Selenium Removal via Alkaline Slurry Precipitation
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Solution Overview
Problem
Current flue gas desulfurization systems face challenges in effectively and cost-efficiently removing selenium contamination from waste water streams, as selenium compounds like selenate are difficult and costly to remove, often requiring additional treatment steps beyond traditional wastewater treatment.
Innovation Solution
The system employs an aqueous alkaline-based slurry to form selenium compounds, controls oxidation to reduce selenate production, and uses a precipitation agent to precipitate selenium compounds as selenium sulfide or elemental selenium, which can be easily removed with gypsum solids, thereby reducing selenium levels in the wastewater.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional wastewater treatment processes are used to remove selenium, then treatment capacity is limited, but cost and complexity increase significantly
Solution Approach 1:
The patent applies preliminary action by converting selenium to a precipitable form before the main wastewater treatment process. Specifically, sodium sulfide is added to the wastewater to convert dissolved selenium species into selenium sulfide precipitates, which are then easily removed through standard solid-liquid separation. This preliminary conversion step makes the subsequent treatment much more effective and less complex.
Solution Approach 2:
The patent changes the chemical state parameter of selenium from dissolved to precipitated form by controlling pH and adding sulfide ions. By adjusting these parameters, selenium is transformed into an easily removable solid phase, fundamentally changing its physical-chemical properties to facilitate removal through conventional treatment methods.
2Productivity
If oxidation is allowed to proceed without control, then selenium compounds form readily, but selenate production increases making removal difficult
Solution Approach 1:
The patent applies preliminary action by adding sodium sulfide before oxidation occurs. This converts selenium to selenium sulfide precipitates that are resistant to oxidation to selenate. By performing this conversion first, the system prevents the formation of hard-to-remove selenate while still allowing controlled oxidation of other components in the wastewater.
Solution Approach 2:
The patent applies preliminary anti-action by introducing sulfide ions that counteract the formation of selenate. The sulfide ions react with selenium to form selenium sulfide, which prevents subsequent oxidation to selenate. This preliminary counter-action eliminates the harmful oxidation pathway while maintaining productive selenium 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
This approach significantly reduces dissolved selenium in the wastewater, making it easier to meet discharge standards by precipitating selenium compounds before they oxidize to selenate, allowing for more effective removal with traditional wastewater treatment processes.
Implementation Method 1
contacting the flue gas stream with an aqueous alkaline-based slurry, such that any selenium byproduct in the flue gas stream forms a selenium compound within the aqueous alkaline-based slurry
Implementation Method 2
adding a precipitation agent to the aqueous alkaline-based slurry to cause the selenium compound within the aqueous alkaline-based slurry to precipitate
Data Source
AI summary
A method of reducing selenium contamination in a waste water stream is described herein. The method includes channeling a flue gas stream through an absorber, contacting the flue gas stream with an aqueous alkaline-based slurry, such that any selenium byproduct in the flue gas stream forms a selenium compound within the aqueous alkaline-based slurry, controlling oxidation of the selenium compound in the aqueous alkaline-based slurry, and adding a precipitation agent to the aqueous alkaline-based slurry to cause the selenium compound within the aqueous alkaline-based slurry to precipitate.