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International Journal of Environment Science and Technology
Center for Environment and Energy Research and Studies (CEERS)
ISSN: 1735-1472 EISSN: 1735-2630
Vol. 4, Num. 3, 2007, pp. 345 -350

International Journal of Enviornmental Science and Technology, Vol. 4, No. 3, Summer 2007, pp. 345 -350

Field tests on a grease trap effluent filter

N. H. Wong; *P. L. Law; S. H. Lai

Department of Civil Engineering, Faculty of Engineering University of Malaysia Sarawak (UNIMAS), 94300 Kota Samarahan, Sarawak, Malaysia

*Corresponding Author Email: puonglaw@feng.unimas.my Tel.: +6082 672 317; Fax: +6082 672 317

Received 16 January 2007;
revised 25 March 2007;
accepted 7 May 2007;
available online 20 June 2007

Code Number: st07043

ABSTRACT

This study investigates the field performance tests of a commercial grease trap effluent filter for removal of total suspended solids, and oil and grease discharged from the clear zone of full service restaurant grease traps. The grease trap effluent filters were installed on 1,000-gallon, 2,000-gallon and 5,400-gallon full service restaurant grease traps over a period of 8 weeks, and samples were taken at the inlets and outlets. On average, the effluent filters demonstrated to be capable of removing 41% to 57% of TSS, and 43% to 52% of O and G. Field test data also showed that the total amount of TSS removed by the grease trap effluent filter installed on 1,000 gallon, 2,000 gallon and 5,400 gallon grease traps were approximately 2,542 kg, 709 kg, and 2,319 kg, respectively; and the total amount of O and G removed over the same period were approximately 1,104 kg, 271 kg, and 897 kg, respectively.

Key words: Total suspended solids, oil and grease, grease trap, effluent filter

INTRODUCTION

Restaurants discharge wastewaters into public sewers have been a problem for many years, but have become a greater problem with the large number of full service and fast food restaurants being built both in large cities and rural communities (Stoll and Gupta, 1993). These restaurants typically discharge large amount of total suspended solids (TSS) and oil and grease (O and G) that would reduce the capacity of public sewers over time (Eddy, 1998). The traditional treatment for this waste prior to discharge into the public sewer is a grease trap that causes separation of the floatable and settleable materials (Stoll and Gupta, 1993). Generally, discharge from a grease trap comes from the clear zone created by this separation process. Even though it is called a clear zone, the water from this zone usually contains a considerable amount of relatively low specific gravity suspended solids and high specific gravity O and G (Fig 1), (Steward, 1997 and Ecotec, 1996). Recently, the application of a number of commercial grease trap effluent filters had been evaluated as a potential tool for the treatment of TSS and O and G in the clear zone wastewaters (Treanor, 1995). A study performed in Sydney, Australia on a 40 seat cafeteria indicated that the discharge from the restaurant cooking area had an average TSS and O and G of approximately 3,024 mg/L and 3,630 mg/L, respectively (Ecotec, 1996). It was demonstrated that Ecotec Grease Extractor effluent filter could improve treatment by reducingTSSlevel to 84 mg/L, and average effluent O and G to 78 mg/L (Ecotec, 1996). The installation of Ecotec Grease Extractor effluent filter on the grease trap resulted in an average 78% reduction in TSS and 84% reduction in O and G (Ecotec, 1996). Another study performed in Australia concluded that the effect of Taylex Queenland grease trap effluent filter achieved a reduction of the TSS levels by 61%, and O and G by 63% (Taylex, 1997). These studies indicated that there is a need for improved treatment and grease trap effluent filters could be an alternative economical option for the treatment of TSS and O and G (Long, 1997). In tank effluent filter installation (Fig 2) the grease trap effluent filter is designed to reduce the TSS and O and G components of the tank (grease trap) effluent. The exterior of this filter consists of a cylindrical plastic housing 16 inches (40.64 cm) high and 12 inches (30.48 cm) in diameter with a 4 inch (10.16 cm) polyvinyl chloride (PVC) couplings, and sheets of plastic in the form of plates comprise of removable interior of the filter. There are 27 individual plates stacked on top of each other with built-in spacers that force the wastewater through the 0.8 mm openings (Fig 2).

