Struvite Crystallization System for Phosphate Recovery
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Solution Overview
Problem
Struvite crystallization in wastewater often results in the formation of small crystals, which compromise effluent quality and economic viability due to low sedimentation rates, and the high operating costs associated with magnesium and alkalinity sources in existing technologies.
Innovation Solution
A two-stage struvite crystallization system using a fluidized bed crystallizer and a settler, where industrial-grade magnesium hydroxide suspension with high MgO content is used as a source of magnesium and alkalinity, promoting the growth of larger struvite granules and efficiently separating small crystals, reducing operating costs and improving product quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional struvite crystallization is used, then phosphate recovery is achieved, but small crystals are formed which compromise effluent quality and economic viability
Solution Approach 1:
The crystallization process is divided into two distinct stages: a first stage for primary crystal formation and a second stage for crystal growth and size enlargement. This segmentation allows different operational conditions to be optimized for each stage, resulting in larger, more marketable crystals while maintaining high phosphate recovery rates.
Solution Approach 2:
The system performs preliminary crystal formation in the first stage, then uses the resulting crystals as nucleation sites in the second stage. This preliminary action ensures that crystals are formed with controlled size and morphology before the final growth stage, preventing the formation of unwanted fine crystals.
2Productivity
If traditional magnesium and alkalinity sources are used, then struvite crystallization is achieved, but operating costs are high
Solution Approach 1:
The system uses the wastewater stream itself as a source of alkalinity through carbon dioxide desorption, eliminating the need for external alkali addition. This self-service approach significantly reduces operating costs while maintaining the crystallization process.
Solution Approach 2:
The system changes the operational parameters by operating at lower temperatures (below 30°C) and optimizing the pH range (8.0-9.0), which reduces energy consumption and operating costs while maintaining efficient struvite crystallization.
3Productivity
If small struvite crystals are formed, then crystallization occurs, but sedimentation rate is low and effluent quality is compromised
Solution Approach 1:
The system dynamically adjusts operational parameters between the two stages: the first stage uses conditions optimized for rapid crystal formation, while the second stage uses conditions optimized for crystal growth and size enlargement. This dynamic adjustment ensures that crystals are both formed efficiently and reach marketable sizes.
Solution Approach 2:
The first stage performs preliminary crystal formation, creating a nucleation foundation that guides subsequent crystal growth in the second stage. This ensures that crystals develop with controlled size and morphology, improving sedimentation rate and effluent quality.
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 effectively recovers phosphates from wastewater, producing struvite granules suitable for use as a slow-release fertilizer, reducing dependence on phosphate rock exploitation and mitigating eutrophication effects, while lowering operational costs compared to traditional methods.
Implementation Method 1
a neutralization of hydrogen ions formed by the gradual desorption of the dissolved carbon dioxide in such streams can be performed
Implementation Method 2
Struvite crystallization is based on a controlled precipitation process in which a salt of ammonium phosphate and magnesium hexahydrate (MgNH4PO4-6H2O) called struvite is obtained
Implementation Method 3
small crystals, which compromise effluent quality and economic viability due to low sedimentation rates
Data Source
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AI summary
The invention relates to a method and a system for struvite crystallization of in order to recover phosphates in urban or industrial wastewater preferably having phosphate concentrations higher than 50 mg P/L, more preferably higher than 100 mg P/L, where phosphates are recovered by means of the crystallization thereof in the form of struvite granules, the diameter of which can reach up to 5 mm. The struvite crystallization system is formed by a crystallizer (1), a decanter (2) with a distribution system (9), and a unit for adding industrial magnesium hydroxide (3). The phosphates are recovered from the wastewater as a result of two steps : a step of growing struvite granules, and a step of growing fine struvite crystals.