Field of the application

The present application relates to a method for treating surplus foundry sand. More particularly the present application relates to a method for treating or cleaning surplus foundry sand by composting, and to a compost containing surplus foundry sand.

Background

So called sand casting is the most applied method to make iron, steel, copper alloy and aluminium alloy castings. Sand is used as a main mould material and it is hardened by different bonding methods. Several sand types may be used in moulds.

Silica sand is most widely used sand type in casting. It is common in nature and its properties such as heat resistance and chemical inertness are satisfactory for most casting processes.

Olivine sand is sometimes used instead of silica sand, due to similar or better properties. Because of higher price, the usage is diminished. Chromite sand is used mainly in steel casting moulds. Its heat resistance and inertness are even better than that of silica sand.

Zircon sand has the best heat resistance properties of all sands. Due to its high price, is normally used only in the surface material of the mould, towards the molten metal.

The main bonding methods for casting moulds include clay (bentonite, kaolin) method ("green sand") and phenol formaldehyde resin method ("phenolic sand"). Also furan resin method ("furan sand") is used.

Green sand method is the most widely used method, due to its simplicity and low cost. Only silica sand, clay, water and some additives are needed. No baking or curing is required. Typically 10% of bentonite, 3-4% water and 1 -4% additives (e.g. carbon) is mixed with sand and the material is made inside a casting frame or by compressing a cake over a pattern. When permanent patterns are used, the mould must be made of minimum two pieces. Green sand can be reused several times by simple mechanical reclamation.

Organic resins are generally used in sand moulds to improve the strength of mould material compared to green sand for better dimensional accuracy and for better surface finish. Alkaline phenolic resin binder cured with an ester is the main method in this group, since it was developed in 80's. After mixing sand, resin and ester the mould material hardens enough at room temperature typically in less than 3 hour. The heat from cast hot metal hardens the mould even more. This resin type can be used with any sand type. 1 -2% alkaline phenolic resin and 0.2-0.5% organic liquid ester are usually needed in the mixture.

Furan and furan-urea-formaldehyde mixed with catalyst hardener is the other main type in organic resins. It is now the most popular of so called no-bake organic resin systems. The amount of furan no-bake binder used is usually 0.9-1 .2%. Catalyst levels generally are in the range of 20-40% based on the weight of the binder. Phosphoric acid is typically used as a catalyst.

Furan resins are commercially classified according to their nitrogen and water contents. Nitrogen content varies in the range of 0-2%, i.e. zero, low, medium, and high nitrogen furan-types. Water content may be in the range of 0-30%. The lower the nitrogen and water content, the higher is the grade of furan binder. The FNB base resin is often modified with urea, formaldehyde, phenol and a variety of "extenders."

After casting and cooling the moulds are crushed and the sand is treated for re-use (sand reclamation). Sand reclamation can include physical, chemical , and/or thermal treatments, depending on bonding method and sand type. After several reclamation and casting rounds, the properties of the sand are deteriorated too much and it has to be separated as surplus sand and be replaced by new sand. Typically 10-20% of the sand in each reclamation round must be replaced and therefore great volumes of surplus foundry sand, ca. 100000 tons in Finland and 18 million tons in Europe is generated per year.

During the casting process, the molten metal causes thermal decomposition of the carbonaceous additives and resin binders, which results in the formation of potentially hazardous organics which are emitted to the atmosphere and condense in the molding sand. Therefore surplus foundry sand contains environmentally detrimental impurities, such as PAHs, BTEXs and cresols, and therefore it is normally landfilled or used in landfill structures. Some surplus sand may contain also heavy metals, especially chromite sand. Disposal of surplus sand causes an economical burden for foundries. Landfill fees for foundry sand are at the moment 20-60€/ton, and they are expected to increase in future. Due to impurities even landfill ing of foundry sand requires environmental permit. The acceptable level of impurities in waste in landfills in Finland is regulated by law. Table 1 shows limit values of certain compounds in inert waste regulated by Finnish law. Surplus foundry sand does not normally fulfil these requirements. Table 1 . Government Decree of Landfills (31 1/2013)

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Brief description

One embodiment provides a compost, preferably as a heap or a windrow, comprising a mixture of

-surplus foundry sand,

-manure material, and

-optionally bedding plant material. One embodiment provides a compost, preferably as a heap or a windrow, comprising a mixture of

-20-80% (w/w) of surplus foundry sand of the total weight of the compost mixture, such as 20-60% (w/w),

-manure material comprising manure derived from feces, and

-plant-based bedding material comprising hardwood.

One embodiment provides a method for treating surplus foundry sand by composting, the method comprising

-providing surplus foundry sand,

-providing manure material,

-mixing the surplus foundry sand and the manure material to obtain a compost mixture,

-preferably forming the compost mixture into a heap or a windrow,

-composting the compost mixture for a sufficient time to obtain cleaned surplus foundry sand.

One embodiment provides a method for treating surplus foundry sand by composting, the method comprising

-providing 20-80% (w/w) of surplus foundry sand of the total weight of the compost mixture,

-providing manure material comprising manure derived from feces, and -plant-based bedding material comprising hardwood, -mixing the surplus foundry sand, the manure material and the plant-based bedding material to obtain a compost mixture,

-forming the compost of any of the preceding claims,

-composting the compost mixture for a sufficient time to obtain cleaned surplus foundry sand.

One embodiment provides a soil product obtained with the method described herein. The main embodiments are characterized in the independent claims. Various embodiments are disclosed in the dependent claims. The embodiments recited in dependent claims and in the description are mutually freely combinable unless otherwise explicitly stated. When surplus foundry sand is combined with manure material, it is possible to obtain an efficient composting process wherein the problematic surplus foundry sand will be purified.

In the composting process the hazardous waste is turned into an acceptable final product, which may be used as such in several applications. There is no need to further process the treated sand as the final soil product is formed in the same process. It is also possible to treat the surplus sand near the production site, for example at the foundry, so there is no need to transport the heavy sand to an external treatment site, which saves costs.

