Effect of enzymatic pretreatment and increasing the organic loading rate of lipid-rich wastewater treated in a hybrid UASB reactor

This study aimed at evaluating the effect of increasing organic loading rates and of enzyme pretreatment on the stability and efficiency of a hybrid upflow anaerobic sludge blanket reactor (UASBh) treating dairy effluent. The UASBh was submitted to the following average organic loading rates (OLR) 0.98 Kg.m−3.d−1, 4.58 Kg.m−3.d−1, 8.89 Kg.m−3.d−1 and 15.73 Kg.m−3.d−1, and with the higher value, the reactor was fed with effluent with and without an enzymatic pretreatment to hydrolyze fats. The hydraulic detention time was 24 h, and the temperature was 30 ± 2 °C. The reactor was equipped with a superior foam bed and showed good efficiency and stability until an OLR of 8.89 Kg.m−3.d−1. The foam bed was efficient for solid retention and residual volatile acid concentration consumption. The enzymatic pretreatment did not contribute to the process stability, propitiating loss in both biomass and system efficiency. Specific methanogenic activity tests indicated the presence of inhibition after the sludge had been submitted to the pretreated effluent. It was concluded that continuous exposure to the hydrolysis products or to the enzyme caused a dramatic drop in the efficiency and stability of the process, and the single exposure of the biomass to this condition did not inhibit methane formation.

Research highlights
► Anaerobic treatment of lids rich effluents is feasible but requires optimization.
► Lipids can cause sludge floatation in granular reactors and clogging in fixed bed.
► The enzymatic pre-treatment was studied in a UASBh treating dairy wastewater.
► Solids retention and volatile acid consumption occurred in the superior foam bed.
► Enzymatic pretreatment caused drop in the efficiency and stability of the process.