title: Removal of phosphate from greenhouse wastewater using hydrated lime.
abstract: Phosphate (P) contamination in nutrient-laden wastewater is currently a major topic of discussion in the North American greenhouse industry. Precipitation of P as calcium phosphate minerals using hydrated lime could provide a simple, inexpensive method for retrieval. A combination of batch experiments and chemical equilibrium modelling was used to confirm the viability of this P removal method and determine lime addition rates and pH requirements for greenhouse wastewater of varying nutrient compositions. Lime: P ratio (molar ratio of CaMg(OH)₄: PO₄‒P) provided a consistent parameter for estimating lime addition requirements regardless of initial P concentration, with a ratio of 1.5 providing around 99% removal of dissolved P. Optimal P removal occurred when lime addition increased the pH from 8.6 to 9.0, suggesting that pH monitoring during the P removal process could provide a simple method for ensuring consistent adherence to P removal standards. A Visual MINTEQ model, validated using experimental data, provided a means of predicting lime addition and pH requirements as influenced by changes in other parameters of the lime-wastewater system (e.g. calcium concentration, temperature, and initial wastewater pH). Hydrated lime addition did not contribute to the removal of macronutrient elements such as nitrate and ammonium, but did decrease the concentration of some micronutrients. This study provides basic guidance for greenhouse operators to use hydrated lime for phosphate removal from greenhouse wastewater.
authors.affiliation: a School of Environmental Sciences , University of Guelph , 50 Stone Road East, Guelph , Ontario , Canada N1G 2W1.
authors.forename: C Siobhan
authors.initials: CS
authors.lastname: Dunets
authors.forename: Youbin
authors.initials: Y
authors.lastname: Zheng
mesh_terms: D000383:Agriculture; D017610:Calcium Compounds / Q000737:chemistry*; D011232:Chemical Precipitation; D006863:Hydrogen-Ion Concentration; D010087:Oxides / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D017610:Calcium Compounds; D010087:Oxides; D010710:Phosphates; D062065:Wastewater; D014874:Water Pollutants, Chemical; C016538:lime
keywords: calcium phosphate; greenhouse wastewater; phosphorus; precipitation; wastewater treatment