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Substance Flow Analysis for Dioxin 2002

5 Formation and turnover by waste treatment and disposal activities

5.1 Metal scrap

5.1.1 Reclamation of cable scrap

Reclamation of cable scrap in Denmark concerns reclamation of electrical cables with lead sheath used for power supply or communication purposes buried in the ground or at the sea bottom. The cables typically consist of solid copper conductors separated by oil-saturated paper surrounded by a solid and impermeable lead sheath wrapped in tar-impregnated textile and finally covered by a thin flexible ring of steel. One reclamation plant for such cables has existed in Denmark until 2002. The company have from 2002 chosen to shot down the reclamation of cable scrap and will in the future only deal with transformer waste. The annual emission in next section will therefore only be valid for 2000-2001.

By the reclamation process the lead sheath is melted away at 500 - 600°C. The air stream that has a high content of soot is afterwards treated in an afterburner at 875°C with a minimum of 6% O₂ for 2 seconds. Via a heat exchanger the air stream is finally led through a bag filter with an inside layer of lime. The temperature around the bag filter is approx. 100°C.

The reclamation plant is also receiving and separating old transformers, which will be the main future activity. The oil is tapped of and burned as fuel. However, this only applies for oil with less than 50 ppm of PCB. In those cases - happens very seldom - in which the oil contains 50 ppm of PCB or more, the transformers are directed to the central Danish facility for hazardous waste (Kommunekemi - reference is made to section 5.2).

Danish cable scrap not treated at this plant is believed to be exported for reclamation in India or the Far East. Illegal cable burning, if any, is believed to be insignificant. However, a separate plant exists for reclamation of modern PEX-coated cables that is separated by purely mechanical processes. Other cables may be treated as mixed metallic waste for shredding (section 5.1.2) or as municipal solid waste directed to incineration (section 5.3.1).

Plant activity

Based on information from the company, the activity of the plant in the periode 2000 - 2001 can be summarised as follows:

Filter dust is sent to the central Danish facility for hazardous waste (Kommunekemi).

Dioxin formation and disposal

The dioxin emission to air has been measured once during reclamation of a mixture of scrap and transformer waste. This measurement was undertaken in December 2000 and showed a dioxin emission of 0.08 ng I-TEQ/Nm³. Taking the result of this measurement as the level of dioxin emission from cable reclamation the total annual emission is estimated to be within the range of 0.03 - 0.2 mg I-TEQ/year. This interval includes an uncertainty of ± factor 3 (reference is made to section 1.5).

In SFA 2000 /Hansen, 2000/ the total emission to air was estimated to be 0.005 - 5 g I-TEQ/year based on international experience.

5.1.2 Shredder plants

6 shredder plants for treatment of cars, white goods and mixed metallic scrap exist in Denmark. In a shredder plant the waste is torn to pieces by large rotating steel hammers. The temperature of the hammers and other parts of the shredder may rise to 600-800 C due to friction, and part of the organic materials present (e.g. as paint and plastics) may actually be burnt away. Air emission from shredders is typically cleaned by scrubbers.

Activity

Approx. 700.000 tonnes yearly of metal scrap was treated by the Danish shredders in the middle of the nineties (H. Dalgaard, Danish EPA quoted by /Jensen 1997/). The figure is believed still to be valid.

Dioxin formation and disposal

One of the Danish shredder plants has made measurements of the dioxin emission from the production air flow in 2000 and 2001. The results of the two measurements show a total dioxin emission within the range of 1 - 15.4 mg I-TEQ/year.

A measurement of dioxin air emission from a second Danish shredder was made in 1999. The annual emission based on this measurement is approximately 0.5 - 4.3 mg I-TEQ/year, assuming an uncertainty of ± factor 3 /Fyns Amt 2000/.

The measurements from the Danish shredder plants correspond to air emission factors in the range of 0.01 - 0.09 µg I-TEQ/ton scrap manufactured. The European Dioxin Inventory (section on Germany) states values for dioxin emission to air of 0.06 - 0.67 g I-TEQ/ton scrap /Landesumweltamt Nordrhein-Westfalen 1997/.

