Abstract
The contact aeration process with anaerobic filter tanks is considered to be promising as a simple and convenient method for small domestic wastewater treatment plants in rural areas.
In this study, data obtained in 15 plants which are in actual operation were analyzed by means of Quantification-I, a kind of multivariate analysis, to determine the factors affecting nitrogen removal in this process and suitable operation and design of the plants using that process.
As a result, the major factors for nitrogen removal were found to be the temperature, the DO concentration, specific surface area of contactors, and the propagation of large invertebrates in aeration tanks, the BOD loading on aeration tanks, and the daily aeration hours.
In order to achieve the higher rate of nitrogen removal, the DO concentration in the final aeration tank should be 5mg/l or higher, the return water ratio should be about 3, the daily aeration hours should be 20 h/d or longer. The lower the BOD loading is, the more satisfactorily nitrogen is removed. The larger the specific surface area is under 50 m2/m3, the higher nitrogen removal is achieved. However, the back washing might be an important operation in using the contactors having over 50 m2/m3. The abnormal growth of large invertebrates has a great effect on the nitrogen removal. Therefore, it is of urgent necessity to develop some appropriate method to exterminate them or prevent their abnormal growth.
It is very important to regulate these factors in winter, when the temperature of wastewater in aeration tanks is low, especially under 14°C
