Trickling filters are complex, with many events occurring simultaneously. A trickling filter functions much like a cooling tower or packed tower, consequently there is both heat and mass transfer between the liquid and air. The changes in heat transfer have an effect on the flow of air through the filter.
Ponding is a potential problem typically associated with rock filters caused by a low hydraulic loading. The hydraulic loading or dosing schedule should be adjusted to provide the fluid shear necessary to keep the biofilms thin, which will prevent ponding.
There was an article titled “Effects of dosing rates on trickling filter performance”. Journal of the Water Pollution Control Federation, 1976 that demonstrated that 2.5 – minute dosing, 7.5 – minute rest period (800 gpd instantaneous flow rate provided less COD removal than a continuous dosing program of 200 gpd instantaneous flow rate.
The results in the study varied somewhat with bed depth. However, the study showed that a continuous dosing program is better than an intermittent dosing. For the 2.5 - minute dosing program, the difference was approximately 15%. For the 5 - minute dosing program (5 – minute dosing, 5 – minute rest period), the difference was approximately 5%.
Therefore, if your dosing is adequate to maintain the minimum hydraulic requirements of the trickling filter, you probably can expect slightly better performance with a more continuous dosing. However, the improvement will be slight and might not show up in the treatment results.
