INFLUENCE OF THE ADDITION OF DIFFERENT METALS TO AN ACTIVATED-SLUDGE SYSTEM ON THE ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL

Activated sludge systems can be operated to select bacteria which accu mulate phosphorus as polyphosphate. By these means, phosphate can be r emoved without the addition of chemical precipitants. This contributio n presents results of experiments with a bench-scale purification plan t for domestic sewage. The goal was to find the concentrations of rele vant metal cations at which the biological P removal may be affected b y competing chemical (precipitation) or physical (adsorption) processe s. For this goal, increasing amounts of iron and calcium, respectively , were added into the pilot plant. During the addition of iron, the pr oportion of chemically (iron-) bound phosphorus increased from 10 to m ore than 50 %. The P-release rare substantially decreased with increas ing amount of added iron. An addition of small amounts of iron enhance d the long-term stability of the P elimination as a whole. During the experimental period with addition of calcium, the proportion of Ca-bou nd phosphorus increased from 1 to 2 % to almost 15 %. In batch experim ents a measurable Ca-phosphate precipitation took place at a pH value of at least 8.0 and a Ca-concentration of at least 100 mg/l. The incre ase in hardness of the influent waste water didn't produce any positiv e effect on the stability of the enhanced biological phosphorus remova l. The metal ions Ca2+, Mg2+ and K+ serve as counter-ions in the polyp hosphate chains. They were identified and quantified by X-ray spectrom etry in combination with scanning transmission electron microscopy. A release of Mg2+ and K+ occured simultaneously with the degration of po lyphosphates (PP). The PP bound to Ca was not redox sensitive.