A Master of Science thesis in Civil Engineering by Alaa Yasser Ahmed Fouad Kamel entitled, “Nutrient Recovery from Wastewater Using Desalination Reject Brine”, submitted in November 2020. Thesis advisor is Dr. Kazi Parvez Fattah. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).
Reject brine, a waste by-product generated during the desalination process, is harmful when discharged into the environment, but it contains some useful minerals such as magnesium. Also, wastewater treatment plants utilizing centrifuge processing of sludge produce an effluent called centrate. This effluent is capable of causing operational problems, such as clogging of pipes and lowering biological treatment efficiency. Yet centrate is rich in nutrients such as phosphorus. This nutrient is the backbone of plant growth and is usually provided in the form of fertilizers. With diminishing availability of natural phosphorus, the cost of fertilizer production has seen rapid increase in recent years. Phosphorus recovery from centrate, with the help of an external magnesium source, can provide a sustainable alternative. Usually it is recovered in the form of struvite (magnesium ammonium phosphate) that can be used as a slow-release fertilizer. In this study, the feasibility of using the reject brine as a source of magnesium to produce struvite from centrate is studied in experiments using a bench scale jar test setup and a fluidized bed reactor. Factors affecting the precipitation of struvite, such as magnesium to phosphorus molar ratio, pH and the influence of other competing ions are investigated. Results show that around 90% of phosphorus removal can be achieved when operating at a Mg:P molar ratio of 3:1 and pH value of 9 when using both centrate or synthetic wastewater as a source of phosphorus and reject brine as a source of magnesium. Statistical analysis performed using Minitab shows that for most cases, the percentage phosphorus removal increases at higher pH and Mg:P molar ratios. The FTIR and XRD analysis shows that the precipitates formed contain primarily struvite. SEM-EDX analysis further validates presence of struvite as the precipitates have Mg:P molar ratios closer to the theoretical values of 1:1. Therefore, this study shows the potential of using reject brine as a magnesium source to efficiently recover phosphorus and produce high quality struvite.