Anaerobic Biological Sulphide Conversion Selectivity
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Solution Overview
Problem
Existing biological conversion processes for bisulphide to elemental sulphur often result in undesirably high formation of sulphate and thiosulphate, even when oxygen supply is controlled, leading to inefficiencies and equipment size issues.
Innovation Solution
The process involves converting bisulphide to elemental sulphur under anaerobic conditions with sulphide-oxidising bacteria, followed by regeneration of the bacteria using an oxidant, and separating elemental sulphur, which reduces sulphate and thiosulphate formation and increases selectivity towards elemental sulphur.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxygen supply is controlled within the range of 0.5 to 1.5 moles of oxygen per mole of sulphide in aerobic bioreactor, then sulphide conversion to elemental sulphur is achieved, but undesirably high amounts of sulphate and thiosulphate are formed
Solution Approach 1:
The process is divided into two separate stages: an anaerobic stage where sulphide is converted to elemental sulphur without oxygen, and a subsequent aerobic stage where any remaining sulphide is converted. This segmentation prevents the simultaneous presence of high sulphide concentrations and oxygen that leads to harmful by-products.
Solution Approach 2:
The anaerobic conversion of sulphide to elemental sulphur is performed first, before introducing oxygen. This preliminary action removes the majority of sulphide under conditions that prevent thiosulphate formation, and subsequent oxygen introduction does not lead to harmful by-products because the sulphide concentration is already low.
2Productivity
If higher bisulphide concentrations are used in the bioreactor, then reactor capacity is increased, but by-product formation increases and selectivity towards elemental sulphur decreases
Solution Approach 1:
The oxidation state parameter is changed by operating under anaerobic conditions (low redox potential) during the main conversion stage. This parameter change enables high bisulphide concentrations to be converted selectively to elemental sulphur without forming thiosulphate, which requires aerobic conditions.
3Speed
If aerobic conditions are used for sulphide oxidation, then conversion speed is maintained, but formation of higher oxidised sulphur compounds such as sulphate increases
Solution Approach 1:
The process uses periodic alternation between anaerobic and aerobic conditions. The anaerobic phase performs the main conversion at high speed without forming sulphate, while the brief aerobic phase that follows completes the conversion of remaining sulphide without significant sulphate formation because the sulphide concentration is already low.
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 approach significantly enhances the selectivity towards elemental sulphur, reduces the formation of undesirable sulphate and thiosulphate, and allows for higher bisulphide concentrations without generating by-products, thus optimizing reactor capacity and reducing the need for make-up chemicals.
Implementation Method 1
converting bisulphide as dissolved in an aqueous solution to elemental sulphur in the presence of sulphide-oxidising bacteria and under anaerobic conditions
Implementation Method 2
regenerating the used sulphide-oxidising bacteria as obtained in step (a) and as comprised in an aqueous solution in the presence of an oxidant
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention is directed to a process for the biological conversion of bisulphide into elemental sulphur, comprising the following steps: a) converting bisulphide as dissolved in an aqueous solution to elemental sulphur in the presence of sulphide-oxidising bacteria and under anaerobic conditions to obtain a first liquid effluent comprising elemental sulphur and used sulphide-oxidising bacteria; b) regenerating the used sulphide-oxidising bacteria as obtained in step (a) and as comprised in an aqueous solution in the presence of an oxidant to obtain a second liquid effluent comprising regenerated sulphide-oxidising bacteria; c) separating elemental sulphur from either the first and/or the second liquid effluent; d) using the regenerated sulphide-oxidising bacteria in step (a) as the sulphide-oxidising bacteria.