Resource Recovery from Synthetic Nitrified Urine in the Hydroponic Cultivation of Lettuce (Lactuca sativa Var. capitata L.)

Abstract

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.

Water and Nutrient Recovery for Cucumber Hydroponic Cultivation in Simultaneous Biological Treatment of Urine and Grey Water

“…Grey water is an abundant source of water, while urine can be a major source of some macro- and microelements that are necessary for plant growth [ 4 , 5 ]. The biological conversion of urine into a nitrate-rich medium diluted with grey water is a candidate for plant fertilizers [ 3 ].…”

“…In recent years, the concept of wastewater reuse in agriculture has increased worldwide. The use of wastewater can be achieved through fertigation practices or through soilless cultivation systems [ 1 , 2 , 3 ]. A detailed description, as well as advantages, disadvantages, and risks, of fertigation can be found in [ 1 , 2 ].…”

“…Macro- and micronutrients are necessary for proper plant growth, creating a strong synergy between the developed recycling processes and plant cultivation. Unprocessed urine left in the environment contributes to the eutrophication of water; however, if used properly, it will become important for crop production [ 3 ]. Therefore, it is necessary to explore the possibility of using urine-based fertilizers for plant cultivation.…”

“…Urine nitrification allows urine stabilization, and ammonium changes to nitrate, which is a form of N that is safer for plants. Biological conversion of urine into a nitrate-rich solution is widely used in terrestrial wastewater treatment plants and is usually carried out in an activated sludge reactor that contains a substantial amount of nitrifying bacteria [ 3 ]. Nitrifying bacteria convert ammonia into nitrate, which is the primary source of N for plants.…”

“…To optimize the cost of hydroponic production, especially water, its efficiency can be revised by recycling waste streams. Recycled urine has been directly applied to hydroponic systems in the case of lettuce [ 3 , 16 ], tomato [ 17 ] and dwarf tomato [ 18 ], as well as vegetables, such as amaranth and jute mallow [ 19 ]. The aim of this study was to investigate the possibility of using nutrient solutions based on recycled urine–gray water for hydroponic cucumber cultivation.…”