Contents

Project objectives and expected results
Actions
National regulations and limit values for composting material

B3 Successfully completed foundry sand composting tests in Finland in Summer 2015
Winter tests 2015-2016
Summer 2016 Composting Tests
Results of odor abatement of biofilter pilot plants

B2 Compost processing on laboratory scale

B4 Composting tests in Spain

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Project objectives and expected results 

The overall objective of the LIFE-Foundrysand project is to foster the green procurement, waste prevention and recycling by studying how different foundry sand types can be cleaned and hazardous organic trace contaminants eliminated through the innovative biological methods piloted in this project. 

The aim is to keep contaminated foundry waste sands away from landfills that in coming years have more and more limited capacity, and to establish and improve acceptance of this generally valuable cleaned and recycled soil material to be used for geo-engineering applications in the future. In Europe, around 18 M tons of foundry waste sand is left over every year and in many cases big landfills do not have enough capacity to deposit those large amounts of surplus foundry sand. In most countries several smaller landfills are being closed and replaced by large so called “EU landfills”, so the distances and transport costs to the landfills are also increasing for the foundry companies and alternative ways of treating those wastes in a more environmental friendly way have to be found. 

There is a future vision of this sustainable composting system (or service) that can be transferred to the areas where several foundries operate in the same region to clean the surplus foundry sand for re-use purposes. There are about 3000 sand foundries in Europe – estimated 200 of them could apply this new method by 2020 and 1000 in Europe by 2025.

The main idea is to study the quality target of the piloted foundry sand specimens to fulfil the product requirements for re-using the cleaned sand as substitute ground construction materials or other geo-engineering applications.

Specific objectives are to:

• Develop a new method for cleaning and re-using foundry sand through composting;
• Produce guides on practical level for foundries and suppliers of the cleaning service in Europe;
• Implement the procedure for foundries to minimize their wastes, for reducing the operational costs for foundries and therefore saving energy;
• Keep away contaminated materials from landfills;
• Improve acceptance of this valuable material (the cleaned foundry sand) for agricultural and geo-engineering applications, especially in areas of low humus content in soils this can be a valuable exercise to create soil as an artificial layer in order to improve fertility, and to substitute synthetic fertilizers;
• Transfer this sustainable method to other regions in Europe where over 4000 sand foundries are operating and foundry sand can be cleaned and re-used.

Quantitative results and outputs of the project:

• Through piloting in 2015-2017 around 500-600 tons of surplus foundry sand will be cleaned with the innovative composting method;
• The hazardous organic compounds (like phenol index, PAHs) are to be cleaned with the efficiency of about 95%. The final composted product has to meet the national requirements;
• Construction recommendations of composters for cleaning the foundry sand by composting;
• Manual for surplus foundry sand quality control in foundries in general
  
   

Actions
 

The main actions may be characterized as follows:

• Two pilot plants for composting foundry waste sand will be established (Finland/Spain).
• In total of 17 small-scale test trials will be carried out in Finland with different foundry sand types (furan/phenol/green sand).
• In total of 12 test trials will be carried out in Spain.
• To overcome the slowness of composting processes in cold climate and to find solutions to accelerate the process, lab-scale parallel investigations will be carried out by Helsinki University, Finland.
• Also the affect of the climate conditions in composting method will be studied in winter time test trials.
• Different foundry sand types (furan, phenol and green sand) will be tested.

Within these pilot plants a set of different materials will be studied. In composting, combinations of foundry sand with different organic materials will be made and the different material portions will be carefully studied and monitored to find out the most effective way of handling and cleaning the waste sand. The process will be steered in a direction that useful humus occurs with good fertilizing abilities.

• The progress of the composting process will be controlled by continuously measurable indicators. Doing so, suitable control parameters for the process will be established.
• Air emissions, odours and effluents from test heaps will be measured and defined and based on the results the modelling of the total impacts to environment will be carried out. 
• Small-scale biofiltration system will be tested in odour abatement of the composting test heaps.

