Charge Neutral Biocide Dosing for Membrane Biofouling Control
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Solution Overview
Problem
Membrane separation processes in water purification face challenges due to biofouling, where microbes grow on the membrane surface, reducing water quality and flow rate, and existing methods for controlling biocides are complicated by the interaction with oxidizing and reducing agents, leading to dynamic control challenges and potential membrane damage.
Innovation Solution
A system and method for controlling the addition of a charge-neutral biocide to the feed stream in membrane separation processes, where the biocide is introduced upstream of the membrane and its concentration measured in the permeate stream, allowing for adjustment of the addition rate based on measured levels, while minimizing excess reducing agents and avoiding membrane oxidation, with metal ion concentrations being managed to prevent catalyzed degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a biocide is added to control biofouling on the membrane surface, then biofouling is inhibited and membrane performance is maintained, but the biocide may interact with oxidizing and reducing agents causing dynamic control challenges and potential membrane damage
Solution Approach 1:
The system employs a feedback control mechanism where the concentration of biocide in the permeate stream is continuously measured and used to adjust the biocide addition rate upstream. This closed-loop control ensures consistent biocidal activity while adapting to changing conditions, resolving the dynamic control challenges mentioned in the contradiction.
Solution Approach 2:
The patent uses charge-neutral biocides as intermediaries that can pass through the membrane into the permeate stream without being rejected. This intermediary approach allows biocidal activity to be maintained in both the feed and permeate streams while minimizing harmful interactions with other chemicals and reducing control complexity.
2Reliability
If oxidizing agents are used to disinfect the feed stream before the membrane, then biofouling is reduced, but the oxidizing agents may damage the membrane structure
Solution Approach 1:
The patent changes the chemical parameter of the biocide by selecting charge-neutral biocides with different chemical properties than traditional oxidizing agents. This parameter change allows for effective disinfection while avoiding the membrane damage associated with oxidizing agents, as the charge-neutral biocides do not have the same oxidative damage potential.
3Reliability
If reducing agents are added to neutralize excess oxidant and protect the membrane, then membrane integrity is maintained, but the reducing agents may react with and deplete the biocide
Solution Approach 1:
The system performs preliminary action by adding the charge-neutral biocide upstream of the membrane, before any reducing agents are introduced. This timing ensures that the biocide is already present in the permeate stream and establishes biocidal activity before potential reactions with reducing agents could occur downstream, minimizing biocide depletion.
4Ease of manufacture
If metal ion concentrations are not controlled, then the system operation is simpler, but metal ions may catalyze degradation reactions between the biocide and the membrane
Solution Approach 1:
The patent converts the potential harm of metal ions by selecting charge-neutral biocides that are less susceptible to metal-catalyzed degradation reactions. This approach acknowledges the presence of metal ions but chooses a biocide chemistry that is inherently more resistant to such reactions, thereby maintaining membrane stability without requiring complex metal ion removal systems.
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 ensures a consistent biocidal activity in the permeate stream, inhibits biofouling, and maintains membrane integrity by dynamically controlling biocide addition and managing metal ions, thereby enhancing the efficiency and reliability of membrane separation processes.
Implementation Method 1
the charge neutral biocide may pass through the membrane and into the permeate stream rather than be rejected by the membrane
Implementation Method 2
an applied pressure is used to overcome an osmotic pressure across the membrane
Implementation Method 3
reverse osmosis is widely used in water purification processes
Data Source
AI summary
Biocide can be controllably added to a feed stream for a membrane. The membrane can separate the feed stream into a purified permeate stream and a concentrate stream containing contaminants from the feed stream. In some examples, a charge neutral biocide is introduced into the feed stream at a first addition rate. The concentration of the charge neutral biocide in the permeate stream is measured to provide a measured concentration of the charge neutral biocide in the permeate stream. The addition rate of the charge neutral biocide can be adjusted based on the measured concentration of the charge neutral biocide in the permeate stream to introduce charge neutral biocide into the feed stream at a second addition rate different than the first addition rate.