| Gravity thickening is one of the most common traditional methods of sewage sludge thickening, and is advantageous because of its simple mechanism and structure, and low energy consumption. Water Path Forming Poles (WPFPs) were developed by upgrading Picket Fence Thickener to improve gravity thickening performances. As of June 2014, WPFPs are in operation at 11 sewage treatment plants in Japan. On-site data analysis was carried out to evaluate the effect of WPFPs on gravity thickening performances. In conventional activated sludge processes, the effect of water temperature was significant, and the performance improvement was observed at less than approximately 28°C. In oxidation ditch processes, the effect of sludge volume index (SVI) was significant, and the performance improvement was possible at SVI of less than 350 mL/g. A questionnaire result revealed that not only installation of WPFPs but also efforts of on-site technicians contributed to the performance improvement. |
