RO Membrane Biocide Control via DPD Monitoring
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Solution Overview
Problem
Biological fouling of reverse osmosis (RO) membranes in water treatment systems leads to reduced membrane performance, increased operation pressure, and shortened membrane service life, with existing biocides either being ineffective or causing membrane damage.
Innovation Solution
The method involves adding a first and second oxidizing biocide at specific injection points upstream of the RO membrane inlet, followed by sampling and measuring the residual oxidant concentrations using N,N-diethyl-p-phenylenediamine (DPD) reagent, to adjust the biocide dosages and maintain optimal concentrations to prevent biofouling without damaging the membranes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxidizing biocides are added to prevent biofouling on RO membranes, then biofouling is inhibited, but the membranes may suffer oxidative damage
Solution Approach 1:
The patent applies parameter changes by precisely controlling the concentration levels of oxidizing biocides (maintaining free residual oxidant below 0.1 mg/L as Cl2 at membrane inlet) and adjusting pH levels (maintaining between 6.5-8.5) to achieve effective biofouling prevention while minimizing oxidative damage to the membrane. This involves continuous monitoring and adjustment of chemical parameters in the feed water.
Solution Approach 2:
The patent uses DPD reagent as an intermediary substance to measure and monitor the concentration of residual oxidants in the feed water. This intermediary measurement system enables precise control of biocide levels, allowing the system to maintain effective concentrations for biofouling prevention while avoiding excessive concentrations that would cause membrane damage.
2Reliability
If multiple oxidizing biocides are added at different injection points, then biofouling control is improved, but the system complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the biocide injection system into multiple separate injection points located at different positions upstream of the RO membrane inlet. Each injection point introduces specific oxidizing biocides (such as chlorine, bromine, or iodine compounds) independently, allowing precise control of biocide distribution and concentration profiles throughout the feed water stream.
Solution Approach 2:
The patent implements feedback control by continuously measuring free residual oxidant concentrations using DPD reagent and adjusting biocide addition rates based on these measurements. The system maintains free residual oxidant levels below 0.1 mg/L as Cl2 at the membrane inlet through closed-loop control, where measurements inform subsequent dosing adjustments to optimize protection while minimizing damage.
3Duration of action of stationary object
If free residual oxidant concentration is maintained low at membrane inlet, then membrane damage is reduced, but biofouling prevention effectiveness may be compromised
Solution Approach 1:
The patent applies preliminary action by introducing and distributing oxidizing biocides at multiple injection points upstream of the RO membrane inlet, allowing the biocides to act on microorganisms and organic matter in the feed water before reaching the membrane. This preliminary treatment reduces biofouling potential while the concentration is controlled to be below 0.1 mg/L as Cl2 at the membrane inlet to prevent damage.
Solution Approach 2:
The patent applies local quality by creating different oxidant concentration zones at different locations in the feed water stream. Higher concentrations are permitted in upstream regions where biocides are injected and mixed, providing strong biofouling prevention. Downstream near the membrane inlet, concentrations are controlled to be low (<0.1 mg/L as Cl2) to protect the membrane, achieving both protection goals through spatial variation.
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 effectively inhibits biofouling on RO membranes, maintaining membrane integrity and extending the device's operational lifespan by ensuring optimal biocide concentrations and minimizing oxidative damage.
Implementation Method 1
measuring a free residual oxidant concentration of the first sample and the second sample using a reagent comprising N,N-diethyl-p-phenylenediamine (DPD)
Implementation Method 2
adding a first oxidizing biocide at a first injection point upstream of a reverse osmosis (RO) membrane inlet. The methods further include adding a second oxidizing biocide at a second injection point upstream of the RO membrane inlet
Implementation Method 3
reverse osmosis (RO) membrane separation device
Data Source
AI summary
The present disclosure provides methods of monitoring and controlling biocides in an aqueous medium, methods of manufacturing the compositions, and various oxidizing biocide compositions suitable for use in aqueous medium treatment processes. Methods include adding a first oxidizing biocide at a first injection point upstream of a reverse osmosis (RO) membrane inlet, adding a second oxidizing biocide at a second injection point upstream of the RO membrane inlet, obtaining a first sample of the aqueous medium from a first location downstream of the first and second injection points and upstream of the RO membrane inlet, and obtaining a second sample of the aqueous medium from a second location downstream of the first location but immediately upstream of the RO membrane. Methods may also include measuring free residual oxidant concentration, total residual oxidant concentration, and oxidation-reduction potential of the first and second samples and adjusting biocide addition based on the measurements.