*2.4. Analysis Methods*

The influent was taken from the reserved sampling port of the inlet pipe of the cascade aeration tank and the effluent was taken from the outlet pipe of the biofilter. All samples were analyzed immediately in the laboratory of the Water Treatment Plant, so no storage measures were adopted. All iron and manganese analyses were performed by a spectrophotometer in accordance with standard methods [26]. Dissolved oxygen was measured by a Dissolved Oxygen Meter (oxi340i, WTW, Munich Germany), pH was determined using an electrode (pH/oxi340i, WTW, Munich Germany)
