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Determination of the Effect of Enzymes in a Grease Trap
Microchemical Journal 61, 53–57 (1999) Article ID mchj.1998.1676, available online at http://www.idealibrary.com on
Determination of the Effect of Enzymes in a Grease Trap 1 Emelie Gary 2 and Joseph Sneddon 3 Department of Chemistry, McNeese State University, Lake Charles, Louisiana 70609 Received August 8, 1998; accepted October 6, 1998
INTRODUCTION A grease trap is a tank located inside or outside of a restaurant that receives all wastewater coming from the kitchen drains and sinks. Once the wastewater enters the grease trap, it passes through a number of compartments with baffles. The baffles increase the retention time causing the fats, oils, and grease (FOG) to become separated and released from the wastewater. Once released the fats, oils, and grease float to the top because they are lighter than water, and accumulate until removed. The capacity of grease traps varies from 30 to 1500 gal or even larger in some cases. Enzymes are designed to reduce FOG, thus reducing waste pumping and transportation costs. They are a protein compound that acts as a catalyst for biochemical reactions. They simply accelerate nature’s own bioremediation process. Enzymes facilitate reactions, but the bacteria must be present to use them. The following example illustrates the principle. Think of a fly as the bacteria. When a fly lands on a slice of bread, it must secrete a solution to help dissolve or emulsify the food into smaller constituents. This liquid has enzymes that do the dissolving. After this enzymatic activity, the fly can then partake of the food. Enzymes can be considered as the “silverware” for the bugs to cut up their “steak” into smaller pieces. The biological process proceeds in a serial step-by-step manner, each step proceeding at a certain rate. The easiest FOG conversions occur first. This is breaking the grease triglyceride molecule into long-chain fatty acids and glycerol. Long-chain fatty acids are sequentially broken into smaller and smaller lengths, until very short chain fatty acids are produced. The breaking of the small acids allows for the bacteria to finally integrate into their cells the now available carbon atoms. The speed of the conversion of each chain is dependent on the number and type of bacterial organisms (or amount of enzymes) present. The last possible biological step conversion would be the attack on the shortest-chain fatty acid to produce carbon dioxide and water. FOG molecules clump together because parts of their structures are water insoluble and are attractive bonding sites to each other. This forms macrosize accumulations. When the conditions are perfect, some types of enzymes can convert grease into different forms by digesting it, but conditions in a grease trap are not perfect. Temperature, pH, sanitizers, and a constant flow of wastewater may not allow the enzymes to work properly or 1 This work was taken, in part, from Chemistry 451c, an undergraduate chemistry research thesis at McNeese State University in Fall 1997/Spring 1998. 2 Ms. Gary is a part-time undergraduate chemistry major in the Chemistry Department at McNeese State University. She is employed full-time by the City of Lake Charles, Department of Public Works, Central Laboratory. 3 To whom correspondence should be sent. Fax: (318) 475–5234. E-mail: [email protected].
53 0026-265X/99 $30.00 Copyright © 1999 by Academic Press All rights of reproduction in any form reserved.
54
GARY AND SNEDDON
completely. Biological enzymes may break FOG molecules into smaller-diameter particles that may become suspended in the supernatant and not separate in the grease trap. The small particles would be hydraulically flushed out of the grease trap, causing clogs in the sewer lines. This can result in a violation of the Industrial Waste and Water Pollution Control Ordinance of cities. The limit in Lake Charles, Louisiana, is 100 mg/liter. This work involves the investigation of two types of enzymes, one with a surfactant and one without, to determine whether they are beneficial or detrimental to the efficiency of a grease trap. EXPERIMENTAL Enzymes The two enzymes used in the study were obtained from International Biochemicals (Baton Rouge, LA). The first, EBR-D-30, is a specialized blend of bacterial cultures specifically selected and adapted to produce enzymes necessary for the degradation of FOG in grease traps. Some of these enzymes include amylase (starches), lipase (FOG), protease (proteins), and cellulase (cellulose). EBR-D-30 is a tan, free-flowing powder and has a total bacterial count of 2 billion/g, a yeastlike odor, a pH that is neutral, an effective pH range of 5–9, an effective temperature range of 10 –110°F, and a shelf lifetime of 1 year. The second, EBR-D-30F, is similar to the first except that it contains surfactants. Typical use involves