PROCEDURE TO SCREEN ILLICIT DISCHARGE OF TOXIC-SUBSTANCES IN SEPTIC SLUDGE RECEIVED AT A WASTE-WATER TREATMENT-PLANT

This paper presents an integrative approach, using toxicological and c hemical analyses, to screen toxic and illegal substances that could be added to the septic sludge transported by a tanker truck to the waste water treatment plant of the Montreal Urban Community (MUC), Microtox, lettuce root elongation, and a bacterial respiration test were used t o establish the toxicity range of a normal sludge and the determinatio n of threshold limit criteria. Septic sludge samples mere spiked with different types and amounts of contaminants (copper, zinc, phenol, ind ustrial sludge). Conservative criteria mere applied to detect abnormal toxicity with great reliability while avoiding false positives (i.e., detecting abnormal toxicity in nonspiked sludge), Taken individually, toxicity tests using Microtox were revealed to be the least discrimin ating toxicological method (efficiency of 45% when the ratio of the IC 50 values is considered), whereas lettuce root elongation was relative ly the most efficient (80% of spiked samples), As a whole, the battery of toxicity tests detected at least 93% of the spiked sludge samples, This procedure is also very efficient, i.e., easy to apply, cost effe ctive, and rapid, In certain cases, an abnormal toxicity level can be determined within a few hours, whereas a septic sludge can be classifi ed as normal within 5 days. (C) 1998 Academic Press.