Upgrading the conventional grease trap using a tube settler

Grease traps are widely used by most restaurants and food processing industries in Hong Kong to reduce oil and grease to an acceptable level before it can be discharged to public sewers. To meet demanding effluent standards in the future, it is necessary to polish the effluent by upgrading the conventional trap design. This study evaluated the possibility of upgrading traditional grease traps by installing tube settlers inside the trap. Their efficiency of removing chemical oxygen demand (COD) and oil/grease was examined to justify the performance. It was found that installing a tube settler is a feasible and cheap way to upgrade the conventional grease trap, since it improved oil/grease removal efficiency by 8-10% compared to the conventional design. In addition, a remarkable improvement in COD removal was observed following a very short hydraulic detention time after the installation of tube settlers. This ensured acceptable effluent quality under peak flowrates. Two mathematical models were also proposed to facilitate trap design.