Grit and grease trap were always a combination. Grit are mentioned as sand, samll stone, egg shell or any small settleable in the grit trap. Grease are mentioned as oil, fat which is normally in solid shape in wastewater. Domestic water in Malaysia are very rich with these kind of organic/oleo contaminat because the culture of cooking.
Grit must be trapped and prevented to enter aeration tank (secondary treatment) because later it will interrupt downstream treatment process. It will also enhance into mechanical failure especially for diffuser inside the aeration tank. The grit also will deposit and accumulated in the aeration tank which will decrease tank depth for long term. As the consequences, surge loading or incresing loading to treatment plant will later damage the treatment process although the plant is planned and constructed based on peak factor flow.
Logically, grit chamber/trap will be constructed prior grease chamber/trap. The reason is, escaped grit hopefully will settle in grease chamber likely grease chamber will be a secondary protection to ensure grit is prevented to enter aeration tank. The grit will be managed for disposal.
Grit chamber will be equipped with either grit pump or airlift suction to remove settleable grit at bottom grit tank/chamber. Grease chamber will be equipped with surface scrapper or scum skimmer, which the equipment will remove floating material in the grease tank. The output from these equipment will also be managed dried (normally using drying bed) and disposed off.
Grease must be prevented to enter aeration tank
1) to ensure compliance of final effluent,
2) to ensure sufficient oxygen requirement for biological growth and activity inside aeration tank (to degrade oil will require more oxygen than other organic material).
3) Failure to treat the oil will increase COD and O&G paramater in FE.
4) To maximise power usage especially for aeration equipment.
Grease that removed from the grease chamber normally will create foul odour. This area is the biggest contributor to public complaint due to foul smell.
