WO2012065250A1

WO2012065250A1 - Integrated dissolved air floatation system and process for the treatment of wastewater

Info

Publication number: WO2012065250A1
Application number: PCT/CA2011/001267
Authority: WO
Inventors: Stephanie Young; Alex Munoz
Original assignee: University Of Regina
Priority date: 2010-11-15
Filing date: 2011-11-15
Publication date: 2012-05-24

Abstract

This disclosure relates to a method, process, and apparatus for the treatment of water. For example, the present methods are useful for the treatment of water containing emulsified lipids, having alkaline pH, and/or wastewater at high temperature. An embodiment of the present method comprises placing water containing fat, oil or grease (FOG) residue in a treatment vessel; adding a coagulant to the water; adding a flocculent to the water; introducing air bubbles generated using an air flow of about 400 to about 800 mL of air / min per L of water and membrane diffusers with pore size ranged from about 1 to about 2.5 mm for a time period sufficient to cause coagulation of at least part of the FOG residue; introducing air bubbles generated using an air flow of about 40 to about 80 mL of air /min per L of water and membrane diffusers with pore size ranged from about 1 to about 2.5 mm for a time period sufficient to cause flocculation of at least part of the FOG residue, forming floes; introducing microbubbles with size ranged from about 20 to about 100 μπι for a time period sufficient to cause the floatation of at least part of the floes; and removing at least a part of the floes from the wastewater.

Description

INTEGRATED DISSOLVED AIR FLOATATION SYSTEM AND

PROCESS FOR THE TREATMENT OF WASTEWATER

FIELD

This disclosure relates to a method, process, and apparatus for the treatment of water. For example, the present methods are useful for the treatment of water containing emulsified lipids, having alkaline pH, and/ or wastewater at high temperature.

BACKGROUND

There is growing awareness that clean water is a limited resource that needs to be preserved, recycled, and reused. Wastewater quality represents a particular issue in the food preparation industry due to the high levels of fats, oils and greases (FOGs). Commonly wastewater will contain small amounts of oils which are broken down by microorganisms via anaerobic digestion during the treatment process. However, wastewater containing higher amounts of FOGs such as dishwasher effluent can overwhelm treatment facilities and consequently may require additional processing. In the United States alone it is estimated that sewers back up 400,000 each year and municipal sewers overflow an estimated 40,000 times per year. The Environmental Protection Agency has determined that FOGs are the leading cause of sewer blockages and, even if the accumulated FOGs don't block the drain, they can cause significant disruption to the wastewater utility operations.

Currently, food preparation facilities often utilize grease traps or other devices designed to intercept FOGs before they enter the water disposal system. Such devices have been in use for many years and provide some relief from the problems associated with FOGs. Grease traps require regular maintenance and usually only have a liquid capacity of about 5 to 15 gallons which can easily be filled with grease in a short time frame at a full service restaurant. Once capacity is reached, the grease trap will no longer work effectively, and will require the grease to be manually removed from the trap. This is a dirty and difficult task which can end up being neglected. A neglected grease trap will not be as effective at intercepting significant amounts of FOGs from the wastewater. Even when a grease trap is being operated properly the wastewater discharged still includes considerable amount of FOG because the traps do not remove emulsified oil and grease.

Dissolved air flotation (DAF) is a water treatment process that removes suspended matter such as oil or solids from water. See, for example, A. A. Al-Shamrani et al. (2002). Separation of Oil from Water by Dissolved Air Flotation. Colloids and Surfaces A: Physicochem. Eng. Aspects 209: 15-26. A DAF process usually involves three stages - coagulation, flocculation, and flotation. The water first enters a flash mixing chamber where a flash mixer and coagulant are used to promote coagulation. Then the water enters a flocculation basin where a slow mixer and flocculent are used to promote flocculation, forming floes. The water then enters a flotation tank. In the flotation tank, separation of the floes is brought about by introducing air bubbles into the water. The air bubbles attach to the floes. The buoyant force causes the floes to rise to the surface where they may be removed.

DAF units usually require the presence of trained operator(s) because: (1) DAF components need regular maintenance, (2) for monitoring of proper flow rates, and/ or (3) for monitoring of proper pH to niinimize protein solubility and break up emulsions. As a result, DAF is widely used for treating industrial effluent but, due to the capital cost, operating cost (including the need for trained operator (s)), and a large footprint, the method is seldom used for small scale operations.

