WO2012172298A2

WO2012172298A2 - Novel aggregates

Info

Publication number: WO2012172298A2
Application number: PCT/GB2012/000530
Authority: WO
Inventors: Raymond Connor
Original assignee: Biotec Limited
Priority date: 2011-06-17
Filing date: 2012-06-18
Publication date: 2012-12-20
Also published as: GB2506299A; WO2012172298A3; GB201110287D0; GB201322141D0

Abstract

There is described a lightweight expanded clay aggregate (LECA) for preventing the release of one or more noxious gases and/or controlling odours.

Description

Novel Aggregates

Field of the Invention

The present invention relates to novel aggregates, to the use of such materials and to methods of their preparation.

More particularly, the present invention relates to novel clay aggregates for industrial and/or agricultural applications which have a coating applied to them, such as a photocatalytic coating.

Background of the Invention

As a result of International Legislation designed to limit ammonia gas and volatile organic compounds (VOC's) being released into the atmosphere, an urgent need has arisen for a cost effective method of reducing emissions from, for example, livestock slurry and other sources. These include the pig, dairy and anaerobic digestion industries as well as land fill run off and waste disposal.

In addition the EU Nitrate Pollution Prevention Regulation 2008 requires a minimum storage capacity of 5 months for all livestock slurry systems within Nitrate Vulnerable Zones (NVZs). To date the most common methods employed to meet these regulatory requirements are to cover the storage tanks or lagoons with floating sheets or permanent roofing structures. These present practical concerns over structural damage to metal tanks and rain water management on tank and lagoon covers. Hexa- Cover® type plastic floating tiles were developed to overcome these problems. However, none of these methods actually deal with potential emissions, they just l contain gases, which will potentially be released into the atmosphere at a future date. These methods cost up to £35.00 per m² service area covered or even more.

Furthermore, the European pig sector comprises of approximately 150million pigs of which about 3.87 million are held on about 2,962 specialist pig units in England.

Under the NVZ directive (NVZ) it is required that all pig units have a minimum of 26 weeks slurry storage and that all units with over 750 breeding sows or 2,000 other pigs are required to comply with the Integrated Pollution Prevention and Control Directive (IPPC). Under the IPPC all slurry storage facilities have to be covered it is estimated that 3 0 pig farms fall into this category in England. It is estimated that the average surface area requiring covering per farm is approximately 2000m².

In addition, other noxious gases are problematical in a variety of industries, for example, in the brewing industry, there is an increasing need to remove carbon dioxide gas and especially hydrogen sulphide gas. Bottom fermenting yeast used in the production of light colour beers, e.g. lagers, produces hydrogen sulphide. It is a colorless, very poisonous, flammable gas with the characteristic foul odor of rotten eggs at concentrations up to 100 parts per million. However, at higher concentrations it may not produce an odor and can be fatal. At 100 to 150 ppm the human olfactory nerve is paralyzed after a few inhalations and consequently the sense of smell disappears, concentrations of 320 to 530 ppm leads to pulmonary edema, 530 to 1000 ppm causes strong stimulation of the central nervous system and loss of breathing, 800 ppm is the lethal concentration for 50% of humans for 5 minutes exposure, and concentrations over 1000 ppm cause immediate collapse with loss of breathing, even after inhalation of a single breath.

LECA are expanded (open cell structure) clay pellets, most commonly known under the brand name LECA (acronym of light expanded clay aggregate), also known as Hydroton and under non-proprietary terms fired clay pebble, grow rocks, expanded clay (pellets) or hydrocorns, are small globes of burnt and puffed clay, used in construction and farming, and especially in hydroponics. LECA is currently produced from selected clays in rotary kilns at temperatures of 1100°C to 1200°C.

LECA is manufactured from natural clay, has a neutral pH and transports and stores water. In the production of LECA, clay is fed into a long rotary kiln. The clay takes a few hours to pass through the rotary kiln, where the clay is dried, pelletised and expanded at temperatures reaching 1200°C. Expansion takes place when the organic matter stored in the clay combusts and the gas formation generates pores. The expanded clay pellets are then screened, sorted and if required crushed into different grading according to customers requirement.

LECA is utilised in a number of applications. In the construction industry, it is used in the production of lightweight concrete blocks as well as both a sound and thermal insulation material, and flue & chimney lining material. LECA is also used in structural backfill against foundations, retaining walls, bridge abutments etc., as it can reduce earth pressure by 75% compared with conventional materials. LECA is also used in water treatment facilities for the filtration and purification of municipal wastewater and drinking water as well as in other filtering processes, including those for dealing with industrial wastewater and fish farms. LECA has good water draining properties, and because it is much lighter than alternatives such as gravel, it is easier to transport and handle. It is also used as a growing medium in hydroponics systems, and blended with other growing mediums such as soil and peat to improve drainage, retain water during periods of drought, insulate roots during frost and provide roots with increased oxygen levels promoting very vigorous growth. However, hitherto LECA has not been used in the removal of gasses.

Summary of the Invention

We have now surprisingly found lightweight expanded clay aggregates provided may be capable of preventing the release of undesirable noxious gases, such as, ammonia, hydrogen sulphide, etc. and controlling odours.

Thus, a first aspect of the present invention provides a lightweight expanded clay aggregate (LECA) for preventing the release of one or more noxious gases and/or controlling odours.

