Phosphorus Recovery from Sewage Sludge Ash via Acid Digestion
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Solution Overview
Problem
Current methods for recovering phosphorus from sewage sludge ash are complex, energy-intensive, and often require separate iron removal processes, limiting their efficiency and applicability to iron-free ash, while also posing environmental concerns due to heavy metal contamination.
Innovation Solution
A process involving acid digestion with dilute mineral acid to solubilize phosphorus compounds, followed by filtration and precipitation of basic aluminum phosphates at ambient temperature, which allows for the inclusion of iron in the solution and efficient separation of heavy metals using sacrificial metals like aluminum or iron, enabling the recovery of phosphorus from a wide range of phosphorus-containing products without the need for complex iron separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional phosphorus recovery methods are used, then phosphorus can be recovered from sewage sludge ash, but the processes are complex and energy-intensive requiring elevated temperatures and separate iron removal steps
Solution Approach 1:
The invention changes the temperature parameter from elevated temperatures to ambient temperature operation. The acid digestion and precipitation processes proceed effectively at ambient temperature, eliminating the need for energy-intensive heating equipment and simplifying the overall process system while maintaining high phosphorus recovery efficiency
Solution Approach 2:
The invention merges the iron removal function into the main phosphorus recovery process. The sacrificial metal addition simultaneously reduces iron ions and facilitates phosphate precipitation, eliminating the need for separate iron removal steps and reducing process complexity
2Quantity of substance
If conventional phosphorus recovery methods are used, then phosphorus can be recovered, but heavy metal contamination occurs in the recovered product
Solution Approach 1:
The invention converts the harmful effect of heavy metals by using sacrificial metals (aluminum or iron) that preferentially reduce and precipitate heavy metal ions from the solution. The heavy metals are transformed from contaminants into separable solid precipitates, allowing the recovered phosphate product to be essentially free of heavy metal contamination
3Adaptability or versatility
If conventional phosphorus recovery methods are used, then phosphorus can be recovered from iron-free sewage sludge ash, but the processes require separate iron removal steps when iron is present
Solution Approach 1:
The invention creates a universal process that handles both iron-containing and iron-free sewage sludge ash using the same procedure. The sacrificial metal addition step automatically addresses iron removal when needed, while the rest of the process remains identical regardless of iron content, greatly enhancing process adaptability and eliminating separate process lines
4Quantity of substance
If acid digestion with dilute mineral acid is used, then phosphorus compounds are solubilized effectively, but acid consumption increases
Solution Approach 1:
The invention recovers and reuses the acid from the digestion process. The acidic filtrate containing dissolved phosphates is used as the digestion medium for subsequent batches of sewage sludge ash, significantly reducing acid consumption while maintaining effective phosphorus solubilization
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 method allows for the economical and ecological recovery of phosphorus as basic aluminum phosphates, which are essentially free of heavy metals, making them reusable, and can process various phosphorus-containing materials, including iron-containing sewage sludge ash, with reduced energy consumption and operational simplicity.
Implementation Method 1
The phosphorus compounds contained in the sewage sludge ash are brought into solution by acid digestion with a dilute mineral acid
Implementation Method 2
efficient separation of heavy metals using sacrificial metals like aluminum or iron
Implementation Method 3
precipitation of basic aluminum phosphates at ambient temperature
Data Source
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AI summary
The present invention relates to a process for recovering phosphorus compounds from sewage sludge ash, phosphorus-containing products, or phosphorus-containing waste. In this process, the phosphorus compounds contained in the sewage sludge ash, phosphorus-containing products, or phosphorus-containing waste are dissolved in a digestion vessel by acid digestion with a dilute mineral acid, and a filter cake is separated from the filtrate by filtration, the filtrate having a pH of 0 to 1.0. During or immediately after the acid digestion, a sacrificial metal is added to the digestion vessel containing the sewage sludge ash and the dilute mineral acid, or to a separate vessel containing the filtrate after separation of the filter cake, in order to reduce heavy metal cations. The resulting metallic heavy metal is then separated by filtration, either together with the filter cake or separately.Subsequently, an aluminum salt is added, the pH value is raised with a base to a range of pH 2.1 to 3.0, and the precipitated product is separated.