EDTA-REDUKTION I EN MULTIBIOANLÄGGNING / EDTA-Reduction in a Multibio Plant
A clear connection between accessible phosphorous and the reduction from EDTA was established. With optimum conditions the EDTA is reduced with more than 90 %. When the phosphorous is low in the untreated effluent, the EDTA-reduction is deteriorated and during some time it almost ceased completely. When the doses of phosphorous was increased the EDTA-reduction returned immediately. Even with the EDTA-reducing organisms in the sludge during the periods with low phosphorous, there was no EDTA-reduction. The tests show that current understanding concerning the connection between pH, sludge age, retention time and the reduction of the EDTA is not correct, at least not if the plant is designed as a Multibio. pH in untreated effluent was during some periods lower than 5 and the reduction has nut been influenced by short retention time and low sludge age. The COD-reduction had an average of 73% during the test runs. The sludge production has been approximately 0,1 kg MLSS/kg COD reduction.