As the surplus foundry sand contains harmful substances, it is important to take care of any wastes formed and released in the composting process itself. With the embodiments it was possible to minimize the amount of harmful waste waters and therefore to provide an environment-friendly process. No waste waters are conveyed to groundwater.

Brief description of the figures Figure 1 shows temperature development in green sand test heap Figure 2 shows pH of different foundry sand types Figure 3 shows pH of all six composting test heaps (1 a and 1 b=green sand, 2a and 2b=phenolic sand and 3a and 3b=furan sand heaps)

Figure 4 shows dissolved organic carbon (DOC) concentrations in green sand sample and green sand compost heaps during the tests

Figure 5 shows dissolved organic carbon (DOC) concentrations in phenolic sand sample and phenolic sand compost heaps during the tests Figure 6 shows dissolved organic carbon (DOC) concentrations in furan sand sample and furan sand compost heaps during the tests

Figure 7 shows fluoride concentrations of green sand sample and green sand compost heaps during the tests

Figure 8 shows fluoride concentrations of phenolic sand sample and phenolic sand compost heaps during the tests

Figure 9 shows fluoride concentrations of furan sand sample and furan sand compost heaps during the tests

Figure 10 shows phenol concentrations of green sand sample and green sand compost heaps during the tests Figure 1 1 shows phenol concentrations of phenolic sand sample and phenolic sand compost heaps during the tests

Figure 12 shows phenol concentrations of furan sand sample and furan sand compost heaps during the tests

Figure 13 shows temperatures of test heaps containing surplus foundry sand and waste water sludge

Figure 14 shows temperatures of test heaps containing surplus foundry sand and horse manure

Figure 15 shows a compost heap containing surplus foundry sand, manure material and wood sticks Figure 16 shows an example of a moisture-controlled coated compost Detailed description

Composting is a method generally used to decompose biological material or bio waste into products, which can be used as fertilizer or soil amendment in landscaping, gardening or agriculture. Composting can be made in specially designed vessels, but in large scale simple heaps are built. To make infiltration possible in compost heaps coarse material such as broken tree branches, hardwood chips or sticks are added, herein especially leafy trees. The degradation of organic material is rather fast in the beginning of the composting because there are plenty of nutrients present that are used as energy resource by the microbes. Easily degradable components will degrade first in the mesophile phase, wherein acids will form and pH will decrease. Heating of the compost in the thermophile phase is the result from the thermal energy production of microbes. In the thermophile phase proteins will degrade and ammonia and carbon dioxide is released. Slowly degradable components, like fibrous matter, such as cellulose and lignin, will degrade at the latter part of the composting process. The activity of microbes in the compost decreases when the amount of nutrients decreases and this can be established by cooling of the compost. The composting process itself continues longer and the degradation of compost will become even. This stage is called the stabilization. Several chemical and physical reactions occur parallel with the degradation of organic compounds. Finally in the post-maturing phase even humus and lignin will degrade. By measuring and following these reactions relevant information of the composting progress and maturity will be gathered.

In prior art after composting regular compostable organic material, it is typical to add 30-80% sand into composted material, to achieve soil material for landscaping or gardening purposes. However, this sand must be environmentally acceptable as such, and it is usually not possible to use recycled foundry sand.

In the present embodiments it was surprisingly found out that when surplus foundry sand was combined with biodegradable material before composting, the composting process purified the foundry sand, especially the harmful and problematic organic contaminants were degraded, such as phenolic and resin compounds. The obtained composted material can be used as a soil amendment, if the product meets the regulations and limit values set for the composted end-product. In Finland these are set in the Decree of the Ministry of Agriculture and Forestry on Fertilizer Products (24/201 1 ): Substrate - Mixture soil (5A2). This regulation sets limit values and demands for heavy metals of the end-product, pathogens (Salmonella and E. coli) and impurities (weeds, garbage). Also this regulation demands that in case mineral soil from metallurgical industry is used as raw material for mixture soil, such as waste foundry sand, it must meet the criteria of harmful metals and organic harmful substances for positioning to the inert solid landfills. The method for treating surplus foundry sand by composting may utilize in general any suitable composting method or compost type. For example the compost may be in the form of a heap or a windrow. However, certain composting ingredients and conditions were found optimal especially for the surplus foundry sand. One embodiment provides a method for cleaning or purifying surplus foundry sand by composting, wherein the method for treating surplus foundry sand as described herein is used. It is in general challenging to obtain an efficient composting process with a compost containing an amount of surplus foundry sand. The surplus foundry sand as a starting material is usually dry and may disturb the composting process, so it is important to provide conditions and compositions adapted for efficient treatment of the surplus foundry sand.

In the method surplus foundry sand is provided. The term "surplus" as used herein refers to material which is in general used at least once and is usually considered as waste material. The surplus foundry sand is recyclable and has been or may be recycled. The surplus foundry sand contains sand originating from used moulds, but it may also contain an amount of unused or uncast mould parts. The surplus foundry sand may comprise silica sand, olivine sand and/or zircon surplus foundry sand. Sands containing soluble heavy metals are not usually desirable since the heavy metals cannot be removed in the composting process and therefore the obtained final product may not be suitable to such variety of uses as a product obtained from the other types of sand. The surplus foundry sand is usually very dry or relatively dry, having a moisture content in the range of 0-5%, such as 0-3% or 0.5-3%. For example green sand may have a moisture content in the range of 2-3% in general, or the moisture content of the sand may be substantially the same as in the ambient conditions, for example outdoor conditions, such as in the range of 5-10%.

The method also comprises providing compostable organic material. The compostable organic material refers to material containing active organic matter, which means that the material contains microorganisms required in the composting process. Examples of such microorganisms include bacteria, actinobacteria, fungi, protozoa and rotifers, and the active organic matter preferably contains one or more thereof. The active organic matter acts as a starter for the compost and accelerates the start and the proceeding of the process.