SUMMARY

The present disclosure provides a method for treating water containing contaminants such as FOGs. The present disclosure further provides an apparatus for treating such water.

In an embodiment, the present method and apparatus may be used for treating wastewater from food preparation facilities such as restaurants. In particular, the present method and apparatus may be used for treating dishwasher effluent.

Embodiments of the present method and apparatus allow for cost-effective and efficacious wastewater treatment. In addition, the present method and apparatus can be utilized in areas where space is at a premium. The present method and apparatus may also treat wastewater comparatively rapidly.

As used herein, the term "wastewater" refers to water that has been adversely affected in quality by anthropogenic activities. For example, wastewater can be greywater or blackwater.

This summary does not necessarily describe all features of the invention. Other aspects, features and advantages of the invention will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a process flow diagram of an embodiment of a DAF process according present disclosure.

Figure 2 shows a schematic representation of an embodiment of the present apparatus. DETAILED DESCRIPTION

Embodiments of the present disclosure provide a method for treating wastewater. For example, the present method may be used for treating dishwasher effluent. Dishwasher effluent is typically characterized by high levels of emulsified oils which may result from the combination of high water temperatures and the presence of liquid vegetable oils and/ or the use of detergents and other alkalis. The use of dishwasher detergents and sanitizers also contribute to an alkaline pH of the wastewater. Conventional measures such as grease traps/interceptors are ineffective at treating such water because emulsified FOGs will usually pass through the traps and into sewer lines. If FOGs make their way to the sewer line, cooler temperatures may cause some of the FOGs to congeal on the interior of pipes. With time, this can lead to clogged sewer lines which can cause numerous problems such as sewage spills, overflows, premature sewer line replacement, more frequent sewer line cleaning, and/or sewage backups in homes and businesses.

The present method utilizes a modified DAF process. For example, embodiments of the present method provide coagulation, flocculation, floatation, and/ or sludge removal in a single unit. Coagulation may be provided by introducing a relatively high flow of air through bubble diffusers by, for example, using an air blower. The bubble diffusers are preferably membrane diffusers with pore size ranged from with 1 to 2.5 mm. High air flow (e.g. 400 to 800 mL of air /min per L of water) can provide the mixing energy requirements to promote coagulation and/ or destabilize any FOG emulsions/ particles in wastewater. Flocculation may be provided by injecting a relatively low flow of air through bubble diffusers by, for example, using an air blower. Bubble diffusers are preferably medium diffusers. Low air flow rate (e.g. 40 to 80 mL of air / min per L of water) can provide the mixing energy requirements to form floes which can be floated and if desired separated from the water. Floatation may be provided by introducing air pressurized saturated water into the vessel. This can lead to the formation of microbubbles (e.g. with sizes ranging from 10 to 100 microns) which float the fiocs to the surface of the water.

Clarified water resulting from the present method may be used, for example, in toilet flushing or reused for dishwashing. The clarified water may be conveyed to a filter where floes that escape from the flotation tank can be removed by a filter. Sludge can be removed from the surface of the liquid by, for example, a surface scraper. The sludge may be conveyed away from the flotation tank to the sludge tank. Alternatively, sludge can be removed by withdrawing the clarified water from bottom of the reactor. After water removal the sludge can be disposed of. For example, by blowing off the sludge from the bottom of the tank. The present method can avoid the necessity of separate flash mixing chamber and/ or a flocculation basin as used in traditional DAF units. This has the benefit that the system can be made compact with small footprint.

The present disclosure provides an apparatus for treating wastewater. The apparatus comprises a treatment unit and a filtration unit. The treatment unit comprises at least one in-flow means for carrying untreated wastewater into the unit, at least one out-flow means for carrying clarified water away from the unit, at least one means for carrying pressurized air into the unit, at least one means for carrying air saturated water into the unit, and at least one means for carrying sludge away from the unit.

