This paper reviews recent technological developments in the filtration of primary effluent. Various studies show that single stage intermittent sand filters attain removal efficiencies of 90% COD, 95% BOD5, 30% TN, 40% TP and 99-99.9% FC at maximum BOD5 loads of around 10 g.m−2.d−1 and hydraulic loads of 5-10 cm.d−1. The permissible organic load can be enhanced by measures such as improved aeration and the use of multilayer filters. Nitrogen removal can be enhanced to 70% by adding a C-source to the filter material or by using two-stage post- and pre-denitrification systems. High organic loading rates (up to around 100 g BOD5.m−2.d−1) are possible with aerated adsorbent foam as a medium.

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