Bacteria are the most numerous of all the microorganisms found in compost. Depending on the phase of composting, mesophilic or thermophilic bacteria may predominate. Actinobacteria are necessary for breaking down paper products such as newspaper, bark, etc. Fungi, such as moulds and yeast help break down materials that bacteria cannot, especially lignin in woody material. Protozoa help consume bacteria, fungi and micro organic particulates. Rotifers help control populations of bacteria and small protozoa. In addition, earthworms not only ingest partly composted material, but also continually re-create aeration and drainage tunnels as they move through the compost.

In one embodiment the compostable organic material is manure material. Manure material was found especially suitable for treating the surplus foundry sand. Because the surplus foundry sand as a starting material is very challenging, i.e. it contains mostly non-compostable matter, the organic matter used in composting must be efficient for obtaining a composting process which is able to purify the sand in reasonable time and preferably in industrial scale. By using regular composting material alone, such as plant parts, it is not possible to obtain such an efficient process. The manure material acts as an efficient compost starter, especially when it is added as fresh and active form. Manure is organic matter, mostly derived from feces. The manure material being active usually means that it contains an amount of moisture. Usually the moisture content is 50% or more, for example in the range of 50-95%. Preferably the manure has not been stored for too long time and/or in conditions which would harm the micro-organisms. The manure material should be substantially fresh, meaning that it has been collected no longer than few months before the use, and especially it has not been burnt out.

The manure material may comprise for example general manure, such as animal manure, waste water sludge, household bio waste and/or slaughter house waste, or a material derived from any of these.

In general manure may be animal manure or human manure. In one embodiment the manure is animal manure. Common forms of animal manure include farmyard manure (FYM) or farm slurry (liquid manure). FYM also contains plant material (often straw), which has been used as bedding for animals and has absorbed the feces and urine. Agricultural manure in liquid form, known as slurry, is produced by more intensive livestock rearing systems where concrete or slats are used, instead of bedding. Manure from different animals has different qualities. Each type of manure has its own physical, chemical, and biological characteristics. For example manure from horses, cattle, pigs, sheep, chickens, turkeys and rabbits all have different properties. Animal manure is preferred as it is in general pure in the sense that it does not contain substantial amounts of heavy metal, hazardous organic waste or the like.

Cattle and horse manures, especially when mixed with bedding, possess good qualities for composting. Horses mainly eat grass and a few weeds or flour so horse manure may contain grass and weed seeds, as horses do not digest seeds the way that cattle do. Sheep manure is high in nitrogen and potash, while swine manure is relatively low in both. Swine manure, which is very wet must be mixed with straw or similar raw materials. In general poultry manure, which is very concentrated in nitrogen and phosphate, may be blended with carbonaceous materials, preferably low in nitrogen, such as sawdust or straw. In one embodiment the manure is horse manure. Horse manure was found especially suitable for the composting of surplus foundry sand. In one embodiment the manure is cattle manure, such as cow manure. In one embodiment the manure is swine manure. In one embodiment the manure is sheep manure. In one embodiment the manure is poultry manure. A combination of said manures may also be used. Moisture content of animal manure may vary, but in general it may be more than 50%, such as in the range of 50-90%, for example in the range of 60-70%. The average dry matter content in horse manure is in the range of 30-40%, in cow manure in the range of 10-30%, but in poultry manure in the range of 70-85%.

Human manure may also be used. It may be provided for example as waste water sludge or sewage sludge, which may be obtained from sewage treatment of municipal wastewater. Sludge may be so called primary raw sludge or secondary sludge which is treated by anaerobic digestion or a combination of both. The term septage is also referring to sludge from simple wastewater treatment but is connected to simple on- site sanitation systems, such as septic tanks. In one embodiment the manure is waste water sludge. The water content of such sludge is usually very high, such as at least 90%, for example in the range of 90-95%. The sludge may be dewatered before applying into the compost, for example by centrifugal dryer or by press filter. In one embodiment the manure is dewatered waste water sludge. The moisture content of dewatered waste water sludge may be in the range of 65-80%, such as 75-80%. A problem with waste water sludge may be that it may contain residual phenols, heavy metals, volatile organic compounds and the like originating from non-fecal waste.

The method comprises mixing the surplus foundry sand and the manure material to obtain a compost mixture. The manure material may be disintegrated if necessary, for example by mixing or blending, to obtain even distribution in the mixture.

In one embodiment the method comprises further providing bedding material, especially bedding plant material. The bedding material improves the conditions in the compost, for example the structure of the mixture is improved, for example by providing porosity, and the compost is aerated. This facilitates aerobic conditions in the compost. Especially when wet compostable organic material is used, the use of bedding material has a great effect on the efficiency of the composting process. Also the presence of sand may require efficient aerating of the compost. The bedding material may be for example wood or other plant parts, for example wood sticks, chips or sawdust, or straw, i.e. plant-based bedding material. When using wood, hardwood is preferred as softwood may have a negative effect on the composting process. The hardwood may be for example birch, aspen, poplar, alder, rowan, bird cherry, maple or the like, or a combination thereof. The bedding material alone is not capable of efficiently acting as a compost starter.

The bedding may be provided as chips, such as wood chips, preferably hardwood chips, which may have an average diameter in the range of 5- 100 mm, such as in the range of 10-50 mm. The average dry matter content of hardwood chips is in the range of 40-60%. The chips acts aeration material and as a carbon source. The bedding may also be provided as sticks, such as wood sticks, preferably hardwood sticks, which may have an average length in the range of 1-50 cm, such as 10-50 cm, or 1-20 cm, and the average diameter thereof may be in the range of 3-150 mm, such as 10-100 mm, or 3-50 mm. The average dry matter content of wood stick may be in the range of 35-55%. The wood sticks may be obtained from freshly cut wood, such from as harvested trees, including stumps, and they may include bark, leaves, dirt and the like. The wood sticks act as aeration material, carbon source and a source of microbes. The wood sticks may be recycled and/or aged. They may me precomposted, i.e. they originate from an existing or a previous compost. Figure 15 shows an example of a compost containing woods sticks with a length of up to 50 cm.

