Multilayer Media Bed Filter Air Backwash Stratification
Solution Overview
Problem
Multi-layer media bed filters with micromedia face challenges in backwashing due to the difficulty in separating contaminants from fine particles, as conventional liquid backwash methods are ineffective, and air backwash disrupts stratification, leading to inefficient contaminant removal and frequent maintenance needs.
Innovation Solution
An air backwash method that uses controlled air flow to suspend micromedia contaminants above the media bed, combined with a low-level liquid flow to flush away contaminants without disrupting the stratification of the media layers, and the use of raw liquid nozzles to clean the surface without displacing micromedia.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional liquid backwash is used to remove contaminants from micromedia, then the liquid flow can fluidize the media bed, but the small micromedia particles remain in suspension and cannot be effectively separated from contaminants
Solution Approach 1:
The patent introduces air as an intermediary substance during backwash. Air bubbles rise through the media bed, carrying micromedia particles and contaminants to the surface where they form a froth layer that can be easily removed. This intermediary mechanism solves the separation difficulty by providing a new phase (gas-liquid-solid froth) that facilitates contaminant removal without requiring direct liquid-liquid separation.
Solution Approach 2:
The patent utilizes phase transition by introducing air (gas phase) into the liquid media bed. The gas bubbles rise through the bed, creating a two-phase flow that transforms the separation mechanism. The gas-liquid mixture carries solids to the surface, and upon reaching the surface, the gas escapes, leaving contaminants that can be skimmed off. This phase transition approach overcomes the suspension problem of liquid-only backwash.
2Quantity of substance
If air backwash is used to effectively clean micromedia, then contaminant removal improves, but media stratification is disrupted and requires restratification
Solution Approach 1:
The patent applies partial air backwash rather than full fluidization. Air is introduced at controlled rates that provide sufficient cleaning action to remove contaminants from micromedia surfaces and interstices, but not enough to completely disrupt the media stratification. This partial action approach achieves effective cleaning while maintaining the stable layered structure of the multi-media bed.
Solution Approach 2:
The patent employs periodic backwash cycles rather than continuous operation. During filtration, media stratification is maintained. During periodic backwash intervals, air is introduced to clean contaminants, followed by a settling period where stratification is restored. This periodic alternation between cleaning and stratification maintenance resolves the contradiction between effective cleaning and stratification stability.
3Reliability
If micromedia is used to trap fine particles effectively, then filtration performance improves, but backwash becomes more challenging due to particle size
Solution Approach 1:
The patent combines pneumatic (air) and hydraulic (water) systems for backwash. Air bubbles provide the primary cleaning mechanism by rising through the media and attaching to contaminants, while water flow supports the media bed and facilitates the removal of the air-contaminant-micromedia froth mixture. This combined pneumatic-hydraulic approach simplifies the backwash process compared to using either system alone, making it easier to handle the fine micromedia particles effectively.
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 significantly increases contaminant removal efficiency compared to liquid backwash alone, maintains media stratification, and reduces downtime by effectively cleaning micromedia filters without losing media particles, thus enhancing filtration performance and reducing maintenance frequency.
Implementation Method 1
uses controlled air flow to suspend micromedia contaminants above the media bed
Implementation Method 2
combined with a low-level liquid flow to flush away contaminants
Implementation Method 3
a top layer of microsand by providing suitable flow properties at the surface of the media. An advantage of such flow properties is an increase in the ability of the media to collect fine particles
Implementation Method 4
The backwash flow is then reduced to allow the filter media to resettle and stratify correctly
Data Source
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AI summary
A multi-layer media bed filter with an increasing density of media from the finest media on the top to the coarsest media on the bottom is backwashed using air without significantly disrupting stratification of the media layers. When the air is stopped, the contaminants in the liquid above the finest media that were removed by the airflow are flushed away either with liquid injected above the media or by a liquid flow through the media that does not remove the finest media. The amount of contaminants that remain in the finest media with the stratification-maintaining air backwash is significantly less than when using liquid backwash alone, whether the liquid backwash uses a flow rate sufficient to suspend the micromedia or below a suspending flow rate.