It will be understood by the person skilled in the art that the chemical composition of LECA may vary. However, generally, the chemical composition is determined as (average values): Si0₂ = 62%; A1₂0₃ = 18%; Fe0₃ = 7%; K₂0 = 4%; MgO = 3%; CaO = 3%; Na₂0 = 2%; and Ct_ot = 0.02%, by weight. Whilst commercially available LECA has been found to be effective in preventing the release of undesirable noxious gases, such as ammonia, hydrogen sulphide, etc. and/or controlling odours as hereinbefore described, it has further been found that it may be advantageous to provide the LECA or other porous aggregates, such as a zeolite, with one or more coatings which are capable of preventing the release of undesirable noxious gases, such as, ammonia, hydrogen sulphide, etc. and controlling odours.

Furthermore, the adsorption of noxious gases, such as, ammonia, hydrogen sulphide, etc. may be enhanced by modifying the chemical composition of the LECA. For example, improved gas adsorption may be achieved by increasing the amount of aluminium oxide (AI2O3) and/or ferric oxide (Fe0₃) in the LECA composition. Generally, when the content of one or more of aluminium oxide and ferric oxide is increased, the silicon dioxide (Si0₂) content will be reduced. In LECA compositions with an increased content of aluminium oxide, the content of aluminium oxide may be from about 19% to about 30%, or 19% to about 28%, or 19% to about 25%, or 19% to about 22%, or 19% to about 20%. In compositions with an increased content of ferric oxide, the content of aluminium oxide may be from about 8% to about 20%, or 8% to about 18%, or 8% to about 15%, or 8% to about 12%, or 8% to about 10%. The present invention further provides a porous aggregate, such as, a lightweight expanded clay aggregate (LECA) with one or more polymer coatings which is adapted to float on the surface of tanks and lagoons to prevent the release of ammonia gas and to control odours. One coating, in the presence of UV light, will decompose ammonia into nitrogen gas and water. Another coating will capture and absorb ammonia and other VOC's long term. The process uses specially modified nano particles of titanium dioxide (Ti0₂), a naturally occurring mineral, dispersed in a silicon binder. It will be understood by the person skilled in the art that the chemical composition of the clay used as a lightweight expanded clay aggregate (LECA) may be varied.

Therefore, according to a further aspect of the present invention there is provided an enhanced aggregate material comprising a core material provided with one or more coatings wherein said one or more coatings is suitable for enhancing the degradation and/or adsorption of pollutants.

It will be understood by the person skilled in the art that combinations of LECA, i.e. uncoated LECA, and an enhanced aggregate material as hereinbefore described may be used. Although a variety of aggregates may be used as core materials in the present invention the aggregate core material is desirably a porous aggregate. Examples of porous aggregates, include, polymeric aggregates, zeolite, etc. However, a preferred aggregate is a clay aggregate and especially an expanded clay aggregate, such as LECA as hereinbefore described. Clay aggregates such as those commercially available as Filtralite™ may also be used as a core material. Although Filtralite™ comprises an expanded clay material, it is generally of higher bulk density than conventional LECA compositions. However, it will be understood by the person skilled in the art that a mixture of aggregates may be used. Thus, for example, an aggregate comprising a composite of LECA and zeolite may be desirable. The aggregates, i.e. the core material, for use in the present invention may vary in diameters, e.g. from about 0.1 to about 40mm in diameter, preferably from about 0.1 to about 20 mm in diameter. Thus, for example, the LECA may be provided in different grades, such as, from about 2 to about 4mm round, from about 4 to about 8mm round, from about 10 to about 20mm round and from about 4 to about 10mm cracked (available from Claytek Limited). Alternatively, MaxitLECA is available from Saint-Gobain with a diameter of from about 0.1 to about 32mm, preferably from about 10 to about 20mm. MaxitLECA is a light weight material, with an average density after compaction of just 300kg/m³ for 10 to 20mm.

Suitable coatings for enhancing the degradation of pollutants include one or more catalytic degradation agents, especially photocatalytic degradation agents, such as, titanium dioxide (Ti0₂). Titanium dioxide occurs naturally as a mineral, e.g. rutile, anatase and brookite. The most common form is rutile, which is also the equilibrium phase at all temperatures, whilst the anatase and brookite are metastable forms that convert to rutile upon heating. Whilst the titanium dioxide used as a coating in the present invention may comprise one or more natural or synthetic forms, it is preferred to use one or metastable forms, such as, anatase or brookite. Anatase is especially preferred.

Preferably the titanium dioxide shall be selected so that the photocatalytic properties of the titanium dioxide will be based upon the absorption of ultra violet radiation, e.g. from about 100 to about 400nm, preferably from about 200nm to about 400nm, especially about, 380nm. Alternatively, a visible light responsive photocatalyst may be used. By the term visible light photocatalyst is meant a photocatalyst that is effective, i.e. is capable of producing hydroxyl radical in the presence of water or moisture, when contacted by visible light, i.e. at about 380 to about 740 nm wavelength. A variety of photocatalysts may be used, for example, titania photocatalysts. Thus, for example, titania doped with carbon (Ti0₂:C) or nitrogen (Ti0₂: ) is commercially available from Nanoptek Inc. and is a photocatalyst engineered to absorb not only UV light, but also visible light.