In addition to aeration properties, the described bedding material enable maintaining the desired moisture content of the compost, and preventing forming of excess waste water, and further any leakage of waste waters from the compost.

In one embodiment bedding material, or at least part of the bedding material, originates or is derived from an existing or a previous compost. Such bedding material, which may be in a form of chips or sticks, has not been degraded completely but contains active microorganisms as an inoculum which helps initiating a new compost. The bedding material may be separated from an existing compost for example by screening. Also other organic material may be added, such as animal or plant based material, or a combination thereof. In one example zero fiber sludge from a pulp or paper plant may be added to the compost mixture. Any recycled material may be used, such as household recycled waste, animal offal (slaughterhouse waste) and the like. Such materials may be added in an amount of 5-20% (w/w) of the total weight of the compost.

In one embodiment at least part of the manure material and optionally plant-based bedding material, in general the organic material, has been precomposted before mixing with the surplus foundry sand. Precomposting may also refer to aging. Precomposting may be carried at the same or different premises than the actual composting of the surplus foundry sand. The precomposted material may be obtained, and provided to the compost. In one embodiment the composting method comprises first precomposting at least part of the manure materials and/or bedding material . At least part may refer to 100%, or to less than 100%, such as 20-90% (w/w) or 50-90% (w/w), such as about 20% (w/w), 30% (w/w), 40% (w/w), 50% (w/w), 60% (w/w), 70% (w/w), 80% (w/w) or 90% (w/w). "Precomposting" as used herein refers to composting the organic materials before adding any surplus foundry sand. Also any other organic material, as described above, such as household bio waste and/or slaughter house waste, may be added to a mixture of organic materials which is to be precomposted. The precomposting may take several weeks, for example 1-10 weeks, such as 2-4 weeks, which is substantially shorter time than the actual composting with the surplus foundry sand. After the precomposting the organic material must still be active. The precomposting may be carried out in a heap or a windrow, but also in a container, for example in a drum compost. A drum compost, also called as a compost tumbler, usually comprises a horizontal cylinder or a tubular tank, a drum, which is arranged to be turned on its horizontal axis to mix the compost material. The drum is isolated and ventilated, the air entering from head flanges on the drum and permeating the compost mass as the drum rotates. Mixing, turning, air blowing and heat may be used to facilitate the precomposting. Using precomposting may accelerate the start of the actual treatment of the surplus foundry sand and make the whole process more efficient. Precomposted bedding material, such as wood sticks or chips, are usually at least partly softened because of decomposition, and they contain a dark layer of humus and/or microbial growth on them. Such material can be distinguished from fresh material in that the fresh material is lighter in colour and harder and does not contain such a dark outer layer.

The moisture content of the formed compost mixture may vary depending mainly on the moisture content of the manure material or other organic material, and the amounts thereof. In general the moisture content of the compost mixture should be in the range of 30-80%, such as 60-75%, 35- 60%, or 50-60%. This may be adjusted by selecting a ratio of sand and manure, and optionally other organic material, such as bedding material, to obtain the desired moisture content. It is also possible to adjust the moisture content after forming the initial mixture, such as during the composting process, by adding more organic material to obtain the desired moisture content. In one example the moisture content is adjusted at the beginning of the composting, i.e. when forming the compost mixture or immediately after forming the compost mixture. When the actual composting process starts the moisture content of the compost may be self-adjusting at least partly. The compost produces water and carbon dioxide as by-products.

In one embodiment the composting method comprises monitoring the moisture content of the compost, and as a feedback providing water to the compost, and optionally blowing air to the compost. These actions may be carried out to obtain a desired moisture content, which may be at a predetermined range. The moisture content of the compost may be monitored by detecting the moisture content of the compost in one or more locations, for example by measuring conductivity of the compost, which correlates with the moisture content. Water may be provided to wet the compost, for example by spraying by one or more nozzle(s), i.e. to increase the moisture content, at one or more locations of the compost. Air may be blown, to one or more locations of the compost, to decrease the moisture content. The water may be raw water, such as groundwater, tap water, or it may be waste water, such as water from the compost, or a combination thereof.

The compost mixture may be formed into suitable form, such as into a heap or into a windrow. A windrow refers to a long row. Composting in windrows is suitable for large volumes of composting. The aim of the composting process is to obtain aerobic conditions. Anaerobic conditions lead to rotting, which is not desired herein, but may happen in minor amounts in small parts of the compost. To avoid anaerobic conditions it should be ensured that sufficient air is available in the compost. This may be done by enhancing the structure of the compost, such as by providing coarse texture, for example by adding an amount of bedding material, or by blowing actively air to the compost heaps. One embodiment provides a compost comprising a mixture of surplus foundry sand and manure material. One embodiment provides a compost comprising a mixture of surplus foundry sand, manure material and bedding material. The compost may be composed as described above. The compost of the embodiments needs not to be in a container. Actually the size and the mass of the required compost mixture are so great that the use of a container is usually impractical. Therefore the compost may be formed as an open form, for example as a pile on the ground, i.e. the compost is uncovered. The compost may be also formed on a floor or similar base or base layer, for example a base made of concrete or asphalt, such as a water tight asphalt layer, wherein the floor, base or layer may include channels or the like conveying structures. However, the compost may be covered, for example by using tarpaulin, roofing or other suitable covering.

