HALGAN PTY LTD
SURGE CONTROL DEVICE (SCD)
Kerry Hall
GREASE TRAPS AND SCD – PRINCIPLES OF DESIGN, PERFORMANCE AND SIZING
CALCULATION FOR RETROFITTING PROGRAMMES.
HALGAN PTY LTD – SCD Retro fit to Existing Pre-treatment Devices
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GREASE TRAPS/SCD – PRINCIPLES OF DESIGN AND PERFORMANCE
Current Designs in Australia.
The State Based Designs do not follow any current Australia Design, American and European
standards. Each states has different inlet and outlet pipework designs and baffle location. Limited
scientific studies have been done evaluating the state base designs and manufactures are not
required to following any length to width ratios or sludge-oil/grease to nominal size calculations.
Any alternative Grease Arrestor designs are limited to designs that still allowed for ease of pump out
maintenance. Consequently, alternative approaches for enhancing total oil and grease removal to
help achieve better Oil/Grease removal cannot be marketed.
Current GA designs with surge baffles in Australia experience a 6 % reduction in performance. This is
due to the surge baffles causing high vector velocities over the top and bottom of the baffle. The
baffles also cause turbulence that produce eddies and resuspend settable solids. (Water
Environment research Foundation – WERF2008).
Grease Arrestor Design Principles.
Grease Arrestors work to remove Oil/Grease and other materials primarily through gravity
separation. Consequently, it is important to provide conditions that will allow Oil/Grease globules or
solids to separate from the liquid stream with minimal disruption that may be caused by local fluid
velocities. These local velocities can interact with the separated Oil/Grease or solids layer, cause
breakup of Oil/Grease globules and reduce their terminal migration velocities, or cause reactor short
circuiting and reduce the separation time necessary for efficient removal of Oil/Grease globules or
food solids.
SCD HOW IT WORKS.
The SCD unit is installed inside existing or new pre-treatment vessels. The SCD unit is located
internally connected to the outlet pipe. The SCD unit is submerged in the pre-treatment vessel
chamber, usually half way from the bottom of the vessel to the natural water level. The SCD is fixed
and cannot be removed. The SCD by virtue of its hydraulic back pressure design principle addresses
the fundamental engineering basic of a batch process. Typically the design on available waste water
treatment devices assumes a continuous process principle. It is therefore a device whereby the
treatment process accommodates the typical surge nature of the influent flow that characterise
most modern waste water flows. Surges are smoothed out in the chamber and pollutant
concentrates partially balanced. Surges of flow rates and variable pollutant concentration are the
major causes of waste water treatment systems inefficiency - the SCD combats this.
The SCD unit comprises of multiple packed plates. The number of plates can be increased to
accommodate higher flow rates. The SCD has a special feature of a flow-restricting device within the
SCD unit and the outlet end. The restricting device balances the pressure within the SCD unit and
external environment. The effluent then is discharged through the outlet pipe into disposal system
or reticulated sewer system. The drawing effect through the SCD unit encourages laminar flow. The
laminar flow is ideal flow for particle separation. The SCD unit will also cause a slight backpressure
within the chamber. This backpressure will help the heavy particles to settle and the lighter particles
to rise to the surface. The backpressure will also stabilise surges within the chamber. The particle
plates will trap and deflect the suspended particles, which will escape through the gap back into the
pre-treatment vessel chamber. When the hydraulic surge stopes, the buoyant particles float to the
surface and heavy particles drop to the bottom of the vessel, this is due to the SCD unit is
submerged inside the pre-treatment vessel.
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Sizing requirements and Applicability for SCD retro fit to existing grease traps.
1.0 General:
The selection of the correct SCD retro fit model shall be based on the nature and quantity of
wastewater to be treated taking into account:
• Maximum flow rate of wastewater
• Maximum temperature of the wastewater
• Density of grease/oils to be separated
• Influence of cleansing and rinsing agents.
• Grease storage capacity
• Solids storage capacity
• Separation zone.
1.01 Structual Integrity
The Grease Trap has to be inspected for structural integrity and and tested for water tightness
test completed.
1.02 Pre Screening devices.
Pre-screening devices to be installed in floorwaste and kitchen sinks. Additional solids traps
maybe required for high loading applications e.g sushi bars, fish mongers and butcher shops.
1.03 House Keeping.
Halgan House Keeping Signs installed in kitchen preparation area. Staff trained in appropriate
house keeping and oil recycling.
1.04 Servicing.
Recommended servicing frequency is 4-8 weeks. Exact frequency depends on size of existing
grease trap and house keeping. Call Halgan for recommended frequency and sludge judging.
