Improvement of organic carbon recovery from wastewater by changing water temperature in high-rate contact stabilization process

The high-rate contact stabilization (HiCS) process, which can effectively recover organic carbon, even from low-strength wastewater, is attracting attention. To evaluate the effect of water temperature in the HiCS process on the organic carbon recovery, a bench-scale test plant was used to treat real municipal wastewater. The operating period was divided into six phases in terms of the solid retention time (SRT) and water temperature in the reactor. The carbon recovery rate varied from 12 to 30% between phases, and it was high at relatively low water temperatures in the range investigated in this study (16–26 °C). The average carbon recovery rates in a phase with an SRT of 0.55 days and an average water temperature of 17.4 °C was 30%, and was significantly higher than those in the other phases (p < 0.05, Tukey’s tests). Water temperature should be fully considered when estimating the amount of sludge generated by the HiCS process because the water temperature is likely to have a nonnegligible effect on the organic carbon recovery.