Time filter

Source Type

Barcelona, Spain

Ferrer O.,Water Technology Center | Lefevre B.,Water Technology Center | Prats G.,Water Technology Center | Bernat X.,Water Technology Center | And 3 more authors.
Desalination and Water Treatment | Year: 2016

Membrane fouling is an inherent phenomenon in ultrafiltration (UF) membrane processes, making it necessary to periodically perform backwashes (BW) and chemical “cleanings in place” (CIP) to restore the initial permeability of the membrane. The objective of this study was (1) to explore systematically the effect of distinct BW-related variables (BW transmembrane pressure, duration, frequency and composition) on the reversibility of UF membrane fouling and on the permeate quality (in terms of total organic carbon, turbidity and UV absorbance) over successive filtration/BW cycles; and (2) to identify which organic fractions were most removed by the membrane and, of these, which were most detached after BW, alkaline and oxidant CIP and acid CIP episodes. For this purpose, a bench-scale outside-in hollow fibre module operated under dead-end filtration mode at constant transmembrane pressure and treating settled water from a drinking water treatment plant was employed. Dissolved organic carbon fractionation was performed by high-performance size-exclusion chromatography. Results showed that, in general, the more intensive the BW was (in terms of high transmembrane pressure, shortened frequency and prolonged duration) the more effective it was in removing fouling from the membrane. Concerning the composition of the water used for the BW, the addition of NaClO led to maximum fouling reversibility, closely followed by the combination of NaOH + NaClO, while citric acid and NaOH contributed little compared to water alone. However, results also showed that irreversible fouling was never completely avoided whatever the BW regime applied, leading to a gradual increase in the total resistance over time. Larger differences in the behaviour of the different organic fractions were observed. UF membrane preferentially retained the heaviest fraction of biopolymers (BP), while the intermediate fraction of humic substances (HS) was removed at a lower percentage and the lighter fractions seemed to entirely pass through the UF membrane. The successive application of BW and CIPs resulted in the detachment from the membrane of a significant percentage of the retained BP, whereas only a modest percentage of the retained HS. © 2015 Balaban Desalination Publications. All rights reserved. Source

Gibert O.,Water Technology Center | Gibert O.,Polytechnic University of Catalonia | Lefevre B.,Water Technology Center | Fernandez M.,Water Technology Center | And 4 more authors.
Water Research | Year: 2013

Under normal operation conditions, granular activated carbon (GAC) employed in drinking water treatment plants (DWTPs) for natural organic matter (NOM) removal can be colonised by microorganisms which can eventually establish active biofilms. The formation of such biofilms can contribute to NOM removal by biodegradation, but also in clogging phenomena that can make necessary more frequent backwashes. Biofilm occurrence and evolution under full-scale-like conditions (i.e. including periodic backwashing) are still uncertain, and GAC filtration is usually operated with a strong empirical component. The aim of the present study was to assess the formation and growth, if any, of biofilm in a periodically backwashed GAC filter. For this purpose, an on-site pilot plant was assembled and operated to closely mimic the GAC filters installed in the DWTP in Sant Joan Despí (Barcelona, Spain). The study comprised a monitoring of both water and GAC cores withdrawn at various depths and times throughout 1 year operation. The biomass parameters assessed were total cell count by confocal laser scanning microscopy (CLSM), DNA and adenosine triphosphate (ATP). Visual examination of GAC particles was also conducted by high-resolution field emission scanning electron microscopy (FESEM). Additionally, water quality and GAC surface properties were monitored. Results provided insight into the extent and spatial distribution of biofilm within the GAC bed. To sum up, it was found that backwashing could physically detach bacteria from the biofilm, which could however build back up to its pre-backwashing concentration before next backwashing cycle. © 2012 Elsevier Ltd. Source

Gibert O.,Water Technology Center | Gibert O.,Polytechnic University of Catalonia | Lefevre B.,Water Technology Center | Fernandez M.,Water Technology Center | And 3 more authors.
Water Research | Year: 2013