MATERIALS AND METHODS

In this study, the sampling sites consisted of four full service restaurants (Cookeville, Tennessee, USA). The grease traps used by the individual restaurants were different in size, dimension, and volume; restaurant # 1 had a 1,000 gallon grease trap with two baffle walls producing a three compartment units; restaurant # 2 had a 2,000 gallon grease trap with baffle for isolating the tank's influent and effluent; restaurant # 3 had a 2,000 gallon grease trap with baffle for isolating tank's influent and effluent; and restaurant # 4 had a 5,400 gallon rectangular grease trap with no compartment or baffle (Fig 1). Details related to restaurant operation information, activities, frequency of kitchen cleaning and so are shown in Table 1.

Two samples were taken from each of the grease traps each day, i.e. one sample from the clear zone at the inlet (influent), and one sample at the outlet from the top of the filter unit (effluent). The locations of the influent and effluent sampling points are indicated in Fig 1. A weekly composite sample was prepared for each site taken over an eight-week period. These composite samples were analyzed for TSS and O and G. Sampling started on May 12, 1997, and ended on July 12, 1997. All samples were taken during the morning hours between 6:30 am. and 10:00 am The samples were collected from each site in the same order during each sampling trip, and the sampling procedure was consistent throughout the study. The samples at the effluent from the filter were first collected followed by the samples at the influent points. The influent samples were collected with a specially constructed sampling device that was put back in place after a day's sampling at each restaurant. This sampling device and procedure would produce a relatively undisturbed sample taken on the following day. The pH values and temperatures of the samples collected were recorded at each of the sampling points and during each sampling trip. An ATI Orion Portable Meter - Model 290A was used to measure the pH and temperature simultaneously, after the sample were placed in the sampling bottle. Laboratory analysis and testing on samples were performed in accordance to the methods set forth in the Standard Methods for the Examination of Water and Wastewater (APHA, 1992). After each sampling trip, a 100 mL volume of each sample was poured into a bottle to prepare the weekly TSS composite sample. The daily TSS composite samples were placed in a refrigerator at 4 °C. After 7 days of composite sample preparation, the composite samples were analyzed for the TSS contents. A 250 mL volume sample from each site was mixed with one gallon bottle and placed in a refrigerator at 4 °C. Approximately 2 to 3 mL of saturated sulfuric acid (H2SO4) were added to the samples for preservation. After 7 days, the preserved composite samples were analyzed for O and G. Analysis on O and G was carried out in accordance to standard procedures and methods of determinations found in the Standard Method 5520 (APHA, 1992).

RESULTS

TSS removal efficiencies recorded during the study are presented in Table 2, indicating that TSS removal efficiencies of the filters were approximately 56%, 47%, 57%, and 41% for restaurants # 1, # 2, # 3 and # 4, respectively. Table 3 shows O and G removal efficiencies achieved by the grease trap effluent filter understudy, and the amount of reductions in O and G were approximately 52%, 47%, 50% and 43% for restaurants # 1, # 2, # 3 and # 4, respectively. During monitoring period, in additional to TSS and O and G, the pH values and temperatures were also recorded at effluent sampling points, and the details of field data gathered over a period of 8 weeks are shown in Table 4.

