The anammox process is an economically favourable nitrogen removal process; however, low growth rates of anammox biomass block its more widespread application. As different approaches on techniques for anammox bacteria growth acceleration were tested, this study focused on long-term evaluation of hydrazine addition in the start-up phase. Effect of hydrazine addition (dose 3.7 mgN₂H₄ dm⁻³) was investigated in a pilot-scale SBR treating ammonia-rich reject water from sludge dewatering after partial nitritation process, and effects were compared to a reference reactor. Hydrazine addition resulted in much higher anammox biomass enrichment observed as higher nitrogen removal rate [0.512 kgN (m³ d)⁻¹ with hydrazine versus 0.256 kgN (m³ d)⁻¹ without reagent]. Sludge from chemically stimulated reactor revealed also higher (by 22.6%) specific anammox activity rate than the reference. After the hydrazine addition was stopped, observed process rates remained stable and no regression in the nitrogen removal efficiency could be noticed. In the final phase, nitrogen removal rate was only 48.7% of process rate in the reactor previously stimulated by hydrazine. Results of the experiment confirmed positive effect of hydrazine presence on anammox bacteria enrichment process.

The application of hydroponic cultivation fertilized with biologically nitrified synthetic urine can produce nitrate-rich fertilizer for lettuce (Lactuca sativa var. capitata L.). The mounting water crisis and depletion of natural resources makes nitrogen recovery from human urine a practical option. Nitrified urine can be used in indoor vertical hydroponic cultivation and is characterized by a high degree of element recovery. Because of its high ammonium content, hydrolyzed fresh urine may be toxic. A nitrification sequencing batch reactor with suspended activated sludge biomass ensured urine stabilization and biological conversion into nitrate-rich fertilizer. The diluted nitrate-rich fertilizer was then supplied for soilless cultivation. The results show that diluted nitrified urine is an excellent source of bioavailable nitrogen and phosphorus and, with proper enrichment with microelements, could replace commercial fertilizers in hydroponic systems. The yield and quality parameters of lettuce cultivated with enriched urine were comparable to those obtained with a commercial fertilizer. The mass balance calculation showed that industry-scale lettuce production can be based on urine fertilizer collected from a few hundred people for a single unit.

Dewatering of sewage sludge is a key operational element of wastewater treatment plants and has major economic implications, as it entails the costs of thickening, transport, and disposal. The aim of this study was to determine the influence of selected polyelectrolytes and their dosages on dewatering efficiency and to present an innovative, multicriteria method of result evaluation using radar charts. In this research, 10 different polyelectrolytes were assessed in terms of sludge dewaterability, considering conditioning parameters including Specific Resistance to Filtration (SRF), Capillary Suction Time (CST), and centrifugation performance. The results were presented in the form of radar charts, enabling both an overall evaluation of the effectiveness of each product and an assessment of their suitability for specific dewatering technologies, such as belt filter presses and centrifuges. The analysis showed that polyelectrolytes with higher cationic charge provided better dewatering performance. The proposed visualization method allows us to analyze the effects across different conditioners and technologies. The best sludge conditioning effect (maximum radar chart area) was achieved with Praestol 665, a polyelectrolyte with a high cationic charge level. This method is a practical tool for selecting the optimal agent for sewage sludge dewatering.