The experiment was conducted in a pilot-scale Orbal oxidation ditch operated for about two years (Fig. 1).
Raw domestic wastewater via preliminary treatments such as bar screen and grit chamber was directly pumped into the wastewater tank, and the seed sludge was inoculated from a full-scale WWTP with Orbal process.
The total working volume of oxidation ditch is 11.4 m3 with the size ratio of three channels of approximately 48%:33%:19%(outer:middle:inner).