Hydroponic production raises economic and environmental issues related to the treatment, recovery or disposal of hydroponic wastewater, which can be rich in eutrophication-related nutrients, nitrogen (N) and phosphorus (P). Little focus has been put on the influence of the growth conditions on the N and P content in hydroponic wastewater, which is of uttermost importance when it is intended to reuse the wastewater for irrigation or other purposes with reduced impact on the environment. This study aimed to optimize an indoor non-recirculating deep-water culture (DWC) hydroponic system for lettuce (Lactuca sativa L. var. crispa) production, in terms of daily light integral (DLI) and volume of nutrient solution (NS) per plant, to maximize both the biomass production and the N and P removal, allowing for the wastewater to meet the criteria established for reusing in irrigation and minimizing the eutrophication impacts. A small-scale DWC hydroponic system with a fluorescent light fixture was built to study lettuce growth indoors for 35 days after transplanting (DAT). A first experiment was conducted under 14, 20 or 23 mol m⁻² d⁻¹ DLI and with 1.5 or 2 L of NS per plant. A pronounced inner leaf tip burn was observed, regardless of the volume of NS solution used, related to the unventilated conditions under high radiation. Total biomass was similar in all treatments and N and P removal was higher than 95% and 94%, respectively, at 35 DAT. Lettuces grown in 2 L of NS per plant exhibited higher average biomass. A second experiment was performed under 8, 10 or 12 mol m⁻² d⁻¹ DLI and with 2 or 3 L of NS per plant, making it possible to achieve healthy biomass at 35 DAT with higher water and light-use efficiency when compared to the first experiment. A DLI of 10 or 12 mol m⁻² d⁻¹ with 2 L of NS per plant and a DLI of 12 mol m⁻² d⁻¹ with 3 L of NS per plant made it possible to achieve both the best total biomass production and the highest N and P removal from water. Under those conditions, hydroponic wastewater complied with N and P criteria for reuse in irrigation, showing potential to be used as an alternative resource for agriculture and to minimize negative impacts on the environment.

The agricultural sector faces significant challenges related to climate change and population growth, which intensify pressure on natural resources and food security. Sustainable resource-efficient systems, alongside wastewater valorisation, are a promising solution. This study evaluated the reuse potential of aquaculture, urban, and swine farm wastewater in hydroponic cultivation. Trials with leafy vegetables and fruit crops were conducted in aquaponic systems containing two fish species (Koi carp and African catfish) and two small-scale hydroponic systems. Water quality, plant development, and environmental parameters were monitored. Results for the best performance scenarios within each cultivation system showed that in urban wastewater, strawberries yielded 183 ± 74 g/plant, exceeding yields in aquaponics (125 ± 60 g/plant). Lettuce performed better in swine farm wastewater (180 ± 39 g/plant) than in urban (65 ± 6 g/plant), with corresponding water-use efficiencies of 117 and 65 g/L. Aquaponics also supported stable yields, up to 108 ± 1 g/plant for lamb’s lettuce and 10,047 ± 8791 g of papaya fruit per plant. Nutrient recovery in hydroponic systems supplied with urban and swine farm wastewater reached up to 95% for N, P, and K. Overall, these systems demonstrated substantially lower water consumption compared with values commonly reported for conventional agriculture, underscoring their strong sustainability advantages.

Hog farm wastewater may require novel biological treatment techniques to improve efficiency and reduce costs. Previous studies combining vermifiltration with downstream hydroponics showed the need for a balanced wastewater nutrient content, particularly the nitrogen-to-phosphorus ratio. Here, a deep-water culture hydroponic system, growing lettuce as model culture, was used to remediate hog farm wastewater after an initial vermifiltration stage, aiming to produce an effluent suitable for irrigation. Supplemented vermifiltered wastewater (SVW) with added nutrients was tested against unsupplemented vermifiltered wastewater (VW) over 35 days, using a synthetic nutrient solution (NS) as a control. Supplementation was shown to improve lettuce growth, light use efficiency, and water use efficiency. Nutrient analysis over time showed a better-balanced phosphorus and nitrogen removal in SVW than in VW; in all treatments nitrogen and phosphorus content was reduced to legally acceptable levels for treated wastewater reuse in irrigation: nitrate 5 mgN L⁻¹ in VW and undetectable in SVW and NS; ammonia undetectable in all treatments; and total phosphorus 2.4 mg L⁻¹ in SVW, 0.9 mg L⁻¹ in NS and undetectable in VW. Coliforms increased in VW and SVW during hydroponic treatment, which should be solved by disinfection. Overall, combining vermifiltration with downstream hydroponic culture proved to be a promising treatment to remediate nutrients in hog farm effluent to make it suitable to be reused for irrigation.