Coupled anaerobic-aerobic treatment of whey wastewater in a sequencing batch reactor: proof of concept

A proof of concept was performed in order to verify if the coupling of anaerobic and aerobic conditions inside the same digester could efficiently treat a reconstituted whey wastewater at 21 degrees C. The sequencing batch reactor (SBR) cycles combined initial anaerobic phase and final aerobic phase with reduced aeration. A series of 24 h cycles in 0.5 L digesters, with four different levels of oxygenation (none, 54, 108 and 182 mgO(2) per gram of chemical oxygen demand (COD)), showed residual soluble chemical oxygen demand (sCOD) of 683 46, 720 +/- 33, 581 45, 1,239 15 mg L-1, respectively. Acetate and hydrogen specific activities were maintained for the anaerobic digester, but decreased by 10-25% for the acetate and by 20-50% for the hydrogen, in the coupled digesters. The experiment was repeated using 48 h cycles with limited aeration during 6 or 16 hours at 54 and 108 mgO(2)gCOD(initial)(-1), displaying residual sCOD of 177 +/- 43, 137 +/- 38, 104 +/- 22 and 112 +/- 9 mg L-1 for the anaerobic and the coupled digesters, respectively. The coupled digesters recovered after a pH shock with residual sCOD as low as 132 mg L-1 compared to 636 mg L-1 for the anaerobic digester. With regard to the obtained results, the feasibility of the anaerobic- aerobic coupling in SBR digesters for the treatment of whey wastewater was demonstrated.