National regulations and limit values for composting material

Following regulations and limit values of waste foundry sand must be fulfilled in order to re-use foundry sand in ground construction or gardening purposes in Finland:

1) The Finnish regulations of waste foundry sand as according to the Government Decree of landfills (331/2013): Foundry sand must fulfill the limit values set for the solid waste. “Waste material may not endanger surface or ground water quality and may not react or no harmful substances can dissolve from it.”

2) The Government Decree (591/2006, changes 403/2009, MARA-asetus) concerning the recovery of certain wastes in earth construction. The revision phase is in progress and new materials like waste foundry sand are expected to be included in the list of potential materials.

Following regulation and limit values of the composting end-product must be fulfilled in order to use the new end-product as the growing medium.

3) Regulations and limit values set for the composted end-product are set in the Decree of the Ministry of Agriculture and Forestry on Fertiliser Products (24/2011): Substrate – Mixture soil (5A2). This regulation sets limit values and demands for heavy metals of the endproduct, pathogens (Salmonella and E. coli) and impurities (weeds, garbage). Also there is a following demand in this regulation:

“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”.


Limit values:






 

The limit values of the Decree of the Ministry of Agriculture and Forestry on Fertiliser Products 24/2011 are compared with the results of the new composting end-product (re-used foundry sand).

Limit values and waste foundry sand applications in other European countries are studied as well.

Successfully completed foundry sand composting tests in Finland in summer 2015

LIFE Foundry Sand composting tests

The environmental permit for composting tests at Koukkujärvi solid waste management site, Nokia, was received on 18th of June 2015 from the Regional State Administrative Agency, Vaasa. Tests were ended on 30th of September 2016.

Six test heaps were constructed at Koukkujärvi pilot site. Test heaps were made in cooperation with project partners, Meehanite Technology Ltd and Tampere Regional Solid Waste Management Ltd (Pirkanmaan Jätehuolto Oy). AX-LVI Consulting Ltd was responsible for the sampling procedure and airborne emission and waste water effluent measurements. Chemical and biological analyses were carried out by Eurofins Viljavuuspalvelu Ltd.

The size of the each test heap was about 20 tons. The most commonly used foundry sand types like furan, phenolic and green sand specimens were used in composting tests. Other organic materials were added in the test heaps. Six test heaps were constructed as follows:




Composting site in Koukkujärvi.


The progress of the composting tests was monitored regularly (temperature, pH). First composting tests in summer 2015 were carried out between June-November. Composting material analyses were made in the beginning, during and in the end of the tests. Also waste water effluents and airborne emissions were measured.



Emission measurements on one of the test heaps.



Sampling procedure from the composting test heap.




Mixing the test heap during the tests.

After three months (in the middle of the test period) the test heaps were mixed and new analyzes and measurements were carried out.



Test heap in the end of the composting test.

Final measurements and sampling procedure of the composting materials were made by AX in November 2015 (after 4 months period test start).
 

Results from the composting end-product at the end of the tests
 

Analyses were made from different composting fractions: 1) waste foundry sand specimen, 2) organic materials added to the test heaps, 3) mixed composting materials and 4) waste waters discharged from pilot field. Analyses were carried out in the beginning, during and in the end of the composting tests:
 - pH, nutrients, fluoride, sulphate, chloride, heavy metals, humidity, pathogenes, hazardous organic compounds, organic matter, and compost maturity test.

pH level in non-hazardous normal waste must be 6 or higher (according GD 331/2013). In the green sand and phenol sand samples the pH was higher than 6. pH of furan sand was lower..

Fluoride concentrations were high in the green sand and phenol sand samples before the composting tests. Therefore also green sand and phenol 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. 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). This will be studied in the balance calculations.

In the beginning of the tests, phenol concentrations were high in phenol sand samples and in organic material samples. Phenol concentrations were reduced during the tests. All phenol concentrations analyzed from the test heaps were under the limit values in the end of the composting tests.

Also other parameters and compounds were analysed but the concentrations were under limit values set in the Decree of the Ministry of Agriculture and Forestry on Fertiliser Products 24/11 and Government Decree of landfills 331/2013 (limit values for inert solid waste).

In other organic material used in the test heaps, there was high phenol, sulfate, and dissolved organic carbon (DOC). In the end of the composting tests, these concentrations were under the limit values demonstrating the successful composting method.

