An Improvement of an Oxidation Ditch Process for the Low Alkalinity Wastewater Treatment and Various Influent Conditions

摘要

The oxidation ditch process (OD) had been propagated for small scale domestic wastewater treatment through the 1960s in Holland, by the benefits of capital and maintenance cost and easy maintenance. But it was not suitable for large scale plants due to the wide area and maintenance problems at the beginning. After that, the process spread through European countries and all over the world in conjunction with improvements in the equipment and the system. In the early stage in Japan, OD plants frequently experienced pH decline problems from low loading and excess aeration, as the alkalinity of domestic waste water in Japan is less than that of western countries. In this paper, a one-point aeration ditch process, developed by using a down-pumping submerged-turbine aerator, is introduced. The formation of an aerobic zone and an anoxic zone in the ditch is confirmed, and it is reported that the pH decline problem is solved by the effective, concurrent nitrification and denitrification in the ditch, with an indication of the alkalinity balance. Furthermore, new preparations and improvements of the OD process suitable to the various influent conditions, such as a counterplan to alleviate excess low loading, a variant water depth operation, etc. are explained by the full-scale examples.