inconsistent with previous study that HRT of grease
trap should not be less than 24 hrs because result
would be lower than 20 mg/L of FOG in effluent [13].
It might be occurred from the characteristics of
wastewater from dishwashing and suitable design
criteria of grease trap for treatment. Moreover, Sonune
and Gahte (2004) [14] studied the characteristics of
wastewater from primary treatment unit at California,
USA. They revealed that BOD (influent) was 112
mg/L when it was treated by using a primary treatment
unit and could provide up to 34.82% of removal as
well as contained of SS 185 mg/L with efficiency for
treatment up to 60%. It was consistent with the basic
design of primary treatment in Thailand, which BOD
and SS removals were 50 - 70% and 60%, respectively.
This study also found that at 2 L/min of flow rate and
10 hrs of HRT resulted effluent having 7.01 and 6.7 of
pH, 42.58 mg/L and 26.13 mg/L of SS, 45.83 mg/L
and 34.17 mg/L of BOD, 12.3 mg/L and 5.95 mg/L
FOG of simple and modified grease traps, respectively.
However, the result in this experiment was found that
the simple and modified grease traps could treat oil and
grease less than 20 mg/L by applying a hydraulic
retention time at 10 hrs which was the higher hydraulic
retention time and the higher removal efficiency. The
appropriate grease trap designed for wastewater
treatment was related to the experimental results of
varying 1, 2, 3 and 6 hrs of HRT for 140 L of grease
trap, which treated wastewater generation from
cafeteria, King Mongkut’s University of Technology