Titanium dioxide (T1O₂) anatase is one of the most attractive semiconductor materials suitable for photodegradation of pollutants, displaying high photocatalytic efficiency, stability, low toxicity and low cost. When activated by UV light radiation the titanium dioxide undergoes electron band gap transitions which result in the interaction of positive "holes" with water absorbed on the surface of the titania species to form hydroxyl radical. The hydroxyl radicals are powerful oxidisers which act to decompose organic matter. Additionally, UV radiation can cause electrons in the titanium dioxide to form superoxide anions by reacting with oxygen in the air. The photocatalytic properties of titanium dioxide based on the absorption of ultra violet radiation (380nm) is used in many applications. Doping the crystal lattice induces changes in the band gap. This formation of interstates between the energy bands offers the possibility not only to use ultra violet light, but visible light as well. By doping the anatase phase with carbon the cut -off wavelength is shifted from 388nm (band gap 3.20eV) to 535nm (2.32eV).

Lab-scale examinations have shown that the photocatalytically generated radicals are able to oxidize organic derivates e.g. hydrocarbons and inorganic molecules e.g. nitrogen oxides. Potential applications are found in the self-cleaning of surfaces and the reduction of pollution of air and water, where superhydrophilicity and high specific surface areas are acceptable.

The photocatalyst needs light and air, direct contact to pollutants (gas, liquid or solid) and should be immobilized on the surface of matrices or embedded in porous, translucent structures. Efficiency of these photo catalysts is determined by reduction of testing substances such as nitrogen monoxide, isopropyl alcohol or acetaldehyde and compared with those of conventional photocatalysts.

When a photocatalyst is applied to the aggregates, it may be applied, for example, by spray coating with a dispersion of a photocatalytic material, e.g. titanium dioxide nanoparticles in the range of from about 5 to about 100 nm diameter, preferably about 6nm diameter particles. Thus, the aggregate particles will have a surface area of about 280m²/g and be modified for ammonia gas, acetaldehyde gas, formaldehyde gas and nitrous oxide and hydrogen sulphide gas decomposition.

The coating can be applied to the aggregate core by a variety of methods, including, for example, spraying, dipping, spin, brushing or tumble coating with a suitable low carbon binder prior to coating the aggregate with the photocatalyst. Preferably, the binder is a silicon binder, for example BS 1042 (Wacker) which is an aqueous hydrophobic emulsion of a reactive polydialkylsiloxane, such as, polydimethylsiloxane or SAF54 or EF38. The silicon binder may be applied in an amount of from about 2% to 5%. The aggregate of the present invention may be provided with an adsorption enhancing coating which may comprise one or more chelating agents. A preferred chelating agent is aluminium triphosphate (Al₅ (Ρ₃0ιο)3)·

A suitable aluminium triphosphate compound (AIH2P3O10 - 2¾0) which is commercially available from Tayca (Japan).

The chelating agent, e.g. aluminium triphosphate compound, may be applied to the aggregate core in admixture with a suitable hydrophobic binder. Examples of a suitable hydrophobic binder include, but shall not be limited to, a hydrophobic acrylic resin, e.g. comprising one or more polymensable monomers or a silicon binder. Such polymensable monomers include, but shall not be limited to, polymerisable unsaturated monomers, for example, unsaturated monomers selected from the group consisting of one or more of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, and cyclododecyl (meth)acrylate. In addition to such polymerisable unsaturated monomers may comprise aromatic monomers monomers selected from the group consisting of one or more of styrene and vinyl toluene, vinyl ester monomers such as vinyl acetate and vinyl pivalate, vinyl ether monomers such as ethyl vinyl ether and isobutyl vinyl ether, olefin monomers such as ethylene and propylene, (meth)acrylonitrile, vinyl chloride, and vinyl fluoride. A preferred binder is a polydialkylsiloxane, such as, polydimethylsiloxane.

The polymerised hydrophilic acrylic resin may have a weight average molecular weight of from about 2,000 to about 100,000, e.g. from about 5,000 to about 50,000.

When a hydrophobic binder is used the amount if hydrophobic binder may vary and may be from about 0. 1% w/w to about 10% w/w, for example, from about 1 to about 5% w/w e.g. about 2% w/w. When the enhanced aggregate material of the invention comprises a material other than a zeolite, for example, LECA, the aggregate may be provided with a zeolite coating. The use of a zeolite coating on a LECA material is advantageous in that, inter alia, it may enhance adsorption, for example a zeolite coated LECA aggregate may provide a nanoporous and microporous structure for adsorption. Furthermore, a zeolite coating may be incorporated into a binder, for example an organic binder resin.

When the enhanced aggregate material is provided with a zeolite coating, the zeolite may be in finely powdered or micronised form. The zeolite may be applied to the LECA in an amount of from about 0.1 % to 5% w/w.

