Due to their general accessibility, affordability, environmental friendliness, and reduced side effects as compared to chemical treatments, herbal plants are becoming increasingly popular as a substitute for wastewater treatment. The purpose of this study was to assess the antibacterial capabilities of essential oils derived from Origanum syriacum, citronella (Cymbopogon winterianus), and their combination with a selection of bacteria present in wastewater.

Hydrodistillation techniques were used to extract the essential oils, and gas chromatography–mass spectrometry (GC-MS) was used to determine the chemical composition of the oils.

The essential oils' chemical profiles varied, according to a preliminary examination. Citronella oil was mainly made up of geraniol (2.9%) and citronellal (32.6%), whereas Origanum syriacum oil had a significant concentration of carvacrol (79.2%) among its constituents. Antioxidant activity was measured for their ethanolic extracts; citronella showed better antioxidant activity with a lower half-maximal inhibitory concentration (IC50) of 131.7μg/ml, while the IC50 for oregano was 180.9 μg/ml. Regarding the antibacterial effect, oregano oil showed minimum inhibitory concentrations (MICs) of 2.5% against all the tested bacteria except for C. freundii, which had an MIC of 5%. In contrast, citronella oil revealed an MIC of 1.25% for all the bacteria except E. coli, which had an MIC of 2.5%. This indicates that Origanum syriacum essential oil has a stronger antibacterial effect than java citronella essential oil.

The ability of Origanum syriacum and Java citronella essential oils to display antibacterial properties makes them suitable natural agents for wastewater treatment, as highlighted in this study. Additional research, including the clarification of their mechanisms of action, should be carried out to confirm their usefulness in wastewater treatment systems.