Rose Oil Distillation Wastewater: By-Products of Essential Oil Extraction as Circular Biostimulants for Tomato Growth.

Rose processing into essentials oil is one of the major sectors providing inputs for cosmetics and health/food supplements industry, generating significant amount of wastewater if applying the steam distillation approach. Rose distillation wastewater (RDW), the major by-product of rose processing, still contains a significant load of polyphenolic compounds. This organic burden poses a significant environmental threat for RDW disposal, while, on the other hand, it still contains valuable compounds that could be valorized in the circular economy framework. This study has investigated the possibility of utilizing RDW in various concentrations (10%, 25%, 100% v/v) as a circular tomato growth biostimulant, addressing the existing research gap in the field of circular RDW valorization and its effects on plant growth modulation. LC-MS/MS and antioxidant assays have confirmed a rich antioxidant profile of RDW samples, with gallic acid, quinic acid, quercetin, kaempferol and their glycosides as the most abundant compounds. Tomato germination assays have resulted in significantly improved germination and initial seedling growth parameters when 10% RDW samples PA ('Pure Aroma'), MA ('Magic Aroma') and NA ('Natural Aroma) had been applied as seed treatment (10 seeds per treatment with each RDW), indicating varying plant growth-promoting potential depending on the RDW chemical composition. The increase in tomato growth parameters compared to the control varied in range 34% (MA)-60% (PA) for root length, 70% (MA)-109% (PA) for shoot length and 43% (MA)-72% (PA) for total seedling length, as well as 43% (MA)-72% (PA) for SVI-I and 40% (NA)-49% (MA) for SVI-II (seedling vigor indices I and II, respectively). Contrarily, the increase in RDW concentration of up to 25% and 100% (v/v) has resulted in inhibition of tomato germination and growth compared to the control (e.g., in range 10-50% (RDW 25%) and 45-87% (RDW 100%) for root length), suggesting the necessity for further optimization of RDW dosage in biostimulant applications. The results of this study open the field of possibilities for further development of circular plant biostimulants based on rose processing by-products, as value-added enrichment of the bio-based solutions portfolio for sustainable agriculture.