Recovery strategies of inhibition for mesophilic anaerobic sludge treating the de-oiled grease trap waste

• De-oiled grease trap waste (GTW) is a feasible substrate for anaerobic digestion.
• Long-chain fatty acid easily inhibits the anaerobic digestion of de-oiled GTW.
• Four recovery strategies for mesophilic inhibited sludge were investigated.
• Bentonite addition, water dilution and mixing with inocula achieved fast recovery.
• Mixing with inocula at high mixing ratio achieved the shortest recovery time.

De-oiled grease trap waste (GTW) could be a feasible substrate for anaerobic digestion. However, due to high concentration of lipid, the long-chain fatty acid (LCFA), as an intermediate in the anaerobic lipid degradation, easily inhibits the anaerobic digestion, resulting in long recovery period. Four recovery strategies: bentonite addition, water dilution, mixing with low LCFA substrate and mixing with inocula, with control test as comparison, were employed in order to accelerate the recovery process of mesophilic anaerobic sludge. Adding bentonite, water dilution with 80% mixing ratio and mixing with active inocula achieved shortening of the recovery process. The whole recovery time took approximately 3.5 months for the control test, as calculated from the beginning to the end of the lag time after de-oiled GTW was re-added as F/I ratio of 0.4. At least 10 g l−1 of bentonite addition was necessary for the fast recovery of the inhibited sludge, with the whole recovery time one month shorter than the control test. 1.5 months could be saved for the whole recovery process when the strategy of water dilution with 80% mixing ratio was considered. The more inocula were mixed with the inhibited sludge, the more the recovery period was lessened. For the strategy of mixing with inocula with the mixing ratio 80%, only 20 days were needed for the whole recovery process.