In certain embodiments, the apparatus comprises at least one, preferably three, means for delivering chemicals into the unit. In certain embodiments, the apparatus comprises at least one out-flow means for carrying sludge away from the unit. In certain embodiments, the apparatus comprises at least one programmable logic control (PLC) for controlling the operation of the unit, and on-line sensor(s) for monitoring treatment performance. In certain embodiments, the apparatus comprises at least one programmable logic control (PLC) for controlling the operation of the unit, on-line sensor(s) for monitoring treatment performance, and an expert system to automate the unit, remote control. For example, it may be arranged so the monitoring of the process can be done at home using a computer. An alarm may be sent to the computer and/ or cell phone if the system requires attention.

The present apparatus and method may comprise an aeration system. The system preferably comprises an air pump, piping, flow control valve and bubble diffusers. The flow control valve controls the air flow rate for coagulation and flocculation.

The present apparatus and method may comprise an air-saturated water system. The system preferably comprises of an air compressor, a saturator, a flow control valve, and a pressure gage. The flow control valve controls the flow rate of air-saturated water for floatation.

The treatment units' operating cycles may be controlled by a PLC that may control the operation of the wastewater flow control valve, air flow control valve, and/ or air saturated water control valve. The PLC may set a predetermined time for coagulation, flocculation, floatation, and/ or sludge withdraw. In addition the PLC may control the rate and the time that chemicals are introduced into the treatment units.

The present apparatus and method may comprise sensors for monitoring performance such as pH, temperature, turbidity, etc. An expert system may be incorporated to manage the operation of the treatment unit remotely. The treatment unit may comprise an equalization basin or it may be sized to treat many batches of wastewater discharged by a dishwasher. The equalization basin can be used to mitigate undesirable changes in flow rate. In the case of restaurants, the rate at which the dishwasher effluent arrives to the treatment unit varies dramatically during the day, so it is useful to equalize the flow before feeding to the treatment unit. The equalization basin can also act as a pH adjustment tank for adjusting the pH of the dishwasher effluent to an optimum level. If the pH of the water is not adjusted in an equalization basin then it may, for example, be adjusted in the treatment unit.

Preferably the in-flow means is a pipe which may, for example, be carrying dishwasher effluent, industrial wastewater, or sewage. In an embodiment the in-flow pipe is carrying dishwasher effluent.

In certain embodiments the reclaimed water meets the guidelines for water reuse for toilet and urinal flushing (see, for instance, The Canadian Guidelines for Domestic Reclaimed Water (January 2010)) or irrigation. In such cases the water may be reused direcdy. In other embodiments the out-flow means leads to a filtration unit. The filtration unit can further improve the water quality such that the reclaimed water can be reused for a variety of purposes such as dish washing or sanitary cleaning. For example, the filtration unit may remove residual particles and other contaminants, and if necessary further improve the water quality such that it can meet Guidelines for Canadian Drinking Water Quality. Preferred filtration units can be conventional cartridge filters or membrane filters.

The reclaimed water may be used for a variety of purposes. For example, the water can be reclaimed for non-potable purposes such as irrigation, toilet flushing, sanitary cleaning, washing, etc. It can also be used as fresh water for dishwashing. Furthermore, the flocculated FOGs may be used for any suitable purpose such as biofuel production, as a fertilizer, for rendering into useful products, and the like.

The treatment unit may be in any suitable form. For example, the treatment unit may be in the form of an elongated cylinder, a square basin, a rectangular basin, or the like. A vertical cylindrical shape is preferred, but not essential, due to the small footprint. It is preferred that the treatment unit be of a shape that ensures there are minimal dead zones, where air bubbles and dissolved air can not reach. Dead zones promote sedimentation of the floes. Another consideration is to allow easy access for cleaning and maintenance of parts.

Preferably the treatment unit is connected via a connecting means to one or more, two or more, three or more chemical storage means such as chemical tanks. These storage means may contain any chemical or mixture of chemical that would provide a useful benefit. For example, pH modifier (e.g. sulfuric acid or hydrochloric acid), coagulant aid (e.g. aluminum sulfate), flocculent aid (e.g. polymer solution). The pH modifier may be used to adjust the pH of the wastewater to an optimum level. The purpose of the coagulant is to promote coagulation and/or to destabilize any FOG emulsions that have formed. This may happen within the treatment unit after the in-flow enters the unit. A predefined dose of coagulant can be discharged into the treatment unit and rapidly mixed with the wastewater by air bubbles. The flocculent can be added after coagulant has been mixed with the wastewater. For example, a predefined dose of polymer may be discharged into the treatment unit and rapidly mixed with air bubbles.

