Alternating Membrane Desalination for Hardness Ion Removal
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Solution Overview
Problem
Conventional desalination systems, such as EDI apparatuses, face challenges in handling high concentrations of hardness ions, requiring rigorous pretreatment and increasing processing costs due to scaling tendencies, with existing methods like RO having lower efficiency and higher costs.
Innovation Solution
A desalination system utilizing alternating cation exchange membranes to separate and remove hardness ions from an aqueous stream, producing a dilute output for further processing in EDI apparatuses, while a second stream carries away the removed ions, enhancing ion removal efficiency and reducing scaling issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional EDI apparatuses are used for pure water production, then stable and relatively higher quality of product water is achieved, but hardness tolerance is limited to less than 1ppm requiring rigorous pretreatment
Solution Approach 1:
The system segments the desalination process into two distinct stages: a first desalination stage using conventional EDI apparatus for high-purity water production, and a second desalination stage using a novel apparatus with alternating cation and anion exchange membranes for further hardness ion removal. This segmentation allows each stage to specialize in different aspects of purification, with the first stage handling general desalination and the second stage targeting residual hardness ions, thereby reducing the pretreatment burden on the first EDI apparatus.
Solution Approach 2:
The system performs preliminary action by introducing a liquid stream into the second desalination apparatus (with alternating membranes) before it enters the first EDI apparatus. This preliminary removal of hardness ions using the alternating membrane configuration reduces the hardness concentration to acceptable levels, enabling the subsequent EDI apparatus to operate within its optimal hardness tolerance range of less than 1ppm without requiring complex external pretreatment systems.
2Quantity of substance
If reversal osmosis apparatuses are employed for pretreatment to decrease hardness, then hardness removal is achieved, but processing efficiency is relatively lower and processing cost increases
Solution Approach 1:
The system replaces the mechanical pressure-driven reversal osmosis process with an electric field-driven electrodialysis process using alternating cation and anion exchange membranes. This substitution eliminates the need for high-pressure pumps and membrane compression associated with RO, reducing energy consumption and increasing processing efficiency. The electric field selectively drives hardness ions through the alternating membranes, achieving effective hardness removal (reducing to less than 1ppm) with lower operational costs and higher productivity compared to conventional RO pretreatment.
3Quantity of substance
If polyvalent cations with higher concentration are present in liquid streams, then ion removal challenge increases, but scaling tendency is caused in EDI apparatuses
Solution Approach 1:
The system converts the harmful effect of polyvalent cations (which cause scaling in conventional EDI apparatuses) into a beneficial separation mechanism by using alternating cation and anion exchange membranes. In this configuration, polyvalent cations are selectively retained in the concentrate channels while monovalent ions are removed in the diluate channels. This selective separation prevents scaling by keeping polyvalent cations away from the conventional EDI apparatus membranes, while still achieving effective hardness ion removal through the alternating membrane system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves a significant 77% removal of hardness ions, maintaining a stable output with reduced hardness levels, thereby alleviating scaling and fouling in EDI apparatuses, ensuring continuous and efficient operation.
Implementation Method 1
passing a first feed stream through first channels of a first group of alternating first and second channels defined by a first group of paired cation exchange membranes of a desalination apparatus for removing ions
Data Source
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AI summary
A desalination system is provided. The desalination system comprises a desalination apparatus. The desalination apparatus comprises first and second electrodes, and a first group of paired ion exchange membranes disposed between the first and second electrodes to form a first group of alternating first and second channels. The first channels are configured to receive a first stream for desalination and the second channels are configured to receive a second stream to carry away ions removed from the first stream, respectively. The desalination apparatus further comprises a plurality of spacers disposed between each pair of the adjacent ion exchange membranes and between the first and second electrodes and the respective ion exchange membranes. Wherein each of the ion exchange membranes in the first group is a cation exchange membrane. A desalination system and a method for removing ions from an aqueous stream area also presented.