Complex oily wastewater from a food industry was treated in three different UASB reactors at different operating conditions. Although all three systems achieved fat, oil, and grease (FOG) and COD removal efficiencies above 80% at an organic loading of 3 kg COD/m3 x d, system performance deteriorated sharply at higher loading rates, and the presence of high FOG caused a severe sludge flotation resulting in failure. Initially, FOG accumulated onto the biomass which led to sludge flotation and washout of biomass. The loss of sludge in the bed increased the FOG loading to the biomass and failure ensued. Contrary to previous findings, accumulation of FOG rather than influent FOG concentrations or volumetric FOG loading rate was the most importantfactor governing the high-rate anaerobic reactor performance. The critical accumulated FOG loading was identified as 1.04 +/- 0.13 g FOG/g VSS for all three reactors. Furthermore, FOG accumulation onto the biomass was identified mainly as palmitic acid (>60%) whereas the feed LCFA contained only 30% of palmitic acid and 50% of oleic acid.

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Pet food industrial wastewater contains high concentration of oil and grease (O&G) which is difficult to treat using conventional biological systems. In this study, anaerobic treatability of pet food wastewater was evaluated in a hybrid packed bed reactor-upflow anaerobic sludge blanket (PBR-UASB) treatment system. The PBR was packed with sol-gel/alginate beads containing immobilized enzyme as media which hydrolyzes the O&G in the wastewater as a pretreatment step while the UASB reactor was seeded with anaerobic sludge. The PBR was operated at 4 L/d for 64 days (phase I) and 8 L/d for another 57 days (phase II). The UASB reactor was operated at an HRT of 2.5 d and 1.25 d with an OLR of 1.27 and 2.5 kgCOD/m 3 .d during phase I and II respectively. Overall COD and O&G removal efficiencies of about 90% were achieved without any sludge floatation and with methane to COD yield of 80%. Despite the loss of immobilized lipase, the performance of PBR was satisfactory at oil loading of 0.9 kgO&G/m 3 .d which hydrolyzed 41% of O&G. Moreover, there was no sludge flotation observed during the period of operation due to pre-hydrolysis of O&G in the PBR. Further studies on system performance at higher organic loading rate and lower HRT are in progress.

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