The effect of enzymatic pre-hydrolysis of dairy wastewater on the granular and immobilized microbial community in anaerobic bioreactors

The effect of a lipase-rich enzyme preparation produced by the fungus Penicillium sp. on solid-state fermentation was evaluated in two anaerobic bioreactors (up-flow anaerobic sludge blanket (UASB) and horizontal-flow anaerobic immobilized biomass (HAIB)) treating dairy wastewater with 1200mg oil and grease/L. The oil and grease hydrolysis step was carried out with 0.1% (w/v) of the solid enzymatic preparation at 30 degrees C for 24h. This resulted in a final concentration of free acids eight times higher than the initial value. The bioreactors operated at 30 degrees C with hydraulic retention times of 12h (HAIB) and 20h (UASB) for a period of 430 days, and had high chemical oxygen demand (COD) removal efficiencies (around 90%) when fed with pre-hydrolyzed wastewater. There was, however, an increase in the effluent oil and grease concentration (from values as low as 17mg/L to values above 150mg/L in the UASB bioreactor, and from 38242mg/L in the HAIB bioreactor), and oil and grease accumulation in the biomass throughout the operational period (the oil and grease content reached 1.7 times that found in the inoculum of the UASB bioreactor). The HAIB bioreactor gave better results because the support for biomass immobilization acted as a filter, retaining oil and grease at the entry of the bioreactor. The molecular analysis of the Bacteria and Archaea domains revealed significant differences in the microbial profiles in experiments conducted with and without the pre-hydrolysis step. The differences observed in the overall parameters could be related to the microbial diversity of the anaerobic sludge.