Vertical Flow Wetland with Forced Aeration for Nitrogen Removal
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Solution Overview
Problem
Conventional Vertical Flow Constructed Wetlands (VFCWs) require large surface areas, are not economically competitive due to the availability of suitable materials, and have low total nitrogen (TN) removal efficiency, limiting their effectiveness in treating wastewater and sludge.
Innovation Solution
A Forced Bed Aeration Unsaturated-Saturated VFCW system with a low-pressure forced aeration device and internal recirculation network, reducing surface requirements and enhancing TN removal efficiency while minimizing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional Vertical Flow Constructed Wetlands are used, then wastewater treatment is provided, but large surface area is required
Solution Approach 1:
The patent transitions from horizontal surface expansion to vertical depth utilization by implementing multiple superimposed layers (aerobic layer, anoxic layer, saturated layer) within the wetland structure. This vertical stratification allows achieving the same treatment capacity with reduced footprint by exploiting the third dimension (depth) rather than expanding horizontally.
Solution Approach 2:
The wetland is divided into functionally distinct segments or layers: an upper aerobic unsaturated layer for nitrification, a middle anoxic layer for denitrification, and a lower saturated layer for phosphorus removal and polishing. Each layer performs specific treatment functions, allowing compact arrangement while maintaining comprehensive wastewater treatment capability.
2Ease of manufacture
If standard French VFCW design is used, then high organic removal and nitrification are achieved, but suitable sand for filters is required
Solution Approach 1:
The patent changes the granulometry parameters of filtering materials from fine sand (2/8 mm) in conventional designs to coarser gravel sizes (4/20 mm in aerobic layer, 10/20 mm in anoxic layer, 20/40 mm in saturated layer). This parameter change improves material availability while maintaining treatment reliability through enhanced permeability and reduced clogging risk.
Solution Approach 2:
Different granulometry qualities are assigned to different layers based on their specific functions: coarser materials in upper layers for better aeration and flow distribution, progressively finer materials toward the saturated zone for effective filtration. This local optimization ensures both material availability and treatment reliability.
3Productivity
If conventional VFCW is used, then treatment is provided, but low total nitrogen removal efficiency is achieved
Solution Approach 1:
The patent adds a vertical dimension to nitrogen removal by creating distinct aerobic and anoxic zones at different elevations within the same structure. The unsaturated aerobic layer enables nitrification while the underlying anoxic saturated layer enables denitrification, achieving complete nitrogen removal through vertical zonation rather than horizontal separation.
Solution Approach 2:
The patent merges nitrification and denitrification processes into a single integrated wetland structure with vertically stacked aerobic and anoxic zones. This consolidation achieves high nitrogen removal efficiency while simplifying the overall system compared to separate treatment units, reducing both complexity and footprint.
4Productivity
If forced aeration is applied to increase oxygen supply, then treatment efficiency improves, but energy consumption increases
Solution Approach 1:
The wetland structure enables self-aeration through its vertical configuration and permeable layers. Water percolating through the unsaturated aerobic zone creates natural air-water interfaces that facilitate oxygen transfer without mechanical intervention. The system serves its own aeration needs through passive physical processes, eliminating energy-consuming aeration equipment.
Solution Approach 2:
The patent replaces mechanical forced aeration systems with passive physical aeration mechanisms inherent in the vertical flow structure. Oxygen transfer is achieved through natural diffusion at air-water interfaces and advection during water percolation, substituting mechanical energy input with thermodynamic and fluid dynamic processes.
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 system achieves a 50% reduction in surface area, ensures TKN < 10 mg/l, TN < 20 mg/l, and TSS < 35 mg/l, with 50% energy consumption reduction compared to prior art, as demonstrated by field experiments.
Implementation Method 1
a low pressure forced aeration device buried at the bottom of the transition layer, which blows a low pressure air flow upwards through the filter
Implementation Method 2
raw wastewater to be treated, distributed over the surface by an inlet pipe network, which percolates uniformly downwards from the surface
Implementation Method 3
The water-unsaturated zone percolates the injected raw water uniformly downwards until reaching the water-saturated drainage zone
Implementation Method 4
an aerobic treatment zone is formed at the top of the wetland, i.e. in the unsaturated layer, which allows the biological degradation of organic matter and a phase of nitrification of part of the ammoniacal nitrogen
Implementation Method 5
a recirculation system returning part of the effluent to the inlet of the constructed wetland
Data Source
Figure 1~2
Figure 3~4
AI summary
The present invention is directed to a vertical flow constructed wetland (VFCW) for the treatment of wastewater and sludge, particularly in small and medium communities, comprising an unsaturated zone at the surface of the ground and a drainage zone partially saturated at the bottom, with a low pressure forced aeration system in the unsaturated layer, and an internal recirculation means. The invention substantially reduces the surface occupied by the construction, and the energy consumption, and improves the nutrient removal of these type of constructed wetlands.