The treatment unit may be connected to a saturator. For example, via a pipeline that has a control valve. The control valve may be programmed to open after the flocculation step is substantially complete and close after a predetermined time.

In contrast with traditional DAF units the present apparatus can be compact and, hence, can be used in settings where it is impractical to have an equalization tank, flash mixing chamber, and/ or a flocculation basin. Furthermore, the present method and apparatus eliminates the need for mixers to enable rapid and slow mixing of the wastewater. In addition, the use of few mechanical parts and short treatment time may lead to a reduction in operating costs and power consumption.

The present method and apparatus may be automated and, once installed, can be used to continuously treat the wastewater stream.

The present method and apparatus may rapidly and efficaciously be used to treat wastewater to remove at least a portion of any FOGs. Preferably the present method and apparatus removes the majority of FOGs from the wastewater. The present method and apparatus may rapidly and efficaciously be used to treat wastewater to remove at least a portion of the particles therein. For example, the present method/apparatus can treat dishwasher effluent in about 10 minutes or less which enables heat recovery from the effluent. Dishwasher effluent retains heat from the washing process, its temperature may drop a little in the treatment unit, but can still be 50 °C or higher. With short treatment times at least some of this heat energy may be reclaimed. For example, the treated water may be returned for reuse in the dishwasher where it will not require such extensive heating in order to bring it up to wash temperature. The present disclosure provides the use of air bubbles to produce mixing force for coagulation and/or floccularion, for the separation of FOGs and/ or other contaminants from wastewater. Any suitable air to oil ratio (A/O) may be used herein. For example, the A/O may be about 0.003 or greater, about 0.004 or greater, about 0.0045 or greater, about 0.005 or greater. The A/O may be calculated using the following equation:

A .3s_a( P - l)R

O O_a where,

A/O— air to oil ratio (mL/mg) s_a - the air solubility (mL/L) = 18.7mL/L at 20°C f — the fraction of air dissolved at pressure P (atm) = 0.5. The saturation efficiency applied in this study was not determined experimentally. Therefore, the typical / value of 0.5 was used.

O_a = the influent oil concentration (mg/L).

R = recycle ratio (%)

Q— influent flow rate (m³/day)

P = pressure within the pressure tank (atm)

For example, if Recycle ratio = 24%, saturator pressure = 60psi = 5.08atm, 0 = 447mg/L A 3s_a{fP - \)R

[(1.3)(18.7mL/L)(0.5x5.08atm - l)(.24)]/(447mg/L)=0.02mL/mg o

The wastewater for treatment preferably has a pH of about 10 or less, about 8 or less, about 6 or less. The pH of the wastewater for treatment preferably ranges from about 5 to about 6.

A coagulant may be used herein. For example, the present disclosure provides for the use of metal coagulant , such as aluminum sulfate, for inducing the coagulation process. Any suitable dose may be used. For example, about 1000 mg of coagulant per liter of water or less, about 900 mg/L or less, about 800 mg/L or less, about 700 mg/L or less, about 600 mg/L or less, about 500 mg/L or less, about 400 mg/L or less, about 300 mg/L or less.

A flocculent may be used herein. For example, the present disclosure provides for the use of polymer as flocculent , such as polyacrylamides, for aiding in the flocculation process. Any suitable dose may be used. For example, about 100 mg of aid per liter of water or less, about 50 mg/L or less, about 10 mg/L or less, about 700 mg/L or less, about 8 mg/L or less, about 6 mg/L or less, about 4 mg/L or less, about 2 mg/L or less.

The ratio of coagulant to flocculent is preferably from 50 to 200 (depending on the characteristics of raw wastewater (such as initial turbidity and pH).

Depending on the particular conditions and configuration the present method and apparatus can be very effective at the removal of FOGs. For example, about 50% or more, about 60% or more, about 70% or more, about 80% or more, about 90% or more of the FOGs may be removed from the wastewater. The present method and apparatus may be effective at removing turbidity, biochemical oxygen demand (BOD), and/or chemical oxygen demand (COD).