dissolving 1 lb of enzyme to 1 gal of water or adding the solid, typically 0.25 to 0.5 lb to a 1000-gal grease trap. This should be added every day. In this laboratory study, 5 g of the enzymes was added to 100 ml of deionized water and vigorously agitated for 15 min. Volumes of 50 ml were added to the samples collected from the grease trap. CAUTION: The powder should be kept in a dry place. Avoid excessive inhalation. Wash hands with soap and water after use. Sampling Samples were collected from a restaurant specializing in fried chicken. Seven separate samples were collected using a long pole with attached clean glass jar. The volume of each sample was approximately 1.50 liters. One sample was preserved using sulfuric acid to a pH , 2 to determine oil and grease. The pH was determined prior to the preservation. The other six samples were labeled as follows: A (standard—1 week), B (EBR-D-30 —1 week), C (EBR-D-30F—1 week), D (standard—2 weeks), E (EBR-D-30 —2 weeks), and F (EBR-D-30F—2 weeks). Initially 50 ml of deionized water was added to A and D, 50 ml of EBR-D-30 to B and E, and 50 ml of EBR-D-30F to C and F. After 1 week, 50 ml of EBR-D-30 was added to E and 50 ml of EBR-D-30F was added to F. Due to the reduction of pH in the samples, an equal amount of baking soda (5 g to 100 ml of deionized water) was added to C and F after the first week. The oil and grease and pH of samples were measured (A) immediately (A, B, and C) after 1 week, and (D, E, and F) after 2 weeks. For analysis, 200 ml of the supernatant from each sample was analyzed. This volume was carefully removed from the original sample using a clean pipet, being careful not to disturb the top layer and sediment. A blank containing approximately 1.5 liters of deionized water plus 50 ml of enzyme was used.
55
EFFECT OF ENZYMES IN GREASE TRAP TABLE 1 Typical Worksheet for Calculation of Oil and Grease Analysis type
Sample volume (ml)
Weight of flask (g)
Weight of residue (g)
Analyzed value (mg/l)
Blank
350
75.9617
75.9556
,2
Analysis type
True value (g)
Weight of flask and residue (g)
Weight of flask (g)
Analyzed value (g)
% Recovery
Standard
0.1171
76.0942
75.9794
0.1148
98
Dilution adjustment
Total sample volume (ml)
Added volume (ml)
% Dilution
EBR-D-30 (1 week) EBR-D-30F (1 week)
1120 1110
50 50
96 96
Description
Natural decomposition (1 week)
EBR-D-30 (1 week)
EBR-D-30F (1 week)
Sample volume (mL) Weight of flask and residue (g) Weight of flask (g) Weight of residue (g) Analyzed value (mg/liter) Dilution adjustment (%) Final analyzed (mg/liter)
200 75.2147 75.1992 0.0155 78 0 78
200 75.9771 75.9617 0.0154 77 96 74
200 74.7734 74.7474 0.0260 130 96 125
Procedure The pH of the samples was determined using a standard glass electrode. The oil and grease concentration was determined using a standard extraction/gravimetric method (1). In this method, the sample is acidified to low pH (,2) and serially extracted with Freon 113 (trichlorotrifluroethane) in a separatory funnel in a preweighed flask. The solvent is evaporated from the residue and the flask weighed. This gives the total mass of oil and grease. In this method, oil and grease is defined as any material recovered as a substance soluble in freon. It is applicable to nonvolatile hydrocarbons, vegetable oils, animal fats, waxes, soaps, greases, and related matter. During the extraction, a clear solvent layer could not be obtained. Emulsion was drained into a glass centrifuge tube and centrifuged for approximately 45 min. On completion of centrifuging there was an aqueous layer on top, a second layer of solids, and a bottom clear solvent, to be analyzed. The unusual length of centrifuging (typically 5 min as opposed to the 45 min in this study) was attributed to the large amounts of solids in the supernatant. It was important to continue to apply a vacuum through the flask on completion of distillation for at least 1 min. This avoided erroneous results due to the heavy weight of the freon vapors. As an extra precaution, the flasks were allowed to sit in a desiccator overnight before weighing. If the drying capacity of the sodium sulfate in the desiccator is exceeded, the sodium sulfate will dissolve and pass into the tared flask. If this occurs, the sodium sulfate crystals will be visible in the flask, and their presence
56
GARY AND SNEDDON TABLE 2 Summary of Experimental Results Observations
Sample type a
Date
pH
Standard (0) Standard (1)
02/08 02/15
4.96 4.45
Oil and grease b
78
02/22 Standard (2)
EBR-D-30 (1)
02/15
EBR-D-30F (1)
4.31
52
a b
Supernatant
Sediment
— Slightly musky
— 1.25 in. of grease (coarse particles) 1.38 in. of grease (coarse particles) 1.13 in. of grease (coarse particles) 1.25 in. of grease (particles coarse starting to fragment) 1.13 in. of grease (particles fragmenting with fermentation)
— Yellowish-orange and turbid Yellowish-orange and turbid Yellow and turbid Yellow with increasing turbidity
— 0.25 in.