Adopting the three Danish measurement as valid to all Danish plants the total emission from shredder plants in Denmark the emission level can be estimated at approximately <1 - 79 mg I-TEQ/year, when a 90 % confidence level is used.

No data on the content of dioxin in scrubber sludge and other shredder residues are available. These residues are normally directed to Kommunekemi.

In SFA 2000 /Hansen, 2000/ the total dioxin emission from shredder plants was estimated at 7 mg I-TEQ/year.

5.2 Hazardous waste

5.2.1 Hazardous waste incineration

Kommunekemi that is the central facility for treatment of hazardous waste in Denmark, has 3 kilns, of which 2 kilns (F3 and F4) are now equipped with dioxin abatement. Hazardous waste is for the time being treated only in these two kilns. The third kiln, F1, has been closed down due to reconstruction in the period 2000 - 2002. In connection with the rebuilding this kiln has also been equipped with dioxin abatement.

Before the air stream enters the dioxin abatement, it is cleaned by a bag filter (one kiln) or an electrostatic precipitator (the other kilns), and a wet flue gas facility. The temperature in the bag filter and the electrostatic precipitator is around 195° C, whereas the temperature over the dioxin abatement is around 145° C. The experience of Kommunekemi confirms the general experience that the temperature through the flue gas system is of the outmost significance to dioxin formation and should be below 200 C.

Besides Kommunekemi, another minor Danish plant has permission for incineration of special types of hazardous waste. This plant also treats clinical hospital waste. Totally the plant treats 4.700 tonnes waste/year of which 1.600 t is hazardous waste, and the rest is clinical hospital waste (Danish EPA 1999c). This plant is covered by section 5.4 on incineration of clinical hospital waste.

Furthermore a Danish company uses turpentine waste as fuel for a combustion plant, which generates heat for the production.

Plant activity

The activity of Kommunekemi can be briefly summarised as follows:

Dusts from the dioxin abatement is incinerated in the kilns, and the content of dioxins is assumed to be destroyed. The fly ash collected by the bag filter and the electrostatic filter is landfilled on Kommunekemi's own depot.

Kommunekemi has no knowledge of and is not analysing dioxin concentrations in waste received for treatment and disposal.

Formation and disposal of dioxin

Kommunekemi has carried out several measurements of dioxin emission by air and water and some earlier measurements have shown very high concentrations of dioxin. In order to fulfil the present limit value of 0.1 ng I-TEQ/Nm³, Kommunekemi has redesigned rotary kilns and flue gas cleaning systems, which means that F3 and F4 have complied with the limit value since July 2000. Dioxin abatement has also been installed in order to comply with the legal conditions for burning of waste.

Until June 2000 Kommunekemi had permission to carry out themal treatment of polluted soil on F1. In 1999 Kommunekemi also used F1 for experiments on incineration of shredder waste (ASR, Automotive Shredder Residue). For a short period Kommunekemi had also permission to use it for treatment of liquid hazardous waste, because F3 and F4 were under reconstruction. The use of F1 for other purposes than thermal treatment of soil gave high emissions and was therefore stopped. /Kjærgaard, 2003/

The total operation time in 1999 was 3,109 hours /Danish EPA 2000b/.

From 1999 until today the following emission results for dioxin (I-TEQ) from F1 have been obtained /Danish EPA 2000b/:

The kiln F1 has been closed down due to reconstruction in the period from July 2000 - 2002, but has re-opened in December 2002. F1 has been closed down because the kiln no longer will be used for treatment of polluted soil. It will instead be used for treatment of hazardous waste like F3 and F4. This adjustment means that F1 has to comply with the demands for combustion of waste and the kiln will therefore be equipped with dioxin abatement, when it goes into operation again. /Kjærgaard, 2003/.

According to /Danish EPA 2000b/ Kommunekemi has estimated the total emission from F1 during 1999 to 2 – 2.5 g I-TEQ. This estimate will probably not correspond to the dioxin emission, when kiln F1 is put into service again. The annual emission for kiln F1 is therefore not calculated.

