Effect of Solubilization on Acidification, Anaerobic Biodegradability, and Economic Feasibility via Ultrasonic-Zerovalent Iron-Acidic pH Pretreatment of Sludge

The present study aimed to evaluate the effect of solubilization obtained via ultrasonic (US) homogenization, combined ultrasonic and zerovalent iron (UZ), and combined ultrasonic and zerovalent iron at acidic pH (UZP) on acidification, biodegradability, and biomethanation. The outcome of the study revealed that obtaining solubilization over 20% via UZ was not possible. Zerovalent iron needs acidic pH to obtain solubilization in excess of 20%. Therefore, 25, 30, and 35% solubilization obtained via US and UZP at low-cost input were subjected to acidification, biodegradability, and biomethanation. The results of the acidification implied that a higher total volatile fatty acid production of 2140.29 and 2675 mg/L was achieved for US and UZP at 30% solubilization. Even though both of the samples possess a similar state of solubilization, a significant increment in acidification was noted for UZP, owing to the synergistic impact of ultrasonic (160 W power and homogenization time of 10 min) zerovalent iron (0.07 g/g of suspended solids dosage) at acidic pH 3. The results of biomethanation implied that UZP showed higher methane production of 0.12 L of CH4/g of chemical oxygen demand (COD) when compared to US (0.108 L of CH4/g of COD) for the same state of solubilization (30%). The results of biodegradability implied that there was no considerable variation among 30 and 35% solubilized samples for US and UZP. The scalable energy and economic analysis outcome of US and UZP with 30% solubilization revealed that UZP demands a lesser net cost of -45.67 USD/ton when compared to US (-3489.3 USD/ton).