A Comparison of Ultrasonic, Ozone, and Enzyme Pre-Treatments on Cheese Whey Degradation for Enhancement of Anaerobic Digestion

Lactose in cheese whey wastewater (CWW) makes it difficult to degrade under normal conditions. The effect of ultra-sonication (US), ozonation and enzymatic hydrolysis on increasing the bioavailability of organic matter in CWW and biogas production were evaluated. The pre-treatment conditions were: specific energy input varied from 2130 to 8773KJ/KgTS for a sonication time of 4.5-18.5 minutes, Ozone (O3) dosages ranging from 0.03 to 0.045gO3/gTS were applied for 4-16 minutes, pH (3.8-7.1), temperature (35°C-55°C), enzyme dosage (0.18-0.52%), was operated from 7.75 to 53 minutes for enzymatic hydrolysis by β-galactosidase. The results of the US reported a maximum sCOD solubilisation of 77.15% after 18.5 minutes of operation, while the corresponding values for ozonation and enzymatic methods were 64.8% at 16 minutes and 54.79%, respectively. The organic matter degradation rates evaluated in terms of protein and lactose hydrolysis were 68.78%,46.03%; 47.83%,16.15% and 54.22%,86.2%respectively, for US, ozonation and enzymatic methods. The cumulative methane yield for sonicated, ozonised and enzymatically hydrolysed samples were 412.4 ml/g VS,361.2 ml/g VS and 432.3mlCH4/gVS, respectively. Regardless of the lower COD solubilisation rates attained, enzymatic pre-treatment showed maximum methane generation compared to US and ozonation. This could be attributable to the increased activity of β-galactosidase in hydrolysing whey lactose. The energy calculations revealed that the pre-conditioning of organic-rich CW with enzymatic hydrolysis is more effective and efficient, yielding a net energy gain (gross output energy-input energy) of 9166.7KJ and an energy factor (ratio of output to input energy) of 6.67. The modified Gompertz model well simulated all experimental values