For the two other incinerators F3 and F4 equipped with dioxin abatement the following emission measurement results for dioxin (I-TEQ) have been obtained:

F 3

*)Without dioxin abatement

F4

The total dioxin emission for kiln F3 and F4 during the period 2000 - 2002 can be calculated as follows:

F3: Average emission for 2000 - 2002 0.013 ng/Nm³ and 300 million Nm³/year. Best estimate for total emission is 3.8 mg I-TEQ/year, ranging from 2.1 - 5.5 mg I-TEQ/year using a 90% confidence level.

F4: Average emission 0.04 ng/Nm³ and 300 million Nm³/Year. Best estimate for total emission is 12 mg I-TEQ /year, ranging from 2.3 - 21.8 mg I-TEQ/year.

In addition to F3 and F4 a CIS plant is used. This plant is a container-based rotary kiln combustion system, which has a capacity of approximately 300 kg/hour and an operation temperature at 1100ºC - 1200ºC. Contrary to F3 and F4 this kiln is a removable pilot plant. It also has a very low capacity compared to these two kilns.

Three measurements of dioxin emission to air have so far been made on the CIS plant during combustion of a combination of fluid and solid waste with low chlorine load:

The measurements correspond to an emission of approximately <0.01 - 0.7 mg I-TEQ/year, when a 90% confidence level is used.

Assessed on the basis of the measurements during 2000 - 2002 from F3, F4 and the CIS plant, the best estimate for the total dioxin emission from Kommunekemi is approximately 16 mg I-TEQ/year with an uncertainty interval ranging from 4.4 - 28 mg I-TEQ/year. The estimate does not include a future emission from the F1 kiln, as F 1 will be equipped with dioxin abatement, when it goes in operation again.

In SFA 2000 /Hansen, 2000/ the total emission to air was calculated at 2.2 - 2.7 g I-TEQ/year, of which F1 had an emission of approximately 2-2.5 g I-TEQ/year. This emission from F1 must be expected to decrease significantly.

Regarding emission with wastewater from flue gas cleaning, Kommunekemi has estimated a total emission of 0.003 mg I-TEQ/year for 2001 /Kommunekemi 2002/.

Regarding dioxin in fly ash and slag from the incineration processes, measurements from March 2000 have given concentrations of 69 ng I-TEQ/kg and 39 ng I-TEQ/kg respectively /Kommunekemi 2000/ equalling a total dioxin quantity of:

The figures, at least the figure for fly ash, are likely to underestimate the amount of dioxin collected during 1999, at least the amount collected from kiln F1. However, measurements for fly ash and slag corresponding to measurements of air emissions are not available. Measurements of dioxin content of gypsum, filter cakes and other materials deposited are not available either.

The fly ash and slag are deposited on Kommunekemi's own landfill at Klintholm.

The dioxin emission in the flue gas from a Danish plant that combusts turpentine waste was measured in 2001. The result shows a dioxin emission at 0.052 ng I-TEQ/Nm³, which means an emission of approximately 0.2 - 1.6 mg I-TEQ/year. This interval is assuming an uncertainty of ± factor 3. The emission factor of the combustion plant is approximately 0.0018 mg I-TEQ/ton turpentine incinerated.

Emission of brominated dioxins

In autumn 2002 the National Environmental Research Institute has conducted four measurements of the air emission of brominated dioxins on kiln 3 and kiln 4 respectively /the National Environmental Research Institute, 2002/.

No official method is at the time being available for converting the measured values into I-TEQ, but as earlier mentioned WHO suggests that the current toxicity equivalency factors for chlorinated dioxins are also applied to brominated dioxins on an interim basis /IPCS 1998/. This is done for the new measurements to get an estimate of the annual dioxin emission of brominated dioxins from treatment of hazardous waste. The measurements do not represent a complete investigation as it only has been possible to include congeners on the tetra and penta level. Hexa-, hepta- and octa-congeners are thus not included in the results presented. Furthermore many of the congeners cannot be identified specifically from the measurements, and this means that it is not possible to use I-TEF for these measured concentrations of brominated dioxins and thereby calculate a total emission in g I-TEQ/year. The measurements have however identified some specific congeners, where I-TEF will be used to estimate a total I-TEQ concentration for the specific congeners, compare table 5.1:

Tabel 5.1
Measured specific congeners and I-TEF.

