Preliminary Study on Mini-Modus Device Equipped with a Bioreactor to Purify and Oxygenate a Synthetic Effluent

To explore the possibility of recovering a polluted anoxic environment characterized by an elevated organic load, a bench-scale novel technology, called the module for the decontamination of units of sediment (MODUS), was studied. The bench-scale apparatus is able to aerate an effluent by a sparger that uses an air flow. The apparatus was implemented with a bioreactor to biodegrade a synthetic effluent made by glucose, urea, and potassium acid phosphate; an apparatus that will be here referred to as the BIOmini-MODUS. To test its performance, seven series of biodegradation experiments were done, each series corresponding to one of the seven different selected air flows in the range 5–20 L min−1. The purpose was to determine the best operative conditions for the BIOmini-MODUS, especially in terms of energy efficiency. These were found by studying eight parameters deemed particularly crucial: (1) dissolved oxygen concentration of the synthetic effluent, (2) time required to complete the substrate biodegradation, (3) air pressure (head losses) of the pumped air, (4) power needed to pump the air, (5) total energy used during a single biodegradation experiment, (6) biodegradation efficiency, (7) biological oxygen demand BOD as a function of time, and (8) the maximum biodegradation velocity reached by each biodegradation experiment. All of them, except BOD, were a function of the air flow. The air flow resulted in being particularly important to optimize the performance of the BIOmini-MODUS in terms of biodegradation velocity and oxygen concentration at the apparatus exit, in conjunction with energy efficiency. This last one, which showed a sharp maximum for an air flow of 10 L min−1, was determined on the basis of the biodegradation rate. At low air flows, a high biodegradation rate resulted in being a good parameter to indicate high energy efficiency; while, on the other hand, a high oxygen concentration resulted in being a good parameter to determine a high biodegradation rate.