Use of physicochemical processing in treating urban waste waters

The principal objective of the present study was to compare two clearly defined purification processes in two stages: the periods 1985–1987 (conventional) and 1988–1990 (physico‐chemical). In general, the mean concentrations obtained were lower in the second period. A z‐test for comparing means was applied, but no significant correlation was observed (p ≤ 0.05). The mean concentrations obtained (with some exceptions) are lower in the second period. With the passing of time, the total volume of sewage flow has increased, and hence the load of contaminants has become diluted. The use of physico‐chemical treatment prior to biological processing may be the cause of the increase in cost.