Water reuse and resource recovery from greenhouse wastewater by capacitive electrodialysis at pilot scale

Abstract

As food production dominates global freshwater consumption and nutrient discharge regulation tightens, the performance of novel technologies at applied scale needs to be studied to optimize water use and minimize environmental impact. Water reuse and the nutrient recovery from greenhouse wastewater were assessed utilizing one-pass capacitive electrodialysis (CED) at a pilot scale (19.32 m2 membrane area, 1–4 m3/day capacity), employing carbon-based electrodes. CED was optimized for key parameters, including applied voltage, cross-flow velocity, staging, water recovery, and varying feed concentrations. High-quality greenhouse irrigation water (conductivity<0.2 mS/cm and Na+ < 0.1 mmol/L) was produced, meeting specified guidelines. Na+ was retained less compared to Ca2+ and Mg2+ (86 % ± 4 %, 97 % ± 2 %, and 98 % ± 3 % removal, respectively) and nutrients concentration factors for K+, NO3− and PO43− reached up to 2.3 (596 ± 5 mg/L), 2.7 (1330 ± 20 mg/L), and 1.9 (130 ± 2 mg/L), respectively. There was no significant improvement in ion removal for all feed compositions beyond 12 V and 80 % water recovery. CED's specific energy consumption (SEC) with optimized parameters was 4-fold lower than the modeled RO system, and lower than previous electrodialysis studies. The highest SEC obtained was 0.24 kWh/m3. These findings suggest that CED is a promising technology for the greenhouse horticulture sector, aiding the move toward zero liquid discharge.