Selenium Removal via Biological and Membrane Treatment
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Solution Overview
Problem
Current wastewater treatment methods for selenium removal from flue gas desulfurization blowdown water are inefficient, as they often rely on single treatment processes and struggle to effectively convert soluble selenium species into insoluble forms, leading to incomplete removal and potential downstream scaling issues.
Innovation Solution
A system combining biological treatment with controlled oxygen reduction potential zones, followed by membrane filtration, using dithiocarbamate compounds and adsorptive agents to convert soluble selenium species into elemental selenium, which is then separated and removed, along with optional aerobic treatment to manage organic compounds and prevent scaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single treatment processes are used for selenium removal, then the treatment process is simple, but selenium removal efficiency is insufficient
Solution Approach 1:
The patent combines multiple treatment processes (chemical treatment with dithiocarbamate compounds, biological treatment, and membrane filtration) into an integrated system. The chemical treatment converts soluble selenium species into insoluble forms, biological treatment further processes the converted selenium, and membrane filtration provides final separation, collectively achieving high removal efficiency while managing process complexity through systematic integration
2Device complexity
If soluble selenium species are not converted into insoluble forms, then the treatment process is simple, but selenium removal is incomplete and scaling issues occur
Solution Approach 1:
The patent employs dithiocarbamate compounds that chemically react with soluble selenium species, changing their chemical form from soluble to insoluble elemental selenium or selenium-containing precipitates. This parameter change in selenium's chemical state enables effective removal and prevents downstream scaling, with the chemical conversion process optimized for reliability
3Device complexity
If membrane filtration is used without prior chemical and biological treatment, then the process is simpler, but membrane fouling and scaling increase
Solution Approach 1:
The patent implements preliminary chemical treatment with dithiocarbamate compounds and biological treatment before the water enters the membrane filtration stage. These preliminary actions convert and remove selenium species and other contaminants that would otherwise cause membrane fouling and scaling, protecting the membrane system and maintaining its performance over time
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 system achieves significant selenium removal, with pilot tests demonstrating up to 60% selenium reduction and maintaining low selenium concentrations in the treated water, effectively addressing the inefficiencies of previous methods while minimizing scaling and nitrate fouling.
Implementation Method 1
The biological treatment includes converting soluble species of selenium to elemental selenium. Negative ORP is maintained in one or more anoxic or anaerobic zones to provide conditions suitable for reducing soluble selenium species
Implementation Method 2
A membrane filtration unit is provided downstream of the biological treatment. The membranes may provide secondary separation of the biologically treated water
Implementation Method 3
Optionally, the treatment may be enhanced with one or more adsorptive agents prior to, or in conjunction with, membrane filtration
Implementation Method 4
The aerobic zone removes carbon, which may include carbon added as a nutrient in a non-aerobic zone
Data Source
AI summary
Water containing selenium, for example flue gas desulfurization (FGD) blowdown water is treated with a combination of biological and chemical treatment and membrane filtration. The biologically treated water is dosed with a dithiocarbamate compound and flocculated prior to membrane filtration. Optionally, the treatment may be enhanced with one or more adsorptive agents prior to, or in conjunction with, membrane filtration. Membrane concentrate may be re-circulated to one or more biological treatment zones. The biological treatment may be by way of suspended growth, fixed growth on a moving bed, or both. One or more biological treatment zones may be controlled considering their oxygen reduction potential (ORP). Optionally, the biological treatment includes an aerobic zone following one or more anoxic or anaerobic zones. The non-aerobic zones remove selenium and optionally nitrogen and sulfur. The aerobic zone removes carbon, which may include carbon added as a nutrient in a non-aerobic zone.