HALGAN PTY LTDhalgan 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

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

Copyright Halgan 2013 Page 1

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.



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.



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



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



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)



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.



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.



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.


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.



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.


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.



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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Documents

HALGAN PTY LTDhalgan pty ltd surge control device (scd) kerry hall grease traps and scd – principles of design, performance and sizing calculation for retrofitting programmes