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 min, Ozone (O3) dosages ranging from 0.03 to 0.045gO3/gTS were applied for 4-16 min, pH (3.8-7.1), temperature (35 degrees C-55 degrees C), enzyme dosage (0.18-0.52%), was operated from 7.75 to 53 min for enzymatic hydrolysis by beta-galactosidase. The results of the US reported a maximum sCOD solubilisation of 77.15% after 18.5 min of operation, while the corresponding values for ozonation and enzymatic methods were 64.8% at 16 min 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 soni-cated, 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 ac-tivity of beta-galactosidase in hydrolysing whey lactose. The energy calculations revealed that the pre-conditioning of organic-rich CWW with enzymatic hydrolysis is more effective and efficient, yielding a net energy gain (gross output energy-input energy) of 9166.7 KJ and an energy factor (ratio of output to input energy) of 6.67. The modified Gompertz model well simulated all experimental values.

Automated summary

The effects of ultrasound, ozonation, and enzymatic hydrolysis on increasing the bioavailability of organic matter in cheese whey wastewater (CWW) and biogas production were evaluated. The enzymatic pre-treatment showed the highest methane generation compared to ultrasound and ozonation.