Anaerobic Digestate Contaminant Removal via Multi-Stage Separation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current solid waste treatment processes face challenges in reducing physical contaminants in digestate to meet stringent regulatory standards, particularly due to the accumulation of floatable and inert contaminants in anaerobic digesters, which hinder biogas release and require complex removal processes.
Innovation Solution
A high-pressure pressing system separates solid waste into dry and wet fractions, with the wet fraction being diluted and processed to comminute floatables, then treated in a hydrocyclone and filter screw press to extract contaminants, allowing for downstream removal and meeting stringent quality standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If anaerobic digestion is used to treat organic waste, then biogas is produced, but physical contaminants (glass, metals, plastics, paper) accumulate in the digestate
Solution Approach 1:
The patent extracts physical contaminants from the digestate through a multi-stage process: first using a drum screen to remove large contaminants, then a hydrocyclone to separate denser particles, and finally a filter press to capture remaining solids. This extraction sequence effectively removes glass, metals, plastics, and paper from the digestate while preserving the biogas production process.
Solution Approach 2:
The contaminant removal process is segmented into multiple distinct stages: (1) drum screening for large particles, (2) hydrocyclone separation for medium-sized denser particles, and (3) filter press for fine remaining contaminants. Each stage targets specific size and density ranges, creating a progressive refinement system that efficiently removes all types of physical contaminants.
2Productivity
If floatables accumulate in the digester, then biogas release is hindered, but complex removal processes are required
Solution Approach 1:
The system performs preliminary action by removing floatables before they can accumulate and hinder biogas release. The drum screen and hydrocyclone are positioned to continuously remove floating contaminants at the beginning of the digestion process, preventing their accumulation and eliminating the need for complex post-accumulation removal systems.
Solution Approach 2:
The patent uses hydraulic principles in the hydrocyclone, which utilizes centrifugal force generated by rotating fluid flow to separate floatables from the digestate. This hydraulic separation method is more efficient and less complex than mechanical skimming or manual removal systems, effectively removing floatables through fluid dynamics alone.
3Reliability
If digestate is applied to land as fertilizer, then regulatory limits on physical contaminants must be met, but contaminant removal increases processing complexity
Solution Approach 1:
The contaminant removal system is segmented into three specialized units, each targeting specific contaminant types and sizes. The drum screen handles large particles, the hydrocyclone handles medium-sized denser particles, and the filter press handles fine remaining contaminants. This segmentation allows each unit to be optimized for its specific function, achieving comprehensive contaminant removal while keeping individual units relatively simple.
Solution Approach 2:
The system discards physical contaminants at multiple stages through the sequential processing units. The drum screen discards large contaminants, the hydrocyclone discards medium-sized particles, and the filter press discards fine contaminants. This multi-stage discarding approach ensures regulatory compliance by removing all significant contaminant types while maintaining manageable system complexity through modular design.
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 process effectively reduces contaminant concentrations in digestate, enabling compliance with regulatory limits and optimizing digester operation by removing floatables and inerts, thereby improving biogas production and digestate quality.
Implementation Method 1
solid waste is pressed at a high pressure, for example 50 bar or more, to separate the solid waste into a dry fraction and a wet fraction
Implementation Method 2
The wet fraction is diluted and floatables (i.e. pieces of plastic and/or paper) in the wet fraction are comminuted. The wet fraction is then de-gritted before being sent to an anaerobic digester
Implementation Method 3
A portion of the waste is sent to an anaerobic digester to produce biogas
Implementation Method 4
The digestate is filtered to extract comminuted floatables
Implementation Method 5
the resulting filtrate is then dewatered to produce a cake, for example with over 18% solids content
Data Source
AI summary
Organic solid waste is pressed at a high pressure to separate the solid waste into a dry fraction and a wet fraction. The wet fraction is diluted and floatables (i.e. pieces of plastic and/or paper) in the wet fraction are comminuted. The wet fraction is then de-gritted before being sent to an anaerobic digester. Digestate is withdrawn from the digester from a free liquid surface of the digester. The digestate is filtered to extract comminuted floatables. The resulting filtrate is then composted or directly applied to land. A corresponding system comprises a press, a grinder, a hydrocyclone, an anaerobic digester, a filter and a dewaterer.