RO Biocide Control Using ORP to Prevent Membrane Biofouling
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Solution Overview
Problem
Existing biocides used in reverse osmosis (RO) systems either lack sufficient biocidal effectiveness or cause membrane damage, limiting their application in wastewater recycle systems where microbial growth is high.
Innovation Solution
A method involving premixing or separate addition of first and second oxidizing biocides, followed by monitoring and adjusting the free residual oxidant concentration or oxidation-reduction potential (ORP) to maintain levels below 0.1 ppm as Cl2 or 500 mV, respectively, to control biofouling without damaging RO membranes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If halogen based oxidizing biocides (e.g., sodium hypochlorite) are used to mitigate biofouling, then biocidal effectiveness is improved, but membrane damage increases and service life decreases
Solution Approach 1:
The patent changes the chemical parameters by using alternative oxidizing agents (peracetic acid, peroxone, ozone, hydrogen peroxide) that have different oxidation mechanisms and strengths. These alternatives provide effective biocidal action while operating at concentrations that do not cause significant membrane damage, thus resolving the contradiction between biocidal effectiveness and membrane protection
Solution Approach 2:
The patent introduces an intermediary substance (one of the alternative oxidizing agents) that mediates between the need for effective biocidal action and the need to protect the membrane. These intermediaries deliver the necessary oxidative stress to kill microorganisms while being less damaging to the polyamide membrane structure compared to traditional halogen biocides
2Object-affected harmful factors
If stabilized chlorine reagents are used to treat RO systems, then membrane damage is reduced, but biocidal effectiveness is insufficient
Solution Approach 1:
The patent changes the oxidizing agent from stabilized chlorine to alternative peroxide-based systems (peracetic acid, peroxone, hydrogen peroxide). These alternatives provide stronger biocidal effectiveness while maintaining membrane compatibility, thus resolving the insufficiency of biocidal action without increasing membrane damage
Solution Approach 2:
The patent employs strong oxidants (peracetic acid, peroxone, ozone, hydrogen peroxide) that deliver more potent oxidative biocidal action than stabilized chlorine. These strong oxidants effectively eliminate microorganisms in wastewater recycle systems while operating at concentrations that do not induce significant membrane damage, thus achieving both high biocidal effectiveness and membrane protection
3Reliability
If bromine-based reagents are used to increase biocidal effectiveness, then biocidal power is improved, but membrane damage increases significantly
Solution Approach 1:
The patent changes from bromine-based chemistry to peroxide-based chemistry (peracetic acid, peroxone, hydrogen peroxide). This parameter change maintains or improves biocidal effectiveness while dramatically reducing membrane damage, as the alternative oxidants do not cause the same level of oxidative stress to the membrane structure as bromine species
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
Effectively inhibits biofouling in RO membranes by maintaining optimal biocide concentrations, thereby increasing membrane lifetime and system efficiency.
Implementation Method 1
premixing a first oxidizing biocide with a second oxidizing biocide to form a composition
Implementation Method 2
measuring a free residual oxidant concentration of the sample using a reagent comprising N,N-diethyl-p-phenylenediamine (DPD)
Implementation Method 3
measuring an oxidation-reduction potential (ORP) at a first location downstream of the first injection point but upstream of the RO membrane inlet
Data Source
AI summary
The present disclosure provides methods of monitoring and controlling biocides in an aqueous medium, methods of manufacturing compositions containing the biocides, and various oxidizing biocide compositions suitable for use in aqueous medium treatment processes. Methods include adding first and second oxidizing biocides upstream of a reverse osmosis (RO) membrane inlet and measuring a free residual oxidant concentration and/or an oxidation-reduction potential downstream of the biocide addition but upstream of the RO membrane inlet. A reducing agent may optionally be added upstream of the RO membrane. The amount of biocide being added may be adjusted based on the free residual oxidant concentration and/or oxidation-reduction potential measurement.