The final waste water samples are not yet analyzed but based on the results received at the beginning and during the tests it is not expected to have remarkable concentrations in the end of the tests either.

Based on the results of the summer 2015 composting tests, we can assume that the tests were successfully completed and the innovative  composting end-product will fulfill the limit values set in the Decree of the Ministry of Agriculture and Forestry on Fertiliser Products 24/2011 and the end-product can be used as substrate and for gardening purposes.

Results were presented and discussed in the project meeting arranged on 25.11.2015 in Tampere and it was decided that the tests can be shut down and the composting end-product can be moved for the post composting in Koukkujärvi site.

Additionally, the results of the waste water samples from the beginning and middle period of the compost test were delivered to the authorities and to the waste water treatment plant, Nokian Vesi Oy. There were no exceptional results or high concentrations and therefore no remark was made.

Emission measurement results
 

The first emission measurements were made while starting the composting tests in June 2015.

Temperature, pH of test heaps and waste waters and weather station data were regularly measured.

Temperatures of test heaps started to rise rapidly right after building the test heaps. Based on the first measurement results, there were high concentrations of ammonia, carbon monoxide, formaldehyde, benzene and odours. In the middle of the tests, emissions were reduced greatly compared to the results in the beginning. In the final emission measurements, carried out in November, most of the emissions were under the detection limits. Methane and carbon monoxide were measured which demonstrated that the composting was not completed yet and the post-composting is still needed for couple of months, even though the concentrations were already now below the limit values. 

Odours existed mainly in the beginning of the composting tests and while construction work. Odour emissions were reduced remarkably during the tests. Occasional odours existed while mixing the test heaps but these can be considered minor. During the final measurements only small odour amounts were detected.
 

Winter tests 2015-2016

Winter tests started in the beginning of December 2015 and the tests ended in June 2016. Three test heaps were constructed of green sand, phenol sand, and a mixture of different foundry sand types. The heaps were larger than summer 2015 test heaps to avoid them cooling down in winter frost.



Two of the winter composting test heaps on the construction day in December 2015.



Winter composting tests in January 2016.

Results of composting tests in winter 2015-2016

Three composting test heaps were constructed for winter test period from December 2015 to June 2016. Furan, phenolic and green sand specimens were tested. The heaps were bigger compared to the summer test heaps to avoid the cooling down.

Based on the analyse results of surplus foundry sand specimens no remarkably high concentrations of harmful compounds were detected before starting the composting tests. Many of the compounds were under the limit values set for the non-hazardous inert waste of the Government Decree of landfills (331/2013).
 

Fluoride concentrations were above the limit value in the green and phenolic sand specimens. Fluoride limit value for inert waste is 10 mg/kg dm. In the end of the composting tests the fluoride concentrations were under the limit value in each test heap.

The phenol concentrations were under the limit value for inert waste of 1 mg/kg in all surplus foundry sand specimens. 

The higher BTEX compounds concentration was detected in the furan sand specimen. The BTEX compound limit value for inert waste is 6 mg/kg. BTEX compounds were degraded during the composting process. 

There were high chloride concentrations above the limit values of 800 mg/kg in each test heap in the beginning of the composting tests. Chloride was not detected in the surplus foundry sand specimens. During the composting process the chlorides were degraded being under the limit value in all composting test heaps in the end of composting tests.

Waste waters of the pilot site were led in one sampling basin and analysed in the beginning, middle and end of the winter tests. There were no high concentrations of harmful substances in waste waters during the tests.

The microbiological parameters were under the limit values (Salmonella, E. coli). Even if the composting end-products were cleaned from harmful substances, it is not yet ready to be used as a growing media. The post-maturing period (about 12 months) is always needed.

Based on the results the winter tests were successfully carried out and the harmful organic compounds were degraded. The composting end-products fulfilled the limit values for the mixture soil according to the Decree of the Ministry of Agriculture and Forestry on Fertiliser Products 24/2011 and the end-product can be used as substrate and for gardening purposes after the post-maturing time. 

After the composting tests the cleaned foundry sand composting material was transported to other site at Koukkujärvi area for landfilling purposes.

