Batch Gravity Thickening and Fermentation for EBPR Carbon Recovery
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Solution Overview
Problem
Conventional activated sludge treatment systems face challenges in maximizing enhanced biological phosphorus removal (EBPR) and biological nitrogen removal due to competition for organic carbon substrate between phosphorus accumulating organisms (PAOs) and denitrifying bacteria, especially when influent wastewater has low rbCOD concentrations, leading to inefficient nutrient removal and high operational costs.
Innovation Solution
A process involving gravity thickening and fermentation of waste activated sludge withdrawn from the surface of an aeration basin, utilizing a sequential batch reactor system with automated control, to promote the growth of Tetrasphaera bacteria, which can produce volatile fatty acids under anoxic conditions, enhancing phosphorus and nitrogen removal efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional activated sludge treatment systems are used, then basic BOD removal is achieved, but phosphorus and nitrogen removal efficiency is insufficient due to competition for organic carbon substrate between PAOs and denitrifying bacteria
Solution Approach 1:
The system is divided into distinct functional zones: an anaerobic zone for phosphorus release and volatile fatty acid production, anoxic zones for denitrification, and aerobic zones for phosphorus uptake and nitrification. This segmentation allows different microbial communities to operate in their optimal conditions without direct competition for the same carbon substrate at the same time and space.
Solution Approach 2:
The system performs preliminary fermentation of waste activated sludge in the anaerobic zone to produce volatile fatty acids before the main treatment process. This preliminary action creates an internal source of readily biodegradable organic carbon that can be utilized by PAOs in the aerobic zone, reducing dependence on external carbon sources and improving overall nutrient removal efficiency.
2Productivity
If external carbon sources are added to enhance phosphorus and nitrogen removal, then nutrient removal efficiency improves, but operational costs increase
Solution Approach 1:
The system utilizes its own waste activated sludge as a carbon source through anaerobic fermentation to produce volatile fatty acids. This self-service approach eliminates or reduces the need for external carbon source addition, thereby improving nutrient removal efficiency while minimizing operational costs associated with chemical purchases and handling.
Solution Approach 2:
Instead of discarding waste activated sludge, the system recovers valuable volatile fatty acids through anaerobic fermentation. This recovered carbon substrate is then utilized by phosphorus accumulating organisms in the aerobic zone, converting a waste product into a valuable resource that drives nutrient removal processes.
3Productivity
If high aeration rates are used to support phosphorus accumulating organisms, then phosphorus removal efficiency improves, but energy consumption increases
Solution Approach 1:
The system maintains continuous anaerobic fermentation of waste activated sludge to ensure a steady supply of volatile fatty acids for phosphorus accumulating organisms. This continuous production of carbon substrate allows for efficient biological phosphorus uptake during the aerobic phase, reducing the need for excessive aeration and associated energy consumption.
Solution Approach 2:
The system optimizes operational parameters including dissolved oxygen levels, hydraulic retention times, and sludge recirculation rates to create favorable conditions for phosphorus accumulating organisms. By carefully controlling these parameters, the system achieves efficient phosphorus removal at lower aeration energy inputs compared to conventional systems.
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 process improves the utilization of available carbon for nutrient removal, reduces the need for external carbon sources, and decreases aeration requirements, resulting in more efficient and cost-effective EBPR and nitrogen removal.
Implementation Method 1
A process involving gravity thickening and fermentation of waste activated sludge withdrawn from the surface of an aeration basin
Implementation Method 2
A Ferment Period for the remaining settled mixed liquor solids, which continues for a predetermined period of time
Data Source
AI summary
An efficient and low-cost process for gravity thickening and fermentation of waste activated sludge withdrawn from the surface of an activated sludge aeration basin for use with treatment systems designed for “enhanced biological phosphorus removal” (EBPR). One or more reactor tanks are used for the process with the steps of: A fill cycle, in which the waste mixed liquor flows into the tank, followed by a settle cycle, in which the mixed liquor is allowed to settle for a period of time, followed by a decant cycle, in which the clear liquid is withdrawn. The withdrawal of a volume of the settling mixed liquor for discharge is then followed by a ferment period for the remaining settled mixed liquor solids and a transfer of the fermented mixed liquor solids back to the activated sludge liquid stream process.