Minimizing the use of chemicals to control scaling in SWRO : improved predicition of the scaling potential of calcium carbonate

A comprehensive and detailed study on the scaling potential of calcium carbonate in seawater reverse osmosis systems (SWRO), this book provides a new approach for calculating the degree of supersaturation and the pH of the SWRO systems concentrates with the assistance of the feed-water pH and the inorganic carbon constituents. Furthermore, the book highlights the weakness in the present supersaturation indices and membrane manufacturers programs. Finally, the research suggested that SWRO concentrate is much lower undersaturated with respect to calcium carbonate than previously thought. This was confirmed by comprehensive pilot testing where acids and antiscalants used to prevent calcium carbonate scaling were completely eliminated from the pilot plant. Content: Chapter 1 1.1 Background 1.2 Problem definition 1.3 The Overall Aim of the research 1.4 Research objectives 1.5 References Chapter 2 2.1 Abstract 2.2 Background Introduction Induction time Measurement tools Effect of exchange CO2 on induction time 2.3 Materials Inductively coupled plasma Conductivity meter pH meter Reactors Synthetic seawater concentrate preparation 2.4 Methods Measurement of calcium with ICP Salinity and accuracy of direct measurement of calcium in solution Measurement of calcium carbonate retained on membrane filters Effect of salinity, stability and accuracy of conductivity and pH measurment Effect of mixing on the induction time 2.5 Results Effect of salinity on the ICP measurements and accuracy Accuracy of measurement of calcium carbonate retained on membrane filters The effect of salinity on the conductivity and the pH measurments The effect of carbon dioxide exchange in an open system 2.6 Conclusions 2.7 List of Symbols 2.8 References Chapter 3 3.1 Abstract 3.2 Background 3.3 Materials Synthetic seawater concentrate preparation 3.4 Methods The effect of particles in synthetic seawater on the induction time The effect of particle addition Mixing effect 3.5 Results and discussion The effect of particles in synthetic seawater on the induction time The effect of particle addition The effect of mixing speed on the induction time The nucleation mechanism 3.6 Conclusions 3.7 List of symbols 3.8 References Chapter 4 4.1 Abstract 4.2 Background Introduction Solubility of salts Common methods used to determine the precipitation potential of CaCO3: Stiff & Davis Stability Index (S&DSI) Saturation Index (SI) Saturation Ratio (Sa) Mechanism of nucleation Homogenous nucleation Heterogeneous nucleation in a solution Induction time CaCO3 phases The formation of hydrated CaCO3 forms 4.3 Materials pH meter Reactors Synthetic seawater concentrate preparation 4.4 Methods Induction time measurements Solutions concentrations Calculation of SI using PhreeqC 4.5 Results The solubility product used by the S&DSI Homogenous and heterogeneous nucleation 4.6 Conclusions 4.7 List of symbols 4.8 References Chapter 5 5.1 Abstract 5.2 Introduction 5.3 Background Saturation indices Calculation of pH in SWRO concentrates Effect of salinity on dissociation constants Effect of salinity on the ion activity 5.4 Materials and Methods Pilot plant Concentrate pH in SWRO systems 5.5 Results and Discussion pH calculations using equilibrium equations pH calculations using manufacturers software pH prediction using Phreeqc evaporation model Field seawater concentrate measurements 5.6 Conclusions 5.6 List of Symbols 5.7 References Chapter 6 6.1 Abstract 6.2 Background Introduction Calcium carbonate phases The role of inorganic ions Solubility of salts Common methods used to determine the precipitation potential of CaCO3: Saturation indices (SI and Sa) Mechanism of nucleation Induction time 6.3 Materials pH meter Reactors Synthetic seawater concentrate preparation 6.4 Methods Induction time measurements Determination of co-precipitation Determination of the final crystal phase of calcium carbonate 6.5 Results and discussion Chapter 7 7.1 Conclusions 7.2 Recommendations for future work "This thesis aimed to improve the accuracy of calcium carbonate scaling prediction, and subsequently prevent overdosing the chemicals employed to control scaling in seawater reverse osmosis (SWRO) systems. The scaling potential was estimated employing theoretical calculations and experimental data. Futhermore, the kinetics of precipitation were investigated employing induction time measurements at different levels of super saturation."--Back cover A comprehensive study on the scaling potential of calcium carbonate in seawater reverse osmosis systems (SWRO). The study provides a new approach for calculating the degree of supersaturation and the pH of the SWRO systems concentrates with the assistance of the feed-water pH and the inorganic carbon constituents.