Thermal Alkaline Oxidative Hydrolysis for High-Salinity Sludge
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Solution Overview
Problem
Anaerobic digestion of depuration sludges from wastewater treatment plants faces limitations due to high salt concentrations and the presence of hydroxides, which hinder hydrolysis and reduce biogas production, especially in industrial sludges with high sulphate and chloride levels, and chemical dephosphatation processes, leading to increased costs and compromised sludge quality.
Innovation Solution
A process involving thermal alkaline oxidative hydrolysis as the sole pretreatment phase, without acid oxidative hydrolysis, to increase bioavailability of organic fractions in depuration sludges, followed by anaerobic digestion, which reduces sludge volume and enhances methane production, particularly effective for sludges with high salinity levels from dairy and biorefinery processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional anaerobic digestion is applied to depuration sludges with high salt concentrations and hydroxides, then the process can be implemented with standard equipment, but the hydrolysis rate decreases and biogas production is reduced
Solution Approach 1:
The patent applies parameter changes by modifying the pH condition from neutral (conventional anaerobic digestion) to alkaline (pH 9-11) to enhance hydrolysis efficiency. This parameter change enables the system to effectively process sludges with high salt concentrations and hydroxides that would otherwise inhibit the hydrolysis process, thereby resolving the contradiction between maintaining standard process conditions and achieving reliable hydrolysis efficiency.
2Productivity
If acid oxidative hydrolysis is added as a pretreatment step, then organic fraction bioavailability increases, but the process complexity and operational costs increase
Solution Approach 1:
The patent extracts and eliminates the acid oxidative hydrolysis step from the conventional two-stage pretreatment process (acid then alkaline oxidative hydrolysis). By removing this intermediate step and proceeding directly to alkaline oxidative hydrolysis, the patent simplifies the process while maintaining or enhancing organic fraction bioavailability, thus resolving the contradiction between improving productivity and reducing device complexity.
3Loss of substance
If sludge volume is reduced through conventional treatment, then disposal costs decrease, but the quality and centrifugability of the treated sludge deteriorate
Solution Approach 1:
The patent applies parameter changes by using alkaline oxidative hydrolysis to modify the sludge structure and composition. This chemical treatment alters the physical properties of the sludge, improving its centrifugability and dehydration characteristics while simultaneously achieving significant volume reduction. The alkaline conditions facilitate better solid-liquid separation, thus resolving the contradiction between reducing sludge volume and maintaining operational ease.
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 achieves a significant reduction in sludge disposal (45-55%) and increases methane production by up to 35%, reducing investment and management costs, while improving centrifugability and dehydration efficiency of sludges, and maintaining process performance across varying sludge types.
Implementation Method 1
thermal alkaline oxidative hydrolysis phase
Implementation Method 2
oxidative hydrolysis
Implementation Method 3
thermal alkaline oxidative hydrolysis
Implementation Method 4
anaerobic digestion process
Implementation Method 5
metabolize the organic material present in the waste in anaerobic conditions with the production of methane
Data Source
Figure 1
Figure 2~3
AI summary
The present invention relates to a process for producing biogas, which comprises: subjecting depuration sludges to a pretreatment phase which comprises, as the sole hydrolysis phase, a thermal alkaline oxidative hydrolysis phase; subjecting the pretreated sludges to an anaerobic digestion process in order to obtain biogas. This process is applicable to a wide range of urban and industrial depuration sludges, in particular to depuration sludges with high salinity levels, characterized by an overall content of sulphates and chlorides equal to or greater than 800 mg/mL. This process allows to increase the methane fraction inside the biogas produced, so as to improve its quality in terms of energy yield.