Evaluation of optimal fermentation conditions for volatile fatty acids production from artisanal fish waste

Abstract

In this research, operational parameters were assessed to optimise the production of volatile fatty acids (VFA) from artisanal fish waste (FW) using mixed-culture fermentation. The experiments were performed using a randomised block design with pH and Inoculum/Substrate (I/S) ratio as factors with three pH levels (5, 7 and 9) and five I/S ratios levels (0.20, 0.15, 0.10, 0.05, 0.00) with VFA production, total ammonia nitrogen (TAN), biogas and soluble chemical oxygen demand (sCOD) as response variables. The results indicated that pH and I/S ratio significantly influenced VFA production and the other variables evaluated. The highest VFA concentration (54.5 g/L) was obtained at pH 7 and with an I/S ratio of 0.05. These conditions were also optimal for TAN and sCOD. External pH control was proved as unnecessary as the highest VFA production (70.3 g VFA/L) was obtained without pH control. In these conditions, the fermentation broth was able to maintain its pH between 6.6 and 7.7. The VFA profile had acetic (35%) and butyric (32%) acids as the dominant species, however, propionic, iso-valeric and iso-butyric were also produced in small amounts (< 10%). These results evidence the potential of artisanal FW as a raw material for producing high concentrations of VFA and smooth the path for the establishment of a VFA and biogas biorefinery from artisanal FW.