When a zeolite coating is used according to this aspect of the invention, the coating may comprise one or more zeolites, i.e. a mixture of zeolites. Many different types of zeolite, with varying ratios of silica to alumina, are known. Zeolites useful in this invention may be based on naturally-occurring or synthetic aluminosilicates. The one or more zeolites may comprise synthetic or natural (non-synthetic) zeolites. When a natural zeolite is used the zeolite may be selected from one or more of Amicite, Analcime, Barrerite, Bellbergite, Bikitaite, Boggsite, Brewsterite, Chabazite, Clinoptilolite, Cowlesite, Dachiardite, Edingtonite, Epistilbite, Erionite, Faujasite, Ferrierite, Garronite, Gismondine, Gmelinite, Gobbinsite, Gonnardite, Goosecreekite, Harmotome, Herschelite, Heulandite, Laumontite, Levyne, Maricopaite, Mazzite, Merlinoite, Mesolite, Montesommaite, Mordenite, Natrolite, Offretite, Paranatrolite, Paulingite, Pentasil, Perlialite, Phillipsite, Pollucite, Scolecite, Sodium Dachiardite, Stellerite, Stilbite, Tetranatrolite, Thomsonite, Tschernichite, Wairakite, Wellsite, Willhendersonite and Yugawaralite.

When a zeolite powder coating is used, the powder coating composition may comprise a mixture, in particulate form, of a zeolite and an organic resin. The resin can be an acrylic, polyester, epoxy or any other type of organic film forming resin which is compatible with the zeolite and/or LECA.

The organic resin when present in the powder coating composition may be any organic resin which is suitable for preparing powder coatings. For example, it may be a thermoplastic resin or a thermosetting resin. Suitable thermoplastic resins include plasticised poly (vinyl chloride), polyamides, polyolefins and poly (vinylidene fluoride). The plasticised poly (vinyl chloride) may be a homopolymer of vinyl chloride. Polyamides may be nylon- 11 or nylon- 12. Polyolefins, such as, polyethylene and polypropylene, may be modified by grafting of carboxylic acid or anhydride groups onto the polymer backbone. Thermosetting resins may be used in the zeolite powder coating compositions of this aspect of the present invention. Suitable resins include epoxy resins, polyester resins, hybrid epoxy-polyester resins, urethane resins and acrylic resins. Epoxy resins are characterised by the presence of an epoxide group and the most commonly used resins are diglycidyl ethers of bisphenol A, derived from bisphenol A and epichlorohydrin. Such resins may be cured after application to a substrate by means of a curing agent, such as a polyamine or a polyamide, and such a curing agent is present in the composition of the invention when epoxy resins are used.

When one or more polyesters are used in the zeolite powder coating compositions of this aspect of the invention the polyesters may prepared from polybasic acids or their esterifiable derivatives and from polyols. Carboxyl-rich and hydroxyl-rich polymers are suitable. Typical polyesters include esters of terephthalic acid, isophthalic acid, trimellitic acid, adipic acid or sebacic acid with ethylene glycol, 1, 2 -propylene glycol, trimethylol propane, a butanediol, glycerol or tris (hydroxyethyl) isocyanurate. Normally, polyesters are cured after application and curing agents may comprise triglycidyl isocyanurate or hydroxyalkyl amides. Urethane polymers which may be used in powder coating compositions may be urethane polyesters. Urethane polyesters may be prepared by reaction of a polyester with a caprolactam-blocked polyisocyanate, this reaction occurring after application of the powder to the substrate. Suitable polyesters include, for example, polyesters of terephthalic acid, isophthalic acid or trimellitic acid with neopentyl glycol. The resin can be either an air dry or bake type. The ratio of resin solids to zeolite can vary from 10:90 by weight to 70: 30 by weight and is typically from 30.70 to 60:40 by weight. Such coated LECA compositions may be further advantageous in that the organic binder may prevent or reduce the likelihood of the LECA from sinking, for example when the LECA is used to cover a storage tank or lagoon.

When the enhanced aggregate material, such as LECA, comprises a core material, the core may be coated with one or more catalytic degradation agents and a buoyancy aid, such as zeolite. Thus, a buoyancy aid coating, may comprise a zeolite powder coating composition which includes a photocatalytic degradation agent, such as, titanium dioxide (Ti0₂).

Furthermore, the coating composition according to this aspect of the invention may optionally include one or more biocidal agents, such as a biocidal metal ion salts, e.g., salts of silver, zinc or copper, or combinations thereof. Suitable salts of the metal ions include, for example silver chlorate, silver bromide, silver chloride, silver nitrate. When one or more biocidal metal ion salts is present in the coating, the amount may be from about 0.1% w/w to about 5% w/w, or 0.2% w/w to about 4% w/w, or 0.5% w/w to about 3% w/w, preferably from about 1 to about 2% w/w, e.g. as a 1:2000 w/w aqueous solution.