Residual sludge may be removed by any suitable means. For example, it may be removed by mechanical means such as a scraper or a blow-off from the bottom of the treatment unit.

The present method, apparatus or system may be used as a pretreatment step prior to the wastewater being treated by other means such as membrane filtration, bio-processing, sewage treatment, and the like.

For the purpose of promoting and understanding of the principles of this invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will be nevertheless understood that no limitations of the scope is thereby intended, such as alteration and further modifications in the illustrated device, and such further application of the principles of the invention as illustrated therein being contemplated as would normally occur to one skill in the art to which the invention relates.

Figure 1 shows a schematic of a system according to the present disclosure. The wastewater (e.g. dishwasher effluent) flows into an equalization basin. Within the equalization basin, wastewater is mixed with acid (sulphuric acid or hydrochloric acid) which is delivered from a chemical tank. The amount of acid to add depends on the alkalinity of the wastewater. From the equalization basin the wastewater flows to the treatment vessel (flotation tank) and enters the vessel through a in-flow means. In the treatment vessel the wastewater is mixed with aluminum sulfate (Al₂(SO₄)₃*14H₂O) which is delivered from a chemical mix tank. Approximately 200 to 300 mg of aluminum sulfate per litre of wastewater is added. The wastewater is then mixed using high air flow rate (400 to 800 mL of air / min per L of water) for approximately 30 to 120 seconds. A pH meter within the treatment vessel is used to monitor the pH of the wastewater after the addition of aluminum sulfate. A polymer (anionic polyacrylamide flocculent) is then added at a dosage of 1.5 mg per litre from a chemical tank. The wastewater is then mixed using high air flow rate (400 to 800 mL of air /min per L of water) for 30 to 120 seconds. The wastewater is then slow mixing using low air flow rate (40 to 80 mL of air / min per L of water) for 60 to 120 seconds. After the slow mixing treatment, the aeration system is shut off and microbubbles are introduced by injecting air saturated water into the treatment unit via a control valve. Microbubbles (20 to 100 micron) are generated by the sudden change of pressure of the air saturated water from about 60 psi to atmospheric pressure. These bubbles attach to suspended floes or slow settling particles and bring them up to the surface. Sludge is then removed by a surface scrapper. Treated water is removed via an out-flow pipe to a further filtration unit (not shown) when reused back to the dish washer ; otherwise can be directly used for toilet and urinal flushing or irrigation. Sludge can also be removed from the bottom of the treatment unit once the clarified water has been removed.

Air-saturated water is produced within the pressure tank (saturator) by dissolving air under pressure (60 psi) into treated effluent via air compressor. The volume of treated effluent recycled to produce air saturated water ranges from 8% to 15%.

On-line sensors are installed to monitor pH, temperature, turbidity, etc. An expert system can be incorporated to manage the operation of the treatment unit automatically and remotely.

The optimum conditions for treatment and results are shown in Table 1.

Table 1

Optimum Operating Conditions

pH 5.5 - 6.0

Temperature 20 - 35 °C

Alum Dosage 300 mg/L

Polymer Dosage 1.5 mg/L

Rapid Mixing Duration with Alum 30 - 120 s

Rapid Mixing Duration with Polymer 30 - 120 s

Slow Mixing Duration 60 -120 s

Saturator Pressure 60 psi

Recycle Ratio 8 - 15%

Characteristics of DAP effluent (before filtration)

Turbidity Removal >95% (99%)

Residual Turbidity <5 NTU

Oil Removal >90% (93%)

Residual Oil Concentration <30 mg/L COD removal >90%

Residual COD < 100 mg/L

BOD removal >90%

Residual BOD <20 mg/L

It is contemplated that any embodiment or aspect discussed in this specification can be implemented or combined with respect to any other embodiment, method, composition or aspect of the invention, and vice versa.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention belongs. Unless otherwise specified, all patents, applications, published applications and other publications referred to herein are incorporated by reference in their entirety. If a definition set forth in this section is contrary to or otherwise inconsistent with a definition set forth in the patents, applications, published applications and other publications that are herein incorporated by reference, the definition set forth in this section prevails over the definition that is incorporated herein by reference. Citation of references herein is not to be construed nor considered as an admission that such references are prior art to the present invention.

