Phosphoric Acid Injection for Struvite Scale Inhibition
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Solution Overview
Problem
Struvite formation and scaling issues in wastewater treatment systems upstream of precipitation reactors lead to inefficiencies and increased costs, as existing inhibitors that prevent scaling also hinder struvite formation in the reactor.
Innovation Solution
Incorporating phosphoric acid (H3PO4) injection at various stages of the treatment process, including upstream of the reactor and in piping systems, to decrease pH and inhibit struvite formation, while allowing controlled pH adjustments to promote struvite formation in the reactor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If inhibitors like polyphosphates or phosphonates are used to prevent struvite formation in piping systems, then scaling issues upstream are reduced, but struvite formation in the reactor is also inhibited
Solution Approach 1:
The patent extracts the harmful effect of premature struvite formation in piping by introducing phosphoric acid injection specifically targeted at upstream sections, while leaving the reactor environment unchanged for optimal struvite formation. This spatial separation of inhibition and promotion zones resolves the contradiction between preventing scaling and maintaining productivity.
Solution Approach 2:
The invention applies different chemical conditions to different locations: phosphoric acid is injected upstream to create a locally acidic environment that prevents premature precipitation, while the reactor maintains its own pH conditions favorable for struvite formation. This local differentiation allows simultaneous achievement of both goals.
2Object-affected harmful factors
If pH is decreased upstream to inhibit struvite formation, then scaling is reduced, but struvite formation in the reactor may be affected
Solution Approach 1:
The treatment process is segmented into distinct zones: an upstream inhibition zone where phosphoric acid injection lowers pH to prevent scaling, and a downstream reaction zone where pH is optimized for struvite formation. This segmentation allows independent optimization of each zone's chemical conditions.
Solution Approach 2:
Phosphoric acid is injected preliminarily upstream of the reactor to prevent premature struvite formation before the effluent reaches the reactor. This preliminary inhibition action ensures that struvite formation is delayed until the effluent enters the reactor environment, where conditions are favorable for controlled precipitation.
3Object-affected harmful factors
If phosphoric acid is injected upstream to delay struvite precipitation, then scaling issues are reduced, but additional costs are incurred
Solution Approach 1:
Instead of using expensive specialized inhibitors like polyphosphates or phosphonates, the patent employs phosphoric acid, which is a more economical and readily available chemical that achieves the same pH-lowering effect for struvite inhibition upstream.
Solution Approach 2:
The invention changes the chemical parameter (pH) through phosphoric acid injection to control struvite solubility upstream, leveraging the known solubility characteristics of struvite at different pH levels. This parameter-based control is more cost-effective than using complex chemical inhibitors.
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 delays struvite precipitation until the effluent reaches the reactor, reducing scaling issues and enhancing struvite recovery with minimal additional costs, as only small quantities of H3PO4 are required, which also adds phosphate for struvite production, resulting in cleaner effluent and optimized ammonia removal.
Implementation Method 1
Incorporating phosphoric acid (H3PO4) injection at various stages of the treatment process, including upstream of the reactor and in piping systems, to decrease pH and inhibit struvite formation
Implementation Method 2
Reactors in general and fluidized bed reactors in particular have been used to remove and recover nutrients (i.e. ammonia and phosphorus) from wastewater that contains significant concentrations of phosphorus, often in the form of phosphate. Such technologies provide fluidized bed reactors for removing phosphorus from aqueous solutions by producing struvite (MgNH 4 PO 4 6H 2 O) or struvite analog or a phosphate compound in the form of pellets.
Implementation Method 3
Struvite can be formed by the reaction: Mg 2+ + NH 4 + + PO 4 3- + 6H 2 O → MgNH 4 PO 4 6H 2 O
Implementation Method 4
Trentelman, U.S. Patent No. 4,389,317 and Piekema et al., Phosphate Recovery by the Crystallization Process: Experience and Developments, paper presented at the 2nd International Conference on Phosphate Recovery for Recycling from Sewage and Animal Wastes, Noordwijkerhout, the Netherlands, March 12-13, 2001, disclose a reactor and method for precipitating phosphate in the form of calcium phosphate, magnesium phosphate, magnesium ammonium phosphate or potassium magnesium phosphate.
Data Source
AI summary
Formation of scale in a wastewater treatment system upstream of a struvite precipitation reactor is inhibited by injection of one or more of CO2 and H3PO4. The injection may be performed at multiple locations. Injection may be controlled based on one or more of pH, fluid flow and fluid pressure. Scale may be inhibited while maintaining production of precipitated struvite.