Primary effluent filtration in small-scale installations

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 BOD_5.m⁻².d⁻¹) are possible with aerated adsorbent foam as a medium.