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Composting tests in Finland

Aim

Organic binders are almost exclusively synthetic resins which are cured by the addition of a separate hardener or catalyst. Inorganic binders are based on sodium silicates. Combinations of foundry sand with animal manure or other organic waste sludges will be made and the different material mixtures will be carefully studied and monitored to find out the most effective way of handling and cleaning the foundry waste sand by composting method. The process will be steered in a direction that useful humus occurs with good fertilizing abilities. The end-product must meet the national regulations and limit values set in the Decree of the Ministry of Agriculture and Forestry on Fertiliser Products (24/2011): Substrate – Mixture soil (5A2).

Composting field 1  Composting field 2
Pictures of the construction of the composting site.


Progress of the composting tests

Temperatures raised rapidly to almost 70 degrees after starting the composting tests (see the temperature curves). The temperatures were well above 60 degrees in the beginning and stayed for over 2 months from July – September. According to the decree of 24/11 the temperatures should stay over 55 degrees for 14 days. The results demonstrate efficient composting process.

Temperature of dust compost  Temperature of waste sand compost
Temperature curves of the dust compost heap (Compost heap 1) and the waste sand compost heap (Compost heap 2).


Composting materials were analysed in the beginning and end of each test period. Wastewater samples were collected in the beginning, middle and end of each test period.

Conclusions of the composting tests

In summer 2019 the composting tests were carried out with organic binder system (phenolic) waste sand and dusts. The “pure” foundry sand type in all cases is silica sand (quartz sand).

DOC concentrations of dust and waste sand samples were above the limit value of non-hazardous inert waste. Fluoride concentration was high in dust specimen and waste sand samples. The fluoride is 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 composting test fluoride concentrations were reduced below the limit values or close to it.


Fluoride concentration
Fluoride concentrations of organic dust and organic waste sand and the compost heaps' start and end situations.


Phenol concentrations of dust and waste sand exceeded the limit value before the composting test. In addition to the sand mould system phenols can also origin from the core production when produced by cold-box system. Phenols were degraded during the composting tests, so that in the end situation the concentrations were below the limit value.


Phenol concentration
Phenol concentrations of organic dust and organic waste sand and the compost heaps' start and end situations.


Dissolved molybdene
concentration in dust was above the limit value of non-hazardous inert waste, but the concentration in dust compost heap was below the limit value already in the beginning and end of the composting test.

Based on the results of the summer 2019-2020 composting tests, we can assume that the tests were successfully completed and the innovative composting end-product fulfilled the limit values set in the Decree of the Ministry of Agriculture and Forestry on Fertiliser Products 24/2011 and The EU Degree on Fertiliser Product (2019/1009) and the end-product can be re-used as substrate and for gardening and geo-construction purposes.

Degradation of the harmful substances during the composting tests demonstrate very good cleaning efficiency rates (see the table). The composting method can be considered as an effective cleaning method.


Degradation efficiency
The degradation of the harmful substances during the composting tests of organic dust compost and organic waste sand compost and the cleaning efficiency rates.


In summer 2020 composting test was carried out with inorganic binder system foundry waste sand. Based on the analyses results the inorganic binder system waste sand samples were very clean already without the composting treatment. The “waste” sand did not contain any organic or inorganic harmful compounds or metals. Based on the analyses results the inorganic binder system foundry sand could be re-used without any additional cleaning method e.g. in geo-engineering purposes as it fulfills the requirements of the Government Decree on the Recovery of Certain Wastes in Earth Construction 843/2017. It could also be mixed with other compost materials in the beginning or end of the composting process instead of virgin soil material that is needed in the compost end-product (mixture soil material).

Temperature of inorganic sand compost
Temperature curve of the inorganic sand compost heap (Compost heap 3).


The quality of waste waters of composting area was observed during the tests. Minor exceeding of phenol concentration (17 mg/kg) was observed in summer 2019 in the beginning of the tests and higher solid matter concentration in autumn 2020 due to the small amount of wastewaters in sampling dam when collecting the final samples.

Further informations

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