Physicochemical characterization of geranium distillation liquid residue (still water) for sustainable valorization

The steam and hydrodistillation of geranium yield not only essential oil but also an aromatic hydrosol, a co-product with promising uses in the cosmetic and pharmaceutical fields. Nevertheless, this process generates a large volume of by-products which are solid residues and liquid residue or still water, that are usually underused despite retaining chemically valuable fractions. The liquid residue remains poorly characterized in the literature. The present work aims to evaluate the physicochemical profile of the steam distillation liquid residue (still water), as a step toward developing a valorization route for this by-product.

The physicochemical characterization of this liquid residue (still water) was carried out using standard analytical methods. Chloride content was determined by the Mohr method, while suspended solids (SS) were measured according to the NF EN 872 standard. Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) was determined. Nitrogen, nitrate, and phosphorus contents were each quantified by spectrometry. In addition, we measure pH, electrical conductivity and salinity.

The measured pH was 3.85, indicating an acidic character, likely attributable to the release of organic acids during hot-water extraction. The chloride content (568 mg/L) confirms the value of electrical conductivity which reached 2.78 mS/cm, with an associated salinity of 1.41 ppt. The five-day biochemical oxygen demand was particularly elevated (BOD₅ = 3,060 mg O₂/L) and the chemical oxygen demand (COD) was measured at 11,520 mg O₂/L for this still water. The concentrations of total nitrogen and total phosphorus are 154 mg/L and 18 mg/L, respectively. The nitrate concentration N-NO₃⁻ reached 80 mg/L. Finally, the suspended solids concentration is 1,470 mg/L.

This study shows that the geranium liquid residue is heavily loaded with organic matter, reinforcing that treatment is essential to valorize this liquid in order to reduce its environmental impact.