On the basis of the measured values for the specific congeners and the I-TEF values from table 5.1, the annual emission of brominated dioxins can be estimated to be approximately <0.009 - 0.06 g I-TEQ/year with a best estimate of approximately <0.04 g I-TEQ/year (90 % confidence level). This emission value represents with certainty an under estimate of the reel emission, but any estimate of the reel emission value must be regarded as highly uncertain. Based on an anlysis of the chromatographies for the congeners it is estimated that the reel estimate can be up to approximately a factor 5 higher, but most likely not a factor 100 /Vikelsøe, 2003a/.

5.2.2 Incineration of waste oil

Apart from the waste oil received and incinerated at the central Danish facility for hazardous waste (reference is made to section 5.2.1), waste oil is also incinerated by district heating plants. Before incineration at district heating plants the oil is typically re-refined in order to reduce the content of heavy metals and other contaminants. The focus on waste oil e.g. comes from the possibility that waste oil may contain traces of PCB originating from transformers and condensers. The knowledge available (reference is made to /Danish EPA1995/) is that PCBs are only registered in unrefined waste oil and in concentrations below 1 mg/kg.

In year 2000 around 20,000 tons waste oil was incinerated at local district heating plants /Danish EPA, 2001/. Measurements of the air emission of dioxins caused by incineration of waste oil at district heating plants have been carried out in three plants during spring/summer 2000 and at one plant in 1999.

One of the plants in question is equipped with an alkaline scrubber for cleaning of off-gases. The fuel incinerated was unrefined waste oil. 4 measurements were conducted each lasting for 4 hours. Air emission factors are ranging between 300 and 1,640 ng I-TEQ/ ton waste oil /Schleicher et al. 2001/.

The second district heating plant, which is firing with re-refined waste oil, shows an emission factor of approximately 30 ng I-TEQ/ton waste oil. At the third plant, also firing with re-refined waste, a similar result has shown, as the one sample taken under normal operation shows an emission factor of 36 ng I-TEQ/ ton waste oil. At the same plant a sample was taken under abnormal combustion conditions, and it shows an emission of 970 ng I-TEQ/ton waste oil. /Schleicher et al. 2001/.

In 1999 a measurement was made at a fourth Danish district heating plant, which is also using re-refined waste oil. This measurement also showed an emission factor of approximately 30 ng I-TEQ/ton waste oil.

In addition to the measurements from district heating plants measurements have been carried out in 2002 at two waste-oil fuelled boilers generating heat for productions. The emission factor is approximately 2.5 µg I-TEQ/ton waste oil for the one boiler and 600 ng I-TEQ/ton waste oil for the other. An earlier measurement from 2001 showed an emission factor of approximately 8 µg I-TEQ/ton waste oil, but this measurement was made while using a too high concentration of salt in the scrubber-cleaning water. This concentration was normalized in the measurements from 2002.

Using the emission factors from the Danish plants, the best estimate of the total dioxin emission to air is 65.4 mg I-TEQ/year, with the uncertainty interval ranging from <1 - 167.3 mg I-TEQ/year, using 90% confidence level. The total emission is most likely not as high as the high interval limit, because most of the waste oil used is incinerated in district heating plants and re-refined before incineration. Re-refined waste oil can according to Schleicher (2003c) be compared to normal oil.

In SFA 2000 /Hansen, 2000/ the annual emission is estimated at 45 mg I-TEQ/year.

No knowledge is available concerning residues from waste oil incineration at district heating plants. Such residues will be directed to landfills.

5.3 Municipal solid waste

5.3.1 Incineration

Solid waste incineration is generally accepted as an important source of dioxin formation and emission. A detailed discussion of the many investigations related to solid waste incineration is outside the agenda for this report – reference is made e.g. to /Jensen 1995, Jensen 1997 and Dam-Johansen 1996 /. As a very brief summary it can be concluded that dioxins will be present in waste materials directed to incineration. Dioxins may furthermore be formed by the incineration process and afterwards during treatment and cooling of flue gasses either from precursors or by "De Novo synthesis".