1.1 Method of Sizing Calculation based on EN1825:
The sizing calculation is based upon the type of kitchen (culinary flow), meals serviced per
day and hours of operation. Equation: NS = QsFtFdFr
where
NS is the calculated nominal size of the grease trap
Qs is the maximum flow rate of wastewater, in litres per second (see 1.2)
Ft is the impediment factor for the temperature of influent ( see 1.3)
Fd is the density facture for the relevant grease/oils (see 1.4)
Fr is the impediment factor for the influence of detergent agents (see 1.5)
1.2 Maximum wastewater flow rate Qs.
The maximum waste water flow rate is calculated from the following equation:
Qs = VF/3600t
where
Qs is the maximum wastewater flow rate, in litres per second
V is the average volume per day (see 1.2.1.), in litres
F is the peak flow coefficient (see 1.2.2)
t is the average duration of operation each day, in hours.
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1.2.1 Average wastewater volume per day V
The average wastewater volume per day can be determined by average water meter reading of
water consumption averaged over one week or by the following calculation:
V =MVm
where
V is the average volume per day, in litres
M is the number of meals per day
Vm is the volume of water used per meal (see table 1.)
Table 1. – Volume of water used per meal Vm.
Type of Culinary Flow Volume of water used per meal Vm
Hotel 100 litres
Restaurant
Asian restaurant with water cooled woks.
50 litres
80 litres
Hospital 30 litres
Process using combi ovens 80 litres
Franchises and catering establishments 24 hrs
operation
15 litres
Café’s canteens 5 litres
Pizza shops 5 litres
Butcher - 15 litres
1.2.2 Peak flow coefficient F.
The peak flow coefficient F is given in Table 2 for various types of culinary flows.
Table 2 – Peak flow coefficient F
Type of Culinary Flow Peak flow coefficient F
Hotel 5.0
Restaurant
Asian food
8.5
20.0
Hospital 13.0
Process using combi ovens 2.0
Franchises and catering establishments 24 hrs
operation
22.0
Café’s canteens 10
Pizza shops 5.0
Butcher - 30.0
1.3 Temperature factor Ft.
High wastewater temperature reduces the efficiency of grease trap. Temperature factors Ft are given
in Table 3.
Table 3 – Temperature factor Ft.
Temperature of wastewater at inlet Temperature facture Ft.
Less than 60 deg C 1.0
Always or occasionally greater than 60 deg C 1.3
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1.4 Density facture Fd.
A density facture Fd = 1.0 shall be used for waste water discharging from standard kitchens. When
the nature of the oil/grease is known, the density coefficient may be taken from figure 1, where Fd is
plotted for a range of different oils and grease densities. Densities of different oils/greases are given
in Table 4.
Figure 1 – Relation between Fd and density.
Table 4 – Density of oils and greases.
Oil/Grease Density at 20 deg C g/m3
Animal Fat 0.85 – 0.94
Aniseseed oil 1.0
Butter Fat 0.91
Cacao butter 0.89-0.94
Coconut oil 0.92-0.93
Corn oil 0.92
Cottonseed oil 0.92
Pine oil 0.87-0.91
Fish oil 0.86-0.94
Jojoba oil 0.86-0.90
Lard oil 0.91-0.92
Linseed oil 0.93-0.94
Majoram oil 0.89-0.91
Oleic oil 0.89-0.90
Palmitic oil 0.91
Palm oil 0.91-0.92
Peanut oil 0.91-0.92
Pine oil 0.93-0.94
Poppy oil 0.92
Rapeseed oil 0.91-0.92
Resin oil 0.87-0.91
Sesame oil 0.92
Soybean oil 0.92-0.93
Stearic acid 0.84
Sunflower oil 0.92-0.93
Tallow 0.92
Vegetable oil 0.95-0.97
Wood oil 0.95-0.97
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1.5 Detergent agent factor Fr .
Detergents, including dishwashing powders and rinsing agents, should carefully be selected and used
sparingly. The agents should not impair the separating effect and not form stable emulsions where
they are used upstream of a separator. A detergent and rinsing agent coefficient shall be chosen
from Table 5.
Table 5 – Detergent and rinsing agent coefficient Fr
Use of detergent and rinsing agents Detergent and rising agent coefficient Fr
Never used 1.0
Occasionally or always used 1.3
Special cases e.g. Hospitals 1.5
2.0. Basic dimensions of grease trap to be retrofitted with SCD.
• Solids storage area is NS x 100 litres (minimum 100 litres)
• Minimum surface of grease separation zone - NS x 0.25 m2
• Minimum volume of grease separator zone - NS x 0.24 m3
• Minimum volume of grease collection area - NS x 0.04 m3
(minimum 40 litres)
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Installation.
