Optimisation of Methane Production During Anaerobic Digestion of Pot Ale after Thermochemical Pre-Treatment Through Response Surface Methodology

Whiskey distillery wastewater, pot ale, is a high strength lignocellulosic waste, therefore its sustainable treatment is crucial from environmental stand point. Anaerobic digestion of pot ale was assessed at lab scale batch mode reactor after implementation 1M NaOH and microwave pre-treatments at varying power settings. A 13.7% of lignin degradation was achieved due to the applied thermochemical pre-treatment and correspondingly a 3-fold increase was seen in the CH4 yield. Furthermore, as a result of anaerobic digestion, chemical and biological oxygen demand removals of 69±1.4, 66±1.7% were achieved respectively. Response Surface Methodology was adopted for process modelling and optimisation. Inoculum substrate ratio (1-3-5 on dry basis), initial digestion pH (7-8-9) and microwave power (10-30-50% of 800W) were investigated. The optimum conditions were identified as I/S of 4.6, initial pH of 8.9 and 39% of microwave power based on combined numerical and graphical optimisation. The optimum CH4 yield was found as 1274ml/g VS. The mineral quality of the digestate, was found mainly to be in alignment with an industrial sample from anaerobic digestion plant for agricultural use