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Optimierung der Verfahrenskombination Flockung und Ultrafiltration zur Entfernung organischer Wasserinhaltsstoffe
Titel (Englisch)
Optimisation of coagulation enhanced ultrafiltration treatment process to improve removal of Natural Organic Matter
Kurzbeschreibung (Deutsch)
Zur Zeit nicht erhältlich. Bitte lesen Sie die englische Fassung.
Kurzbeschreibung (Englisch)
Water supply companies currently face a challenge of supplying high-purity contaminant-free water at minimal addition of chemicals in the treatment process. Whether that task is forced by strengthen regulations, enhanced public awareness or availability of the reliable technologies, new and perhaps more promising applications such as membrane processes are increasingly installed and applied worldwide. Applications of backwashable capillaries, either driven inside-out or outside-in microfiltration (MF) and ultrafiltration (UF) membrane processes for direct treatment of surface water are currently considered a safe and reliable water treatment technology. However, one of the main barriers in further implementation of that technique are considerable pore blocking and irreversible fouling effects caused by Natural Organic Material (NOM) and small colloids (<1 um), making the direct treatment of surface water by MF/UF possibly economically unaffordable.
The term NOM represents a complex mixture of compounds formed as a result of the breakdown of animal and plant material in the environment. Along with colloidal minerals and microorganisms NOM is found in varying concentrations in all natural water sources and known to be a precursor for noxious disinfection by-products. NOM is a broad range of compounds, from small hydrophilic acids, proteins and amino acids to medium high molecular weight organic polymers, such as humic and fulvic acids, polypeptides, and carbohydrates. The predominant humic (HAs) and fulvic (FAs) acids can have both aliphatic and aromatic character and possess a negative charge in drinking water. The charge is attributed to carboxylic and phenolic groups and this causes the larger compounds to behave as polyelectrolytes in solution. Numerous studies suggested that NOM are accountable for a rapid 30-40% decline in initial flux upon UF membrane treatment.
The common solution to minimise a rapid and often irreversible flux decline in membrane operation is to combine membrane filtration with coagulation/flocculation of NOM into a hybrid process. Here, coagulation/flocculation is used to embed NOM into the formed flocs. The flocs then will be retained by the membrane and later removed by backwashing the membrane. This application is accountable for two main improvements, namely: 1) enhanced retention of NOM that might otherwise not be removed by MF or UF; and 2) prolonged stable operation of the membrane module due to formation of a porous cake on the membrane surface, preventing or minimising a direct contact between the membrane and the foulants. An additional improvement of the UF system performance could be given when dosing additional particles like silicate or powdered activated carbon (PAC) prior coagulant dosage. The higher amount of available particles may improve coagulation by functioning as germ cells for the forming of micro flocs. In case of using PAC, additional NOM adsorption effects may be superimposed if contact time is sufficient. This effect may also occur if PAC is substituted by geopolymers (activated silicate). However, these positive effects will be limited by a certain maximum particle concentration where negative coating layer effects at the membrane wall, e. g. higher flux declines due to the thicker coating layer, will start to dominate. This could be shown in an earlier research project at backwashable outside-in driven MF capillaries (BMBF 02WT0282). Directly linked to the above mentioned improvements are further accompanying advantages like the minimisation of noxious disinfection by-products, reduced operational expenses due to a stable operation of the membrane at lower or moderate transmembrane pressures (TMP), reduction of chemical cleanings and chemical enhanced backwashes, therefore increasing life time of the membrane modules and decreasing operational expenses, and increased filtration sequences between backwashes.
Yet, many studies have addressed the combined water treatment by coagulation and UF to remove NOM highlighting the importance of membrane, solution and organic matter properties. The current research effort is devoted towards investigation of the effect of the coagulation conditions and particle concentration on the removal of NOM and colloidal and particulate material. The other important parameter is the impact of these conditions on fouling of the UF capillaries operated in inside-out mode, which can be determined by measuring the flux decline of the filtration system. The proposed research is a part of the long time research effort initiated in order to improve UF or MF membrane filtration, able to reduce the concentration of organic material commonly found in raw surface water.