DISCUSSION AND CONCLUSION

The performance of TSS removal efficiencies of the effluent filter installed on 1,000 gallon grease trap (restaurant # 1) indicates that the lowest achievable effluent levels attained by the effluent filter with a detention time of 6.7 h was approximately 679 mg/L, and the highest achievable removal efficiency attained was about 76%. The average detention time on the 2,000 gallon grease trap (restaurants # 2 and # 3) was approximately 17.5 h with the lowest filter achievable TSS removal effluent level of approximately 180 mg/L, and highest removal efficiency recorded at 70%. The effluent filter installed on the 5,400 gallon grease trap (restaurant # 4) with a detention time of 19.1 h indicated relatively less efficient in removing TSS, ranging from 33% to 53%. In this study, it was found that the total amount of TSS (in kg) removed by the filters installed on 1,000 gallon, 2,000 gallon and 5,400 gallon grease traps over a period of 8 weeks were approximately 2,542 kg, 709 kg, and 2,319 kg, respectively.

In terms of O and G removal efficiencies of the effluent filter installed on 1,000 gallon grease trap of restaurant # 1 showed an achievable effluent levels of O and G of approximately 214 mg/L at 6.7 h detention time and the highest achievable O and G removal efficiencyattained was approximately78%. The average detention time on the 2,000 gallon grease trap (restaurants# 2 and # 3) was approximately17.5 h with a lowest achievable removal effluent level of 43 mg/L, which is equivalent to 63% removal efficiency. The effluent filter installed on 5,400 gallon grease trap (restaurant # 4) with a detention time of approximately 19.1 h indicated a relatively less efficient in removing O and G that ranged from 20% to 51%. Field tests data showed that the total amount of O and G (in kg) removed or absorbed by the filters installed on 1,000 gallon, 2,000 gallon and 5,400 gallon grease traps over a period of 8 weeks were approximately 1,104 kg, 271 kg, and 897 kg, respectively. Restaurant # 1 samples had an average pH and temperature values of 4.0 (SD = 0.24) and 33.5 °C (SD = 2.0), respectively. Restaurant # 2 samples had an average pH value of 5.23 (SD = 0.29) and temperature of 28.2 °C (SD = 1.73). For restaurant # 3, the mean pH value was 4.71 (SD = 0.27) and mean temperature of 32.8°C (SD = 2.97). The samples of restaurant #4 recorded a mean pH of 4.12 (SD = 0.36) and a temperature of 39.9 °C (SD = 1.38). Even though there were significant differences in grease trap volumes, grease trap detention times and amount of wastewaters generated by the individual restaurants, there were negligible differences in pH values and temperatures among all the four restaurants understudy. The maximum differences in pH values and temperatures were approximately 1.23 and 11.7 °C, respectively.

REFERENCES
  • APHA, (1992). Standard methods for the examination of water and wastewater. American Public Health Association, American Water Works Association (AWWA) and Water Environment Association (WEA), Washington D.C.: , 18th. Ed.
  • Ecotec Grease Extractor of Berry Café North Sydney, (1996). Grease-Traps Studies on Total Suspended Solids and Oil& Grease in Sydney, Australia.
  • Eddy, N., (1998). Restaurants and commercial facilities present specific problems for onsite systems. Small Flow J., 12(2), 1-5
  • Long, S.M., (1997). Total volatile suspended solids removal by septic tank effluent filters. Master's Thesis, Tennessee
    Technological University (TTU), Cookeville, Tennessee, USA.
  • Stewart, K.R., (1997). An extended study of the treatment capability of three in-tank filters for septic tank effluent. Master's Thesis, Tennessee Technological University, Cookeville, Tennessee, USA.
  • Stoll, U.; Gupta, H., (1993). Management strategies for oil and grease residues. Waste Manag. Res., 15(1), 23-32.
    Taylex Queensland Pty. Ltd., (1997). Grease-Traps studies on total suspended solids and oil & grease in perth, Western
    Australia: Taylex Queensland Pty. Ltd.
  • Treanor, W.O., (1995). Treatment capacity of three filters for septic tank effluent. Master's Thesis, Tennessee
    Technological University, Cookeville, Tennessee, USA.

© 2007 Center for Environment and Energy Research and Studies (CEERS)


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