Development and optimization of pilot plant for nutrient recovery from reject water

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Insinööritieteiden korkeakoulu | Master's thesis
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Master's Programme in Water and Environmental Engineering (WAT)
Reject water is produced by de-watering of anaerobically digested activated sludge in municipal wastewater treatment plants. This liquid contains a significant amount of, nitrogen (mostly as ammonium), phosphorus and suspended solids (organic matters) which needs to be removed before disposal. Currently, reject water is recirculated into the treatment system by Waste water treatment plants. This increases the ammonium concentration which also increase energy and resource consumption of the treatment process. A novel nutrient recovery technique (NPHarvest technique) has been developed in this study that can effectively remove the suspended solids, nitrogen and phosphorus from reject water and recover nutrient during the treatment process. The recovered nutrients are the raw materials for fertilizers. This work also supports circular economy. The purpose of this thesis was to design a batch process into the continuous process and construct a pilot plant in order to test and analyse the feasibility of the NPHarvest technique. This technique has a pre-treatment followed with the nitrogen recovery process. The nutrient recovery was performed using commercially available Liqui-Cel 3M membrane contactor to test its performance. This thesis presents a successful construction of pilot scale pre-treatment unit of NPHarvest technique for continuous flow. The pilot designed capacity is 100 l/hr. The experiment was carried out using a pilot plant in Viikinmäki wastewater treatment plants using their reject water. The optimal dose of coagulant (PAX XL 100), polymer (Super floc A120) and lime kiln dust (LKD) was 1.3 g/l, 1.3 mg/l, and 3.5 g/l, respectively. These doses are valid when the influent (reject water) suspended solid concentration is in range of 0.9 -1.6 g /l. The results from the pre-treatment showed that 82% suspended solid removal, 81% phosphorus recovery in sludge liquor. The Liqui-Cel 3M membrane contactor showed 78% ammonia recovery efficiency in the extraction solution. The NPHarvest technique operation cost was estimated to 3.18 €/m3 reject water or 5.10 €/kg NH4-N recovery. Estimated for the energy used in maintaining the flow and chemical dose in NPHarvest technique was 5.4 kWh/ m3 of reject water.
Vahala, Riku
Thesis advisor
Mikola, Anna
Pradhan, Surendra
coagulation, flocculation, ballasted sedimentaion, reject water, pretreatement, nutrient recovery
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