Constructed Wetland System for Nitrous Oxide Reduction in Sewage Treatment
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Solution Overview
Problem
Conventional sewage treatment systems in sequencing batch constructed wetlands lack an anoxic section, leading to low removal efficiency of total nitrogen (TN) and high emission of nitrous oxide (N2O) due to neglect of the denitrification process.
Innovation Solution
A system comprising a regulating pool, a first aerobic constructed wetland, an anoxic pool, and a second aerobic constructed wetland, where the first aerobic wetland operates in sequencing batch mode with hydraulic drop aeration and the anoxic pool maintains an anoxic state for enhanced denitrification, reducing N2O production and improving TN removal efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If only aerobic condition is provided in nitrification phase, then N2O production is controlled, but TN removal efficiency is low due to absent anoxic section for denitrification
Solution Approach 1:
The treatment system is divided into distinct functional segments: aerobic nitrification zones and anoxic denitrification zones. The anoxic pool is separated from aerobic constructed wetlands, allowing independent optimization of each process. This segmentation enables simultaneous N2O control in aerobic zones and TN removal through denitrification in the anoxic zone.
Solution Approach 2:
The system employs periodic switching between aerobic and anoxic conditions in the constructed wetlands. During nitrification phase, aerobic conditions prevail; during denitrification phase, anoxic conditions are established. This periodic action allows the same system to perform both nitrification and denitrification functions, improving TN removal while controlling N2O emissions.
2Productivity
If anoxic section is added for denitrification, then TN removal efficiency is improved, but system complexity increases
Solution Approach 1:
The system uses internal recycling of treated water to provide carbon source for denitrification. The anoxic pool receives recycled water from aerobic zones, which contains nitrate that can be reduced. This self-service approach eliminates the need for external carbon source addition and reduces system complexity while maintaining high TN removal efficiency.
Solution Approach 2:
The system merges multiple functions into integrated units. The anoxic pool serves both as a denitrification reactor and as a mixing zone for recycled water. The constructed wetlands perform both filtration and biological treatment functions. This merging reduces the number of separate components needed while achieving the desired TN removal.
3Device complexity
If conventional aerobic-only system is used, then system structure is simple, but energy consumption is high and TN removal is insufficient
Solution Approach 1:
The system is designed with gravity-driven flow paths where water flows from higher to lower elevation through different treatment zones. The anoxic pool is positioned to receive water by gravity flow from aerobic zones, eliminating the need for energy-intensive pumping between stages. This equipotential design reduces energy consumption while maintaining effective TN removal.
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 effectively reduces N2O emission, enhances TN removal efficiency, and decreases energy consumption by maintaining high dissolved oxygen levels in aerobic wetlands and ensuring an anoxic state in the anoxic pool, meeting urban recycling water quality standards.
Implementation Method 1
Because the first aerobic constructed wetland is fed with water in the form of hydraulic drop, a contact area between the sewage and the air is increased in the hydraulic drop process
Implementation Method 2
the anoxic pool maintains an anoxic state for enhanced denitrification, reducing N2O production
Implementation Method 3
The aerobic constructed wetland adopts the sequencing batch operation, and the reaction time thereof is short. When a content of dissolved oxygen (DO) decreases to 0.5 mg/L below before reaching an anoxic state
Data Source
AI summary
A system for reducing emission of nitrous oxide during sewage treatment, including: a regulating pool, a first aerobic constructed wetland, an anoxic pool, and a second aerobic constructed wetland. The water outlet of the regulating pool is connected to the water inlet of the top of the first aerobic constructed wetland via a pipe and a first control valve. The first aerobic constructed wetland includes sequencing batch constructed wetlands arranged in parallel. A branch pipe and a second control valve are disposed on the pipe between the regulating pool and the first aerobic constructed wetland. The outlet of the branch pipe and the water outlet of the first aerobic constructed wetland are combined together and connected to the water inlet of the bottom part of the anoxic pool. The anoxic pool is an upward flow biological filter.