Installation procedures.
General: Ensure the SCD being installed is the correctly sized for the application. When carrying out
the installation adhere to the current Occupational Work Health and Safety requirements and
building codes.
Step 1. Pump out grease trap as per the local water authority’s requirements.
Step 2. The SCD (B) is installed inside the grease trap, at the outlet end. Clean grease trap
connection point inside grease trap. Using solvent cement, glue bend (A) to the grease trap
connection point. The SCD (B) has to be horizontal and 90 degrees to the outlet connection
wall.
Step 3. Measure and cut to the length of the servicing pipe (D). This is done by locating the access
cap (F) above the water level near the grease trap access lid.
Step 4. Install servicing pipe and install support bracket (E).
Step 5. Fill grease trap with potable water to its working level.
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Case Study 1.
Operation: Chinese Restaurant
Operating hours: Tuesday to Sunday 10am to 10pm.
Commercial Fixtures: 1 x double sink, 1 dishwasher.
SCD Model: SCD500.
Pump out frequency: 8 weeks.
Grease Trap Type: Triple interceptor.
Conclusion: The existing 500 GT experience high oil/grease discharge causing blockages in the
council manholes. After the SCD retro fitted it was noted considerable amount of grease was trap in
the 2nd
chamber and last compared to pre retro fit. Sludge was completed before and after and the
GT trap 46% oil/grease and solids than before the SCD retro fit.
GT before retro fitting Emptied GT in preparation for retrofitting
Outlet prepared for retrofitting SCD and associated fittings assembled
Completed installation.
GT Before retro fitting After retro fit. Operation for 8 weeks.
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Case Study 2.
Operation: Country Motor Inn
Operating hours: Monday to Sunday 6 am to 2 pm – Breakfast and Lunch only
Commercial Fixtures: 1 x double sink, 1, single bowl sink, 3 floorwaste, 1 dishwasher.
SCD Model: SCD1000.
Pump out frequency: 8 weeks.
Grease Trap Type: Boat Shape.
Notes: Ongoing effluent quality programme implemented by the local water authority to reduce the
loading on the sewerage treatment plant. The existing Sewerage Treatment Plant reach operating
capacity and instead upgrading the plant, at a cost to local rate payers, the council reduced the
loading by retro fitting SCD’s to exisiting GT’s or replacing with MGT/MGTS.
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Case Study 2. Jupiters Hotel and Casino
Operation: Hotel commercial kitchen
Operating hours: Monday to Sunday 24/7
Commercial Fixtures: Flow rate 6000 litres per hour.
SCD Model: 6 x SCD1000.
Pump out frequency: 6 weeks.
Grease Trap Type: Triple interceptor with baffles remove.
Notes: Existing DAF unit experiencing solid overloading due to short circuiting of existing GT/Solids
trap. The SCD retro fitted to hold back solids to increase the performance of the DAF unit.
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Technical information for Surge Control Device (SCD) Retro fit .
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Boat shape Flat Bottom
Triple interceptor Other
Hours/day___________. Days/week______________
Staff no. Part time:__________ Full Time:__________
Seating capacity_______________________________
Flow rate/day:________________________________
Meals per day:________________________________
Length_______ Width________ Depth 1.__________
Depth 2.________ Outlet invert to bottom ________
Dishwasher:_______ Sink:_________ F/Waste_______
Cleaners sink ____________ Woks: ________________
Combi Ovens: __________
Others:______________________________________
_____________________________________________
Above ground Below ground
Outlet Inlet
Fast Food Franchise
Supermarket
Chinese/Thai
Butcher
Bakery
Hotel/Motel/Hostel
Conference Centre
Sporting Club
Hospital/Nursing Home
Sink Strainers: Yes No. Basket Traps: Yes No
Automatic Grease Recovery units: Yes No
Bio Additives e.g Grease Busters. If yes what type:
_____________________________________________
Others:_______________________________________
Yes No
If yes pump flow rate:__________________________
Capacity of pump vessels: ______________________
Halgan Pty Ltd Unit 2 187 South Creek Road, Cromer NSW 2099. Ph. 02 99721355, Fax: 0299721455,
email: [email protected]. www.halgan.com.au
Food court
Wholesale Food
Meat Processing
Restaurant
Night Club with food
Takeaway Food
Fish Shop
Others__________________
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