Scale precipitation on HDPE pipe by degassing of CO2 dissolved in water

Abstract

In Algeria, high-density polyethylene (HDPE) is widely used in drinking water pipes. This study is focused on the precipitation of calcium carbonate, a major constituent of scale, from calcocarbonically pure (CCP) water in HDPE pipe. Studying scaling in natural conditions is very difficult because it occurs over many years. For this, accelerated scaling is caused by the degassing CO2 dissolved in water. The kinetic study has shown that the germination time and the critical pH decrease with the hardness (30, 40 and 50 °f) and temperature (30, 40 and 50 °C) of water. On the other hand, scaling process efficiency (η) and the supersaturation coefficient (Ωcal) of CaCO3 increase with these parameters. The CaCO3 precipitation occurs both in solution and on walls of HDPE. By the weighing method, it is shown that the deposit mass increases with hardness and temperature. Calcium carbonate precipitates much more in homogeneous phase than in heterogeneous one. The study also showed that heterogeneous nucleation on HDPE is much less important than on PA, PVC, chrome and Inox. These measurements are supported by the characterization of X-ray diffraction deposits and by scanning electron microscopy, which recognizes that the precipitate obtained consists mainly of calcite.

Risk-Based Inspection and Rehabilitation Planning of Service Connections in Intermittent Water Supply Systems for Leakage Management in Arid Regions

“…EC is a measure of dissolved salts, cations (calcium, magnesium, sodium, potassium), and anions (chlorides, sulfates, nitrates, carbonates, and bicarbonates). Scale formation on the walls of plastic pipes due to precipitation of calcium carbonate was reported in a recent study in Algeria [39], which further leads to corrosion and finally structural failure [40]. pH represents the aggressiveness of water, which primarily causes wall leaching and deterioration in cement and metal pipes [18].…”

Impact of the surface aging of potable water plastic pipes on their lead deposition characteristics

“…However, the role of the pipe surface characteristics in the scale formation process has not been discussed. 38 A study conducted by Ketrane and Yahiaoui (2021) showed that CaCO 3 scale forms more in the aqueous phase than on the surface of HDPE pipes. However, no mechanistic discussion is provided on the role of plastic pipes in providing nucleation sites.…”

“…The half-life, t 1/2 , is the amount of time needed for the pipe to deposit half of the equilibrium Pb surface loading. 39 The FO kinetics model best describes the physical adsorption process. It assumes that the rate of deposition of the solute onto the adsorbent is proportional to the difference between the saturation surface loading and the amount of adsorbed solute over time, as shown in eqn (3).…”

“…However, no mechanistic discussion is provided on the role of plastic pipes in providing nucleation sites. 39 Although most of the prior studies focused on the release mechanisms of particulate lead, no attention has been paid to the transport of this particulate matter through the building's plumbing system and its subsequent deposition onto downstream plastic piping materials in distinction with dissolved lead species.…”