Alternatively, a biocidal agent, such as biocidal metal ion salts, e.g., salts of silver, zinc or copper, or combinations thereof, may be incorporated into the clay composition itself. Such biocidal clay compositions may be suitable for use in, inter alia, hydroponic irrigation systems. When one or more biocidal metal ion salts is incorporated in the clay composition coating, the amount may be from about 0.1% w/w to about 5% w/w, or 0.2% w/w to about 4% w/w, or 0.5% w/w to about 3% w/w, or from about 1 to about 2% w/w. The enhanced aggregate material of the invention may be provided with one or both of the catalytic degradation coating and the adsorptive coatings. In an especially preferred aspect of the present invention the aggregate is provided with a catalytic degradation coating and an adsorptive coating as hereinbefore described. Pollutants which may suitable be removed by the enhanced aggregate material of the invention comprise materials such as, organic compounds, for example, trimethylamine, methyl mercaptan, formaldehyde, acetaldehyde, etc.; inorganic materials, especially noxious gasses, such as, ammonia, oxides of nitrogen, hydrogen sulphide, hydrogen disulphide, and the like. The Ti0₂ coating is especially suitable for the degradation of gasses, such as, ammonia, hydrogen sulphide, and the like. The adsorptive coating is especially suitable for the adsorption of materials such as, ammonia, trimethylamine, hydrogen disulphide, methyl mercaptan, formaldehyde, acetaldehyde, and the like. Applications for the enhanced aggregate material of the invention particularly include the agricultural and livestock industry which is responsible for significant emissions of, for example, ammonia and hydrogen sulphide gases to the atmosphere. However, other applications include fish farming, industrial effluent & sewage treatment plants, cooling towers, oil/effluent spills, water treatment plants, for example, open waste water treatment plants and/or drinking water treatment plants, etc. The enhanced aggregate material of the invention may be used in a number of potential sectors:

1 Pig industry

2. Dairy Industry

3 Anaerobic Digestion industry

4. Landfill run off

5 Waste Disposal

It will be understood by the person skilled in the art that when the enhanced aggregate material of the invention is used in the agricultural and livestock industry, the use may comprise covering a storage tank or a lagoon with the enhanced aggregate material. In addition, the enhanced aggregate material may be used inside a livestock house. For example, a floor in an animal house may be arranged such that a slurry or manure cellar is provided underneath the floor of the livestock house so that animal manure is discharged into the cellar away from the livestock and/or the animal bedding. The slurry cellar will be emptied at intervals, for example, to a slurry lagoon or storage tank. However, prior to the cellar being emptied noxious gasses can escape from the cellar into the livestock house, which may be injurious to the environment and/or give rise to unpleasant odours. This problem can give rise to difficulties for persons working in these areas and living adjacent to these areas and to the livestock. In recent times pollution control authorities have begun to issue strict controls on these areas and to limit the number of animals which may be housed. This obviously has large cost implications for the owners of such enclosures with regard to the numbers of livestock that can be housed. Thus, a further object of the present invention is to attempt to alleviate the problem of the emission of such gases and odours from livestock housing and to reduce the exposure that workers and/or livestock might be subjected to.

In a further aspect, the invention provides a method of removing a pollutant, e.g. an odour and/or noxious gasses, from a pollution source, which method comprises substantially covering the pollution source with LECA as hereinbefore described. In a yet further aspect, the invention provides a method of removing a pollutant, e.g. an odour and/or noxious gasses, from a pollution source, which method comprises substantially covering the pollution source with an enhanced aggregate material provided with one or more coatings suitable for enhancing the degradation and/or adsorption of pollutants as hereinbefore described.

The method according to this aspect of the invention may also comprise incorporating the LECA and/or enhanced aggregate material in an air filter for use, for example, in an animal or poultry house. According to a further aspect of the invention there is provided the use of a catalytic degradation agent, especially photocatalytic degradation agent, such as titanium dioxide, in the manufacture of an enhanced aggregate material as hereinbefore defined suitable for enhancing the degradation of pollutants. According to a further aspect of the invention there is provided the use of a chelating agent, such as aluminium triphosphate, in the manufacture of an enhanced aggregate material as hereinbefore defined suitable for enhancing the adsorption of pollutants.

The enhanced aggregates of the present invention are advantageous in that, inter alia,

• The enhanced aggregates do not degrade over time.

• The catalyst remains active for prolonged periods as long as there is UV light, oxygen and water in contact with the surface substrate.

• It is estimated that the chelating agent should remain active for long periods of time.

• The enhanced aggregate works at low (winter) temperatures and in ice and snow conditions.

• The enhanced aggregate is not and does not form a clay crust.

• Agitating, pumping or emptying slurry lagoons or storage tanks is not adversely affected by having the surface covered by the enhanced aggregate.

• The enhanced aggregate is designed as a long-term solution to meeting the growing international regulatory requirements for the control of Volatile Organic Compounds (VOCs) as well as meeting any social responsibilities farmers and others have towards their neighbours. Independent tests show the removal of up to 100% of ammonia and hydrogen sulphide and an average removal of 45% carbon dioxide (see appendix 1 & 2). The invention will now be described by way of example only and with reference to the accompanying figures in which Photo 1 is a representation of a UASB treatability rig;

Figure 1 is a schematic representation of a column of enhanced aggregate material; Figure 2 is a schematic representation of a gas collection device;

Figure 3 is a graph of hydrogen sulphide concentrations;

Figure 4 is a graph of ammonia concentrations;

Figure 5 is a graph of percentage removal of hydrogen sulphide and ammonia;

Figure 6 is a graph of methane concentrations; and

Figure 7 is a graph of carbon dioxide concentrations.

Example 1

Summary

This trial was designed to test the effectiveness of an enhanced aggregate material of the invention at removing odour. This specifically looked at the removal of ammonia and hydrogen sulphide. A laboratory scale trial was carried out over a 57 day period to determine the effectiveness of enhanced aggregate material at removing gaseous compounds (ammonia and hydrogen sulphide) that are responsible for odour problems. Biogas from an anaerobic digestion was passed through a column packed with enhanced aggregate material and the gas composition was measured before and after the column.

