Abstract
The contact aeration process with anaerobic filter tanks is considered to be promising as a simple and convenient method for the simultaneous removal of organic matter and nitrogen in small scale plants treating domestic wastewater. In this process, wastewater is first led into an anaerobic filter tank and then it is led into a contact aeration tank before some of the treated wastewater is returned to the anaerobic filter tank.
In this study, plant site investigations on the contact aeration process with anaerobic filter tanks were made to find a suitable operation of the plants using this process.
As a result, the efficiency and stability of BOD and SS removal, and of denitrification were found to be satisfactory. Therefore, the important point of the plants' operation is how to obtain a high rate of nitrification, and then keep the return water ratio high. The intermittent operation of blowers was worthwhile in terms of saving energy, but the stopping period of aeration should be restricted in a few hours in order to make the nitrification satisfactorily. The abnormal growth of large invertebrate in the aeration tanks greatly deteriorated the progress of nitrification.
To exterminate the invertebrate, the method of stopping aeration for a few days was available. The intermittent aeration, and the increase of the BOD loading on the aeration tanks changed the dominant species of invertebrate, but could not prevent their abnormal growth. The periodical back washing of contactors probably was effective for prevention of their abnormal growth. In the situation of abnormal growth, the increase of aeration intensity was available for the promotion of nitrification.
