Process for 2=stage purificn. of sewage using iron salt flocculant

摘要

A two-stage process for purifying sewage with circulation of a flocculant in the sewage is claimed. The process comprises feeding the sewage without mechanical pre-clarifying into an anaerobic stage, then into an aerobic stage, using an iron salt as a flocculant/precipitant in the sewage; and the flocculated/precipitated sludge and the excess sludge of the aerobic stage is carried over to the anaerobic stage. In the anaerobic process, the bonded Fe<3>+ from the flocculated/precipitated sludge is reduced and goes back into solution; sewage flowing through the anaerobic stage transports the redissolved Fe<2>+ to the aerobic stage; and the dissolved Fe<2>+ is oxidised to Fe<3>+ for reuse for flocculation/precipitation.