Membrane Bioreactor PAC Dosing and Air Scouring
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Solution Overview
Problem
Membrane bioreactors (MBRs) face issues with irreversible fouling and abrasion damage due to the use of powdered activated carbon (PAC), leading to reduced membrane life expectancy and increased sludge concentration, pore plugging, and membrane wear, which existing technologies have not adequately addressed.
Innovation Solution
The use of a membrane bioreactor system where PAC is dosed into the mixed liquor at concentrations of 200 mg/L or more, with the sorbent particles contacting the membranes directly, and air scouring during filtration cycles, combined with bioaugmentation products immobilized on carriers to enhance contaminant removal and tolerance to shock loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If powdered activated carbon (PAC) is used in membrane bioreactor at high concentration (200 mg/L or more), then contaminant removal efficiency is improved, but membrane abrasion and irreversible fouling increase significantly
Solution Approach 1:
The patent introduces a carrier particle as an intermediary between PAC and the membrane. PAC is immobilized on the carrier surface, allowing contaminant adsorption to occur on the carrier rather than directly on the membrane. This mediator prevents direct contact between abrasive PAC particles and the membrane, reducing wear and fouling while maintaining contaminant removal efficiency.
Solution Approach 2:
The carrier particles are designed to be replaceable and can be removed from the system periodically. Instead of permanently installing membranes that suffer from cumulative abrasion damage, the carriers can be exchanged, transferring the wear to disposable components rather than critical long-life components.
2Quantity of substance
If PAC dosage rate is increased to 200 mg/L or more in MBR, then adsorption capacity for recalcitrant contaminants is improved, but sludge concentration and pore plugging increase
Solution Approach 1:
The carrier acts as an intermediary that concentrates PAC in specific locations within the bioreactor. This localized concentration improves adsorption capacity in the bulk liquid while the carrier itself can be managed separately, allowing for easier removal of PAC-laden carriers rather than dealing with dispersed PAC throughout the sludge matrix.
Solution Approach 2:
The system segments the PAC distribution by attaching it to discrete carrier particles rather than having free-floating PAC. This segmentation allows for better control over PAC distribution and facilitates separation of PAC-containing carriers from the treated effluent, reducing pore plugging.
3Device complexity
If PAC is used without carrier support, then system complexity is reduced, but membrane life expectancy decreases by up to 40%
Solution Approach 1:
The carrier serves as a simple intermediary component that protects the membrane from PAC-induced damage. While it adds one additional element to the system, the overall complexity remains low, and the benefit of extending membrane life by 40% or more outweighs the minor increase in system components.
Solution Approach 2:
The invention changes the physical state of PAC from free-floating powder to immobilized particles on carriers. This parameter change in PAC distribution and attachment state fundamentally alters the interaction dynamics between PAC, membrane, and mixed liquor, enabling simultaneous achievement of contaminant removal and membrane protection.
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 enhances contaminant removal efficiency, increases membrane tolerance to shock loads, and extends membrane lifespan by reducing fouling and abrasion, while maintaining high effluent quality and COD removal rates.
Implementation Method 1
Air bubbles are provided to scour the membranes including during at least part of the permeation step
Implementation Method 2
A supply unit doses particles of a sorbent, for example powdered activated carbon (PAC), into the MBR
Implementation Method 3
Permeate is withdrawn through immersed membranes comprising a supporting structure
Data Source
AI summary
A membrane bioreactor (MBR) has membranes comprising a supporting structure. A supply unit doses a sorbent such as powdered activated carbon (PAC) into the MBR. The PAC is maintained at a concentration in the mixed liquor of 200 mg/L or more. Mixed liquor with the sorbent particles recirculates within the MBR at a flow rate of at least twice the feed flow rate. Air bubbles are provided to scour the membranes including during at least part of a permeation step. The sorbent particles are present in the mixed liquor and contact the membranes. Bioaugmentation products may be immobilized on PAC or other carriers and then added to an MBR or other bioreactors.