Slight musky
02/22
Strong slightly septic
03/01
Stronger septic
02/15
4.19
80
02/15
Slightly musky Stronger musky
4.99
78
Slightly musky
02/22
Strong slightly septic
03/01
Strong septic
02/15
4.22
135
02/22
EBR-D-30F (2)
Top layer
Stronger musky
02/22 EBR-D-30 (2)
Odor
02/15
Slightly musky Strong slightly septic
5.07
142
Slightly musky
02/22
Strong, slightly septic
03/01
Strong septic
1.25 in. of grease (coarse particles) 1.25 in. of grease (coarse particles) 1.50 in. of grease (particles coarse) 1.88 in. of grease (particles coarse but starting to fragment) 1.12 in. of grease and (particles fragmenting with fermentation) 1.50 in. of grease (particles coarse) 1.58 in. of grease (particles coarse but starting to fragment) 1.25 in. of grease (particles coarse) 1.25 in. of grease (particles coarse but starting to fragment) 1.12 in. of grease and (particles fragmenting with fermentation)
(0) Initial collection, (1) after 1 week, (2) after 2 weeks. Incorrect results obtained due to water contamination.
0.25 in. 0.25 in. 0.25 in.
Yellow with increasing turbidity
0.25 in.
Yellow and turbid Yellow and turbid Yellow-orange and turbid Yellow-orange but more turbid
0.25 in. 0.25 in. 0.25 in. 0.25 in.
Yellow-orange with increasing turbidity
0.25 in.
Yellow-orange and turbid Yellow-orange but more turbid
0.25 in.
Yellow-orange and turbid Yellow-orange but more turbid Yellow-orange with increasing turbidity, higher suspended solids
0.25 in. fluffy
0.25 in. 0.25 in.
0.25 in.
EFFECT OF ENZYMES IN GREASE TRAP
57
will cause an error in the experiment. Therefore, fresh sodium sulfate was used in the desiccant of not more than 2 weeks old. Calculations The oil and grease is calculated as mg/liter total oil and grease 5
a2b2c , total volume in liters
(1)
where a 5 weight (mg) of residue and flask, b 5 weight (mg) of flask, and c 5 weight (mg) of blank (5weight of flask with blank residue 2 weight of flask without blank residue). % Dilution adjustment 5 % Recovery 5
volume added 3 100. volume of sample 1 added volume
(2)
analyzed value (g) 3 100. true value (g)
(3)
A typical worksheet is shown in Table 1. RESULTS AND DISCUSSION The results of this study are summarized in Table 2. The supernatant for the samples treated with enzymes revealed an increase in turbidity and decomposition of the top layer of grease. The change in the sediment for EBR-D-30 and EBR-D-30F after 1 week also indicates a possible effect of the enzymes. The enzyme with surfactant (EBR-D-30F) revealed a high concentration of oil and grease (135 and 142 mg/liter, for 1 and 2 weeks, respectively), exceeding the 100 mg/liter for the City of Lake Charles Water Pollution Control Ordinance for both 1 and 2 weeks. This suggests that enzymes with surfactants may have a detrimental effect on the efficiency of a grease trap. The enzyme without the surfactant (EBR-D-30) did not show this result (,100 mg/liter). This result was unexpected as there was a definite increase in turbidity for both weeks of the EBR-D-30. The increase in turbidity may indicate other potential problems. CONCLUSION These results suggest that an enzyme without surfactant is more useful than an enzyme with surfactant for use in the degradation of grease and oil in a grease trap. However, each grease trap presents a different set of circumstances, and factors such as pH, sanitizers, type of grease (restaurant), and flow rate should be considered before an enzyme is selected for use in degrading grease to comply with a local ordinance. Future work should also include total suspended solids and biological oxygen demand. REFERENCE 1. Standard Methods for the Examination of Water and Wastewater, 18th ed., method 5520 B. Am. Public Health Assoc., Washington, DC, 1992.
