Return Activated Sludge Recirculation for High-TSS Bioreactors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional wastewater treatment processes, such as CAS and MBR, face limitations in handling high TSS content, leading to increased plant size, operational costs, and inefficiencies during high inflow conditions, with issues like dilution of biomass, sedimentation challenges, and membrane clogging.
Innovation Solution
A method involving a bioreactor system that introduces a concentrate of treated wastewater with high TSS into an inlet zone, aerates the mixture, filters it to produce low-TSS filtrate, and recycles the concentrate to maintain high TSS levels, using a permeable substrate to foul and remove deposited solids, and controls oxygen and nitrate levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional activated sludge process is used to treat wastewater, then the treatment process can consume organic matter, but the bioreactor size becomes large to enable the process to be completed
Solution Approach 1:
The patent changes the concentration parameter of suspended solids in the bioreactor from conventional levels (around 4 g/L) to high concentrations (10-50 g/L). This parameter change allows the same treatment capacity to be achieved in a much smaller reactor volume, directly resolving the contradiction between productivity and bioreactor size
Solution Approach 2:
The patent creates different zones within the bioreactor with different oxygen concentrations (aerated zone with high DO, anaerobic zone with zero DO). This local quality differentiation allows simultaneous nitrification and denitrification in different regions, enhancing treatment efficiency per unit volume and reducing overall reactor size
2Adaptability or versatility
If rainwater inflow increases the input flow of untreated water by a factor of 5 or more, then the treatment plant must cope with higher flows, but additional tank storage and non-treated or poorly treated water must exit the plant
Solution Approach 1:
The patent employs parameter changes in suspended solids concentration (maintaining high TSS of 10-50 g/L) and dissolved oxygen levels (varying from 0 to high saturation) to maintain efficient biological activity during high-flow conditions. This allows the system to handle rainwater inflows 5 times normal capacity while maintaining treatment quality without requiring additional storage tanks
Solution Approach 2:
The system dynamically adjusts operational parameters during high-flow events, maintaining high biomass concentration and appropriate oxygen levels to adapt to varying loads. The high TSS buffer provides resilience against flow variations, enabling the plant to maintain productivity across a wide range of inflow conditions
3Productivity
If membrane bioreactor treatment process is used, then treatment efficiency can be improved, but the cost increases substantially
Solution Approach 1:
The patent replaces expensive, fragile membrane components with a more robust, biologically-based high TSS sludge system that is cheaper to construct and operate. The high concentration suspended solids perform the separation function traditionally requiring membranes, eliminating membrane clogging issues and substantial operational costs while maintaining treatment efficiency
Solution Approach 2:
By changing the operational parameter of suspended solids concentration to very high levels (10-50 g/L), the system achieves MBR-level treatment efficiency using conventional activated sludge principles, thereby obtaining the productivity benefits of MBR without the substantial construction and operational costs of membrane systems
4Quantity of substance
If high TSS concentrate is returned to the bioreactor, then the biomass concentration can be maintained at high levels, but the system complexity increases
Solution Approach 1:
The patent merges the return activated sludge (RAS) function with the high TSS concentrate recycling function into a single integrated process. The same high TSS concentrate that is naturally produced by the system serves both as the biomass source and the return sludge, eliminating the need for separate RAS pumping systems and reducing operational complexity despite maintaining high biomass levels
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 the size and cost of treatment plants, maintains high flux rates, and effectively filters influent with high TSS content, enhancing the system's ability to handle varying inflows without membrane clogging or dilution.
Implementation Method 1
where an aeration system (254) increases the DO in the fluid to 2 mg/L and saturates the ORP to 100 mV, creating a favorable environment for aerobic bacteria to digest BOD and to transform ammonia into nitrate
Implementation Method 2
filtering the treated waste water to produce a filtrate and the concentrate, wherein the filtrate created by the filtering has total suspended solids of less than 10 mg/L
Implementation Method 3
deliberately fouling the permeable substrate to form a layer of deposited suspended solids from the treated waste water on the permeable substrate
Implementation Method 4
The flow rate (Q) at various points of the process are shown in FIG. 1. Here, anaerobic bacteria release phosphorous (ORP drops to approximately −300 mV)
Implementation Method 5
where the low DO regime favors bio-reactions leading to de-nitrification (nitrates are transformed into nitrogen gases) of the influent water (200)
Data Source
AI summary
A method of processing waste water to produce a filtrate is provided. The method includes the steps of: introducing untreated wastewater to an inlet zone of a bioreactor; introducing a concentrate of treated waste water with at least 10,000 mg/L of total suspended solids into the inlet zone of the bioreactor to form a biological active mixture; aerating the biological active mixture in an aeration zone of the bioreactor to produce treated waste water; filtering the treated waste water to produce a filtrate and the concentrate, wherein the filtrate created by the filtering has total suspended solids of less than 10 mg/L; transferring at least a portion of the concentrate to the inlet zone of the bioreactor; and transferring the filtrate external to the bioreactor as clean water.