Degradation of Phosphonate-Based Scale Inhibitor Additives in the Presence of Oxidizing Biocides: “Collateral Damages” in Industrial Water Systems

Organic, phosphorus-based additives are commonly used in water treatment technologies such as mineral scale and corrosion inhibitors, and dispersing agents. Phosphonates find extensive use as anti-precipitation inhibitors for sparingly soluble salts such as calcium carbonates and phosphates, calcium/barium/strontium sulfates and others, commonly formed in supersaturated process waters in a wide spectrum of industrial applications. In open recirculating cooling water systems strong oxidizing biocides (eg. ClO, BrO, etc.) are also added to control microbiological growth but have detrimental effects on other water treatment chemicals that are sensitive to oxidative degradation. In this paper we report the effect of a hypobromite-based biocide towards the scale inhibitor AMP (amino-tris-(methylene phosphonate)). AMP reacts rapidly with the biocide at room temperature. AMP degradation continues, but it slowly reaches a plateau after 1000 minutes. Even after 50 h the reaction time, only 20% of AMP has decomposed. AMP reacts with the biocide to give the orthophosphate much more rapidly at 438C than at 258C due to faster kinetics of decomposition. Results on various other oxidizing biocides on PBTC (2Phosphonobutane-1,2,4-Tricarboxylic acid) are also presented. PBTC is a very “robust” scale inhibitor. This is confirmed by our degradation studies using biocides such as chlorine (ClO), bromine (BrO), their stabilized analogs, BCDMH, and Received 20 September 2006, Accepted 11 December 2006 Address correspondence to Konstantinos D. Demadis, Crystal Engineering Growth and Design Laboratory, Department of Chemistry, University of Crete, Voutes, Heraklion, Crete, GN 71003, Greece. E-mail: [email protected] Separation Science and Technology, 42: 1639–1649, 2007 Copyright # Taylor & Francis Group, LLC ISSN 0149-6395 print/1520-5754 online DOI: 10.1080/01496390701290532