In one example the compost is covered by a roofing, which may be a canopy, shed, cantilever roof, or any other suitable roof structure, wherein the roofing is not directly on the compost. Preferably there is empty space between the compost and the roofing, for example to enable aeration and/or to provide space for machinery. By using the cover, especially the roofing, it is possible to control the moisture of the compost and runoff waters. For example rain does not wet the compost, and the amount of waste waters from the compost may be minimized. The covered composting area may be surrounded by a sealed threshold to avoid any ambient rain waters to flow inside the composting area However, in one example the compost covered by a roofing is equipped with one or more devices, such as spray nozzles, for spraying water to the compost, preferably as a feedback for measured moisture content of the compost, to maintain the moisture content of the compost at a desired range. In one example the compost arrangement includes a roofing above the compost, and one or more channels on the ground or on the base layer, such as an asphalt layer, for recovering water, such as waste water or runoff water, from the compost. The one or more channels may be connected to one or more well(s) or container(s) for collecting the water. The channel(s) may include tubing, grooves, such as grooves or channels on the floor or base layer, bars for conveying water flows, such as wooden bars, and the like. As the water obtained from the compost containing surplus foundry sand may contain substantial amounts of hazardous organics or harmful substances described herein, it is not desired to lead these waste waters to collecting system or to discard the waste waters to ground, wherein they may end into groundwater. In one example the collected water is led or recycled back to the compost, wherein it will moisten the compost and is also purified. The content of the harmful substances in the collected water may be monitored and if needed, the water may be recycled back to the compost for purification, until the content of the harmful substances in the water is lowered below a predetermined level. The harmful substances may include one or more of the substances described herein, such as PAHs, BTEXs and/or cresols, which may also be called as hazardous substances. The system may contain one or more sensors, one or more controlling units, one or more pump(s) and or other actuator(s) operatively connected together, and to required tubing or other plumbing parts, to obtain this functionality. Such system would provide environmentally safe composting arrangement or system together with moisture control. Figure 16 shows an example of an arrangement wherein a compost heap 10 is covered with a roofing, more particularly a tarpauling shelter 12, and the arrangement includes an irrigation and waste water basin 14, wherein the waste water is arranged to be pumped from the basin for wetting the compost via nozzles 20 when necessary. There is a threshold 16 around the composting area, which is located on an asphalt layer 22. A pay loader 18 can drive in the shelter to load and mix the heaps. In case the limit values of the waste waters are not reached after repeating the composting treatment, the waste waters will be transported elsewhere for further treatment. A "compost arrangement" or a "composting arrangement" refers to an entirety including the compost and one or more supporting structures, such as cover(s), base or floor, liquid channel(s), well(s) or container(s), controlling unit(s), actuator(s), pump(s), tubing(s), wiring(s), and the like.

In one embodiment the compost is covered with a roofing, and comprises one or more channel(s) for conveying water from the compost, and one or more well(s) or container(s) for collecting the water from the channel(s). In one embodiment the water is arranged to be conveyed back to the compost. This may be carried out in case the content of one or more monitored harmful substances in the water exceeds a predetermined limit, as explained in previous. The predetermined limit may be a concentration of a substance in water. In one embodiment the composting method comprises conveying water from the compost to one or more well(s) or container(s), monitoring the content of one or more harmful substance(s) in the water, and conveying the water back to the compost in case the content of the one or more monitored harmful substance(s) in the water exceeds a predetermined limit

After forming the compost it may be necessary to carry out certain actions to ensure the efficient start of the process. At the beginning it is possible to accelerate the process by providing heat to the compost, especially if the amount of the surplus foundry sand is substantial. For the same reason at the beginning it may be necessary to adjust the moisture content of the compost mixture to a desired level. One option is also to provide an amount of precomposted material.

The amount of the ingredients in the compost mixture may vary. In one embodiment the compost mixture contains 1-90% (w/w) of the surplus foundry sand of the total weight of the compost mixture. In one embodiment the compost mixture contains 20-80% (w/w), such as 20- 60% (w/w), for example 20-40% (w/w) of the surplus foundry sand of the total weight of the compost mixture. In one embodiment the compost mixture contains 20-35% (w/w) of the surplus foundry sand of the total weight of the compost mixture. In one embodiment the compost mixture contains 39-60% (w/w) of the surplus foundry sand of the total weight of the compost mixture. In many cases 80%, preferably as a dry weight of the sand, is the maximum amount of the sand in the compost wherein the process is efficient. If the sand content is too high there is not enough organic material in the compost mixture to enable the composting. The percentages may refer to dry weights from the total dry weight of the compost mixture.

In one embodiment the compost mixture contains 7-80% (w/w) of the manure material of the total weight of the compost mixture. In one embodiment the compost mixture contains 10-70% (w/w), for example 20-70% (w/w), of the manure material of the total weight of the compost mixture. In one embodiment the percentages disclosed herein refer to dry weights from the dry weight of the compost mixture, which helps eliminating the varying moisture content of different kind on manure material which may be used in the compost so that comparable percentages are obtained. A sample of the compost mixture may be obtained, dried and analysed to obtain the dry weights of the materials, or the dry weights may be calculated. Naturally the compost mixture in the actual composting process shall not be dry. In one embodiment the compost mixture contains 25-50% (w/w), for example 28-45% (w/w), of manure material as dry weight from the total dry weight of the compost mixture. In one embodiment the compost mixture contains 25-40% (w/w) of waste water sludge as dry weight from the total dry weight of the compost mixture, and/or 4-10% (w/w) of animal manure, such as horse manure or cow manure, as dry weight from the total dry weight of the compost mixture.

In one embodiment the compost mixture contains 3-30% (w/w) of the bedding material of the total weight of the compost mixture. In one embodiment the compost mixture contains 3-10% (w/w), of the bedding material of the total weight of the compost mixture. In one embodiment the compost mixture contains 3-5% (w/w) of the bedding material as dry weight from the total dry weight of the compost mixture.

