Can Higher Loadings Reduce Secondary Sludge Yields from Trickling Filter/Activated Sludge Plants?

The trickling filter/activated sludge (TF/AS) process is a process configuration that has been used to upgrade trickling filter plants for additional capacity or improved effluent quality. Despite the abundance of information available about sludge production in the activated sludge process, less has been published for the TF/AS process. This paper provides a summary of reported yields (lb TSS produced/lb BOD5 removed) by TF/AS processes, and examines the impact various loading conditions have on the yield for five municipal facilities in California. One of the interesting observations is the apparent decrease in the net yield as the organic and solids loading increases to the trickling filter. This is contrary to what one expects, and to what has been reported in previous studies.