Christian Drakides and Meiling Lay-Son
The treatment of confectionary wastewaters by a biological aerobic treatment plant encountered strong failures when wastewaters concentration exceeded 30 g/l of chemical oxygen demand (COD), although the COD inlet flow remained under design specifications. Treatment performances stayed under 50%, and strong acid production and Hydrogen potential drop lead to heavy corrosion of equipments. During a laboratory scale study using the same organic load, with residence times ranging from 1 to 15 days, Hydrogen potential (pH) drop proved to be caused mainly by aerobic production of organic acids from sugars, leading thus to an auto-inhibiting process. The study demonstrated the influence of pH, acids and aeration rate upon key parameters as respiration rates and degradation kinetics. A reduction of 30 to 35 g/l of COD was obtained in laboratory scale reactors with pH and oxygen control. A comparison between the laboratory scale reactors and the full scale plant was made by measuring in the reactors the clean water oxygenation transfer rates and comparing its values to the data issuing from the plant. Compared to the data issuing from the full-scale wastewater treatment plant, the results of this study allowed giving recommendations for its upgrade.
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