The method comprises composting the compost mixture for a sufficient time to obtain cleaned surplus foundry sand. Also the term "purified" may be used interchangeably. The length of the sufficient time may depend on the composition of the compost and/or on the conditions, such as the conditions in the compost and/or ambient conditions. The sufficient time to obtain cleaned surplus foundry sand may also be defined with the desired properties of the obtained final product, for example if a certain degree of purification or quality of the cleaned surplus foundry sand is obtained, the time is sufficient. This may be determined by determining the amount of the organic contaminants in the final product or in the treated sand, which contaminants were subject for the treatment. Such organic contaminants may include organic resins, such as furan resins and/or phenolic resins. "Phenolic" as used herein refers to a class of chemicals containing a phenol group. It may be for example desired that the amount of an organic contaminant in the final product is below the limit value for non-hazardous inert waste, as provided for example in the law (see Table 4). The sufficient time, or more particularly time period, may be in the range of at least 3 months, such as 3-6 months, or even more up to 12 months. In one embodiment the method comprises composting the compost mixture for at least 3 months. In one embodiment the method comprises composting the compost mixture for at least 6 months. In one embodiment the method comprises composting the compost mixture for at least 9 months. These time periods may depend on the ambient temperature and/or other conditions, i.e. the climate of the location of the compost in case the compost is outdoors. In one example the time periods are applicable on summer conditions, for example wherein the mean daily temperature is consistently above 10°C.

The mass of the compost may also have an effect to the efficiency of the composting process. It was found out that too small compost is not efficient for purifying surplus foundry sand. In one embodiment the mass of the compost mixture is at least 5000 kg. In one embodiment the mass of the compost mixture is at least 10000 kg. In one embodiment the mass of the compost mixture is at least 15000 kg. In one embodiment the mass of the compost mixture is at least 20000 kg. During the process the compost may be turned to improve porosity and oxygen content, mix in or remove moisture, and redistribute cooler and hotter portions of the pile. In general the compost should be turned or mixed at least once so that the parts on the surface of the compost pile would be moved into the compost. This will facilitate the purification of these parts of the compost, because otherwise the temperature of the compost on the surface would not rise high enough, such as to at least 55°C. Turning of the compost will usually cause a rise of the temperature and an increase in the microbial activity of the compost. In case the temperature increases after turning there may be no need to add any additional organic materials during the composting.

The temperature of the compost may be measured and logged constantly to determine the optimum time to turn them for quicker compost production. In one embodiment the method comprises monitoring the temperature of the compost. In one embodiment the temperature of the compost, such as compost heap or compost windrow, is monitored, checked and/or controlled continuously, such as weekly, or more often, for example between six days, five days, four days, three days, two days, or even daily. Controlling refers to monitoring or measuring of the temperature and optionally, as a feedback, carrying out adjusting actions to change the temperature to a desired range or value. Such adjusting actions may comprise mixing or turning the compost, blowing air to the compost, such as hot air or cold air, covering the compost, uncovering the compost, heating the compost with a heating device, cooling the compost with a cooling device, adding new matter to the compost mixture etc. The desired temperature of the compost may be in the range of 30-70°C, such as 40-70°C, 50-70°C, 60-70°C or 65-70°C. Some composting may happen at the temperature around 30°C, but higher temperatures are preferred, such as at least 40°C, at least 50°C, at least 60°C, or at least 65°C, to speed up the process. In one embodiment the method comprises monitoring the temperature of the compost and adjusting the compost if temperature drops below 60°C, or below 65°C, for example by mixing, turning and/or heating. In one embodiment the method comprises monitoring the temperature of the compost and adding organic material to the compost if temperature is or it lowers below 60°C, or below 65°C, such as manure material and/or bedding material. The compost usually needs to be mixed when new material is added. This may be also necessary if the content of the surplus foundry sand is too high. In general, effective composting occurs at mesophilic stage at 20-40°C by mesophilic bacteria and at thermophilic stage at over 40°C by thermophilic bacteria. When temperature rises over 70°C most bacteria types die and composting begins to slow down. One effect provided at the high temperature is killing the pathogenic microbes and harmful plant seeds. In the process a sterilized material is obtained so the final product is hygienic and may be used in a variety of applications. It is also possible to provide additional heat, especially at the end of the composting process, to facilitate the sterilizing.

Also other process parameters beside the temperature may be controlled, monitored and/or adjusted during the process. Such parameters include initial ratios of carbon and nitrogen rich materials, amount of bulking agent added to assure air porosity, pile size, moisture content, pH, and turning frequency. In one embodiment the method comprises heating the compost. This may be carried out by using external heating means, such as a warm air blower, or the like. When air is blown through a heap or a windrow it may accelerate the composting process. Heat may be provided at the beginning of the composting or at the end of the composting as described herein, but also at any phase if it is necessary for obtaining optimal conditions. In one example the composting arrangement comprises one or more tubes conveyed below the compost heap or pile, the tube(s) connected to one or more warm air blower(s). Preferably such a heap or pile is uncovered. Providing heat may be important during wintertime, especially at the beginning of the composting, to start and accelerate the process.

A soil product is obtained from the compost or from the composting process described herein. The amount of the harmful organic matter in the original sand has decreased to a level which is far below the acceptable level provided in the law. Therefore the soil product may be used as a soil for example in gardens, landscaping, horticulture, and agriculture. It may also be used as a soil conditioner, a fertilizer, addition of vital humus or humic acids, and as a natural pesticide for soil. In ecosystems, the soil product may be used for erosion control, land and stream reclamation, wetland construction, and as landfill cover. The soil product may contain 1-90% of purified surplus foundry sand of the total weight of the product, for example 20-80% (w/w), or 20-60% (w/w), for example presented as dry weights.

