ABSTRACT
Biofilters (also called trickling filters, percolating filters and bacteria beds) are an old process for the secondary treatment of domestic wastewater dating from the beginning of the 20th century (Institution of Water and Environmental Management, 1988), and there are many thousands of biofilters in use in both industrialized and developing countries. However, for use in warm climates (whether in industrialized or developing countries) they should now only be used with modern fly control techniques (see below). Biofilters produce high quality effluents (eg <20 mg BOD/l and <30 mg SS/l) without requiring large areas of land or consuming vast quantities of electricity. In many situations in developing countries they are much more appropriate than activated sludge.
