Mesophilic Sludge Fermentation for Phase Separation
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Solution Overview
Problem
Current methods for removing excess water from sludge before or during digestion are inefficient, particularly in increasing solid residence time in digesters, and often require expensive equipment or modify sludge rheology, making them unsuitable for widespread use.
Innovation Solution
A method involving mesophilic fermentation of sludge at temperatures between 15°C to 45°C under hydraulically quiescent conditions to achieve phase separation, allowing for the separate removal of solid and liquid phases, which can be fed to a digester for biogas conversion, and an apparatus to facilitate this process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional thickening methods (settling vessels with moving rake, gravity belt thickener) are used to remove excess water from sludge, then solid residence time in digester is increased, but equipment cost and complexity increase significantly
Solution Approach 1:
The sludge itself performs the thickening function through biological fermentation and self-phase separation. Microorganisms in the sludge consume volatile fatty acids and produce gas bubbles that attach to sludge particles, causing them to float and separate from the liquid phase without requiring external mechanical thickening equipment
Solution Approach 2:
The patent replaces mechanical thickening systems (moving rakes, gravity belt thickeners) with a biological-chemical system where microorganisms and gas bubbles naturally separate the sludge phases through fermentation and buoyancy forces
2Duration of action of moving object
If gravity belt thickener with polymer addition is used to remove water from sludge, then solid residence time is increased, but sludge rheology is modified making it difficult to pump and mix
Solution Approach 1:
The sludge maintains its natural rheological properties throughout the process. The phase separation is achieved through biological fermentation and gas bubble attachment rather than polymer flocculation, preserving the sludge's original pumpability and mixability characteristics
Solution Approach 2:
The patent converts the typically harmful effect of excess water in sludge into a beneficial feature by using the liquid phase as a medium for microbial fermentation that produces gas bubbles, which in turn aid in phase separation without requiring polymers that would worsen rheology
3Loss of substance
If digestion time is extended to achieve maximum biogas conversion, then organic content reduction is improved, but processing productivity decreases
Solution Approach 1:
The patent divides the sludge treatment into two distinct phases: (1) a short mesophilic fermentation stage (1-3 days) that thickens the sludge and produces volatile fatty acids, and (2) a subsequent digestion stage that processes the pre-thickened sludge. This segmentation allows each stage to be optimized independently
Solution Approach 2:
The patent performs preliminary thickening and volatile fatty acid production through mesophilic fermentation before the main digestion process. This preliminary action increases the solid content and prepares the sludge for more efficient digestion, reducing the required digestion time
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 method effectively increases the solid residence time in digesters by 100% to 200% while producing a volatile fatty acid-rich liquor stream useful as a carbon source, without the need for expensive equipment or altering sludge properties, and achieves consistent solid concentrations in separated phases.
Implementation Method 1
fermenting the sludge at a temperature in the mesophilic temperature range
Implementation Method 2
In an anaerobic digestion process the organic substrate is biologically converted to a biogas
Implementation Method 3
maintaining the fermenting sludge for a predetermined period under a hydraulically quiescent condition to achieve phase separation
Implementation Method 4
The phase separation is assisted by nascent biogas bubbles
Data Source
AI summary
A method and related apparatus for the removal of excess water from sludge, the method comprising the steps of: (1) fermenting the sludge at a temperature in the mesophilic temperature range, (2) maintaining the fermenting sludge for a predetermined period under a hydraulically quiescent condition to achieve phase separation, (3) separately removing the solid phase and liquid phase and (4) feeding the solid phase to the digester for conversion to biogas.