The effect of the ammonium ion on activated-sludge settling properties

High levels of sodium in wastewater have been found to be detrimental to ac tivated-sludge. settling and dewatering. Another potentially troublesome mo novalent cation in activated-sludge systems is the ammonium ion. This study was conducted to determine if the ammonium ion could alter activated-sludg e settling and dewatering properties. Side-by-side laboratory activated-slu dge reactors were fed equal concentrations of an organic substrate (bactope ptone), and the same divalent cations were provided in the feed. However, t he monovalent cations were varied either by inhibiting nitrification so tha t the ammonium concentration would increase or by adding sodium. These stud ies showed that an increase in either sodium or ammonium would cause activa ted-sludge settling properties to deteriorate. When the monovalent-to-dival ent cation ratio on a charge-equivalent basis was increased from 2.4 to 4.7 either by addition of sodium or ammonium, the interfacial settling velocit y decreased, although the greatest drop was in the reactor containing ammon ium. When addition of the nitrification inhibitor was stopped, rapid recove ry of nitrification occurred but the settling properties improved more slow ly. It seemed that recovery was due to replacement of the activated sludge with new floes rather than alteration of the existing biomass.