All samples were collected in the beginning, middle and end of each test period. Analyses were made from foundry sand specimens, mixed composting materials and waste waters. Sampling procedures were carried out by Meehanite and AX personnel and samples were delivered to accredited laboratory, Eurofins Viljavuuspalvelu, for analyses.

Summer 2016 composting tests

The summer 2016 composting tests started in May 2016. In total 9 test heaps were constructed. Phenolic, furan, cement and green sand specimens were tested.


The Summer 2016 composting tests consist of nine test heaps and a meadow field test. The odour abatement of compost heaps is tested with biofilters.

The nine composting test heaps in Summer 2016 consist of different foundry sand types (green sand, phenolic sand, furan sand and concrete sand), organic materials.

The odour abatement of compost heaps is tested with biofilters. Odour and emission measurements were carried out at test the test site in August 2016.



The hooded composting test heaps for the emission measurements in August 2016.


The biofilters at the composting test site in August 2016.
 

Test results of summer 2016 test period

In summer 2016 green, phenolic, furan and cement foundry sand specimens were tested.

Sampling procedure from each composting test heap was made in the beginning, middle and end of the test period. Also waste waters were collected and analysed.

In all three test periods in 2015-2016 the pH values of the green sand and phenolic sand specimens were an average 7-8. Furan sand is more acid (pH 3) because different kinds of acids are used as hardeners of the sand mould resins in the furan sand system. During the composting tests the pH increased and in composting end-products the pH was an average 6 in all test heaps.

Also in summer 2016, low concentrations of harmful substances were detected in surplus foundry sand specimens. Foundry sands were delivered also from new pilot foundries to get different kinds of surplus sand qualities for tests. 

Some fluoride concentrations in green sand and cement sand specimens exceeded the limit value of 10 mg/kg. During the tests fluoride was degraded and it was under the limit value in the end of the composting tests.

High BTEX compounds concentration was measured in one furan sand specimen in the beginning of the test. Also in previous tests, there where high BTEX concentrations in furan sand specimens, exceeding the limit value of 6 mg/kg. In the end of the composting tests the BTEX concentrations were under the limit value.

Phenol concentrations were under the limit value in all foundry sand specimens and also in the composting end-products.

During the tests the waste waters of the pilot site were collected and analysed. There were no high concentrations of harmful compounds in waste waters.

The summer tests in 2016 were carried out successfully and all composting end-products fulfilled the limit values set in the Decree of the Ministry of Agriculture and Forestry on Fertiliser Products (24/2011) for mixture soil used as a substrate.

After the composting tests, the cleaned foundry sand composting materials were used in landfilling purposes at Koukkujärvi site.

As a conclusion all surplus foundry sand specimens tested in this project were cleaned from harmful organic substances. The results are most promising for the re-use of surplus foundry sands in other green engineering applications and to foster the green procurement between foundry industry and waste treatment industry. Cleaning the surplus foundry sands by the composting method is very cost-effective and it also reduces the need of virgin sand that is mixed with the composting and soil material products. 

Results of odor abatement of biofilter pilot plants

To reduce the odours emitted from the composting process, the efficiency of the biofiltration system was tested during the composting tests. Meehanite built two small-scale biofiltration pilot plants. The cleaning efficiency of biofilters was measured in summer 2016. Odour abatement measurements were carried out by AX Consulting according to the EN 13725:2003 (Air quality. Determination of odour concentration by dynamic olfactometry).

Biofilters fit to all waste gas cleaning purposes involving air pollutants that are readily biodegradable. Biodegradation of the pollutants is accomplished by micro-organisms living in solid support media. Typical support media are chopped wood and wood bark, composts or other organics. All materials are normally arranged as packed beds through which the waste gas flows. As the waste gas passes through the bed of media, the pollutants are sorbed onto the surface of the filter media where they are degraded by micro-organisms.  

Odour abatement measurement of two biofilter abatement pilot plants.

Biofilters odour abatement measurements were carried out twice in summer 2016. First measurement was carried out after two months in the middle of the tests when there were minimal amount of odours left in the test heaps. The second odor abatement measurement was carried out with a “fresh” and new test heap. So the results present a situation in the beginning of the composting process. The odour reductions of the two biofilters were calculated to be about 85-95%. Slight differences were detected between the two biofilters due to the different organic materials used in the biofilters.

