Experimental study on CELSS-based domestic wastewater recycling for sustainable vegetable cultivation

Elevated contamination levels of domestic wastewater pose challenges to its treatment and reuse in Controlled Ecological Life Support System (CELSS). To address this, biologically treated domestic wastewater was employed as a primary nutrient source for leafy vegetables. A comparative analysis of growth parameters and nutrient assimilation was performed on two vegetables with distinct salt tolerance capacities, ice plant (Mesembryanthemum crystallinum) and lettuce (Lactuca sativa), under two cultivation systems: recycled wastewater and Hoagland solution. Key findings indicated that: Both had comparable edible biomass in recycled wastewater (ice plant: 127.28 g·plant⁻¹; lettuce yield marginally lower) vs Hoagland controls (ice plant: 124.87 g·plant⁻¹), with no significant difference. Lettuce exhibited enhanced root development in wastewater, with significantly greater underground biomass (p < 0.05) than Hoagland-grown counterparts, suggesting adaptation to saline stress (wastewater EC: 6.39 mS·cm^-1). Nutrient-wise, recycled wastewater had gently changed elemental ratios and pH maintained weakly acidic during cultivation. Vegetables in recycled wastewater took up more K⁺, Na⁺, and trace elements vs. Hoagland (e.g. lettuce Na content: 3.2× Hoagland controls). ∼13.12 m² of ice plant could intake sodium from one person's daily urine under the experiment. These results demonstrate that recycled wastewater serves as a viable primary nutrient source for CELSS agriculture. Ice plant exhibited higher sodium assimilation efficiency and systemic adaptation to recycled wastewater, whereas lettuce developed compensatory root morphological modifications to mitigate high salinity.