As the temperatures in modern Danish incineration plants are typically around 1000° C, which should be appropriate for degradation of dioxins present in the waste, it is assumed fair to believe that most dioxins in the incoming waste (see table 5.2) are destroyed by the process (reference is made to section 1.5).

However, as indicated by tables 5.2 and 5.3 a very significant emission of dioxins also takes place. As the amount of dioxins emitted from waste incineration by flue gas and incineration residues is significantly higher than the amount destroyed the figures presented documents that municipal waste incineration also in Denmark should be regarded as a very important source of dioxin formation and emission.

Table 5.2
Sources of dioxins in combustible waste assumed to be directed to municipal waste incineration in Denmark

It should be noted that investigations on dioxin emission from incineration plants have focused on chlorinated dioxins only, and no precise knowledge on brominated dioxins or "mixed" dioxins containing bromine as well as chlorine exists. The following discussion is therefore addressing chlorinated dioxins only.

Uncontrolled burning of waste in backyards etc. is not widespread in Denmark, but cannot be excluded, particularly in rural areas. No statistics covering this practice are available, and the amount of waste disposed of this way can only be estimated with a high degree of uncertainty.

Plant activity

In Denmark 31 municipal waste incineration plants (MWI) are currently operating. By the end of year 2002 2/3 of the Danish waste was incinerated at waste incineration plants which are capable of complying with the new limit value for dioxin of 0,1 ng I-TEQ/Nm³/Danish EPA 2002/. Most of the remaining waste incineration plants are planning to install dioxin abatement before the end of year 2004. Two of the 31 incineration plants are however first planning to finish the installation of filters in 2005 and three of the 31 incineration plants have no intention of installing dioxin abatement, because they already have measured low emissions that comply with the limit value 0.1 ng I-TEQ/Nm³. /Danish EPA 2003/. Dioxin filtration is done with charcoal/coal dust, and the filter material with its content of dioxin is disposed of by being fed into the oven.

The total amount of municipal solid waste incinerated in Denmark comes up to approx. 2.9 million tonnes per year (2000-figure /Danish EPA 2001/). In table 5.3 is indicated the knowledge available as per spring 2000 regarding installation of special dioxin abatement and for plants without such abatement the type of flue gas cleaning process otherwise employed.

Dioxin formation and disposal

The available knowledge regarding dioxin emissions from Danish waste incineration plants is also indicated in table 5.3. To the best of knowledge none of the measurements undertaken is based on a sampling time exceeding 6 hours. Continuous long term measurements, lasting 2 - 6 weeks, is a new way of measuring the emission, but so far Belgium is the only country that has implemented long term measurements on municipal waste incineration plants. Long term measurements were implemented in Belgium after a number of long term measurements detected emissions limits being exceeded massively, namely exceedings and/or deviating process conditions that the random 6 hour sampling did not detect. The annual expences to long term measurements constitute more than 2 - 3 time as much as the annual expences to conventional biannual 6 hour sampling. /Schleicher, 2003b/. As dioxin formation is extremely process dependent and the actual formation may differ considerably from "normal" process conditions to "deviating" process conditions, deviating process conditions may contribute significantly to the total dioxin formation and emission. E.g. even if deviating process conditions only rules 5% of the total operation time for a specific plant the dioxin formation during this time could perhaps be 10-100 times higher than under normal process conditions. It is the impression of the authors that most of the emission factors reported reflect normal process conditions and thus do not include the consequences of deviating process conditions. Only little factual knowledge is available on this issue, but the significance to the total emission should not be overlooked.

The available Danish measurements from the periode 2000 - 2002 is summarised in table 5.3. Considering the uncertainty related to e.g. the importance of deviating operation conditions, the choice is made to rely more on the assumed interval of uncertainty than on the calculated best estimate.

Table 5.3
Dioxin emissions to air from municipal waste incineration in Denmark 2000 - 2002.

