Dual Mixed Liquor Recycle for Nutrient Removal
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Solution Overview
Problem
Conventional wastewater treatment systems face inefficiencies in nutrient removal due to fluctuations in wastewater influent flow rate and nutrient concentration, leading to excessive oxygen and nitrates recycling, which can poison biological reactors and suppress denitrification, resulting in nutrient levels exceeding design requirements and increased operating costs.
Innovation Solution
The implementation of a dual mixed liquor recycle stream system, where a first recycle stream from the second biological reactor is introduced into the first anoxic zone and a second recycle stream from the third biological reactor is introduced into a separate zone of the first biological reactor, allowing for finer control and longer residence times for nutrient conversion, reducing oxygen and nitrates overload, and enhancing denitrification and phosphorus removal processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single mixed liquor recycle stream is used in conventional wastewater treatment systems, then the system structure is simple, but oxygen and nitrates overload occurs leading to biological reactor poisoning and suppressed denitrification
Solution Approach 1:
The single mixed liquor recycle stream is segmented into two separate streams: a first recycle stream from the aerobic reactor to the first anoxic zone, and a second recycle stream from the aerobic reactor to a second zone of the first biological reactor. This segmentation allows independent control of oxygen and nitrates recycling, preventing overload and biological reactor poisoning while maintaining reliable denitrification.
Solution Approach 2:
Different zones of the biological reactor are provided with different quality mixed liquor recycles: the first anoxic zone receives a first recycle stream optimized for denitrification, while the second zone receives a second recycle stream with different characteristics. This local quality differentiation enables each zone to perform its specific function effectively without interference from excessive oxygen or nitrates.
2Loss of energy
If conventional single recycle stream is used, then operating costs are high due to nutrient levels exceeding design requirements, but implementing dual recycle streams increases system complexity
Solution Approach 1:
By segmenting the recycle stream into two controlled streams, the system achieves better nutrient removal efficiency that offsets the increased complexity. The first recycle stream targets denitrification needs while the second addresses oxygen control, together reducing nutrient levels below design requirements and lowering operating costs through improved efficiency.
Solution Approach 2:
The dual recycle stream system enables independent adjustment of flow rates and composition parameters for each stream. This parameter control allows optimization of oxygen and nitrates levels separately, achieving superior nutrient removal that reduces effluent nutrient concentrations and associated operating costs despite the added system complexity.
3Productivity
If mixed liquor residence time is short in conventional systems, then the treatment process is fast, but nutrient conversion efficiency is insufficient leading to excessive nutrient levels
Solution Approach 1:
The treatment process is segmented into zones with different residence time characteristics. The first anoxic zone provides extended residence time for denitrification, while subsequent zones maintain faster throughput. This segmentation allows sufficient nutrient conversion efficiency without compromising overall treatment speed, achieving both rapid processing and effective nutrient removal.
Solution Approach 2:
Denitrification is performed as a preliminary action in the first anoxic zone before the mixed liquor proceeds to subsequent treatment zones. By establishing this preliminary denitrification step with appropriate residence time, the system achieves thorough nutrient conversion early in the process, maintaining high productivity in later stages without compromising removal efficiency.
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 approach reduces inefficiencies and costs by improving nutrient removal efficiency, maintaining effluent nutrient levels within acceptable limits, and providing better control over the treatment process, leading to a more stable and effective wastewater treatment system.
Implementation Method 1
treating the wastewater in a first biological reactor to produce a first biologically treated mixed liquor
Implementation Method 2
suppress denitrification, resulting in nutrient levels exceeding design requirements
Implementation Method 3
separating the fourth biologically treated mixed liquor in a separator to produce an activated sludge and an effluent stream
Data Source
AI summary
The present invention relates to systems and processes of wastewater treatment and, in particular, to systems and methods of treating wastewater utilizing biological treatments utilizing two mixed liquor recycle streams for nutrient removal.