The soil product obtained with the composting process described herein differs from a soil product obtained with other processes, such as from processes comprising combining sand with already composted material. As the sand used in the process is surplus foundry sand, the origin of the sand may be detected from the final soil product, for example by detecting the residual resin and phenolic compounds present in the sand. The sand may also contain trace amounts of metals from the foundry processes, wherein small amounts of metals may dissolve into foundry sand during casting at high temperatures.

Examples The first tests were made in Koukkujarvi (Tampere, Finland) during summer 2015. The place is solid waste management site with water tight bottom and waste water collection. Different types of surplus foundry sands have been analysed before composting. Sand is then added to different organic materials; hardwood chips from deciduous trees, horse manure and waste water sludge. The amount of sand was 21-34% in the composed six test heaps.

Six first test heaps were constructed as follows (amounts presented in wet masses):

1 a. Test heap of total weight 23.84 t

-green sand 22%

-waste water sludge 66%

-hardwood chips 5%

-horse manure 7%

2a. Test heap of total weight 23.64 t

-phenolic sand 22%

-waste water sludge 66%

-hardwood chips 4%

-horse manure 8%

3a. Test heap of total weight 24.76 t

-furan sand 21 %

-waste water sludge 69%

-hardwood chips 3%

-horse manure 7% 1 b. Test heap of total weight 24.34 t

-green sand 34%

-waste water sludge 57%

-hardwood chips 3%

-horse manure 6%

2b. Test heap of total weight 22.48 t

-phenolic sand 34%

-waste water sludge 56%

-hardwood chips 3%

-horse manure 6%

3b. Test heap of total weight 20.77 1

-furan sand 30%

-waste water sludge 61 %

-hardwood chips 4%

-horse manure 5%

Dry material percentages of the test heaps were determined for better comparison as follows:

1 a. Test heap of dry weight 9.8 t

-green sand 52%

-waste water sludge 37%

-hardwood chips 5%

-horse manure 6%

2a. Test heap of dry weight 9.8 t

-phenolic sand 53%

-waste water sludge 37%

-hardwood chips 4%

-horse manure 6%

3a. Test heap of dry weight 10.0 t

-furan sand 51 %

-waste water sludge 39%

-hardwood chips 4%

-horse manure 6% 1 b. Test heap of dry weight 12.1 t

-green sand 67%

-waste water sludge 26%

-hardwood chips 2%

-horse manure 4%

2b. Test heap of dry weight 1 1 .4 t

-phenolic sand 67%

-waste water sludge 25%

-hardwood chips 3%

-horse manure 5%

3b. Test heap of dry weight 9.8 t

-furan sand 63%

-waste water sludge 29%

-hardwood chips 4%

-horse manure 4% The temperatures development in different location of pilot heaps with green sand is shown in figure 1 .

Results of the composting tests Analyses were made from different composting fractions: 1 ) waste foundry sand specimens, 2) organic materials added to the test heaps, 3) mixed composting materials and 4) waste waters from the pilot field. Analyses were carried out in the beginning, during and in the end of the composting tests. The analyses included one or more of the following: pH, nutrients, fluoride, sulfate, chloride, heavy metals, humidity, pathogenies, hazardous organic compounds, organic matter, and compost maturity tests. Figures 1-9 show the results from the tests. pH

Composting progress can be followed by measuring nitrogen compounds and pH changes. In the beginning of the composting pH can reduce but it will rise again during the maturation of compost. There is no limit value for pH for non-hazardous inert waste. For comparison the limit value of pH of non-hazardous ordinary waste (pH >6) (331/2013) is marked to the pH diagrams (Figures 2 and 3).

In the green sand and phenolic sand samples the pH was 8-9 before mixing with other organic materials. pH was under 4 in furan sand sample.

In the beginning of composting tests pH lowered but in the end pH was about 6 in green and phenolic sand test heaps and little lower in furan sand heaps.

Dissolved organic carbon (DOC) Dissolved organic carbon (DOC) is a broad classification for organic molecules of varied origin and composition within aquatic systems. The limit value for non-hazardous inert waste is 500 mg/kg of dry material. Phenol and furan sand samples exceeded the limit value of DOC for non- hazardous inert waste slightly (Figures 5 and 6). In green sand sample there was no remarkable DOC concentration (Figure 4).

Waste water sludge had high concentrations of dissolved organic carbon, sulphate and phenols before mixing with other composting materials. However, in the end of the composting tests, these concentrations were under the limit values demonstrating successful composting process.

Fluoride concentrations were below the limit value for non-hazardous inert waste (10 mg/kg of dry material) in furan sand samples (Figure 9). Fluoride concentrations were high in green sand and phenolic sand samples gathered from these two foundries (Figure 7 and 8). Therefore also green sand and phenolic sand composting test heaps had higher fluoride concentrations in the beginning of the tests. The fluoride is most probably coming from the fluoride containing feeders used in the molds used in all sand systems. It is expected that less foundries use the fluoride containing feeders in the future. Substitute materials are available in the market already. During the tests fluoride concentrations were reduced below the limit values. It was assumed that fluoride was dissolved into the rest of the material (organic portion). In the beginning of the composting tests, phenol concentrations of phenolic sand samples were high. Extremely high phenol concentrations existed in waste water sludge sample.

Phenol concentrations were reduced during the tests. Phenol concentrations analysed from all test heaps were under the limit values (1 mg/kg of dry material) in the end of the composting tests (Figures 10-12). Some values (marked with asterisks ^* ) were even below detection limit.

Dissolved metals and total concentrations of metals

The concentrations of dissolved metals and total concentrations of metals in foundry sand type samples, waste water sludge sample and composting test heaps were under limit values set in the Finnish Decree of the Ministry of Agriculture and Forestry on Fertiliser Products 24/1 1 and Government Decree of landfills 331/2013 (limit values for inert solid waste). Table 2 shows the results. The units are mg/kg dm (dry material). Table 2. Water soluble metals in green sand, phenolic sand, furan sand and composting end-products (1 a and 1 b = green sand composting test heaps, 2a and 2b = phenolic sand composting test heaps, 3a and 3b = furan sand test heaps).