Table 1. Odour measurement results of biofilters in 30.9.2016 (a fresh heap)

The odour abatement results demonstrate good odour abatement efficiency. The odour reduction by biofiltration system can be recommended, especially after construction of the composting heaps. After couple of weeks, no heavy odours will be emitted anymore.

Compost processing on laboratory scale
 

University of Helsinki (UH) is focusing on a short-term laboratory scale composting test using the same sand specimens that will be used in B3 (Composting in Finland). These controlled small scale indoor experiments were complemented by outdoor experiments at Jokimaa test field in Lahti in order to achieve information regarding to 1) compost construction including organic material, 2) time zero chemical status of compost and different foundry sand types tested (furan/phenol/green sand) for comparative purposes and 3) understanding the composting process and it’s limitations in a small scale operational level vs. the test heaps of bigger size.




Construction of compost pile in Jokimaa ground research station.

A relatively small, ca. 5 m3 compost pile (length 4.2 m x width 1.5 m x maximum height 0.8 m) was constructed to Jokimaa ground research station by UH technical staff using mixture of organic materials (Fig. 1 and 2). The pile was used as a platform for the 6 treatments with three different foundry sand types (furan, phenolic and green sand specimens). Each treatment compost consists of either 25 or 50 % of sand and 50 or 75 % of organic material mixture, respectively. Two replicates with a volume of 10 L were used for each treatment. Dig and drop method was applied and composting sand material was placed in a bucket size holes in the compost pile (Fig. 2 and 3). Temperature of each treatment system and the whole pile were continuously monitored by data loggers (Fig. 3) from 10th April to 22th April, 2015.





Small-scale outdoor compost treatment set-up for three foundry sand type in the Jokimaa ground research station.

Automatic temperature monitoring unit in action (Jokimaa) for recording temperature of the compost pile and different foundry sand composting tests.

 
A laboratory-scale composting testing, using green, phenolic and furan sands plus their mixture (Foundry 50%), was performed at the Department of Environmental Sciences, Lahti. Before that, on 30th June, 2015 four Biolan composters (Model 220eco ) were filled in Tampere with the compost material from the test heaps constructed at Koukkujärvi pilot site in June 2015. The portions of surplus foundry sand varied in test heaps between 20-33%.  Other organic materials like  were added in the test heaps. Composters were transported from Tampere to Lahti where composting process were followed over period of 8 week. The samples from each composter (400 g in triplicate) for the chemical analyses were taken in days 0, 14, 28, 40 and 49 during the relatively short composting period.




The composters (Biolan 220eco) at the beginning of the composting test in Lahti.

Results of the composting tests

Analyses consist of temperature monitoring of small scale outdoor and indoor composting tests either by 3 or 4 foundry sand specimens, chemical analyses of foundry sand specimens and mixed composting materials carried out in the beginning, middle, and in the end of the composting tests. Both total and soluble concentrations were reported, if available.

Temperature

Temperature of composting pile remained relatively low in the Jokimaa outdoor tests during the short term composting period between 11th April and 22nd April 2015. However, maximum pile temperature of 45 °C was almost twice as high as in the most of foundry sand tests (Fig. 5.). The result reflect both low outdoor temperature and small compost pile size. In the laboratory composting tests under controlled room temperature equal time-related temperature pattern was observed and the compost temperature never exceeded 50 °C during composting process of eight week (Fig. 6).




Temperature changes in the outdoor test compost (Jokimaa, April 2015) including either 25 or 50 % phenolic, furan and green foundry sand specimens in duplicate treatments.

Temperature changes in the small-scale laboratory compost testing with four foundry sand specimens (Department of environmental sciences, Lahti, July-August 2015). Valimo50 % = mixture of three foundry sand specimens, Tuore= green foundry sand, Fenoli= Phenolic foundry sand, Furaani= furan foundry sand.

