
Several membrane fouling mechanisms have been identified in membrane bioreactors. While cake layers can be removed by physical cleaning, irreversible fouling such as a gel layer is difficult to remove by physical cleaning during filtration. Harsh mechanical cleaning was applied in this study to evaluate how much fouling could be maximally removed and distribution of remaining fouling was investigated. The fouling resistance of several membranes operated at different relatively low fluxes was followed during long term continuous flux operation. Remaining fouling was observed with scanning electron microscopy (SEM) and magnetic resonance imaging (MRI). Dead-end filtration tests with mechanically cleaned membranes showed a decreased permeability. To determine whether bacteria were present in the remaining fouling, oxygen consumption was quantified. Even after harsh mechanical cleaning, membrane samples showed considerable oxygen consumption. SEM did not show fouling inside the membrane. Of several membranes operated for at least 1 year, the permeate side was covered with bacteria and extracellular polymeric substances (EPS). These results show that fouling cannot be removed completely by harsh mechanical cleaning and that both feed and permeate side of the membrane contains biofouling. This fouling on the permeate side should not be neglected when designing membrane cleaning.
Low powdered activated carbon concentrations to improve MBR sludge filterability at high salinity and low temperature
Remy, M.J.J. ; Temmink, B.G. ; Brink, P. van den; Rulkens, W.H. - \ 2011
Desalination 276 (2011)1-3. - ISSN 0011-9164 - p. 403 - 407.
waste-water treatment - membrane bioreactor - critical flux - performance - substances - impact - smp
Previous research has demonstrated that powdered activated carbon (PAC), when applied at very low dosages and long SRTs, reduces membrane fouling in membrane bioreactor (MBRs). This effect was related to stronger flocs which are less sensitive to shear. Low temperature and high salt concentration are known to drastically decrease the filterability of the sludge. In this paper the effect of PAC addition on the robustness of MBR when submitted to these disrupting conditions was investigated. PAC amended sludge showed a higher resistance to high salinity with a lower fouling development and release of foulants. When submitted to lower temperatures, the sludge without PAC showed a clear decrease of the filterability, while the filterability of PAC amended sludge was much less affected. PAC addition does not only improve the filterability in the MBR under normal conditions but also when the sludge is submitted to stress. A low PAC dosage could be used during startup and difficult conditions (e.g. winter) to minimize detrimental effects of such conditions
Effect of free calcium concentration and ionic strength on alginate fouling in cross-flow membrane filtration
Brink, P. van den; Zwijnenburg, A. ; Smith, G. ; Temmink, B.G. ; Loosdrecht, M.C. van - \ 2009
Journal of Membrane Science 345 (2009)1-2. - ISSN 0376-7388 - p. 207 - 216.
extracellular polymeric substances - waste-water treatment - reverse-osmosis membranes - activated-sludge - light-scattering - sodium alginate - physical aspects - bioreactor mbr - critical flux - model
Extracellular polymeric substances (EPS) are generally negatively charged polymers. Membrane fouling in membrane bioreactors (MBRs) by EPS is therefore influenced by the water chemistry of the mixed liquor (calcium concentration, foulant concentration and ionic strength). We used alginate as a model compound to study this fouling in detail. Flux-step experiments were performed with a flat sheet test cell, varying the free calcium concentration, total ionic strength and alginate concentration. There was a strong relation between calcium concentration and fouling rate. An increased ionic strength had no impact on fouling rate in low fouling experiments, but decreased fouling with 66–72% at high fouling conditions. Reversibility of the fouling decreased with increasing calcium concentrations to values as low as 3%. Several fouling mechanisms were identified and the reducing effect of increased ionic strength on alginate fouling was explained by competition for carboxyl groups on the alginate polymer. Further research will focus on the interaction of polysaccharides with other compounds typically present in the MBR supernatant (e.g. proteins, humic acids and sludge particles) and a more detailed analysis of the fouling layer
Bio-layer management in anaerobic membrane bioreactors for wastewater treatment
Jeison, D. ; Lier, J.B. van - \ 2006
Water Science and Technology 54 (2006)2. - ISSN 0273-1223 - p. 81 - 86.
cross-flow microfiltration - critical flux
Membrane separation technology represents an alternative way to achieve biomass retention in anaerobic bioreactors for wastewater treatment. Due to high biomass concentrations of anaerobic reactors, cake formation is likely to represent a major cause of flux decline. In the presented research, experiments are performed on the effect of biomass concentration and level of gas sparging on the hydraulic capacity of a submerged anaerobic membrane bioreactor. Both parameters significantly affected the hydraulic capacity, with biomass exerting the most pronounced effect. After 50 days of continuous operation the critical flux remained virtually unchanged, despite an increase in membrane resistance, suggesting that biomass characteristics and hydraulic conditions determine the bio-layer formation rather than the membrane's fouling level. The concept of bio-layer management is introduced to describe the programmed combination of actions performed in order to control the formation of biomass layer over membranes
On-line cake-layer management by trans-membrane pressure steady state assessment in Anaerobic Membrane Bioreactors for wastewater treatment
Jeison, D. ; Lier, J.B. van - \ 2006
Biochemical Engineering Journal 29 (2006)3. - ISSN 1369-703X - p. 204 - 209.
critical flux - submerged membrane - microfiltration - aeration
Membrane bioreactors have been increasingly applied for wastewater treatment during the last two decades. High energy requirements and membrane capital costs remains as their main drawback. A new strategy of operation is presented based on a continuous critical flux determination, preventing excessive cake-layer accumulation on the membrane surface. Reactor operation is divided in cycles of 500 s filtration followed by a short back-flush of 15 s. If cake-layer formation is detected during continuous operation, a decrease in flux or an increase in cross flow velocity is performed. The proposed approach keeps reactor operation oscillating around the critical flux, minimizing reactor maintenance and maximizing performance. An easy to operate statistical steady state determination tool for the trans-membrane pressure was used to detect cake-layer formation. The developed control approach was tested on two Anaerobic MBRs equipped with submerged membranes. Despite the existence of very different critical fluxes and cake-layer formation characteristics, proposed approach was able to keep pressure increase during filtration cycles below 20 mbar. The developed approach is an efficient tool for on-line control of cake-layer formation over the membranes, changing cross flow velocities by manipulating gas sparging in submerged MBRs