Reverse Osmosis Membrane Scale Inhibitor Dosing via Fluoride Ion Feedback
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Solution Overview
Problem
The increasing concentration of scale components in treated water due to water recovery leads to higher operating costs for water treatment equipment, as excessive scale inhibitors are required to prevent membrane scaling, while insufficient inhibitor use results in shortened membrane lifespan and corrosion issues under low pH conditions.
Innovation Solution
A water treatment method involving measuring fluoride ion concentration in water adjusted to a pH of 5 or higher, determining the appropriate amount of scale inhibitor based on this measurement, and adding it to suppress calcium fluoride precipitation, using a reverse osmosis membrane system with integrated pH adjustment, measurement, and inhibitor addition mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of scale inhibitor is increased to prevent membrane scaling, then the protection against scale precipitation is improved, but the operating cost increases
Solution Approach 1:
The system measures the actual fluoride ion concentration in the feed water and uses this measurement to dynamically adjust the scale inhibitor dosing rate. This feedback mechanism ensures that the inhibitor amount precisely matches the scaling risk, preventing both over-dosing (wasted cost) and under-dosing (insufficient protection).
Solution Approach 2:
The scale inhibitor dosing system transitions from a fixed, static dosing rate to a dynamic, adjustable rate that responds to changing water quality conditions. The dosing pump's injection rate is continuously modified based on real-time fluoride concentration measurements and calculated scaling tendency, optimizing both protection and cost efficiency.
2Reliability
If the pH is lowered to suppress calcium fluoride precipitation, then the scale inhibition is improved, but the corrosion risk to pipes and components increases
Solution Approach 1:
Instead of changing the pH parameter to suppress scaling, the system changes the dosing rate parameter of the scale inhibitor. This allows scaling prevention through chemical inhibition at moderate pH levels, avoiding the corrosive effects of low pH while achieving the same scale protection goal through a different control parameter.
3Productivity
If water recovery is increased to meet water demand, then the water production efficiency is improved, but the concentration of scale components in concentrated water increases
Solution Approach 1:
The system calculates the scaling tendency based on the concentration of scale components in the concentrated water, which increases with higher recovery rates. This calculated scaling tendency feeds back to dynamically adjust the inhibitor dosing rate, ensuring adequate protection even as scale component concentrations rise due to increased water recovery.
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
This approach optimizes the use of scale inhibitors, reducing operating costs by ensuring sufficient prevention of membrane scaling while minimizing corrosion risks at moderate pH levels, thereby extending membrane lifespan and reducing maintenance costs.
Implementation Method 1
a reverse osmosis membrane apparatus in which scale adhesion is suppressed
Implementation Method 2
obtaining permeate water and concentrated water by passing the scale inhibitor and the water to be treated after addition to the reverse osmosis membrane
Implementation Method 3
measuring the fluoride ion concentration in the water to be treated after the pH is adjusted to 5 or higher
Data Source
AI summary
As a countermeasure for calcium fluoride scale in reverse osmosis membranes, a water treatment method and apparatus are provided that can add a scale inhibitor at an appropriate addition amount. A water treatment apparatus for treating water to be treated that contains fluorine and calcium by passing the water through at least a reverse osmosis membrane includes pH adjustment means for adjusting the pH of the water to be treated in a supply line, means for measuring the concentration of fluoride ions in the water to be treated and then determining the amount of scale inhibitor to be added by an addition means based on the measured fluoride ion concentration. After the scale inhibitor is added from an addition line, permeate from a permeate line and concentrate from a concentrate line are discharged from the reverse osmosis membrane.