Quality of foundry sand specimens

Foundry sand specimens have major differences in their chemical characteristics. Furan sand had the lowest pH and the highest DOC concentration (Table 1). Phenolic sand had logically the highest phenol index but also high fluoride concentration. The green sand had the highest metal concentrations, and also relatively high BTEX level. The concentration of the ionic forms of metals were low in all foundry sand specimens.


Table 2. Major chemical properties of three foundry sand specimens



Fate of the PAH compounds in the composting tests

The total concentrations of polyaromatic hydrocarbons were decreased during every foundry sand compost test (Fig. 7). The results also showed that concentration of the naphthalene was the highest among the 16 PAH compounds analyzed, followed by phenanthrene, anthracene and fluorene.

Logically the highest total PAH concentrations were found from the foundry sand mixture. Interestingly quantity of different PAH compounds in green sand, phenolic sand and furan sand composts were almost identical.




Total concentrations of PAH compounds during eight weeks composting test for 4 foundry sand type. Va50= mixture of three foundry sand specimens, Furaani= furan, Fenoli= phenol, Tuore= green sand. Alku= day 0, keski= day 20, loppu= day 49

Concentrations of chloride, fluoride, sulphates and phenol index in the short term laboratory composting tests

Concentration of chloride and sulphates were the highest in furan sand (Table 2). Phenolic sand has the highest phenol index but opposite to sand only situation phenol index was measurable also from all foundry sand specimens’ compost tests. Fluoride was found only from 1) the mixture compost and 2) green sand. The concentrations of sulphates. Phenol concentration was clearly reduced during the tests. On the other hand concentration changes of other parameters did not have any logical patterns during the tests excluding chloride in green sand composting test.


Table 3. Concentrations of chloride, fluoride, sulphates and phenol index in four foundry sand compost tests.

 

Conclusions

In terms of experimental compost construction laboratory-scale was a challenging starting point especially in Jokimaa outdoor experiments. However, it helped to understand the composting process and it’s limitations compared the test heaps of bigger size in Tampere experiments. Size truly matters also in composting. Similarly indoor small-scale composting experiments at the Department of environmental sciences were only partly successful. However, concentrations of PAH compounds, fluoride and phenol index decreased during the composting process. Results also indicated that waste water sludge used in the composting had high concentrations of dissolved organic carbon (DOC), sulphate and phenols before mixing with other composting materials. And opposite to Koukkujärvi experiments, in the end of the composting tests, these concentrations were partly over the limit values demonstrating unsuccessful composting process. End concentrations of fluoride and presence of pathogen E. coli (>1000 cpu/g was exceeded only in one treatment) were another negative indicators.

Composting tests in Spain 2015-2017

The location of the composting tests required a site with the appropriate environmental permit already in place. The pilot site located in Composgune, S.L in the centre of the Basque Country, Ormaiztegi, northern Spain, 50 km from the Cantabrian Sea. The size of the heaps was restricted to those stipulated in the permit terms and conditions obtained by Composgune, S.L. from the Basque authority.

In order to evaluate scope, different sand mixes including green sand, phenol sand, silicate sand and furan sand were trialed in Spain. Different foundry waste sands were mixed with different organic materials and suitable recipes were tested during 2015-2017. By the end of the project in total of 8 composting test heaps were constructed and tested in Spain. The total amount of cleaned surplus foundry sand composting material was 304 tons.

Regulations in Spain:

In Spain the compost end-product must fulfil the limit values set in the Royal Decree 506/2013 on fertilizers, Royal Decree 1039/2012 and Government Instruction PRA/1943/2016 on growing substrates.

First tests started in September 2015 following a fact-finding visit to the Finnish pilot site in June 2015. Using their set-up as a reference for like-for-like comparison but in different climate and with different foundry sand types.

Monitoring visit by Meehanite personnel in Spain in 2015.

The weight of the test heaps was approx.13 tons and the proportion of surplus foundry sand was about 18%. Mixes of the most commonly used foundry sand types such as green sand and silica sand specimens were used in composting tests.

