OPTIMIZATION OF DIGESTION METHODS FOR SEWAGE-SLUDGE USING THE PLACKETT-BURMAN SATURATED DESIGN

The Plackett-Burman saturated factorial design was used to select opti mized dissolution conditions for sewage sludge samples. Three differen t digestion methods were applied: i) microwave oven digestion in a dom estic oven with Parr-type reactors; ii) microwave oven digestion with controlled-pressure reactors; iii) pressure bomb reactor heated on a h ot plate. The three methods were validated by statistically comparing the metal contents found with the certified ones of the sewage sludge sample (BCR 145R). No significant differences were obtained and the RS D values were lower than 3% in all cases. The metals were determined b y flame-AAS. The variables studied were the following: microwave power ; digestion time; predigestion; volume of hydrochloric acid; volume of hydrofluoric acid; volume of nitric acid. The operative advantages of fered by microwave digestion with controlled-pressure reactors were al so considered.