The data showed that the average hydrogen sulphide removal was 94% with 100% removal recorded on a number of days. The average ammonia removal was 61.3% with a maximum of 100% removal being recorded. The media also showed an average carbon dioxide removal of 45% during the course of the trial.

No deterioration in removal performance was recorded during the 57 day period.

The following conclusions were drawn from the study:

• The enhanced aggregate material of the invention performed consistently well with an average hydrogen sulphide removal of 96.7% over a 57 day period, with 100% removal being recorded on a number of days. Chemical dosing to increase the incoming hydrogen sulphide concentration to 5,000 ppm did not have any negative impact on removal rates and did not exhaust the capacity of the material. The ammonia removal was more variable with an average of 61.3% but the values fluctuated between almost complete removal on some days and virtually no removal on others. After 57 days of operation no decline was observed in the performance of the enhanced aggregate material.

• The overall quantity of hydrogen sulphide and ammonia removed during the trial equates to 4.7 and 0.253 cubic litres of hydrogen sulphide and ammonia respectively.

• The media showed no methane removal (except for 4 anomalous days when 50% removal was observed) and a small amount of carbon dioxide removal. The ability of this material to remove high concentrations of hydrogen sulphide and ammonia from gas, make it a potentially suitable material for abatement of nuisance odours from agricultural slurries. It may also have a potential application for scrubbing of biogas but it would have to compete with a wide range of systems that are already on the market and its ability to do this would depend upon its absorption capacity as well as the potential for re-generating the material in-situ.

1.1 A trial was carried out to determine the performance of the enhanced aggregate material at removing odour, particularly in relation to ammonia and hydrogen sulphide.

The trial was initially scheduled to run over 14 days but as there was no decline in performance of the material during this period, the trial was extended to provide a more comprehensive data set.

1.2 Aims and Objectives

The aim of the trial was to determine the performance of the enhanced aggregate material at removing the odour causing compounds hydrogen sulphide and ammonia from a test gas stream. This was met through the following objectives:

1. Set up a laboratory scale anaerobic digester to provide a steady stream of biogas with high stable concentrations of hydrogen sulphide and ammonia

2. Pass the biogas stream through a packed column of enhanced aggregate material and determine the composition of the gas before and after the column 3. Assess the gas removal properties of the material over a minimum of a 14 day period

4. Provide a report assessing the performance of the material and its suitability for use in odour abatement

1.3 Methodology

A laboratory scale upflow anaerobic sludge blanket (UASB) digester (figure 1) was set up and operated to give a continuous supply of biogas. The digester was fed on a molasses feed with suitable macro and micro nutrients to supply process stability. The UASB was operated at a loading rate of 5 kg COD/m³ reactor volume per day, which provided between 15-20 litres of biogas per day for the trial.

A suitable analysis regime was employed to ensure the process remained stable so that a constant stream of biogas with a consistent quality was produced. Over time the analysis regime was reduced once the process had stabilised.

Table 1: Analysis monitoring regime

The enhanced aggregate material was packed into a im long circular column with an internal volume of 2.22 litres. The weight of the material required to fill the column was 0.596kg, giving the material a bulk density of 0.27. The biogas was analysed before and after the column for methane, carbon dioxide, oxygen, hydrogen sulphide and ammonia (figure 1).

It was expected that the material should be able to remove ammonia and hydrogen sulphide, thus removing the worst odour and purifying the biogas. The volume of biogas produced was recorded using a liquid displacement gas trap (figure 2), thus giving a daily total biogas flow to allow the total quantity of contaminants removed to be calculated. 1.4 Results

1.4.1 Ammonia and Hydrogen Sulphide Removal

The media showed a high level of hydrogen sulphide removal throughout the study with the concentrations being reduced from between 2,000 to 5,000 ppm in the biogas to mostly <100ppm in the column outlet, with some peaks of up to 300ppm observed when the inlet concentrations increased up to 5,000 ppm (figure 3).

The hydrogen sulphide and ammonia concentrations were higher in the latter part of the study as the digester feed was dosed with ammonium sulphate to increase the concentrations of both compounds in the biogas to see if the media would become saturated. As no significant decline was observed in performance then it can be concluded that after 57 days the media was still not saturated and treatment performance had not been reduced. During the course of the trial, 954 litres of biogas was passed through the column and this equates to a removal of 4.7 cubic litres of hydrogen sulphide per kg of enhanced aggregate media, after which time the material was not exhausted. The ammonia removal was more variable with the concentrations being typically reduced from around 200ppm to ~50ppm although no removal was seen on some days, whilst on other days almost all the ammonia was removed (figure 4). The overall ammonia removal during the trial equates to 0.253 cubic litres of ammonia per kg media after which time the media was not exhausted.

The average hydrogen sulphide removal was 96.7% whilst the average ammonia removal was 61.3% (figure 5).

1.4.2 Carbon Dioxide and Methane

The media did not show any removal of methane except on days 4, 5 and 6 when around 50% of the methane was removed (figure 6). ' If this had occurred from the start of the study and then ceased, it would be concluded that the methane treatment capacity had been exhausted but there does not appear to be an explanation as to why this did not occur initially and then only occurred for a 4 day period.

