Behaviour of physicochemical and microbiological characteristics of vertical flow constructed wetland substrate after treating a mixture of urban and olive mill wastewaters

The aim of the current work is to evaluate the effect of a mixture of olive mill wastewater (OMWW) and urban wastewater (UW) on constructed wetland (CW) substrate physicochemical parameters, and to study the abundance and behaviour of microbial community at different depths. In this regard, substrate samples were investigated at three depth levels (0–10 cm, 10–20 cm and 20–30 cm) inside a pilot scale CW treating the mixture. In order to compare the obtained results with the conventional case, a control (CW pilot plant treating only UW) was implemented. Result shows that an increase in electrical conductivity (from 0.134 to 0.222 mS/cm in 0–10 cm and from 0.131 to 0.283 mS/cm in 10–20 cm), total dissolved salts (from 65.45 to 108.67 mg/kg in 0–10cm and from 64.33 to 135.3 mg/kg in 10–20 cm), total organic carbon (from 0.86 to 6.84%), total nitrogen (from 0.1 mg/kg to 0.45, 0.43 and 0.41 mg/kg, in 0–10 cm, 10–20 cm and 20–30 cm respectively) and C/N ratio take place in the substrate after the treatment of the mixture. As for the microbiological parameters, treating the mixture in a CW results in an increase in the yeast and fungi which may optimize the biodegradation of compounds such as polyphenols that are non-easily degraded.