title: Extraction and precipitation of phosphorus from sewage sludge.
abstract: Raw sewage sludge from East Rand Water Care Association (ERWAT) had high phosphorus (P) content, approximately 15.2% (w/w) P2O5, which indicates a potential resource for the limiting nutrient. Leaching sewage sludge with 1M sulphuric acid at 5% solid loading for 2h resulted in an 82% phosphorus extraction. However, the phosphorus was recovered as iron phosphates, thus a further purification step using ion exchange to remove iron was required to increase the degree of P release. Magnesium oxide and ammonium hydroxide were used as magnesium and nitrogen sources, respectively, as well as pH regulators to precipitate P as struvite. 57% struvite was precipitated and the total phosphorus content of the precipitate was 25.9%. Kinetic studies showed that the leaching of phosphorus follows the Dickinson model for the first 100min with a rate of reaction of about 2×10-5s-1. The rate limiting step is controlled by diffusion. Phosphorus solubility in 2% critic acid was almost 96%, which is the amount of phosphorus available to plants if the precipitate is applied as a fertiliser. Environmental, gram-positive Bacillus subtilis were found in the precipitate, which are harmless to the environment since they already exist in the soil where the precipitate can be applied as a fertiliser.
authors.affiliation: Department of Chemical Engineering, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, Johannesburg, South Africa.
authors.forename: Nothando Cynthia
authors.initials: NC
authors.lastname: Shiba
authors.affiliation: Department of Chemical Engineering, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, Johannesburg, South Africa. Electronic address: fntuli@uj.ac.za.
authors.forename: Freeman
authors.initials: F
authors.lastname: Ntuli
mesh_terms: D011232:Chemical Precipitation; D007700:Kinetics; D010758:Phosphorus / Q000737:chemistry*; D012722:Sewage / Q000737:chemistry*; D013019:South Africa; D000069877:Struvite / Q000737:chemistry*; D013464:Sulfuric Acids / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D012722:Sewage; D013464:Sulfuric Acids; D010758:Phosphorus; D000069877:Struvite; C033158:sulfuric acid
keywords: Phosphate fertiliser; Phosphorus extraction; Sewage sludge; Struvite precipitation