Wastewater characterization and performance upgrading of a domestic wastewater treatment plant: The Erzincan case

A detailed characterization of the incoming wastewater and a performance evaluation were carried out for the domestic wastewater treatment plant of Erzincan City. Conventional characterization results showed that Erzincan has a medium strength wastewater quality. Structural characterization of the chemical oxygen demand (COD) indicated that the biodegradable fraction of the total COD was 64.7%. The soluble inert fraction was computed as 10.9% of the total COD. In Erzincan, an activated sludge plant provides secondary treatment using Carrousel treatment units. Because some operational problems, such as sludge bulking and foaming, have been experienced, and performance failures related to carbonaceous matter removal have been recorded many times, a new operational strategy suitable for this type of treatment plant was developed. In the new strategy the sludge age was kept at 22 days, intermittent aeration was abandoned and replaced by continuous aeration, and the sludge recycle ratio was increased to 1.35 from 0.85. The developed operational strategy showed its merit in that previous operational problems largely disappeared and COD concentrations remained below the Turkish discharge limits of 100 mg/l and the NH4 removal rate was in the range 87-95%.