Fattah, Kazi ParvezSinno, Sarah Samir2023-03-012023-03-012022-1235.232-2022.54http://hdl.handle.net/11073/25173A Master of Science thesis in Civil Engineering by Sarah Samir Sinno entitled, “Investigating the impact of calcium presence in dairy wastewater on struvite precipitation”, submitted in December 2022. Thesis advisor is Dr. Kazi Parvez Fattah. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).The rapid increase in global population, and consequently, demand for crops and agricultural products, is putting a strain on the production of phosphorus (P) needed in the production of fertilizer. Phosphorus is a non-renewable and non-rechargeable finite resource that is expected to be exhausted within this century. Along with population, increase in the demand for dairy product has escalated the production of nutrient (nitrogen and phosphorus) rich wastewater that is associated with pollution of soil and water bodies. A sustainable approach for nutrients removal and recovery from waste and wastewater is through precipitation of magnesium ammonium phosphate (struvite, MAP) which is an effective slow-release fertilizer. This study investigated the impact of calcium presence in dairy wastewater on struvite precipitation, in addition to the need and effectiveness of two calcium (Ca) removal methods - seeded aeration and electrodialysis. The impact of calcium molar ratios and pH on struvite formation was modelled using VMINTEQ and then validated through a set of experimental runs. The chemical speciation model indicated that the optimal conditions for struvite precipitation is a pH of 9 and a Magnesium/Phosphorus (Mg/P) molar ratio of 1 in the absence of Ca. Calcium presence in a Ca/Mg molar ratio as low as 0.2 reduces the struvite precipitation by 30%, whereas a Ca/P molar ratio higher than 1.5 completely inhibits the struvite formation regardless of the concentration of Mg. Substrate prepared by anaerobically digesting cow manure in the laboratory for phosphorus and nitrogen release was treated by seeded aeration for calcium removal as calcium carbonate precipitate was found to be inefficient for reaching the desired Ca/P molar ratio, as high phosphate removal rates were achieved. The electrodialysis process showed promising results with a Ca removal rate of 50%, however, the removal was not enough to reach the desired Ca/P molar ratio.en-USAnaerobic digestionDairy wastewaterStruviteCalciumElectrodialysisSeeded aerationThesis