A combined photocatalytic-biological wastewater treatment approach: The importance of recycling

Zach Shidlovsky, Chemical Engineering, Technion, Haifa, Israel

Water purification is often challenged by the co-presence of a large number of organic and inorganic industrial contaminants, some of which are too toxic for bacteria or too opaque for photocatalytic processes. A combined photocatalytic-biological treatment approach requires optimizing the design of the system in terms of retention time of each reactor and their sequence in real conditions, where the toxicity and turbidity might vary over time.

A model that may assist the design and operation of combined photocatalytic-chemostat facilities is presented hereby. The model, easily run on a MATLAB platform while using experimental values for its parameters, examines the effect of co-existing toxicity and turbidity on the optimal sequence, on the relative retention times in the two reactors and on the effect of recycling, under an estimated cost function constrain.

Based on the model, it is concluded that recycling the combined reactors system significantly reduces the required volumes of the reactors, and consequently reduces the required cost. The benevolent effect of recycling was found to be quite general, i.e. irrespective of the toxicity and turbidity of the feed. Accordingly, the issue of the sequence of the reactors becomes less crucial. These findings are easy for implementation in commercial systems.