Water soluble Green Phenolic Furan 1 a 1 b 2a 2b 3a 3b Limit value Limit value for metals sand sand sand for non- non- hazardous hazardous inert waste ordinary waste

Aluminium (Al) 28 12 31 0.2 0.2 0.4 0.4 0.4 0.2 - -

Antimony (Sb) < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 0.06 0.07 L/S=10

Arsenic (As) 0.02 < 0.01 < 0.01 0.02 0.03 0.03 0.02 0.03 0.03 0.5 2 L/S=10

Barium (Ba) 0.01 0.02 0.26 0.1 0.06 0.12 0.04 0.18 0.07 20 100 L/S=10

Cadmium (Cd) <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 <0.008 <0.003 0.04 1 L/S=10

Chromium (Cr) <0.01 <0.01 0.13 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 0.5 10 L/S=10

Copper (Cu) <0.05 <0.05 <0.05 0.3 0.41 0.23 0.3 0.19 0.25 2 50 L/S=10

Lead (Pb) < 0.01 < 0.01 0.04 0.04 0.07 0.04 0.29 0.09 0.09 0.5 10 L/S=10

Molybdenum 0.09 0.08 < 0.01 0.04 0.04 0.05 0.04 0.03 0.06 0.5 10 (Mo) L/S=10 Nickel (Ni) <0.01 0.03 0.12 0.1 0.08 0.07 0.07 0.07 0.1 0.4 10 L/S=10

Iron (Fe) <0.1 3.2 76 1.2 1.2 1.4 2.2 1.5 3.3 - -

Selenium (Se) <0.01 <0.01 <0.01 0.08 <0.01 0.08 <0.01 <0.01 <0.01 0.1 0.5 L/S=10

Zink (Zn) <0.1 0.5 0.4 0.4 0.3 0.3 0.2 1 0.4 4 50 L/S=10

Mercury (Hg) <0.002 <0.002 <0.002 <0.002 <0.002 <0.002 <0.002 <0.002 <0.002 0.01 0.2 L/S=10

Table 3. Total metal concentrations in waste water sludge, green sand, phenolic sand, furan sand and composting end-products in six test heaps.

Also other parameters and compounds were analysed but almost all of the concentrations were under limit values set in the Decree of the Ministry of Agriculture and Forestry on Fertilizer Products 24/1 1 and Government Decree of landfills 331/2013 (limit values for inert solid waste). Only sulphate and total organic carbon (TOC) concentrations were higher than the limit values for non-hazardous inert waste, but there are no limit values for sulphate and TOC in compost product, so the concentrations do not cause any problems in utilizing the end-product in growing media purposes.

BTEX compounds were detected from the furan sand specimen in concentration that exceeded the limit value, but the BTEX compounds were degraded during the composting process. Table 4. Other hazardous compounds and TOC analysed from waste water sludge and foundry sand specimens. The values that exceed the limit values are bolded.

(n.c.= not

calculated)

(-= not

analyzed)

In certain examples compost windrows have the following composition (presented in wet masses):

4. Test windrow of total weight 43.95 t

-green sand 39%

-horse manure 30%

-hardwood chips 18%

-wood sticks 4%

-cow slurry 9%

5. Test windrow of total weight 53.5 t

-phenolic sand 39%

-horse manure 31 %

-hardwood chips 18%

-wood sticks 8%

-cow slurry 4%

6. Test windrow of total weight 50.3 t

-phenolic sand 38% -furan sand 22%

-horse manure 15%

-hardwood chips 10%

-wood sticks 8%

-cow slurry 7%

Dry material percentages of the test heaps were determined for better comparison as follows: 4. Test windrow of dry weight 25.8 t

-green sand 66%

-horse manure 18%

-hardwood chips 13%

-wood sticks 3%

-cow slurry 0.4%

5. Test windrow of dry weight 32.4 t

-phenolic sand 64%

-horse manure 18%

-hardwood chips 12%

-wood sticks 6%

-cow slurry 0.2%

6. Test windrow of dry weight 37.0 1

-phenolic sand 52%

-furan sand 30%

-horse manure 7%

-hardwood chips 6%

-wood sticks 5%

-cow slurry 0.3%

Heated air, temperature between 30-40°C, is blown through the test windrow 7 by holed tube. The holed tube is set under the windrow and covered by leafy three chips.

Test heap 1 is turned around and left to further compost over the winter. Temperatures of the test windrows are measured constantly. Example 7.

Phenol-furan sand compost heap Phenol and furan sands were combined. 600 kg of wood chips were placed below the heap. The composition of the heap was the following:

Furan sand 1 1 .2 t

Phenol sand 19.2 t

Wood chips 5.15 1

Wood sticks 3.85 t

Horse manure 7.4 t

Cow manure sludge 3.5 t

Total 50.3 1

The content of the phenol-furan sand mixture was 60.4%. The cow manure sludge was very dilute including washing waters from an animal shelter, containing approximately 10% solids. The wood sticks were substantially large wood pieces, in general having an average length in the range of 10-50 cm.

Especially the BTEX content of the furan sand was very high at the beginning, about 30 mg/kg. However, the BTEX content lowered quickly below the limit (6 mg/kg dm). All the final products from the composts fulfilled the limits concerning fertilizer products.

Example 8

Composts containing approximately 50% of surplus foundry sand and 50% of aged horse manure, and composts containing approximately 50% of surplus foundry sand and 50% of aged waste water sludge from sewage treatment of municipal wastewater were composted on June 16 to August 9, 2016. The temperatures of composts were continuously measured from the composts by using temperature sensors. The results are shown in Figures 13 and 14. It was noticed that the temperatures of the composts containing waste water sludge remained at approximately 40°C or below. On the other hand, the temperatures of the composts containing horse manure rose to approximately 60°C or above.