REALITY IN PACKAGE ON-SITE GREASE TRAP PERFORMANCE: SUCCESS AND FAILURE IN FOG REMOVAL

Abstract

Package on-site grease traps are widely used in household and restaurant in Thailand for oil and grease removal although frequent failures in FOG removal have been reported. Theoretically, too small of operating hydraulic retention time (HRT) takes the blame, but some suppliers claim that their grease traps can be well operated even with HRT of 15 minutes. This study was to investigate the performance of grease trap with various HRTs (15 minutes to 20 hours) and FOG concentrations in the feed (50 to 600 mg/l). Results showed that the operating HRTs of 15, 30 and 60 minutes could represent a kind of shock hydraulic loading condition, which insufficient FOG removal efficiencies were observed. Also, the experiment to enhance the grease trap’s performance was set up by withdrawing certain volume of grease trap waste. The operating HRT of 60 minutes with the feed contained FOG of 200 mg/l and dishwashing detergent of 0.5% (v/v) was investigated for seven-day period. The experiment without daily withdrawal was operated in parallel as a control. The results showed that the FOG removal efficiencies in the control began to fall down to 50% on the fifth day of operation. The experiment with daily withdrawal showed more stable FOG removal efficiencies, which its efficiencies was still higher than 50% after seven days of the experiment. However, this could be said that the 15-litre package on-site grease trap fed with operating HRT of 60 minutes (or lower) could not maintain sufficient removal efficiency for long period (months).