Kinetic analysis of the psychrophilic anaerobic digestion of wastewater derived from the production of proteins from extracted sunflower flour

A kinetic analysis of the anaerobic digestion process of wastewater derived from the production of protein isolates from extracted sunflower flour was carried out. The digestion was conducted in a laboratory-scale fluidized bed reactor with saponite (magnesium silicate) as support for the mediating bacteria at psychrophilic temperature (15-19degreesC). Soluble chemical oxygen demand (CODs) removal efficiencies in the range of 95.9-69.0% were achieved in the reactor at organic loading rates (OLR) of between 0.57 and 2.49 g total COD (CODt)/L cl, hydraulic retention times (HRT) of between 20.0 and 4.5 days, and average feed total COD concentration of 11.3 g/L. The yield coefficient of methane production was 0.32 L of methane (at STP) per gram of CODt removed. The total volatile fatty acid (TVFA) levels and the TVFA/alkalinity ratio were lower than the suggested limits for digester failure for OLR and HRT up to 2.26 g CODt/L d and 5.0 days, respectively. The specific rate of substrate uptake, r (g CODs/g VSS d), correlated with the concentration of biodegradable substrate, S (g CODs/L), through an equation of the Michaelis-Menten type. The maximum substrate utilization rate, k, and the Michaelis constant, K-s, were found to be 0.125 g CODs/g VSS d and 124 mg CODs/L, respectively. This proposed model predicted the behavior of the reactor very accurately showing deviations lower than 10% between the experimental and theoretical values of substrate uptake rates. A mass (CODt) balance around the reactor allowed the COD equivalent of methane volume (W-CH4) to be obtained, which gave a value of 2.89 g CODt/L CH4, which was virtually coincident with the theoretical value of 2.86 g CODt/L CH4.