The removal of natural organic matter (NOM) and, more particularly, its individual fractions by two different GACs was investigated in full-scale filters in a drinking water treatment plant (DWTP). Fractionation of NOM was performed by high performance size exclusion chromatography (HPSEC) into biopolymers, humic substances, building blocks and low molecular weight organics. The sorption capacity of GAC in terms of iodine number (IN) and apparent surface area (SBET), as well as the filling of narrow- and super-microporosity were monitored over the 1-year operation of the filters. Both GACs demonstrated to be effective at removing NOM over a wide range of fractions, especially the low and intermediate molecular weight fractions. TOC removal initially occurred via adsorption, and smaller (lighter) fractions were more removed as they could enter and diffuse more easily through the pores of the adsorbent. As time progressed, biodegradation also played a role in the TOC removal, and lighter fractions continued to be preferentially removed due to their higher biodegradability. The gained knowledge would assist drinking water utilities in selecting a proper GAC for the removal of NOM from water and, therefore, complying more successfully the latest water regulations. © 2013 Elsevier Ltd. Source

Gibert O.,Water Technology Center | Gibert O.,Polytechnic University of Catalonia | Lefevre B.,Water Technology Center | Ferrer O.,Water Technology Center | And 3 more authors.
Desalination and Water Treatment | Year: 2016

The primary problem for the application of microfiltration (MF) and ultrafiltration (UF) membrane technology is membrane fouling. Such is the case that understanding membrane fouling has become one of the major factors driving MF and UF membrane technology forward. Nevertheless, identifying the constituents that most contribute to membrane fouling and quantifying how they are detached when backwashing (BW) and cleaning-in-place (CIP) are applied still remains a challenging task. The aim of the present study was to quantify membrane fouling development during filtration and membrane fouling detachment during BW and CIP in terms of membrane permeability changes and masses of inorganic and organic constituents accumulated on the membrane. The study was conducted using bench-scale MF and UF modules fed with coagulated and settled water coming from a drinking water treatment plant and operated under dead-end and cross-flow operation modes. The experiments consisted inconsecutive permeation (20 min) alternated with BW with permeate water (1.0 min) (periodically chemically assisted with NaClO and NaOH) and followed by a two-stage CIP consisting first in an oxidising and basic step (NaClO and NaOH) and second in an acidic step (citric acid). Feed, permeate, retentate (when present) and cleaning discharge streams were monitored for turbidity, total and dissolved organic carbon (TOC and DOC, respectively), UV254 and inorganic ions (Al, Fe, P). DOC was fractionated by high-performance size exclusion chromatography to gain insight into the behaviour of the different organic fractions. Results showed that both MF and UF membranes successfully removed turbidity, Al and Fe, whereas UV254 was moderately removed and TOC and DOC poorly removed, with removal percentages higher for UF than for MF. With regard to the organic fractions, the largest molecular weight compounds were moderately removed while the smallest organic fractions seemed to totally permeate through both membranes. The results also showed that foulants were poorly washed out from the membrane by BW, but better extracted by the two-stage CIP up to a complete detachment for some foulants. © 2016 Balaban Desalination Publications. All rights reserved. Source

Planas C.,CSIC - Institute of Environmental Assessment And Water Research | Ventura F.,CSIC - Institute of Environmental Assessment And Water Research | Caixach J.,CSIC - Institute of Environmental Assessment And Water Research | Martin J.,Aigues de Barcelona S.A. | And 2 more authors.
Talanta | Year: 2015

A simple, selective and sensitive method for the analysis of the strong mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) and its brominated analogues (BMXs) in chlorine-treated water has been developed. The method is based on gas chromatography coupled to triple quadrupole tandem mass spectrometry (GC-QqQ-MS/MS), previous liquid-liquid extraction (LLE) of a smaller sample volume compared to other methods and on-line derivatization with a silylation reactive. GC-QqQ-MS/MS has been raised as an alternative easier to perform than gas chromatography coupled to high resolution mass spectrometry (GC-HRMS) for the analysis of MX and BMXs, and it allows to achieve low LODs (0.3 ng/L for MX and 0.4-0.9 ng/L for BMXs). This technique had not been previously described for the analysis of MX and BMXs. Quality parameters were calculated and real samples related to 3 drinking water treatment plants (DWTPs), tap water and both untreated and chlorinated groundwater were analyzed. Concentrations of 0.3-6.6 ng/L for MX and 1.0-7.3 ng/L for BMXs were detected. Results were discussed according to five of the main factors affecting MX and BMXs formation in chlorine-treated water (organic precursors, influence of bromide ions, evolution of MX and BMXs in the drinking water distribution system, groundwater chlorination and infiltration of water coming from chlorination processes in groundwater). © 2015 Elsevier B.V. All rights reserved. Source

Discover hidden collaborations