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Chemical phosphorus removal model based on equilibrium chemistry
I Takács1, S Murthy, P M Fairlamb
1EnviroSim Associates, 7 Innovation Drive, Suite 205, Flamborough, ON L9H 7H9, Canada. imre@envirosim.com
Summary
Achieving very low ortho-phosphate (OP) levels in wastewater effluent is crucial for environmental regulations. This study recalibrates a precipitation model, showing that residuals as low as 10 microgP/L OP are achievable over a wider pH range.
Area of Science:
- Environmental Engineering
- Water Treatment Technologies
- Analytical Chemistry
Background:
- Global regulations mandate stringent total phosphorus (TP) limits in wastewater effluents, often below 0.10 mgP/L.
- Chemical precipitation is a key technology for reducing effluent ortho-phosphate (OP) concentrations, either independently or alongside biological treatment.
- Achieving extremely low OP levels involves complex chemical and physicochemical mechanisms influenced by pH.
Purpose of the Study:
- To refine existing empirical models for predicting OP residuals in chemical precipitation.
- To investigate the feasibility of achieving ultra-low OP concentrations (<10 microgP/L) in real-world wastewater treatment.
- To compare empirical and mechanistic precipitation models for enhanced accuracy in predicting OP removal.
Main Methods:
- Recalibration of an empirical precipitation model using effluent data from the Blue Plains plant.
- Integration of the precipitation model with biokinetic and pH models for comprehensive performance prediction.
- Comparison of the recalibrated empirical model with a new mechanistic model based on chemical solubility and dissociation constants.
Main Results:
- The empirical model, when recalibrated, accurately predicts OP residuals achievable over a broader pH range.
- Effluent data analysis revealed consistent OP residuals as low as 10 microgP/L.
- The study highlights the necessity for precise measurement techniques for ultra-low OP concentrations and consideration of factors like organics, adsorption, and coagulation.
Conclusions:
- Chemical precipitation, when optimized and modeled accurately, can consistently achieve ultra-low OP effluent concentrations.
- The recalibrated empirical model provides a practical tool for predicting OP removal efficiency and sludge production.
- Further research into the role of complex interactions (organics, adsorption, coagulation) is needed for advancing phosphorus removal technologies.