Trickling filters following anaerobic sewage treatment: state of the art and perspectives

High-rate anaerobic treatment of sewage using upflow anaerobic sludge blanket (UASB) reactors is a consolidated technology in warm climate countries. Nevertheless, since anaerobic treatment only removes organic carbon, post-treatment is required to remove nitrogen, besides residual organic carbon. Trickling filters (TFs) constitute a cost-effective post-treatment option, assuring low sludge production, low operational costs and maintenance simplicity compared to other post-treatment technologies (e.g. activated sludge). This paper reviews the experience of the last 20 years of research, design and operation of UASB/TF systems. Three main topics are addressed: i) the development of trickling filters for UASB reactor effluent treatment, building on first experiences with TFs preceded by primary settlers; ii) the design criteria, performance and empirical models for predicting the efficiency of TFs post-UASB reactors; and iii) the future challenges associated with elimination of secondary settlers and nitrogen removal in sponge-bed trickling filters (SBTFs).