Use of examples in the specification, including examples of terms, is for illustrative purposes only and is not intended to limit the scope and meaning of the embodiments of the invention herein. Numeric ranges are inclusive of the numbers defining the range. In the specification, the word "comprising" is used as an open-ended term, substantially equivalent to the phrase "including, but not limited to," and the word "comprises" has a corresponding meaning.

The invention includes all embodiments, modifications and variations substantially as hereinbefore described and with reference to the examples and figures. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims. Examples of such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way.

Claims

1. A method of treating water, comprising;

a. Placing water containing fat, oil and/ or grease (FOG) residue in a treatment vessel;

b. Adding a coagulant to the water;

c. Adding a flocculent to the water;

d. Introducing air bubbles generated using an air flow of about 400 to about 800 mL of air / min per L of water and membrane diffusers with pore size ranged from about 1 to about 2.5 mm for a time period sufficient to cause coagulation of at least part of the FOG residue;

e. Introducing air bubbles generated using an air flow of about 40 to about 80 mL of air / min per L of water and membrane diffusers with pore size ranged from about 1 to about 2.5 mm for a time period sufficient to cause flocculation of at least part of the FOG residue, forming floes;

f. Introducing microbubbles with size ranged from about 20 to about 100 μτη for a time period sufficient to cause the floatation of at least part of the floes; and g. Removing at least a part of the floes from the wastewater.

2. A method according to claim 1 wherein the water is dishwasher effluent.

3. A method according to claim 1 wherein the coagulant is selected from metal salts.

4. A method according to claim 1 wherein the flocculent comprises anionic polyacrylamide polymer.

5. A method according to claim 1 wherein the pH of the wastewater for coagulation

treatment is from about 5 to about 6.

6. A method according to claim 1 wherein the pH of the wastewater for flocculation

treatment is from about 5 to about 6.

7. A method according to claim 1 wherein the microbubbles are generated by releasing pressurized air-saturated water into the bottom of the treatment vessel.

8. A method according to claim 1 wherein step (d) lasts for at least about 30 seconds.

9. A method according to claim 1 wherein step (e) lasts for at least about 30 seconds.

10. A method according to claim 1 wherein the accumulated floes on the surface of the water are separated using mechanical separation means.

11. A method according to claim 1 wherein the accumulated floes on the surface of the water are separated by blowing the floes off from the tank after the clarified water is withdrawn.

12. A system for separating FOGs from water, the system comprising subjecting the water to air bubbles until at least a portion of the FOGs coagulate, subjecting the water to air bubbles until at least a portion of the FOGs form floes, and separating the floes from the water.

13. Use of air bubbles to aid the coagulation of fats, oils, and/ or grease in water.

14. Use of air bubbles for aid the formation of floes of fats, oils, and/ or grease in water.

15. An apparatus for dissolved air flotation treatment of wastewater, the apparatus

comprising a treatment vessel having an in-flow pipe, an out-flow pipe, a means for delivering air-saturated water, and a means for delivering pressurized air through membrane bubble diffusers.

16. An apparatus for dissolved air flotation treatment of wastewater, the apparatus

comprising a treatment vessel having an in-flow pipe, an out-flow pipe, a means for delivering air-saturated water, a means for delivering pressurized air through membrane bubble diffusers, and a pH monitor.

17. An apparatus for dissolved air flotation treatment of wastewater, the apparatus

comprising a treatment vessel having an in-flow pipe, an out-flow pipe, a means for delivering air-saturated water, a means for delivering pressurized air through a membrane bubble diffuseis, wherein the apparatus is connected to a PLC that monitors and controls the wastewater level in the treatment tank, flow rate of compressed air and air- saturated water, chemicals metering pumps, wastewater pH and temperature, and the operation cycle including of filling, coagulation, flocculation, flotation and sludge scrapper and/ or sludge blow off.

18. The apparatus of claim 15 wherein the apparatus comprises several sensors for

monitoring treatment performance.

19. The apparatus of claim 15 wherein the apparatus comprises an expert system to

automate and remotely control the apparatus.

20. The method according to claim 1 or the use according to claim 13 or 14 wherein air to oil ratio (A/O) is about 0.004 or greater.