Phosphate precipitation as struvite from municipality wastewater
type: CreativeWork
description: Tshwane Municipality produces approximately 4Ml/day of dewatering liquors arising from municipal sludge from a wastewater treatment plant. The sludge being dewatered is a combination of an anaerobically digested primary sludge and an undigested waste activated sludge. High phosphate and nitrogen are released into water during the anaerobic treatment process. High concentrations of these nutrients in the wastewater lead to eutrophication, which is a major environmental problem (Doyle et al., 2000). In view of the above problem, the aim of this project was to investigate the feasibility of precipitating phosphate in the form of struvite (MgNH4PO4.6H2O) from the Tshwane Municipality dewatering liquors and consequently recovering it as a valuable and marketable product. The project was investigated in three sequential stages consisting of: 1. An aqueous thermodynamic modelling study using OLI Systems Inc. Stream Analyser Version 2.0.57 to determine the precipitation conditions required for the removal of phosphates in the dewatering liquor. 2. Bench'scale laboratory experiments to investigate the feasibility of phosphate precipitation as struvite under different pH conditions, Mg: P molar ratios and Ca:P molar ratios. 3. Fluidised bed experiments to establish the characteristics of phosphate removal at varying levels of supersaturation. The results suggest that the pH of the system has a significant effect on phosphate removal due to its influence on the availability of PO4 3, NH4 + and Mg2+. According to the thermodynamic modelling results, phosphates are removed as Ca3(PO4)2 and Mg3(PO4)2.8H2O. Removal of phosphate as Mg3(PO4)2.8H2O starts at a pH above 7 with the maximum removal achieved at pH 10. Thereafter, phosphate removal as Mg3(PO4)3.8H2O drops to zero due to Mg(OH)2 precipitation being favoured at the higher pH values. Thermodynamic modelling shows that a high NH4 +:P molar ratio is required to induce struvite precipitation. For sample C1, which had a PO4 P an…
abstract: Tshwane Municipality produces approximately 4Ml/day of dewatering liquors arising from municipal sludge from a wastewater treatment plant. The sludge being dewatered is a combination of an anaerobically digested primary sludge and an undigested waste activated sludge. High phosphate and nitrogen are released into water during the anaerobic treatment process. High concentrations of these nutrients in the wastewater lead to eutrophication, which is a major environmental problem (Doyle et al., 2000). In view of the above problem, the aim of this project was to investigate the feasibility of precipitating phosphate in the form of struvite (MgNH4PO4.6H2O) from the Tshwane Municipality dewatering liquors and consequently recovering it as a valuable and marketable product. The project was investigated in three sequential stages consisting of: 1. An aqueous thermodynamic modelling study using OLI Systems Inc. Stream Analyser Version 2.0.57 to determine the precipitation conditions required for the removal of phosphates in the dewatering liquor. 2. Bench'scale laboratory experiments to investigate the feasibility of phosphate precipitation as struvite under different pH conditions, Mg: P molar ratios and Ca:P molar ratios. 3. Fluidised bed experiments to establish the characteristics of phosphate removal at varying levels of supersaturation. The results suggest that the pH of the system has a significant effect on phosphate removal due to its influence on the availability of PO4 3, NH4 + and Mg2+. According to the thermodynamic modelling results, phosphates are removed as Ca3(PO4)2 and Mg3(PO4)2.8H2O. Removal of phosphate as Mg3(PO4)2.8H2O starts at a pH above 7 with the maximum removal achieved at pH 10. Thereafter, phosphate removal as Mg3(PO4)3.8H2O drops to zero due to Mg(OH)2 precipitation being favoured at the higher pH values. Thermodynamic modelling shows that a high NH4 +:P molar ratio is required to induce struvite precipitation. For sample C1, which had a PO4 P an…
author: Ramaru, Rendani
language: eng
date published: 2009
date modified: 2026-07-22T22:23:44Z
provider: University of Cape Town
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Department of Chemical Engineering

PropertyValue
property ID: Handle
value: http://hdl.handle.net/11427/5412