Sludge Dewaterability via Pre-Fermentation and Thermal Hydrolysis
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Solution Overview
Problem
The presence of phosphorus, ammonia, and magnesium in sludge makes dewatering difficult and increases the potential for struvite formation and ammonia toxicity during anaerobic digestion, leading to reduced dry solids content and increased polymer doses, as well as struvite scaling issues in wastewater treatment processes.
Innovation Solution
Pre-treating sludge by controlling temperature and hydraulic retention time in a biological fermenter to release phosphorus and ammonia, followed by pre-dewatering and subsequent thermal hydrolysis, which allows for the recovery and utilization of these components to form struvite, thereby improving dewaterability and reducing struvite formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sludge is subjected to anaerobic digestion, then phosphorus is released from biomass as orthophosphate, but dewaterability deteriorates due to high PO4 concentration and shifted cation ratio
Solution Approach 1:
The patent applies preliminary action by conducting a pre-fermentation step before anaerobic digestion to release phosphorus, ammonia and magnesium from biomass. This preliminary release allows these components to be removed via pre-dewatering, preventing their negative impact on subsequent dewatering operations. The pre-fermentation is controlled to optimize component release while maintaining biomass integrity for later digestion.
Solution Approach 2:
The patent segments the sludge treatment process into distinct stages: pre-fermentation in a biological fermenter, pre-dewatering in a solids-liquid separator, thermal hydrolysis, and anaerobic digestion. This segmentation allows phosphorus and other components to be released and removed before the main digestion process, eliminating the contradiction between phosphorus release and dewaterability.
2Quantity of substance
If sludge contains phosphorus, ammonia and magnesium, then struvite formation potential increases, but this causes scaling issues in pipes and conduits
Solution Approach 1:
The patent extracts phosphorus, ammonia and magnesium from the sludge matrix through controlled pre-fermentation and removes them via pre-dewatering. By taking out these components before they can react to form struvite, the process eliminates the source material needed for struvite scaling in pipes and conduits, while the extracted components can be separately managed or recovered.
3Quantity of substance
If thermal hydrolysis is performed, then high ammonia concentrations are released, but this reaches inhibiting levels in the anaerobic digester
Solution Approach 1:
The patent applies preliminary action by releasing ammonia during the pre-fermentation stage before thermal hydrolysis and anaerobic digestion. This allows ammonia to be partially removed via pre-dewatering, reducing the total ammonia load that would otherwise be released during thermal hydrolysis and potentially inhibit the anaerobic digester.
4Productivity
If polymer dose is increased to maintain dewatering performance, then treatment effectiveness is maintained, but operational cost increases
Solution Approach 1:
The patent applies preliminary action by removing phosphorus, ammonia and magnesium through pre-fermentation and pre-dewatering before the main dewatering step. This preliminary removal of dewatering-inhibiting components allows subsequent dewatering to achieve high performance with reduced polymer dosage, as the sludge matrix is already conditioned and less resistant to water removal.
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 enhances dewaterability, reduces struvite formation and ammonia toxicity, and minimizes phosphorus in landfills, while potentially decreasing reactor and storage system requirements, and improving overall dewatering performance.
Implementation Method 1
Sludge is directed to a biological fermenter and by controlling the temperature of the sludge and/or the hydraulic retention time of the sludge in the fermenter, phosphorus and ammonia is released from the biomass in the sludge
Implementation Method 2
The concentrated sludge is then directed to a thermal hydrolysis reactor and undergoes thermal hydrolysis
Implementation Method 3
the thermally hydrolyzed sludge is directed to an anaerobic digester and subjected to anaerobic digestion
Implementation Method 4
the sludge is directed to a solids-liquid separation or pre-dewatering device which yields a concentrated sludge and a liquid stream rich in phosphorus, ammonia and magnesium
Data Source
Figure 1
AI summary
The present invention relates to a method of treating sludge containing phosphorus, ammonia and magnesium and enhancing the dewaterability of the sludge. The sludge is directed into a biological fermenter operated under anaerobic conditions. By controlling the temperature of the sludge in the fermenter or the hydraulic retention time of the sludge in the fermenter, phosphorus, ammonia and magnesium is released from the solids in the sludge into a liquid forming a part of the sludge. Sludge from the fermenter is subjected to a solids-liquid separation process that produces a concentrated sludge and a liquid. The concentrated sludge or separated solids is directed to a thermal hydrolysis reactor that thermally hydrolyzes the concentrated sludge. After thermally hydrolyzing the concentrated sludge, the concentrated sludge is directed to an anaerobic digester that anaerobically digests the concentrated sludge.