The total annual emission of dioxin from Danish municipal waste incineration plants can, on the basis of the 92 measurements used in the investigation, be estimated at approximately 15.7 g I-TEQ/year. The assumed interval of uncertainty for this value is 6.4 - 28.9 g I-TEQ/year. The annual value was estimated to be 21.1 g I-TEQ/year in SFA 2000 /Hansen, 2000/, within a range of 11 - 42 g I-TEQ/year (also 90% confidence).

The investigation from 2002 supports the theory that the type of flue gas cleaning system to some extent determines the dioxin emission level. In the report from 2000 it was found that dry processes are better than wet and semidry - the same picture can by and large be seen in the investigation from 2002.

During the period from 1999 to 2001 the amount of waste that is dioxin-cleaned has grown from 839,000 tons to 1,423,000 tons. This is the primary reason for the reduction of the annual emission, since the amount of waste has moved from wet flue gas cleaning to dioxin cleaning. It should be noted that the dioxin abatement systems are still in commisioning fase on some of the plants. The full effect of the installed dioxin abatement has perhaps not shown yet, as most of the abatement equipment has a running-in period before it is getting the total efficiency.

With respect to uncontrolled burning of waste recent American investigations have revealed that burning of domestic waste containing 0.0%, 0.2 %, 1% and 7.5 % PVC generated 14 ng I-TEQ/kg respectively 80, 200 and 4900 ng I-TEQ/kg waste /Gullett et al 1999/. The tests with 0.2 % PVC were considered baseruns illustrating the normal content of PVC in domestic waste.

As already stated the amount of waste burned uncontrolled in Denmark is not known, but should be considered small. Assuming a figure of 2,700 tonnes of waste, corresponding to 0.1 % of the total waste quantity, and an emission factor of 80 ng I-TEQ/kg waste, the total emission may be estimated at 0.2 g I-TEQ/year. It is noted that a figure of 2,700 tonnes of waste burned uncontrolled most likely should be regarded as an overestimate rather than the opposite. Thus, uncontrolled burning cannot be expected to significantly contribute to the total dioxin emission from waste incineration in Denmark.

Emission of brominated dioxins

The National Environmental Research institute has in autumn 2002 conducted an investigation of the content of brominated dioxins in the flue gas from the municipal waste incineration plant Vestforbrænding /the National Environmental Research Institute, 2002/. These measurements have been made according to the same method as the measurements that have been carried out at Kommunekemi, compare section 5.4, and the same problem with estimating I-TEQ emission is therefore present. As for Kommunekemi the measurements from Vestforbrænding A/S only include tetra- and penta congeners.

Only five measurements from the same plant are available, but it is chosen to use these measurements as an indication of the level of the annual emission of brominated dioxins. This estimate is indeed very uncertain, because the 31 Danish plants have different processes, waste and flue gas cleaning systems (Vestforbrænding has installed dioxin abatement). Furthermore the calculation only includes the specific measured congeners with an I-TEF value (compare section 5.2.1).

Using the measured values for the specific congeners and the I-TEF- values in table 5.1, the annual emission from Danish waste incineration plants can be estimated to be approximately <0.001 - 0.03 g I-TEQ/year. This emission value represents with certainty an under estimate of the reel emission, but any estimate of the reel emission value must be regarded as highly uncertain. Based on an anlysis of the chromatographies for the congeners it is estimated that the reel estimate can be up to approximately a factor 5 higher, but most likely not a factor 100 /Vikelsøe, 2003a/.

Residues

The available knowledge regarding dioxin content in residues from Danish waste incineration plants is indicated in table 5.4 from SFA 2000 /Hansen, 2000/. More measurements have been carried out in 2000 after finishing SFA 2000, but these measurements are covered by the 90 % confidence interval stated in table 5.4. The waste quantities have been updated, which means that the annual emission has changed. As shown the total quantity may be estimated at 52 - 407 g I-TEQ/year. Of this quantity around 98 % is collected with flue gas cleaning residues.

Table 5.4
Dioxin in residual products from waste incineration.

