Utilization of natural coagulants for improving nutrient recovery with membrane contactor technology

Nitrogen and phosphorus are the main compounds used in fertilizers production. In recent years, new technologies have been developed to recover these compounds from wastewater streams. In this study, the use of natural coagulants for improving nitrogen recovery with membrane contactor technology was explored as part of the NPHarvest project at Aalto University. Natural coagulants were considered as a sustainable alternative to traditional coagulants. Starch-based (PrimePHASE 3545) and tannin-based (HTH) products were tested with two types of wastewater in order to evaluate their effectiveness and compare it with that of inorganic coagulants. Digested reject water (RW) was treated with PrimePHASE 3545 leading to 89% SS removal and 80% TP removal. Landfill leachate treated with HTH led to 47% TP removal and at the same time it removed heavy metals and other pollutants commonly found in landfill leachate. Both treatments led to ammonia increase by around 20%, which was adequate for the subsequent nitrogen recovery unit. The membrane contactor technology selected for the ammonia extraction was tested at the lab-scale using landfill leachate. In the lab, the ammonia transfer rate was highly affected by the initial ammonia concentration, the mixing regime, the leachate treatment, and the membrane treatment (UV + H2O2). When running treated leachate, the ammonia transfer rate increased by around 20% if compared to the untreated leachate run. Moreover, when evaluating ammonia transfer rate using treated leachate and treated membrane, it increased by around 90% compared to the untreated leachate run. Based on the findings of this thesis, the use of natural coagulants could be implemented in coagulation-flocculation processes to reduce the environmental impact of the treatment and to possibly reduce its overall costs. Studying the membrane performance is relevant to establish the membrane life-span and to develop an optimized process where the design and the membrane maintenance are well defined.