Development of a three-stage system for wastewater toxicity monitoring: a design and feasibility study.

A three-stage system was developed to automate a batchwise toxicity testing protocol designed for assessing wastewater toxicity to activated sludge. The three-stage system used the luminescent bacterium Shkl. The three stages were cell storage, cell activation, and continuous toxicity testing. Shkl cells were stored in a bioreactor at 4 degrees C when the system was not in use and activated in another bioreactor for use in toxicity tests conducted in a continuous manner. The system could quickly be switched between the "off" and "on" modes, and operation of the system was easy. The stability of the system, in terms of cell density and bioluminescence in the storage and activation bioreactors, and the response of the activated cells to a metal and an organic toxicant were studied. The feasibility of the system design was demonstrated by simulating zinc toxicity episodes in synthetic wastewater. The needs for further modifications and improvements of the system were discussed.