A Study of Electrolyte Effects in Water Treatment Processes

Abstract

Electrolytes of different types are almost always present in wastewater and they can control some of the properties of the water. These electrolytes can even determine the appropriate method for wastewater treatment. Recently, these electrolyte effects were used in a suitably designed bubble column evaporator (BCE) for a surprisingly large range of water treatment processes, including solute decomposition and coliform inactivation, which were pioneered in the present work. It was discovered that hot inlet air, e.g. at 150°C, could be pumped into a BCE to produce a continuous flow of hot bubbles, whose surfaces can decompose thermally unstable solutes, such as NH₄HCO₃ and K₂S₂O₈. The experimental results indicated that the BCE process was more efficient than direct heating, especially when bubble coalescence inhibition effects caused a reduction in bubble sizes and increased bubble densities of the hot bubbles within the column. A continuous stream of hot bubbles in a BCE was also used to develop a novel coliform inactivation method. In this process, it appears that the membranes of microorganisms colliding with these hot bubbles can be thermally disrupted, which leads to their failure and leakage and so the inactivation of the organism. Importantly, in addition to the inhibition effects of electrolytes on bubble coalescence, specific electrolytes can also affect electrostatic surface forces between bubbles and cells and so can play a significant role, in one example increasing the inactivation rate from 29% to 99.9%, by the addition of a low level of CaCl₂. Lastly, the study of the effects of different ions (e.g. monovalent, divalent and trivalent) on a monitor microorganism (i.e. Escherichia coli) was carried out. This led to a comprehensive and relatively integrated understanding of the cell’s surface charging properties in aqueous solutions, of use in the development of water treatment processes. Many techniques like zeta potential, light scattering size measurement, coliform colony incubation and so on were applied in this study. In addition, phospholipid vesicles were used as surface charging models for these cells and the effects of various ions were studied on their stability and charge.