FULL-SCALE ONLINE ASSESSMENT OF TOXIC WASTEWATERS CAUSING CHANGE IN BIODEGRADATION MODEL STRUCTURE AND PARAMETERS

Detecting wastewater toxicity in due time is essential for protection of a sewage works and the receiving waters. A respirometric method is presented that performs short batch experiments, so-called In-Sensor-E xperiments for toxicity detection. Two types of wastewater samples can be added to the reactor in the device: either the potentially toxic w astewater entering the plant or, a defined mixture of acetate and ammo nia. From the latter experiments models are identified that describe t he heterotrophic and autotrophic activity of the sludge. Since these ' calibration' experiments are alternated with experiments in which wast ewater is injected, me effect of the wastewater on the sludge can be q uantified unequivocally. Full-scale toxicity detection (and the corres ponding effluent quality) results are reported for a plant treating a mixture of hospital and municipal wastewaters. The respirometer was in stalled at the influent line of the plant It was evaluated during a 6- month period for its on-line toxicity detection capacity. Both deliber ate and accidental intoxications were recorded and compared with off-l ine toxicity measurements. Inhibitory wastewaters affected the nitrifi cation activity of the sludge. This was confirmed by the concomitant i ncrease in NH4+ discharge of the treatment plant. To evaluate the effi ciency of control actions, the deliberate addition of toxicant was int errupted at the time a toxicity alarm was triggered by the respiromete r. it was observed that plant performance then remained unaffected for all monitored criteria. Copyright (C) 1996 IAWQ. Published by Elsevie r Science Ltd