Quantifying the quality and sampling time of oil and grease in urban stormwater runoff

Abstract

Oil and Grease (O&G) pollution in urban stormwater runoff is an important issue especially for tropical country with high intense and frequent storms. Monitoring of O&G pollution is comparably more difficult than other conventional constituents due to the requirement of manual grab sampling technique. Thus, this paper was aimed to investigate the O&G quality and quantify an appropriate sampling time for collecting sample that approximating Event Mean Concentration (EMC) of O&G (EMCO&G) from residential, commercial and industrial catchments. An average of 16 storm events was collected from each land use in order to assess the quality of O&G in stormwater runoff. A series of stormwater samples were manually grabbed by sampling personnel along with the storm flow measurements. Results showed that industrial catchment always exhibited the highest EMCO&G value, followed by commercial and residential catchments. Correlation analysis indicated that EMCO&G was correlated well with EMCs of NO3-N, NH3-N, TP and SP in the commercial catchment. The EMCO&G was also found to be independent of all storm characteristics, except for storm duration in the industrial catchment. Results obtained from this study suggested that the mean sampling times for collecting EMCO&G sample (TEMCO&G) at residential, commercial and industrial catchments are 17, 17 and 20 minutes, respectively. The TEMCO&G had mostly preceded the peak flow by a time-based ratio of 0.70. Thus, this best time sampling strategy can be implemented based on forecasting rainfall and estimated time to peak flow at catchment outlet.