Volatile Fatty Acids by Acidogenic Fermentation of Wasted Domestic Sludge from IFAS-MBR: The Effect of Sludge Retention Time

Rapidly emerging as valuable resources, volatile fatty acids (VFA) can be obtained from sewage sludge by acidogenic fermentation of its organic content. Existing work focuses on optimising VFA generation by altering pH and temperature, integrating chemicals, or pre-treating the sludge. Nonetheless, little is known about the impact of sludge properties, namely the sludge retention time (SRT). It is essential to comprehend how the characteristics of sewage sludge affect acidogenic fermentation when constructing fermenters that can be expanded to industrial sizes. Through the effective reuse of waste streams, standardised fermenter designs would not only improve VFA output but also advance into sustainability. The literature lacks thorough investigations or defined criteria necessary to fill this knowledge gap. In this sense, fermentation batch tests were carried out utilising surplus sewage sludge from an Integrated Fixed Film Activated Sludge Membrane Bioreactor (IFAS-MBR) pilot plant to provide insights into the fermenter reactor’s design. The preliminary results show that the sludge with the lowest SRT tested proved to be the one with the best quality and quantity of produced VFA. VFA accounted for 63% of the organics produced, expressed as chemical oxygen demand (COD). Moreover, a higher share of acetic acid was made (76%) compared to sludge with highest SRT tested, highlighting the increased efficiency in VFA production when sludge with low SRT is used.