Polyphosphate dosing

Another approach is the use of polyphosphate-based blends including proprietary chemicals. The exact mechanism of the observed effect is not completely understood. In the polyphosphate mode of operation, the polyphosphate is dosed ia quantities of 2—5 ppm periodically, sludge resulting from phosphate treatments is removed by acid cleaning (see Dispersants). 

Glassy polysilicates are similar in inhibition properties to polyphosphates and also have an indefinite crystalline structure. For simple threshold effect protection against hardness destabilization and red-water, they are effective but require a higher dose rate (typically 8 to 15 ppm SiC>2 above that of the natural orthosilicate found in water). 

Attempts were made under conditions dose to those in practice to clarify whether modified zinc layers have a better corrosion resistance than standard galvanisation [59]. Inhibition by pure o-phosphate and a long-chain polyphosphate was also investigated. The electrolytic water treatment process proven in practice (called the electrolysis process for short) was induded in the studies. The experimental conditions can be seen from Figure 29, and Table 40 contains the water analysis. 

The inhibition of metal corrosion in industrial water systems was first achieved by the use of inorganic salts or their blends, including chromates (Evans, 1936 Mayne and Pryor, 1949), nitrites (Hatch, 1952), phosphates (Patterson and Jones, 1952), borates (Mercer, 1990), silicates (Lehrman and Shuldenen, 1952), zinc salts (Hatch, 1965 a) and other cations (Hinton, 1989). Additionally, chromates and nitrites were mainly applied, and from the end of the 1950s the use of polyphosphates increased (May et al., 1981 Hwa, 1971). Treatments with anodic inhibitors such as nitrites or chromates require a high initial dose and a relatively high continuous dose in order to achieve an effective passive layer on the metal surface. The concentration of chromate and nitrite can be decreased in the presence of polyphosphates and zinc ions. 

Associations of dispersant hydrosoluble polymers and low doses of shorter-chain specific growth inhibitors such as linear polyphosphates are also very effective in reducing cotton incrustation and in increasing primary detergent effect. 

The detection of labelled polyphosphoinositides were the experimental prerequisite for the search of an auxin effect on the membrane-bound inositol phospholipids [9]. Actually, the kinetics of the lipid phosphorylation in the absence or presence of 1 pM lAA were analyzed. In comparison with the control a very rapid reduction of the p2p]-label was observed in the phospholipid fraction in the presence of auxin (fig.1). This decrease of [ 2pj. a ei vvas not originated from an auxin-mediated inhibition of the lipid phosphorylation reaction but it was really caused by an auxin-mediated hydrolysis of [22p]-iabelled lipids, since p2p]-iabelled inositol polyphosphates (IPx) could be detected in the aqueous extracts of the same assays after anion exchange chromatography (fig.1). The kinetics of the l/ A-mediated release of the p2p]-labelled inositol compounds IP3 and IP2 correspond well with the kinetics of the loss of the [22p]-iabel in the lipid fraction. The auxin-dependent reactions exhibit also a dose response relationship either by a continuous loss of [32p]-iabel of the phospholipids or by a stimulated release of p2p]-iabelled IPx with increasing lAA concentrations as demonstrated previously [9,11]. 

Until recently, a proprietary ortho-polyphosphate blend has been dosed at about 1 mg/1 (as PO4) resulting in typical orthophosphate concentrations in the City s distribution network of about 0.5 mg/1 (as PO4). Orthophosphate is now being dosed to the City s water supplies at the two treatment plants. It should be noted that polyphosphate is a metal chelating agent and may acmally exacerbate plmnbosolvency (IWA, 2010). Also, from widespread UK experience, the concentration of orthophosphate required for optimal reduction in plumbosolvency could be about 3 mg/1 (as PO4) for the type of water quality in City C. 

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