Oxidation ditch nutrient removal via ORP-DO control
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Solution Overview
Problem
Conventional oxidation ditch activated sludge treatment systems face challenges in achieving consistent nitrogen removal and bulking sludge control, and require complex and costly systems for enhanced biological phosphorus removal, often relying on external anaerobic tanks and high energy consumption.
Innovation Solution
Implementing a process control method that includes a deeply anaerobic fermentation period, automated microprocessor control using ORP and DO probes, dynamic dissolved oxygen control, surface wasting of excess sludge, and quiescent periods to optimize phosphorus and nitrogen removal, favoring the growth of denitrifying phosphate accumulating organisms (dnPAOs) without the need for additional tankage or pumping systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional oxidation ditch systems are used for nitrogen removal, then nitrogen removal efficiency ranges from 60% to 85%, but the system requires complex DO control systems and variable speed aeration equipment to maintain performance
Solution Approach 1:
The system uses the endogenous respiration of mixed liquor bacteria to naturally create anoxic zones for denitrification, eliminating the need for complex external control systems. The bacteria consume nitrate as they migrate through the oxidation ditch, providing self-regulating nitrogen removal without requiring variable speed motors or comprehensive DO control infrastructure
Solution Approach 2:
The invention extracts the nitrogen removal function from the main aeration process by allowing it to occur naturally in the anoxic zones created by endogenous respiration. This separates the nitrification (aerobic) and denitrification (anoxic) functions in space and time, achieving reliable nitrogen removal without integrating complex control mechanisms into the aeration system
2Productivity
If mechanical surface aeration and mixing are used in oxidation ditches, then channel flow is maintained, but nitrogen removal performance becomes variable and requires vigilant control
Solution Approach 1:
The system creates periodic anoxic conditions through the natural migration and respiration of mixed liquor bacteria along the oxidation ditch. As bacteria consume oxygen and migrate, they create alternating aerobic and anoxic zones that periodically pass through the system, providing consistent nitrogen removal opportunities without requiring continuous mechanical intervention
Solution Approach 2:
The endogenous respiration rate of the mixed liquor serves as a natural feedback mechanism that automatically regulates denitrification. The bacteria's consumption of nitrate is driven by their metabolic needs, creating a self-balancing system that adapts to varying loads without external control input
3Ease of operation
If denitrification is driven by endogenous respiration rate, then the process is self-regulating, but reaction rates are slower and denitrification efficiency is lower
Solution Approach 1:
The system performs preliminary carbon storage in the anaerobic zone before denitrification occurs. Phosphate accumulating organisms store carbon compounds during anaerobic conditions, then utilize these stored compounds as electron donors for rapid denitrification in subsequent anoxic zones, accelerating the reaction rate while maintaining self-regulation
Solution Approach 2:
The invention changes the chemical parameters available for denitrification by introducing readily biodegradable carbon sources and manipulating redox conditions through zoned aeration. This transforms the limiting factor from carbon availability to oxygen distribution, dramatically increasing denitrification rates while preserving the self-regulating nature of the process
4Reliability
If external anaerobic tanks are added for enhanced biological phosphorus removal, then phosphorus removal is achieved, but capital expenditure and system complexity increase
Solution Approach 1:
The invention merges phosphorus removal with the existing oxidation ditch aeration basin by creating anaerobic, anoxic, and aerobic zones within the same reactor. This eliminates the need for separate external anaerobic tanks while achieving enhanced biological phosphorus removal through spatial zonation and temporal cycling of redox conditions
Solution Approach 2:
The oxidation ditch aeration basin is transformed into a multi-functional reactor that simultaneously performs BOD removal, nitrification, denitrification, and phosphorus removal. By adjusting aeration patterns and creating zones with different redox conditions, the single basin executes multiple treatment functions that traditionally required separate dedicated tanks
5Ease of operation
If conservative secondary clarifier loadings are used, then the system is easy to operate and handles variable loads well, but the overall treatment capacity is limited
Solution Approach 1:
The invention changes the operational parameters of the oxidation ditch by implementing extended aeration cycles with prolonged anaerobic and anoxic periods. This modifies the kinetic conditions to favor phosphorus accumulating organisms and enhance nutrient removal, increasing treatment capacity without requiring changes to clarifier design or operational complexity
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 enhances biological phosphorus and nitrogen removal efficiency, improves sludge settling, reduces energy consumption, and promotes a diverse microbial population, achieving cost-effective and resilient nutrient removal without the need for external anaerobic tanks, while maximizing the use of available organic carbon.
Implementation Method 1
a deeply anaerobic fermentation period, automated microprocessor control using ORP and DO probes
Implementation Method 2
enhances biological phosphorus and nitrogen removal efficiency
Implementation Method 3
promotes a diverse microbial population, achieving cost-effective and resilient nutrient removal while maximizing the use of available organic carbon
Implementation Method 4
oxygen is utilized by the biomass to absorb, assimilate and metabolize the BOD available in the wastewater
Implementation Method 5
carefully controlling 'dissolved oxygen' (DO) levels in the basin. As the channel flow leaves the aeration zone in the oxidation ditch, the DO concentration decreases until it is depleted, and anoxic zones occur in the ditch where nitrate is used instead of DO to accomplish nitrogen removal
Implementation Method 6
automated microprocessor control using ORP and DO probes
Data Source
AI summary
An activated sludge process for the treatment of municipal wastewater, particularly applicable to oxidation ditch activated sludge treatment systems which utilize a conventional race track or continuous loop reactor basin configuration. The process removes phosphorus and nitrogen from an activated sludge wastewater treatment system, with an anoxic cycle followed by an aerobic cycle, and followed by a surface wasting cycle until a low flow diurnal period is reached in a diurnal or twenty-four hour period. Automated microprocessor control system using “oxidation-reduction potential” (ORP) and “dissolved oxygen” (DO) as process variable inputs automate aerated and anoxic cycles to optimize phosphorus and nitrogen removal using the available carbon in the influent wastewater resulting in an energy efficient dynamic dissolved oxygen control during the aerated periods.