Determination of the Effect of Enzymes in a Grease Trap 1 Emelie Gary 2 and Joseph Sneddon 3 Department of Chemistry, McNeese State University, Lake Charles, Louisiana 70609 Received August 8, 1998; accepted October 6, 1998
INTRODUCTION A grease trap is a tank located inside or outside of a restaurant that receives all wastewater coming from the kitchen drains and sinks. Once the wastewater enters the grease trap, it passes through a number of compartments with baffles. The baffles increase the retention time causing the fats, oils, and grease (FOG) to become separated and released from the wastewater. Once released the fats, oils, and grease float to the top because they are lighter than water, and accumulate until removed. The capacity of grease traps varies from 30 to 1500 gal or even larger in some cases. Enzymes are designed to reduce FOG, thus reducing waste pumping and transportation costs. They are a protein compound that acts as a catalyst for biochemical reactions. They simply accelerate nature’s own bioremediation process. Enzymes facilitate reactions, but the bacteria must be present to use them. The following example illustrates the principle. Think of a fly as the bacteria. When a fly lands on a slice of bread, it must secrete a solution to help dissolve or emulsify the food into smaller constituents. This liquid has enzymes that do the dissolving. After this enzymatic activity, the fly can then partake of the food. Enzymes can be considered as the “silverware” for the bugs to cut up their “steak” into smaller pieces. The biological process proceeds in a serial step-by-step manner, each step proceeding at a certain rate. The easiest FOG conversions occur first. This is breaking the grease triglyceride molecule into long-chain fatty acids and glycerol. Long-chain fatty acids are sequentially broken into smaller and smaller lengths, until very short chain fatty acids are produced. The breaking of the small acids allows for the bacteria to finally integrate into their cells the now available carbon atoms. The speed of the conversion of each chain is dependent on the number and type of bacterial organisms (or amount of enzymes) present. The last possible biological step conversion would be the attack on the shortest-chain fatty acid to produce carbon dioxide and water. FOG molecules clump together because parts of their structures are water insoluble and are attractive bonding sites to each other. This forms macrosize accumulations. When the conditions are perfect, some types of enzymes can convert grease into different forms by digesting it, but conditions in a grease trap are not perfect. Temperature, pH, sanitizers, and a constant flow of wastewater may not allow the enzymes to work properly or 1 This work was taken, in part, from Chemistry 451c, an undergraduate chemistry research thesis at McNeese State University in Fall 1997/Spring 1998. 2 Ms. Gary is a part-time undergraduate chemistry major in the Chemistry Department at McNeese State University. She is employed full-time by the City of Lake Charles, Department of Public Works, Central Laboratory. 3 To whom correspondence should be sent. Fax: (318) 475–5234. E-mail: [email protected].
53 0026-265X/99 $30.00 Copyright © 1999 by Academic Press All rights of reproduction in any form reserved.
54
GARY AND SNEDDON
completely. Biological enzymes may break FOG molecules into smaller-diameter particles that may become suspended in the supernatant and not separate in the grease trap. The small particles would be hydraulically flushed out of the grease trap, causing clogs in the sewer lines. This can result in a violation of the Industrial Waste and Water Pollution Control Ordinance of cities. The limit in Lake Charles, Louisiana, is 100 mg/liter. This work involves the investigation of two types of enzymes, one with a surfactant and one without, to determine whether they are beneficial or detrimental to the efficiency of a grease trap. EXPERIMENTAL Enzymes The two enzymes used in the study were obtained from International Biochemicals (Baton Rouge, LA). The first, EBR-D-30, is a specialized blend of bacterial cultures specifically selected and adapted to produce enzymes necessary for the degradation of FOG in grease traps. Some of these enzymes include amylase (starches), lipase (FOG), protease (proteins), and cellulase (cellulose). EBR-D-30 is a tan, free-flowing powder and has a total bacterial count of 2 billion/g, a yeastlike odor, a pH that is neutral, an effective pH range of 5–9, an effective temperature range of 10 –110°F, and a shelf lifetime of 1 year. The second, EBR-D-30F, is similar to the first except that it contains surfactants. Typical use involves dissolving 1 lb of enzyme to 1 gal of water or adding the solid, typically 0.25 to 0.5 lb to a 1000-gal grease