Process intensification of anaerobic digestion for biohydrogen and methane production from crude glycerol and dairy wastewater using cavitation techniques

This study investigates methane production from the mono-digestion of dairy wastewater (DWW) and hydrogen production from the co-digestion of DWW and crude glycerol (CG), both of which are abundantly available in India. In this study, ultrasonication (US) and hydrodynamic cavitation (HC) were employed as pretreatment methods for DWW prior to mono and co-anaerobic digestion, with the aim of enhancing methane and hydrogen production. The results show that these methods significantly improve methane yield, offering a sustainable solution for efficient bioenergy recovery from organic waste. The highest methane yield from DWW was achieved using US at an amplitude of 60% and a treatment duration of 30 min, resulting in a maximum cumulative methane yield (<i>P</i> _max) of 413 mL, with a production rate (<i>r</i> _m) of 26.31 mL per day and a lag phase (<i>λ</i>) of 23.19 days. In a similar experiment, treating DWW with HC using a venturi with a 2 mm hole size, the <i>P</i> _max was 341.21 mL at a pressure of 5 bar and a treatment time of 30 min. This process resulted in a <i>r</i> _m of 24.43 mL per day and a <i>λ</i> of 29.74 days. Additionally, when CG was combined with DWW, the maximum cumulative hydrogen yield reached 330.8 mL at a 4% v/v concentration of CG, with <i>r</i> _m of 45.6 mL per day and a <i>λ</i> of 0.69 days. At CG concentrations ranging from 0.2 to 1% v/v, both hydrogen and methane were produced. However, beyond a 1% v/v CG concentration, methane production began to decrease. It was also found that pretreatment using HC and US did not enhance hydrogen production when CG was co-digested with pretreated DWW. These findings highlight the potential of integrating US, HC, and co-digestion strategies to enhance biofuel yields, promoting sustainable waste management and renewable energy solutions.