Anoxic Bioreactor and Peroxide-Iron Treatment for Selenium Removal
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Solution Overview
Problem
Existing methods for treating selenium-containing wastewater, particularly from coal-fired power plants and refineries, are inadequate in reducing selenium concentrations to permissible levels, as anoxic biological treatment alone is insufficient, and conventional processes produce excessive sludge and fail to effectively remove selenium species like selenate and selenocyanate.
Innovation Solution
A method involving anoxic biological treatment followed by pH adjustment, inline addition of hydrogen peroxide, and a coagulant, such as ferric chloride, to oxidize and precipitate selenium species, with solids-liquid separation, optimizing oxidation reduction potential (ORP) and pH to enhance selenium removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If anoxic biological treatment alone is used, then the treatment process is simple, but selenium concentration cannot be reduced to permissible levels
Solution Approach 1:
The treatment process is divided into distinct sequential stages: anoxic biological treatment stage, oxidation stage (with hydrogen peroxide), and coagulation stage (with ferric chloride). Each stage performs a specific function to progressively reduce selenium to permissible levels, with the ability to optimize parameters independently at each stage.
Solution Approach 2:
The process utilizes controlled changes in oxidation-reduction potential (ORP) and pH parameters throughout the treatment stages. The anoxic stage maintains low ORP for biological reduction, followed by oxidation stage increasing ORP, with pH adjustment to optimize coagulation efficiency, achieving precise selenium concentration control.
2Loss of substance
If conventional treatment processes are used, then the process is straightforward, but excessive sludge is produced
Solution Approach 1:
Hydrogen peroxide is introduced as a strong oxidant in the oxidation stage to convert reduced selenium species back to oxidized forms that can be efficiently co-precipitated with ferric chloride. This accelerated oxidation enhances selenium removal precision while the controlled dosing minimizes excess sludge generation compared to conventional methods.
3Manufacturing precision
If anoxic biological treatment is used, then operational simplicity is maintained, but selenium species like selenate and selenocyanate are not effectively removed
Solution Approach 1:
Ferric chloride acts as an intermediary coagulant that co-precipitates with selenium species including selenate and selenocyanate. The iron hydroxide flocs formed during coagulation entrain and remove these difficult-to-remove selenium species, achieving comprehensive selenium species removal beyond what biological treatment alone can accomplish.
4Manufacturing precision
If treatment time in anoxic bioreactor is extended, then selenium reduction is improved, but hydraulic retention time increases
Solution Approach 1:
The anoxic bioreactor performs preliminary biological reduction of selenium to elemental form or reduced species during the initial treatment stage. This preliminary action creates a foundation that enables the subsequent oxidation and coagulation stages to achieve final polishing to permissible concentrations more rapidly, reducing overall retention time requirements.
Solution Approach 2:
The process replaces extended biological treatment time with chemical oxidation and coagulation mechanisms. Instead of relying solely on prolonged biological activity to achieve low selenium concentrations, the system uses hydrogen peroxide oxidation followed by ferric chloride coagulation, which achieves the same or better removal efficiency in shorter hydraulic retention times.
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 effectively reduces selenium concentrations to below 15 ppb, achieving compliance with regulatory standards and improving treatment efficiency by converting selenium species into insoluble forms for removal, while minimizing sludge production.
Implementation Method 1
introducing an oxidant into the first liquid to form an oxidant-treated first liquid
Implementation Method 2
introducing a coagulant into the oxidant-treated first liquid to form a second liquid having selenium-containing solids
Implementation Method 3
removing the selenium-containing solids from the second liquid in a solids-liquid separation operation
Data Source
AI summary
A method of treating selenium-containing wastewater comprises performing anoxic biological treatment of the selenium-containing wastewater to produce a first liquid including a residual dissolved selenium species, introducing an oxidant into the first liquid to form an oxidant-treated first liquid, introducing a coagulant into the oxidant-treated first liquid to form a second liquid having selenium-containing solids, and removing the selenium-containing solids from the second liquid in a solids-liquid separation operation.