trap. This should be added every day. In this laboratory study, 5 g of the enzymes was added to 100 ml of deionized water and vigorously agitated for 15 min. Volumes of 50 ml were added to the samples collected from the grease trap. CAUTION: The powder should be kept in a dry place. Avoid excessive inhalation. Wash hands with soap and water after use. Sampling Samples were collected from a restaurant specializing in fried chicken. Seven separate samples were collected using a long pole with attached clean glass jar. The volume of each sample was approximately 1.50 liters. One sample was preserved using sulfuric acid to a pH , 2 to determine oil and grease. The pH was determined prior to the preservation. The other six samples were labeled as follows: A (standard—1 week), B (EBR-D-30 —1 week), C (EBR-D-30F—1 week), D (standard—2 weeks), E (EBR-D-30 —2 weeks), and F (EBR-D-30F—2 weeks). Initially 50 ml of deionized water was added to A and D, 50 ml of EBR-D-30 to B and E, and 50 ml of EBR-D-30F to C and F. After 1 week, 50 ml of EBR-D-30 was added to E and 50 ml of EBR-D-30F was added to F. Due to the reduction of pH in the samples, an equal amount of baking soda (5 g to 100 ml of deionized water) was added to C and F after the first week. The oil and grease and pH of samples were measured (A) immediately (A, B, and C) after 1 week, and (D, E, and F) after 2 weeks. For analysis, 200 ml of the supernatant from each sample was analyzed. This volume was carefully removed from the original sample using a clean pipet, being careful not to disturb the top layer and sediment. A blank containing approximately 1.5 liters of deionized water plus 50 ml of enzyme was used.
55
EFFECT OF ENZYMES IN GREASE TRAP TABLE 1 Typical Worksheet for Calculation of Oil and Grease Analysis type
Sample volume (ml)
Weight of flask (g)
Weight of residue (g)
Analyzed value (mg/l)
Blank
350
75.9617
75.9556
,2
Analysis type
True value (g)
Weight of flask and residue (g)
Weight of flask (g)
Analyzed value (g)
% Recovery
Standard
0.1171
76.0942
75.9794
0.1148
98
Dilution adjustment
Total sample volume (ml)
Added volume (ml)
% Dilution
EBR-D-30 (1 week) EBR-D-30F (1 week)
1120 1110
50 50
96 96
Description
Natural decomposition (1 week)
EBR-D-30 (1 week)
EBR-D-30F (1 week)
Sample volume (mL) Weight of flask and residue (g) Weight of flask (g) Weight of residue (g) Analyzed value (mg/liter) Dilution adjustment (%) Final analyzed (mg/liter)
200 75.2147 75.1992 0.0155 78 0 78
200 75.9771 75.9617 0.0154 77 96 74
200 74.7734 74.7474 0.0260 130 96 125
Procedure The pH of the samples was determined using a standard glass electrode. The oil and grease concentration was determined using a standard extraction/gravimetric method (1). In this method, the sample is acidified to low pH (,2) and serially extracted with Freon 113 (trichlorotrifluroethane) in a separatory funnel in a preweighed flask. The solvent is evaporated from the residue and the flask weighed. This gives the total mass of oil and grease. In this method, oil and grease is defined as any material recovered as a substance soluble in freon. It is applicable to nonvolatile hydrocarbons, vegetable oils, animal fats, waxes, soaps, greases, and related matter. During the extraction, a clear solvent layer could not be obtained. Emulsion was drained into a glass centrifuge tube and centrifuged for approximately 45 min. On completion of centrifuging there was an aqueous layer on top, a second layer of solids, and a bottom clear solvent, to be analyzed. The unusual length of centrifuging (typically 5 min as opposed to the 45 min in this study) was attributed to the large amounts of solids in the supernatant. It was important to continue to apply a vacuum through the flask on completion of distillation for at least 1 min. This avoided erroneous results due to the heavy weight of the freon vapors. As an extra precaution, the flasks were allowed to sit in a desiccator overnight before weighing. If the drying capacity of the sodium sulfate in the desiccator is exceeded, the sodium sulfate will dissolve and pass into the tared flask. If this occurs, the sodium sulfate crystals will be visible in the flask, and their presence
56
GARY AND SNEDDON TABLE 2 Summary of Experimental Results Observations
Sample type a
Date
pH
Standard (0) Standard (1)
02/08 02/15
4.96 4.45
Oil and grease b
78
02/22 Standard (2)
EBR-D-30 (1)
02/15
EBR-D-30F (1)
4.31
52
a b
Supernatant
Sediment
— Slightly musky
— 1.25 in. of grease (coarse particles) 1.38 in. of grease (coarse particles) 1.13 in. of grease (coarse particles) 1.25 in. of grease (particles coarse starting to fragment) 1.13 in. of grease (particles fragmenting with fermentation)
— Yellowish-orange and turbid Yellowish-orange and turbid Yellow and turbid Yellow with increasing turbidity
— 0.25 in.
