Bioretention System with Composite Filtration Media
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Solution Overview
Problem
Bioretention systems with sandy media and free discharge outlets are less effective for long-term removal of dissolved nitrogen and phosphorus, failing to meet Total Maximum Daily Load (TMDL) criteria for nutrient pollutants in stormwater and wastewater.
Innovation Solution
A bioretention system using a filtration media with a coarse-textured matrix of well-graded sand blended with organic material like peat moss and a fine fraction of clay-like material with high phosphorous sorption capacity, along with an outlet system that extends residence time for improved nitrogen removal, is proposed. This system includes a blend of materials such as crushed limestone, iron-coated sand, and water treatment residuals, and incorporates vegetation for enhanced biological uptake and transformations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If typical bioretention systems use sandy media with free discharge outlets, then the system is simple to construct and operate, but the system is less effective for long-term removal of dissolved nitrogen and phosphorus
Solution Approach 1:
The patent applies composite materials by blending multiple media components together: coarse-textured sand (50-80% by volume) for filtration and structure, organic material like peat moss (10-20% by volume) for nutrient uptake, and fine fraction clay-like material with high phosphorous sorption capacity (10-40% by volume) for chemical retention. This composite media composition resolves the contradiction by achieving superior long-term nutrient removal effectiveness while maintaining a manageable system structure through defined blending ratios and material specifications.
Solution Approach 2:
The patent applies local quality by assigning different functional properties to different fractions of the media: the coarse sand fraction provides mechanical filtration and structural stability, the organic material fraction provides biological nutrient uptake pathways, and the fine clay-like fraction provides chemical sorption capacity for phosphorous. This functional differentiation within the media composition enables the system to address multiple nutrient removal mechanisms simultaneously, resolving the effectiveness-complexity contradiction.
2Reliability
If the outlet system extends residence time for improved nitrogen removal, then nitrogen removal efficiency increases, but the system complexity increases
Solution Approach 1:
The patent applies dynamics by implementing an outlet system that adjusts residence time based on flow conditions. The system extends residence time during low-flow conditions to maximize nitrogen removal through denitrification processes, while allowing faster discharge during high-flow events. This dynamic adjustment of hydraulic retention time resolves the contradiction between achieving high nitrogen removal efficiency and maintaining system simplicity.
3Quantity of substance
If the system retains high flows during large events, then more pollutant load is treated, but the residence time for nutrient removal decreases
Solution Approach 1:
The patent applies partial action by designing the outlet system to provide full treatment capacity for baseflow conditions while allowing bypass of excess flow during large storm events. The system treats a sufficient portion of the total pollutant load under normal conditions to meet TMDL criteria, while accepting that complete treatment of all flow conditions is not necessary. This resolves the contradiction by achieving adequate pollutant load treatment without requiring excessively long residence times for all flow conditions.
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 retains over 70% of phosphorus and 90% of nitrogen from stormwater, maintaining high removal efficiency even after decades of stormwater loads, while allowing high flows during large events, thus meeting stringent environmental criteria.
Implementation Method 1
As the effluent passes through the bioretention system, particulate pollutants are removed by filtration
Implementation Method 2
Dissolved phosphorus can be removed from the effluent by biological processes of the system such as vegetative and microbial biomass uptake, as well as chemical adsorption/precipitation processes (herein referred to under the category of sorption)
Implementation Method 3
Dissolved phosphorus can be removed from the effluent by biological processes of the system such as vegetative and microbial biomass uptake
Implementation Method 4
Dissolved nitrogen can also be removed from the effluent by vegetative and microbial biomass uptake, as well as biological transformations, including denitrification, that eventually convert nitrogen into nitrogen gas
Data Source
AI summary
A bioretention system and method are provided for removing phosphorus, nitrogen and other materials from effluent such as wastewater and stormwater. The system and method can include a filtration media comprising water treatment residuals and other fill such as soil. Plants can be growing in the soil. The system can also include a drainage system to regulate outflow, to function during both low and high throughputs of water.