The term NOM represents a complex mixture of compounds formed as a result of the breakdown of animal and plant material in the environment. Along with colloidal minerals and microorganisms NOM is found in varying concentrations in all natural water sources and known to be a precursor for noxious disinfection by-products. NOM is a broad range of compounds, from small hydrophilic acids, proteins and amino acids to medium high molecular weight organic polymers, such as humic and fulvic acids, polypeptides, and carbohydrates. The predominant humic (HAs) and fulvic (FAs) acids can have both aliphatic and aromatic character and possess a negative charge in drinking water. The charge is attributed to carboxylic and phenolic groups and this causes the larger compounds to behave as polyelectrolytes in solution. Numerous studies suggested that NOM are accountable for a rapid 30-40% decline in initial flux upon UF membrane treatment.
The common solution to minimise a rapid and often irreversible flux decline in membrane operation is to combine membrane filtration with coagulation/flocculation of NOM into a hybrid process. Here, coagulation/flocculation is used to embed NOM into the formed flocs. The flocs then will be retained by the membrane and later removed by backwashing the membrane. This application is accountable for two main improvements, namely: 1) enhanced retention of NOM that might otherwise not be removed by MF or UF; and 2) prolonged stable operation of the membrane module due to formation of a porous cake on the membrane surface, preventing or minimising a direct contact between the membrane and the foulants. An additional improvement of the UF system performance could be given when dosing additional particles like silicate or powdered activated carbon (PAC) prior coagulant dosage. The higher amount of available particles may improve coagulation by functioning as germ cells for the forming of micro flocs. In case of using PAC, additional NOM adsorption effects may be superimposed if contact time is sufficient. This effect may also occur if PAC is substituted by geopolymers (activated silicate). However, these positive effects will be limited by a certain maximum particle concentration where negative coating layer effects at the membrane wall, e. g. higher flux declines due to the thicker coating layer, will start to dominate. This could be shown in an earlier research project at backwashable outside-in driven MF capillaries (BMBF 02WT0282). Directly linked to the above mentioned improvements are further accompanying advantages like the minimisation of noxious disinfection by-products, reduced operational expenses due to a stable operation of the membrane at lower or moderate transmembrane pressures (TMP), reduction of chemical cleanings and chemical enhanced backwashes, therefore increasing life time of the membrane modules and decreasing operational expenses, and increased filtration sequences between backwashes.
Yet, many studies have addressed the combined water treatment by coagulation and UF to remove NOM highlighting the importance of membrane, solution and organic matter properties. The current research effort is devoted towards investigation of the effect of the coagulation conditions and particle concentration on the removal of NOM and colloidal and particulate material. The other important parameter is the impact of these conditions on fouling of the UF capillaries operated in inside-out mode, which can be determined by measuring the flux decline of the filtration system. The proposed research is a part of the long time research effort initiated in order to improve UF or MF membrane filtration, able to reduce the concentration of organic material commonly found in raw surface water.
Zeitraum
10/2007 - 12/2007
Art der Finanzierung
Drittmittel
Projektleiter
- Herr Dr.-Ing. André Lerch
- Herr Prof. Dr.-Ing. Wolfgang Uhl
Weitere Mitarbeiter (außerhalb des Lehrstuhls)
Elizabeth Arkhangelsky
Finanzierungseinrichtungen
- BMBF PTWT+E
Kooperationspartnerschaft
international
Externe Kooperationspartner
- Dr. Vitaly Gitis, Ben Gurion University of the Negev, Israel (Israel)
Website zum Projekt
Zugeordnete Profillinie
Wasser, Energie und Umwelt
Relevant für den Umweltschutz
Ja
Relevant für Multimedia
Nein
Relevant für den Technologietransfer
Nein
Berichtsjahr
2007