Slight musky
02/22
Strong slightly septic
03/01
Stronger septic
02/15
4.19
80
02/15
Slightly musky Stronger musky
4.99
78
Slightly musky
02/22
Strong slightly septic
03/01
Strong septic
02/15
4.22
135
02/22
EBR-D-30F (2)
Top layer
Stronger musky
02/22 EBR-D-30 (2)
Odor
02/15
Slightly musky Strong slightly septic
5.07
142
Slightly musky
02/22
Strong, slightly septic
03/01
Strong septic
1.25 in. of grease (coarse particles) 1.25 in. of grease (coarse particles) 1.50 in. of grease (particles coarse) 1.88 in. of grease (particles coarse but starting to fragment) 1.12 in. of grease and (particles fragmenting with fermentation) 1.50 in. of grease (particles coarse) 1.58 in. of grease (particles coarse but starting to fragment) 1.25 in. of grease (particles coarse) 1.25 in. of grease (particles coarse but starting to fragment) 1.12 in. of grease and (particles fragmenting with fermentation)
(0) Initial collection, (1) after 1 week, (2) after 2 weeks. Incorrect results obtained due to water contamination.
0.25 in. 0.25 in. 0.25 in.
Yellow with increasing turbidity
0.25 in.
Yellow and turbid Yellow and turbid Yellow-orange and turbid Yellow-orange but more turbid
0.25 in. 0.25 in. 0.25 in. 0.25 in.
Yellow-orange with increasing turbidity
0.25 in.
Yellow-orange and turbid Yellow-orange but more turbid
0.25 in.
Yellow-orange and turbid Yellow-orange but more turbid Yellow-orange with increasing turbidity, higher suspended solids
0.25 in. fluffy
0.25 in. 0.25 in.
0.25 in.
EFFECT OF ENZYMES IN GREASE TRAP
57
will cause an error in the experiment. Therefore, fresh sodium sulfate was used in the desiccant of not more than 2 weeks old. Calculations The oil and grease is calculated as mg/liter total oil and grease 5
a2b2c , total volume in liters
(1)
where a 5 weight (mg) of residue and flask, b 5 weight (mg) of flask, and c 5 weight (mg) of blank (5weight of flask with blank residue 2 weight of flask without blank residue). % Dilution adjustment 5 % Recovery 5
volume added 3 100. volume of sample 1 added volume
(2)
analyzed value (g) 3 100. true value (g)
(3)
A typical worksheet is shown in Table 1. RESULTS AND DISCUSSION The results of this study are summarized in Table 2. The supernatant for the samples treated with enzymes revealed an increase in turbidity and decomposition of the top layer of grease. The change in the sediment for EBR-D-30 and EBR-D-30F after 1 week also indicates a possible effect of the enzymes. The enzyme with surfactant (EBR-D-30F) revealed a high concentration of oil and grease (135 and 142 mg/liter, for 1 and 2 weeks, respectively), exceeding the 100 mg/liter for the City of Lake Charles Water Pollution Control Ordinance for both 1 and 2 weeks. This suggests that enzymes with surfactants may have a detrimental effect on the efficiency of a grease trap. The enzyme without the surfactant (EBR-D-30) did not show this result (,100 mg/liter). This result was unexpected as there was a definite increase in turbidity for both weeks of the EBR-D-30. The increase in turbidity may indicate other potential problems. CONCLUSION These results suggest that an enzyme without surfactant is more useful than an enzyme with surfactant for use in the degradation of grease and oil in a grease trap. However, each grease trap presents a different set of circumstances, and factors such as pH, sanitizers, type of grease (restaurant), and flow rate should be considered before an enzyme is selected for use in degrading grease to comply with a local ordinance. Future work should also include total suspended solids and biological oxygen demand. REFERENCE 1. Standard Methods for the Examination of Water and Wastewater, 18th ed., method 5520 B. Am. Public Health Assoc., Washington, DC, 1992.