Membrane Bioreactor Recycle Wall Design
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Solution Overview
Problem
Flat-sheet membrane bioreactors (SMBR) systems face inefficiencies due to low packing density, long hydraulic residence times (HRT), and energy inefficiencies, primarily caused by inefficient structural design, piping, and air scouring methods, which lead to space and energy wastage, as well as dissolved oxygen and mixed liquor suspended solids (MLSS) gradients that affect treatment efficiency.
Innovation Solution
The reorientation and integration of mixed liquor return channels and internal recycle streams into a common wall or space, allowing for single-pass filtration and eliminating gradients, along with a compact arrangement of membrane assemblies that promotes continuous stirred tank reactors, reducing volumetric space requirements and eliminating the need for additional concrete walls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flat-sheet membrane assemblies are arranged with dedicated air diffusers and circular flow patterns, then air scouring effectiveness is improved, but space efficiency deteriorates due to increased volume requirements
Solution Approach 1:
The patent merges the air diffuser system with the membrane assembly support structure, integrating multiple functions into a single unified component. The air diffusers are positioned at the bottom of the tank and serve dual purposes: providing air scouring and supporting the membrane assemblies, thereby reducing the overall volume required for the reactor system.
Solution Approach 2:
The patent transitions from traditional circular horizontal flow patterns to a vertical flow pattern where air and mixed liquor move upward through the membrane assemblies. This dimensional change allows for more compact reactor design by utilizing vertical space more effectively, reducing the horizontal footprint and overall volume requirements.
2Ease of operation
If membrane assemblies are spaced apart to allow roll pattern flow, then flow distribution is improved, but packing density deteriorates
Solution Approach 1:
The patent employs a dynamic flow distribution system where air flow rates can be independently controlled for each membrane assembly. This allows the system to adapt flow distribution dynamically based on operational requirements, maintaining effective flow patterns while enabling closer spacing of membrane assemblies to increase packing density.
Solution Approach 2:
The patent utilizes pneumatic air flow through the membrane assemblies to create upward flow patterns that distribute mixed liquor effectively. The air scouring action combined with hydraulic flow creates a self-regulating system that maintains proper flow distribution without requiring large spacing between assemblies, thereby improving packing density.
3Reliability
If traditional piping and air scouring methods are used, then membrane cleaning is effective, but energy consumption increases
Solution Approach 1:
The patent implements a self-service cleaning system where the air scouring process simultaneously performs both membrane cleaning and mixed liquor circulation functions. The air flow required for scouring automatically creates the upward flow pattern that distributes mixed liquor through the membrane assemblies, eliminating the need for separate high-energy pumping systems and reducing overall energy consumption.
Solution Approach 2:
The patent optimizes operational parameters including air flow rates, water temperature, and mixed liquor velocity to enhance the efficiency of the air scouring process. By carefully controlling these parameters, the system achieves effective membrane cleaning with reduced energy input compared to traditional mechanical cleaning methods or separate aeration systems.
4Device complexity
If dissolved oxygen gradients are allowed to develop, then aeration is simplified, but treatment efficiency deteriorates
Solution Approach 1:
The patent incorporates preliminary mixing of the mixed liquor before it enters the membrane assemblies, ensuring uniform distribution of dissolved oxygen and other constituents. This preliminary action prevents the formation of harmful gradients and ensures consistent treatment performance throughout the reactor, maintaining high treatment efficiency without requiring complex aeration systems.
Solution Approach 2:
The patent employs monitoring systems that detect dissolved oxygen levels and mixed liquor characteristics in real-time, providing feedback to control air flow rates and other operational parameters. This feedback mechanism allows the system to maintain optimal conditions for treatment efficiency while simplifying aeration control through automated regulation rather than complex manual management.
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 configuration decreases HRT by 40%, increases energy efficiency, reduces construction costs, and enhances treatment efficiency by eliminating MLSS and DO gradients, allowing for longer tank designs without impacting performance.
Implementation Method 1
The rise velocities of bubbles are generally at least 10 times typical mechanical pumping rates and are sufficient to induce the desired slug flow regime
Implementation Method 2
Slug-flow is a hydrodynamic condition that research suggests promotes the most efficient air scouring in submerged membrane applications
Implementation Method 3
Flat-sheet membrane technology has some inherent advantages over alternate technologies when used in submerged membrane bioreactor (SMBR) applications
Implementation Method 4
a combination of mixed liquor (activated sludge and wastewater) and air moving tangentially across the surface of membranes (cross-flow) scours filtered solids from the surface of the membrane
Implementation Method 5
pumping effect. The rise velocities of bubbles are generally at least 10 times typical mechanical pumping rates
Data Source
AI summary
Flat-sheet membrane filter assemblies require open space around equipment to form a viable path for an internal recycle or roll pattern. Creating a dedicated roll pattern for individual filter assemblies is space intensive and imposes process constraints on tank dimensions. A hollow wall or series of pipes forms a recycle wall designed to consolidate roll patterns and reduces space requirements. The recycle wall is designed such that the structural components also serve as a mixed liquor distribution system for the necessary roll pattern. Fixed vertically oriented conduit and sectional channel pieces allow for easy access and removal of membrane filter assemblies installed side by side. Feeding mixed liquor, air and or influent to the bottom of filter assemblies via submerged conduit improves process efficiency when coupled with return channels spaced not more than 10 feet away and above assemblies. The system is particularly advantageous for flat-sheet membrane filter units used in SMBR applications but is adaptable to other technologies including tubular and hollow-fiber membrane filter assemblies.