The composting process was monitored through the continuous measurement of temperature and pH. Analysis of the composting material in each heap was carried out at the beginning, in the middle and at the end of the experiment. Waste water seeping from the heaps (from both natural rainfall and simulated rainfall added to compensate for the below average rainfall during the trial) was channeled to a deposit for analysis. These measurements were carried out in phases one and two, and again in two and three. Airborne emissions were measured during stage three when these were expected to be at their height. Temperature monitoring was carried out using two thermocouples in each heap.

Results of summer 2015-spring 2016 composting tests:

Fluoride concentrations were high in green sand and they origin from fluoride containing feeders during casting. This is higher in green sand (iron casting) due to the higher absorption capacity. It is expected that fewer foundries will use the fluoride containing feeders in the future as substitute feeder systems are coming onto the market. However, fluoride concentrations reduced to level below the limit values in both foundry sand types by the end of the process. It was assumed that the fluoride was transformed and dissipated by the organic material.

Water seeping from the heaps had high concentrations of DOC, sulphate and phenols in the beginning. However, at the end of the composting tests these concentrations were under the limit values. In addition airborne emissions of the green sand test heap were measured during the three stages of composting test period. The aim was to evaluate the total environmental impact of the composting test.

In order to aerate the heaps and facilitate composting, the heaps were turned-over approx. every two weeks. We found that carbon dioxide (CO2) was formed due to the active degradation of microbes during composting. Oxygen consumption remained stable at over 20% throughout the process. Methane (CH4) emissions in the beginning were higher than in the middle and disappear in the end of the test period.

Based on the results of the autumn 2015-summer 2016 composting tests, the experiment was successful with the limit values set out for growing media according to the Royal Decree 506/2013 on fertilizers, Royal Decree 1039/2012 and Government Instruction PRA/1943/2016 on growing substrates. The results demonstrate that hazardous organic compounds such as phenols and PAHs were reduced by 97%.

Results of summer 2016 composting tests:

In summer 2016 two phenolic surplus sand test heaps were piled up. The proportion of waste foundry sand was 15%.

Summer 2016 test heap.

In general, concentrations of soluble, heavy metals and hazardous components in the phenolic waste sand as well as the composting material were under the stipulated limit values for end products according to the legislation on waste disposal to landfill, fertilizers and substrates. So these foundry sand specimens fit well to be cleaned by composting method.

Hazardous components were degraded sufficiently during the composting process. In the beginning of the composting test, chloride and fluoride concentrations showed high values but at the end of the test, these values fall within the limit values. No remarkable fluoride concentrations were detected in waste water samples analysed during test.

In case of phenol, this also exceeded the required values for inert solid waste but it has to be considered that phenolic compounds origin from cores produced by the Cold box method. Moreover, at the end of the composting tests, these concentrations were under the limit values demonstrating successful composting process.

DOC (Dissolved Organic Carbon) and TOC (Total Organic Carbon) concentrations were higher than limit values due to the nature of the materials. Likewise this also happened in the case of BOD (Biological Oxygen Demand) and COD (Chemical Oxygen Demand) in waste water seeping from the heaps, related to each other and originated from materials used in the composting process

Compost end-product from phenolic waste sand, despite containing higher concentrations of fluorides, chlorides, sulphates and phenol at the start of the composting process, showed similar results as end compost material from green waste sand developed in autumn 2015-2016. The level of soluble and heavy metals required according to the legislation was under the limit value in both types of sands. Likewise both phenolic waste sand samples and green waste sand samples contained BTEXs and PAHs far under the limit established. Therefore, the trials showed that the composting of phenolic waste foundry sand is potentially an effective way of recycling this industrial by-product.

As a conclusion it is very important to know the origin of the sand: steel foundry, iron foundry, etc. Depending on this we can obtain relevant and different results.

Results of summer 2017 composting tests:

For this test four heaps from silicate waste sand were piled up in the pilot site. The proportion of waste foundry sand in the four heaps was 15%.

Silicate sand is an inorganic binder system used in steel foundries.

Summer 2017 test heaps.

Due to nature of silicate moulding process, in general, the concentrations of soluble, heavy metals and hazardous components in the silicate waste sand were under the stipulated limit values. This was also the case in the compost end-products where the concentrations were very low according to the legislation of inert waste to landfills and fertilizers. One exception was with nickel. In the end of the composting tests, the total nickel concentration was slightly exceeded (limit value of 100 mg/kg dm) in one test heap. Nickel is commonly used in stainless steel production.

