Dual Media Wastewater Reactor for Selenium and Nitrogen Removal
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Solution Overview
Problem
Existing biological reactors face flow path blockages due to nitrogen gas produced during denitrification in wastewater with high nitrate concentrations, necessitating frequent backwashing, especially when treating influent with nitrate levels over 50 ppm.
Innovation Solution
A biological reactor with two types of media, a porous upstream medium for denitrification and a compact downstream medium for selenium reduction, allowing nitrogen gas to rise and be released, reducing the need for backwashing and increasing treatment capacity by enabling expansion of the selenium reduction medium into the upstream medium during backwash.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a compact media bed is used for selenium reduction, then selenium removal efficiency is improved, but flow path blockage occurs due to nitrogen gas accumulation
Solution Approach 1:
The reactor is divided into two distinct zones: a denitrification zone with coarse media for nitrogen removal and a selenium reduction zone with compact media for selenium removal. This segmentation allows each zone to perform its specific function without interference, preventing flow path blockage while maintaining high selenium removal efficiency.
Solution Approach 2:
The coarse media in the denitrification zone acts as an intermediary that facilitates nitrogen gas release before wastewater enters the selenium reduction zone. This intermediary zone prevents nitrogen gas from accumulating in the compact media bed, thereby avoiding flow path blockage.
2Reliability
If denitrification is performed in a compact media bed, then nitrogen removal is achieved, but backwashing frequency increases
Solution Approach 1:
By separating denitrification and selenium reduction into different zones with appropriate media types, the system eliminates the need for frequent backwashing. The coarse media in the denitrification zone allows nitrogen gas to escape freely, preventing the flow path blockages that would otherwise require frequent backwashing.
Solution Approach 2:
Different media properties are assigned to different zones: coarse porous media in the denitrification zone for gas release, and compact media in the selenium reduction zone for efficient selenium removal. This local optimization of media properties prevents flow path blockage while maintaining high productivity.
3Device complexity
If a single media bed is used, then device complexity is reduced, but treatment capacity is limited
Solution Approach 1:
The reactor is segmented into two functional zones with different media types, each optimized for its specific purpose. This segmentation increases treatment capacity by allowing simultaneous denitrification and selenium reduction without requiring complex external treatment systems.
Solution Approach 2:
The system merges denitrification and selenium reduction functions into a single integrated reactor with two zones. This combination achieves high treatment capacity while maintaining relatively simple device structure, as both processes occur within one reactor vessel.
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 dual-medium reactor effectively reduces selenium and nitrogen concentrations, minimizing backwashing frequency and enhancing treatment capacity by allowing free release of nitrogen gas and expansion of the selenium reduction medium, thus addressing flow path blockages and improving operational efficiency.
Implementation Method 1
An upstream medium is relatively porous and suitable for denitrification
Implementation Method 2
dissolved selenium is removed from contaminated water by treating the water in a reactor containing selected endemic and other selenium reducing organisms
Data Source
AI summary
A bioreactor has a biofilm supporting bed with at least two types of media. An upper media is relatively porous, preferably porous enough to admit particles of a lower media. In use, wastewater flows downwards through the bed. Soluble nitrogen is reduced in the upper media and converted into nitrogen gas. Nitrogen gas bubbles rise through the upper media and escape from the bed. Selenium is reduced in the lower media and converted into elemental selenium. The elemental selenium is released periodically by backwashing the bed, which may cause fluidization or other expansion of the lower media into the upper media.