Cationic Polymer Pre-treatment for Ultrafiltration Membrane Fouling
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Solution Overview
Problem
The second-stage ultrafiltration (UF) or microfiltration (MF) membranes in water treatment systems foul quickly due to high contaminant levels in backwash water, leading to increased capital and operating costs, reduced membrane lifespan, and lower flux rates.
Innovation Solution
Treating backwash water with water-soluble cationic polymers, such as cationic copolymers of acrylamide and cationic monomers, before passing it through a membrane system, which can include additional reverse osmosis or nanofiltration membranes, to reduce fouling and enhance flux rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If backwash water is treated with a second-stage UF/MF membrane system, then water recovery is increased to 96-98%, but membrane fouling occurs quickly requiring frequent cleaning and operation at lower fluxes
Solution Approach 1:
The patent applies preliminary action by adding water-soluble polymers to backwash water before membrane filtration to modify contaminant properties. This pre-treatment prevents fouling substances from adhering to membrane surfaces during subsequent filtration, enabling sustained high-flux operation and reducing cleaning frequency while maintaining 96-98% water recovery
Solution Approach 2:
The patent uses water-soluble polymers as intermediary substances that interact with contaminants in backwash water. These polymers act as mediators by binding to suspended solids and colloidal materials, preventing them from fouling the membrane surface while allowing clean permeate passage, thus resolving the contradiction between high recovery and fouling resistance
2Productivity
If membrane flux is increased to improve productivity, then treatment capacity increases, but membrane fouling accelerates requiring more frequent cleaning
Solution Approach 1:
The patent applies preliminary action by pre-treating backwash water with water-soluble polymers before high-flux membrane filtration. This pre-modification of contaminants allows the membrane to operate at elevated flux rates without rapid fouling accumulation, extending cleaning intervals while maintaining high productivity
Solution Approach 2:
The patent changes the chemical parameters of backwash water by adding water-soluble polymers, which alter the physical-chemical properties of contaminants. This parameter change prevents contaminant-membrane interaction at high fluxes, allowing sustained high-rate operation with extended cleaning intervals
3Productivity
If more membranes are installed to handle fouling, then treatment capacity is maintained, but capital cost increases
Solution Approach 1:
The patent applies preliminary action by pre-treating backwash water with water-soluble polymers to prevent fouling before it occurs. This approach allows existing membrane capacity to operate at full potential for extended periods, eliminating the need for additional membrane installations to compensate for frequent fouling-related capacity losses
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
Significantly reduces membrane fouling, increases permeate flux by up to 200% compared to untreated backwash water, and lowers the need for frequent cleaning and membrane replacement, thereby reducing operational and capital costs.
Implementation Method 1
treating backwash water with water-soluble cationic polymers, such as cationic copolymers of acrylamide and cationic monomers
Implementation Method 2
processing backwash water via the use of a membrane system including a microfiltration membrane or an ultrafiltration membrane
Data Source
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AI summary
A method of processing backwash water by use of a membrane separation process is disclosed. Specifically, the following steps are taken to process backwash water: collecting backwash water in a receptacle suitable to hold said backwash water; treating said backwash water with one or more water soluble polymers, wherein said water soluble polymers are selected from the group consisting of: amphoteric polymers; cationic polymers, wherein, said charge density is from about 5 mole percent to about 100 mole percent; zwitterionic polymers; and a combination thereof; optionally mixing said water soluble polymers with said backwash water; passing said treated backwash water through a membrane, wherein said membrane is an ultrafiltration membrane or a microfiltration membrane; and optionally back-flushing said membrane to remove solids from the membrane surface.