All concentrations for soluble metals were below the limit value set for the inert waste. Only DOC concentrations slightly exceeded the limit value of inert waste (500 mg/kg dm).

Silicate sand pH was 11.1 due to the moulding process. This level is a basic character of the olivine sand. There is no limit value for pH set in the inert waste. In the end-products the pH was about 7.

The composting trials demonstrated that the composting of foundry surplus silicate sand is one of the most potentially effective ways of recycling this industrial by-product and to generate a new compost material for geoengineering purposes.

Based on the results over the test period of three years (from the autumn 2015 to autumn 2017), we can say that the tests were successfully completed and the innovative composting end-product will comply with the limit values set in the Decree of the Ministry of Agriculture and Forestry on fertilizers in Spain and thus the end-product can be used for gardening purposes after the post-maturing time.

The experiments carried out demonstrated that the proposed method is a viable way to recycle waste foundry sand in different climate conditions.

Conclusions

Based on the results, the composting method can be recommended as a cleaning method when high concentrations of harmful organic substances are present in surplus foundry sands. Composting method is not suitable for all surplus foundry sand specimens as written in the project proposal. Surplus foundry sands and dusts which include heavy metals can not be degraded by composting method. All surplus foundry sands and dust specimens must be always carefully analysed in forehand and based on the results suitable treatment methods will be presented. But the aim is that majority of all the surplus foundry sands could be cleaned by composting method because it is a very efficient and cost-effective method. Other treatment methods such as a stabilisation or incineration can be recommended for certain specimens. This would both cost-efficient and save space on deposits.

Based on the project test results, only some harmful organic substances exceeded the inert waste limit values (Decree of landfills 331/2013) in the surplus foundry sand specimens e.g. phenols, fluoride and BTEX. With some foundry sand types DOC and TOC concentrations exceeded the limit values of inert waste but the Fertiliser Products Decree (24/2011) has no limit values for organic compounds for the compost end-product when it is reused as growing substrate. Also other harmful substances were measured from the waste sands and composting materials during the project. No high concentrations of PAHs but no high were met. PAH compounds are carsinogenic. The existing PAHs were degraded during the composting tests (not soluable).

Emission measurements from the test heap were carried out in the beginning, middle and end of the composting process. Exhaust gas concentrations were very low. Some sulphur compounds, like ammonia, occurred. Odour limit value of ammonia is very low (~ 0,1 mg/m³). Also VOC emissions were measured but they were very low (under 10 ppm). Because VOCs are volatile they are partly reduced already at the foundry “back yards” while waiting for transportation. Foundrysand project results demonstrated that airborne emissions were formed only during the first weeks after constructing the composting test heaps and then reduced radically. In the project biofiltration pilot plants were tested and the results demonstrated odour reduction of 85-95%.The odor reduction can be recommended in the beginning and while mixing the composting heaps.

The composting process will be carried out on a site with a proper asphalt surface and waste waters treatment system is regulated according to national environment permit and environmental impacts are monitored regularly. In the future the composting companies could replace the use of virgin sand by cleaned surplus foundry sands to be added in their compost end–products. Based on the project environmental impact assessment no high concentrations of harmful substances were measured from the waste sands, test heaps, waste waters or air emissions. As presented in the construction recommendations the composting heaps could be also covered to avoid waste waters or even odours from the composting heaps. When the heaps are placed in a hall or covered by a tarpaulin, the emissions can be reduced and treated e.g. by biofiltration system.

The analyse results demonstrated that the surplus foundry sand specimens used in the project contained only low concentrations of harmful organic substances before starting the composting method and the concentrations were reduced during the composting process effectively. In case the concentrations are low already in the beginning of the composting process it would not be cost-effective to treat the foundry sands by other energy intensive way such as thermal incineration. In Foundrysand project the degradation of harmful organic substances were monitored in the beginning, middle and end of the tests. The end-products fulfilled the limit values set for the mixture soil material (Fertilizers product 24/11) which can be reused in geoengineering applications.

Published on 5.4.2017