Wastewater DAF Solids Recycle for BOD Removal
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Solution Overview
Problem
Conventional wastewater treatment systems face inefficiencies in removing biological oxygen demand (BOD) and suspended solids, leading to increased energy consumption and larger treatment unit sizes, as they typically do not recycle solids from dissolved air flotation (DAF) units back to contact tanks.
Innovation Solution
Incorporating a DAF unit in a wastewater treatment system to remove solids from a portion of the mixed liquor before it enters the biological treatment unit and recycling at least a portion of these solids back to the contact tank, reducing the biological oxygen demand and increasing biogas production in the anaerobic digester.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If solids are not recycled from DAF unit to contact tank, then system complexity is low, but BOD removal efficiency is insufficient and energy consumption is high
Solution Approach 1:
The patent implements a feedback mechanism by recycling a portion of the solids removed by the DAF unit back to the contact tank. This creates a closed-loop system where treated solids are returned to enhance further treatment, improving BOD removal efficiency while maintaining manageable system complexity through controlled feedback routing.
Solution Approach 2:
Instead of completely discarding the solids removed by the DAF unit, the patent recovers a portion of these solids and returns them to the contact tank. This selective recovery approach maximizes BOD removal efficiency by utilizing the adsorption capacity of the recycled solids while avoiding the complexity of complete solids recycling.
2Productivity
If larger biological treatment units are used to treat all BOD, then BOD removal efficiency is high, but system size and capital cost increase
Solution Approach 1:
The patent applies preliminary action by having the DAF unit perform initial BOD removal and solids concentration before the mixed liquor enters the biological treatment unit. This pre-treatment reduces the BOD load on the biological treatment units, allowing them to be smaller while maintaining high overall BOD removal efficiency.
Solution Approach 2:
The patent segments the BOD removal process into two distinct stages: (1) physical-chemical separation in the DAF unit that removes a significant portion of BOD and solids, and (2) biological treatment in the subsequent units that polish the effluent. This segmentation allows each unit to be optimized for its specific function, reducing the size requirement of biological treatment units.
3Productivity
If more energy is consumed in biological treatment, then BOD removal efficiency is high, but operating cost increases
Solution Approach 1:
The DAF unit performs preliminary BOD removal through dissolved air flotation, which consumes less energy than extensive biological treatment. By removing a significant portion of BOD in this energy-efficient preliminary stage, the subsequent biological treatment units require less energy input to achieve the same overall removal efficiency.
Solution Approach 2:
The patent partially replaces the mechanical biological treatment process with a physical-chemical DAF process. The DAF unit uses dissolved air bubbles to float and remove solids and associated BOD, substituting some of the energy-intensive biological oxidation process with a more energy-efficient physical separation mechanism.
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 the operating efficiency of the wastewater treatment system by reducing the energy consumption and the size of biological treatment units, while increasing biogas production and improving BOD removal efficiency.
Implementation Method 1
a dissolved air flotation tank having an inlet in fluid communication with the outlet of the contact tank, a first outlet, and a second outlet
Implementation Method 2
The gas inlet is configured to introduce gas into the DAF unit to facilitate the flotation of suspended matter from the first mixed liquor
Implementation Method 3
recycling solids from the DAF unit to the contact tank in an amount sufficient to increase biogas production of an anaerobic digester
Implementation Method 4
aerobic tank having a first inlet in fluid communication with the outlet of the aerated anoxic tank, a second inlet in fluid communication with the first outlet of the dissolved air flotation tank, and an outlet
Data Source
AI summary
Systems and methods for treating wastewater including a dissolved air flotation operation performed upon a portion of a mixed liquor output from a contact tank prior to the mixed liquor entering a biological treatment tank.