The data on these days does not appear anomalous in any other way. The overall conclusion is that the enhanced aggregate material has little or no capacity to absorb methane. Whilst methane does not contribute to odour, the removal of methane would have been desirable for applications such as covering open lagoons as methane is a greenhouse gas. However, methane removal would have been an undesirable property if this media is to be used for scrubbing of biogas, where the energy is recovered from methane in downstream processes.

There is a slight reduction in the concentration of carbon dioxide although this may in part be due to the change in the overall gas balance from the removal of other contaminants in the biogas (figure 7).

1.5 Conclusions

• The enhanced aggregate media performed consistently well with an average hydrogen sulphide removal of 96.7% over a 57 day period, with 100% removal being recorded on a number of days. Chemical dosing to increase the incoming hydrogen sulphide concentration to 5,000 ppm did not have any negative impact on removal rates and did not exhaust the capacity of the material.

• The ammonia removal was more variable with an average of 61.3% but the values fluctuated between almost complete removal on some days and virtually no removal on others.

• The media showed no methane removal (except for 4 anomalous days when 50% removal was observed) and a small amount of carbon dioxide removal.

• After 57 days of operation no decline was observed in the performance of the enhanced aggregate media. The ability of this material to remove high concentrations of hydrogen sulphide and ammonia from gas, make it a potentially suitable material for abatement of nuisance odours from agricultural slurries. It may also have a potential application for scrubbing of biogas but it would have to compete with a wide range of systems that are already on the market and its ability to do this would depend upon its absorption capacity as well as the potential for re-generating the material in-situ.

0257P.WO.Spec(3)

Claims

1. A lightweight expanded clay aggregate (LECA) for preventing the release of one or more noxious gases and/or controlling odours.

2. An enhanced aggregate material comprising a core material provided with one or more coatings wherein said one or more coatings is suitable for enhancing the degradation and/or adsorption of pollutants.

3. An enhanced aggregate material according to claim 2 wherein the core material comprises a porous material.

4. An enhanced aggregate material according to any one of claims 2 or 3 wherein the core material comprises an expanded clay aggregate.

5. An enhanced aggregate material according to any one of claims 2 to 4 wherein the porous core comprises LECA.

6. An enhanced aggregate material according to any one of the preceding claims wherein the porous core comprises LECA with an increased content of aluminium oxide.

7. An enhanced aggregate material according to any one of the preceding claims wherein the porous core comprises LECA with an increased content of ferric oxide.

8. An enhanced aggregate material according to any one of the preceding claims wherein the porous core is an aggregate comprising a composite of LECA and zeolite.

9. An enhanced aggregate material according to any one of claims 2 to 8 wherein the core material has a diameter of from about 0.1 to about 40mm.

10. An enhanced aggregate material according to any one of claims 2 to 9 wherein the coating comprises a catalytic degradation agent.

11. An enhanced aggregate material according to claim 10 wherein the catalytic degradation agent is a photocatalytic degradation agent.

12. An enhanced aggregate material according to claim 11 wherein the photocatalytic degradation agent absorbs ultra violet radiation.

13. An enhanced aggregate material according to claim 11 wherein the photocatalytic degradation agent comprises a visible light photocatalyst.

14. An enhanced aggregate material according to any one of claims 10 to 13 wherein the catalytic degradation agent comprises titanium dioxide.

15. An enhanced aggregate material according to claim 14 wherein the catalytic degradation agent comprises a metastable titanium dioxide.

16. An enhanced aggregate material according to any one of claims 14 or 15 wherein the catalytic degradation agent comprises anatase.

17. An enhanced aggregate material according to any one of claims 10 to 16 wherein the catalytic degradation agent comprises nanoparticles in the range of from about 5 to about 100 nm diameter.

18. An enhanced aggregate material according to any one of claims 2 to 17 wherein the coating comprises a chelating agent.

19. An enhanced aggregate material according to claim 18 wherein the chelating agent comprises aluminium triphosphate (Als^C^o^).

20. An enhanced aggregate material according to any one of claims 10 to 19 wherein the chelating agent and/or the catalytic degradation agent is applied to the aggregate core in admixture with an hydrophobic binder.

21. An enhanced aggregate material according to claim 20 wherein the binder is a polydialkylsiloxane.

22. An enhanced aggregate material according to any one of claims 10 to 21 wherein the coating comprises a catalytic degradation agent and a chelating agent.

23. An enhanced aggregate material according to any one of claims 10 to 22 wherein the coating comprises a titanium dioxide catalytic degradation agent and an aluminium triphosphate chelating agent.

24. An enhanced aggregate material according to any one of the preceding claims wherein the enhanced aggregate material is provided with a zeolite coating.

25. An enhanced aggregate material according to claim 24 wherein the zeolite coating is in finely powdered or micronised form.

26. An enhanced aggregate material according to claims 24 or 25 wherein the zeolite coating is applied to the enhanced aggregate material in an amount of from about 0.1% to 5% w/w.

27. An enhanced aggregate material according to any one of claims 24 to 26 wherein the zeolite comprises a synthetic zeolite.

28. An enhanced aggregate material according to any one of claims 24 to 27 wherein the zeolite comprises a natural (non-synthetic) zeolite.

29. An enhanced aggregate material according to any one of claims 24 to 28 wherein the zeolite powder coating comprises a particulate form of a zeolite; and an organic resin.

