Gravity Membrane Filter Conversion Using Static Head Pressure
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Solution Overview
Problem
Conventional water treatment systems face inefficiencies in filtration processes, particularly in maintaining membrane permeability and flux without frequent regenerative chemical cleaning, and in integrating membrane filtration into existing gravity sand filters without significant modifications.
Innovation Solution
The system converts a conventional gravity sand filter into a membrane gravity filter by replacing the granular media with immersed membranes, operating without a permeate pump and using static head differential for filtration, and incorporates a low-dose oxidant in backwash water to maintain biofilm porosity, allowing for extended periods without regenerative cleaning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional media filters are used, then the system is simple to operate, but filtration efficiency and water quality are insufficient
Solution Approach 1:
The patent changes the fundamental parameter of the filtration medium from granular media to membrane material, enabling ultrafiltration-level filtration efficiency while maintaining operation simplicity through gravity-driven flow and periodic backwashing similar to conventional filters
Solution Approach 2:
The patent replaces the mechanical granular media filtration system with a membrane-based filtration system that achieves superior water quality through molecular-level separation while maintaining compatibility with existing filter infrastructure and operational procedures
2Productivity
If membrane filters are used, then filtration efficiency is improved, but frequent regenerative chemical cleaning is required
Solution Approach 1:
The patent applies low-dose oxidant to the backwash water before it contacts the membrane, performing preventive cleaning action that maintains biofilm porosity and prevents fouling accumulation, thereby extending the time between regenerative cleanings
Solution Approach 2:
The patent uses oxidizing agents in the backwash water to chemically clean the membrane surface by oxidizing organic matter and maintaining biofilm porosity, reducing the frequency of intensive regenerative chemical cleaning required
3Productivity
If membrane filters are used, then water quality is enhanced, but system complexity increases
Solution Approach 1:
The patent designs the membrane filter to perform multiple functions within a single system: filtration, biofilm management through oxidant treatment, and self-cleaning via backwashing, thereby achieving enhanced water quality without proportionally increasing system complexity
Solution Approach 2:
The patent introduces oxidant as an intermediary substance that mediates between the membrane surface and fouling agents, maintaining membrane performance and reducing the need for complex cleaning systems through chemical prevention of fouling
4Productivity
If conventional gravity sand filters are converted to membrane filters, then filtration efficiency is improved, but existing infrastructure requires modification
Solution Approach 1:
The patent segments the membrane filtration system into modular components that can be integrated into existing filter tanks, allowing incremental conversion of conventional gravity sand filters to membrane filters without complete system replacement
Solution Approach 2:
The patent merges membrane filtration technology with existing gravity filter infrastructure by adapting conventional filter tanks, distribution systems, and backwashing mechanisms to accommodate membrane modules, thereby reducing conversion difficulty and cost
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 maintains stable membrane flux and permeability over extended periods, reduces the need for frequent backwashes, and enhances water quality without increasing the filtration system's footprint or water usage, achieving comparable yields to rapid sand filters.
Implementation Method 1
the membrane pore size is usually in the ultrafiltration or microfiltration range
Implementation Method 2
the membrane pore size is usually in the ultrafiltration or microfiltration range
Implementation Method 3
Transmembrane pressure to cause a flow of permeate through the membrane is optionally created by a static head differential
Implementation Method 4
incorporates a low-dose oxidant in backwash water to maintain biofilm porosity
Data Source
Figure 1~2A
Figure 2B~3
Figure 4~5
AI summary
A conventional media filter such as a gravity sand filter is converted into a membrane filter. The media is removed and replaced by immersed membrane modules. Transmembrane pressure is created by a static head pressure differential, without a suction pump, thereby creating a membrane gravity filter (MGF). Preferred operating parameters include transmembrane pressure of 5-20 kPa, 1-3 backwashes per day, and a flux of 10-20 L/m2/h. The membranes are dosed with chlorine or another oxidant, preferably at 700 minutes*mg/L as Cl2 equivalent per week or less. The small oxidant does is believed to provide a porous biofilm or fouling layer without substantially removing the layer. The media filter may be modified so that backwash wastewater is removed from near the bottom of the tank rather than through backwash troughs above the membrane modules. Membrane integrity testing may be done while the tank is emptied after a backwash.