Draft Tube Backwash for Layered Wastewater Filter Media
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Solution Overview
Problem
Existing filter beds for wastewater treatment face challenges in maintaining the integrity of multi-material layers during backwash processes, as thorough mixing occurs, making it difficult to effectively clean and maintain filter efficiency.
Innovation Solution
A wastewater filter design featuring a draft tube within a stratified media bed, where a backwash fluid is injected into one layer and a backwash gas is introduced into the draft tube, allowing for the separate fluidization and rolling of different filter media layers without significant mixing, thereby preserving the interface plane and maintaining layer integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional backwash process is used to clean filter media, then the filter media is thoroughly mixed and cleaned, but the stratified multi-material filter bed structure is disrupted and layer integrity is lost
Solution Approach 1:
The backwash process is segmented into two distinct zones: an upper expansion zone where media is fluidized and cleaned, and a lower support zone where media remains stable. The draft tube creates this segmentation by confining gas injection to the upper portion, allowing differential treatment of different media layers during backwash.
Solution Approach 2:
Different regions of the filter bed receive different treatments during backwash. The upper region near the draft tube experiences vigorous gas injection and media expansion for cleaning, while the lower region maintains fluid flow for support and gradual cleaning, preserving the overall stratified structure.
2Productivity
If multi-material filter beds are used to improve filtration performance, then filtering efficiency is enhanced, but the backwash process causes mixing of different media layers making maintenance difficult
Solution Approach 1:
The draft tube acts as an intermediary structure that mediates between the backwash gas injection and the stratified media layers. It directs gas flow to fluidize and clean the upper media layers while preventing excessive mixing, enabling maintenance of multi-material beds without losing their functional stratification.
3Ease of operation
If backwash gas is injected directly into the filter media bed, then media fluidization occurs for cleaning, but excessive mixing of different media layers happens
Solution Approach 1:
The draft tube is nested within the filter media bed, creating a confined zone for gas injection. This nested structure allows gas to fluidize media within the tube's confines while the surrounding media remains relatively undisturbed, preventing excessive mixing of different media layers.
Solution Approach 2:
The draft tube introduces a vertical dimension to gas distribution, injecting gas upward through a confined channel rather than distributing it horizontally across the entire bed. This dimensional change creates localized fluidization zones that clean media without causing widespread mixing.
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
The solution effectively cleans and maintains the filter media layers by minimizing mixing, ensuring continued efficient operation and separation of media layers, enhancing the backwash process's efficacy.
Implementation Method 1
injecting a backwash gas into the draft tube, the backwash gas having a second flow rate selected to draw a portion of the second filter media from a bottom portion of the second media layer to a top portion of the second media layer
Implementation Method 2
injecting a backwash fluid into the first media layer, the backwash fluid having a first flow rate that is selected to mix and roll the first media layer and fluidize the second media layer
Data Source
Figure 1
Figure 2
AI summary
A wastewater filter includes a vessel having a bottom and a side wall that cooperate to define a filter space. A first filter media is positioned within the filter space to define a first media layer, and a second filter media different from the first filter media is positioned within the filter space above the first media layer to define a second media layer, the first media layer and the second media layer cooperating to define an interface plane. A draft tube is positioned within the second media layer and has a first end positioned a first non-zero distance above the interface plane, and a second end disposed a second non-zero distance from a top surface of the second media layer. A backwash fluid line is positioned to inject a backwash fluid into the first filter media, and a backwash gas line is positioned to inject a backwash gas into the draft tube.