30. An enhanced aggregate material according to claim 29 wherein the organic resin is a thermoplastic resin or a thermosetting resin.

31. An enhanced aggregate material according to any one of the preceding claims wherein one or more biocidal agents are incorporated in the clay aggregate composition.

32. An enhanced aggregate material according to any one of claims 2 to 30 wherein the coating includes one or more biocidal agents.

33. An enhanced aggregate material according to any one of claims 31 or 32 wherein the biocidal agent comprises a biocidal metal ion salts.

34. An enhanced aggregate material according to claim 33 wherein the biocidal metal ion salt comprises one or more silver salts.

35. An enhanced aggregate material according to claim 34 wherein the one or more silver salts is select from silver chlorate, silver bromide, silver chloride, silver nitrate.

36. An enhanced aggregate material according to any one of the preceding claims which is suitable for removing one or more of organic compounds, for example, trimethylamine, methyl mercaptan, formaldehyde, acetaldehyde, etc.; inorganic materials, especially noxious gasses, such as, ammonia, oxides of nitrogen, hydrogen sulphide, hydrogen disulphide, and the like.

37. An enhanced aggregate material according to any one of the preceding claims which is suitable for removing one or more of ammonia and hydrogen sulphide.

38. An enhanced aggregate material according to any one of the preceding claims which is suitable for removing ammonia.

39. An enhanced aggregate material according to any one of the preceding claims which is suitable for removing hydrogen sulphide.

40. A method of removing a pollutant e.g. an odour and/or a noxious gas, from a pollution source, which method comprises substantially covering the pollution source with LECA.

41. A method of removing a pollutant from a pollution source, which method comprises substantially covering the pollution source with an enhanced aggregate material comprising a core material provided with one or more coatings wherein said one or more coatings is suitable for enhancing the degradation and/or adsorption of pollutants.

42. A method according to claim 41 wherein the core material comprises a porous material.

43. A method according to any one of claims 41 and 42 wherein the core material comprises an expanded clay aggregate.

44. A method according to any one of claims 41 to 43 wherein the porous core comprises LECA.

45. A method according to any one of claims 41 to 44 wherein the core material has a diameter of from about 0.1 to about 40mm.

46. A method according to any one of claims 41 to 45 wherein the coating comprises a catalytic degradation agent.

47. A method according to any one of claims 41 to 45 wherein the catalytic degradation agent is a photocatalytic degradation agent.

48. A method according to claim 47 wherein the photocatalytic degradation agent comprises a visible light photocatalyst.

49. A method according to any one of claims 47 or 48 wherein the photocatalytic degradation agent absorbs ultra violet radiation.

50. A method according to any one of claims 47 to 49 wherein the catalytic degradation agent comprises titanium dioxide.

51. A method according to any one of claims 47 to 50 wherein the catalytic degradation agent comprises a metastable titanium dioxide.

52. A method according to , any one of claims 47 to 51 wherein the catalytic degradation agent comprises anatase.

53. A method according to any one of claims 47 to 52 wherein the catalytic degradation agent comprises nanoparticles in the range of from about 5 to about 100 run diameter.

54. A method according to any one of claims 47 to 53 wherein the coating comprises a chelating agent.

55. A method according to claim 54 wherein the chelating agent comprises aluminium triphosphate (Al₅ (P₃0]o)3)

56. A method according to any one of claims 54 or 55 wherein the chelating agent is applied to the aggregate core in admixture with an hydrophobic binder.

57. A method according to any one of claims 47 to 56 wherein the coating comprises a catalytic degradation agent and a chelating agent.

58. A method according to any one of claims 47 to 57 wherein the coating comprises a titanium dioxide catalytic degradation agent and an aluminium triphosphate chelating agent.

59. A method according to any one of claims 47 to 58 which is suitable for removing one or more of organic compounds, for example, trimethylamine, methyl mercaptan, formaldehyde, acetaldehyde, etc.; inorganic materials, especially noxious gasses, such as, ammonia, oxides of nitrogen, hydrogen sulphide, hydrogen disulphide, and the like.

60. A method according to any one of claims 47 to 59 which is suitable for removing one or more of ammonia and hydrogen sulphide.

61. A method according to any one of claims 47 to 60 which is suitable for removing ammonia.

62. A method according to any one of claims 47 to 61 which is suitable for removing hydrogen sulphide.

63. A method according to any one of claims 47 to 62 which comprises incorporating the LECA and/or enhanced aggregate material in an air filter for use, for example, in an animal or poultry house.

64. A method according to any one of claims 40 to 63 wherein the pollution source comprises one or more of a slurry lagoon, slurry storage tank or livestock housing cellar.

65. The use of a catalytic degradation agent, in the manufacture of an enhanced aggregate material suitable for enhancing the degradation of pollutants.

66. The use according to claim 65 wherein the catalytic degradation agent is a photocatalytic degradation agent.

67. The use according to claim 66 wherein the catalytic degradation agent is titanium dioxide.

68. The use of a chelating agent in the manufacture of an enhanced aggregate material suitable for enhancing the adsorption of pollutants.

69. The use according to claim 68 wherein the chelating agent is aluminium triphosphate.

70. The LECA, enhanced aggregate material, method or use substantially as hereinbefore described with reference to the accompanying examples.

0257P.WO Spec(3)