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Although the use of microalgae-based wastewater treatment (MWWT) processes is demonstrated to recover nutrients and produce clean water for agriculture, very scarce evidence of this use has been reported. This work aims to solve this gap and provide reliable data at this respect. For that, raceway reactor was operated in continuous mode for the treatment of municipal wastewater, the recovery of nutrients and water, and the production of biomass. After confirming the accomplishment of regulation for water discharge the treated water was evaluated for its use as irrigation water for lettuce, using both clean water and untreated wastewater as control. The microbiological quality of inlet and outlet water was analyzed by evaluating the total load and bacterial composition. Fertigation parameters, nutrient absorption and yield were measured. The wastewater treatment step confirms removal rates of 50 gCOD m-2·day-1, 1.7 gN m-2·day-1 and 0.8 gP m-2·day-1, in addition to a biomass production rate of 23 gbiomass·m-2·day-1, moreover the accomplishment of water discharge limits. Treatment with microalgae shows an improvement in the composition of bacterial taxa. The use of this water enhanced the root absorption of water and nitrate. The lower value of the drainage electrical conductivity when using water from MWWT indicates a higher metabolic activity in the roots, due to an increase in the absorption of nutrient ions concerning the volume of water absorbed. The treated water with microalgae was the treatment that showed the highest growth values (fresh and dry weight). Wastewater treatment process demonstrated to be efficient and releases up to 165,000 m3·ha-1·year-1 of clean water for irrigation. The use of MWWT processes has shown an increase in the beneficial bacterial load, the yield of the crops and to decrease the environmental pollution, therefore it is a clear example of an activity to be considered in the circular economy.

Changes in plant responses have been associated with different fractions of the visible spectrum and light intensity. Advances in light emitting diodes (LED) have enabled the study of the effect of narrow wavelengths on plant growth and antioxidant compound synthesis. LED technology also facilitates the incorporation of light sources in a controlled setting where light spectra and intensity can be regulated. The objective of this study was to compare the effect of two commercial light spectra (S1: standard white light with 32.8% blue, 42.5% green, 21.7% red and 2.4% far red;S2: AP67 spectrum, designed for horticultural growth, with 16.9% blue, 20.5% green, 49.7% red and 12.3% far red) at two light intensities [LI: low intensity (78 µmol·m-2s-1 of photons for S1 and 62 µmol·m-2s-1 for S2, and HI: high intensity (102 and 100 µmol·m-2s-1 for S1 and S2, respectively)] on growth and antioxidant compound contents in two leafy vegetables: endive (Cichorium endivia L.) and lettuce (Lactuca sativa L.). Fresh weight (FW), dry weight (DW), and DW% of plants were taken as growth indicators. Leaf number, SPAD index, leaf area (LA) and specific leaf area (SLA) were also evaluated. Antioxidant synthesis was measured as total phenol content (TPC), total flavonoid content (TFC) and antioxidant activity (AA). The results showed that S2 and HI increased the FW, DW, and LA in both species. On the other hand, antioxidant compound contents were significantly increased by HI but did not vary with the spectrum.