Organic phosphonates are often used as antiscalants in nanofiltration and reverse osmosis plants. To clarify the composition and purity, 24 technical products were characterised in chemical analyses during the project.
If nanofiltration or low-pressure reverse osmosis membranes are used for water softening, then water components concentrate on the membrane side and this can lead to an excess of salts that are difficult to dissolve using solubility products. To prevent salts accumulating on the membrane surface, antiscalants are dosed. In the list of preparation substances and disinfection processes in accordance with Section 11 of the German Drinking Water Ordinance 2001, 14 substances are currently approved as antiscalants. Two of these are polyphosphonates and nine are phosphonic acids. There is a large number of formulations on the market from several manufacturers and frequently there is no information on their precise composition or the levels of active ingredients. The application quantity of phosphonates as antiscalants in membrane systems has risen in recent years because of the increasing use of the technology and its good performance. It appears from laboratory tests and practical experience that the various antiscalants are suited to different requirements to varying degrees (e.g. calcium carbonate vs. calcium sulphate). It is therefore preferable to have more detailed information on the composition and mode of action in order to more quickly find the appropriate product.
In the project, 24 formulations that contain phosphonate were chemically analysed to provide meaningful information on the composition, the substance content and undeclared additives or impurities. In the investigations it was shown that there were often considerable quantities of organic phosphorus compounds in addition to the normal compound.
Publications:
Armbruster, D.; Müller, U.; Happel, O.: Characterization of phosphonate-based antiscalants used in drinking water treatment plants by anion-exchange chromatography coupled to electrospray ionization time-of-flight mass spectrometry and inductively coupled plasma mass spectrometry, J Chrom A, 1601, 189-204 (2019)
Happel, O.; Armbruster, D.; Müller, U.; Brauch, H.-J.: Reinheitsprüfung phosphonathaltiger Antiscalants [Purity testing of antiscalants that contain phosphonates]. DVGW energie|wasser-praxis 04/2018, 25-29 (2018)
Happel, O.; Armbruster, D.; Müller, U.: Verhalten von Phosphonaten als Antiscalants bei der Membranfiltration [Behaviour of phosphonates as antiscalants in membrane filtration]. Veröffentlichungen aus dem Technologiezentrum Wasser [Publications from TZW] 78, ISSN 1434-5765 (2017)