Three of the measurements of dioxin of "flue gas treatment residues" were on filter cakes. These measurements constitute both the two highest and the lowest figure, i.e. 35.566 and 22.176 ng I-TEQ/kg and 135 ng I-TEQ/kg respectively. The other 18 measurements show much lower difference. The highest and lowest figures are 380 and 6.476 ng I-TEQ/kg respectively with a 90% confidence interval around the mean of 1.037 – 2.243 ng I-TEQ/kg /Dansk RestproduktHåndtering 2000/.

Clinker will primarily be utilised for civil works (in this context also regarded as landfilling) or secondly landfilled, whereas flue gas treatment residues will be directed to landfilling only. In 2000 85,700 tonnes of flue gas treatment residues were exported for landfilling. This number is higher than the actual amount of created flue gas treatment residues, probably due to export of stored up flue gas cleaning products. It is therefore assumed that the major part of the dioxin in the flue gas treatment residues is exported.

5.4 Healthcare risk waste

The dominant part of healthcare risk waste generated in Denmark is incinerated together with municipal solid waste in 7 of the ordinary municipal waste incineration plants, and all small incineration plants previously operating at hospitals have been closed. Danish investigations have concluded, that incineration of healthcare risk waste together with ordinary solid waste do not seem to influence the dioxin emission to air from ordinary waste incineration plants /Vikelsøe 2000; Vestforbrænding 2000/. The emission from healthcare risk waste in that context is thus assumed to be included in the figures stated for waste incineration (reference is made to section 5.3.1).

However, one small plant incinerating partly hazardous waste and partly healthcare risk waste is in operation. This plant treats approx. 4,000 tons waste per year. The plant is equipped with bag filter, but has no special dioxin abatement. 2 measurements from 1999 gave results of 1.4 and 5.8 ng N-TEQ/Nm³ respectively. Since then 10 measurements have been carried out, where the highest value is 31.4 ng I-TEQ/Nm³ and the lowest value is 0.1 ng I-TEQ/Nm³. Assuming that the measurements are normal distributed the average emission equals 3.9 ng I-TEQ/Nm³. The measurement are within the range of <1 - 9,5 ng I-TEQ/Nm³ using a 90 % confidence level. This interval results in annual emissions that range from approximately <1 - 350 mg I-TEQ/year, using the annual air flow of approximately 37400000 Nm³/year.

In SFA 2000 /Hansen, 2000/ the annual emission was estimated at 34 - 140 mg I-TEQ/year.

No measurements exist of filter dust and clinkers. The amount of dioxin collected with these residues is assessed as insignificant compared with residues from municipal waste incineration.

5.5 Municipal landfills

The total quantity of waste to be directed to landfills comes up to approx. 1.87 million tonnes/year (1998 – figure /Teknologisk Institut 2000/). From 1 January 1997 it has not been permitted to landfill waste suitable for incineration.

Included in this quantity will be around 37 - 415 g I-TEQ/year of dioxins as detailed in table 5.5.

The fate of dioxins in landfills is not well known, and no Danish investigations on this issue have been undertaken. Based on the physical-chemical characteristics of dioxins it should be expected that transport of dioxins out of landsfills is a very slow process. Evaporation as well as leaching would have to be considered. Concerning leaching attention should be paid to the risk that dioxins may be transported by leachate adsorbed to organic matter.

Investigations on the content of dioxins in leachate have been carried out in Japan. Dioxin concentrations of <0.001-50 pg I-TEQ/l raw leachate have been reported /Yoshikawa et al 1999; Nishikawa et al 1999/. Assuming a leachate generation from Danish landfills of around 5 million m³/year, the dioxin emission may be estimated at < 0.05 g I-TEQ/year. This emission will primarily be directed to municipal wastewater treatment plants.

Dioxin concentrations in leachate have been investigated from four Danish landfills during 2002. These investigations have shown that leachate from normal Danish landfills does not contain traceable amounts of dioxin. Leachate from special deposits containing for example sludge, ash or other types of special waste will be investigated, but only one result is so far available. One measurement has been taken from a deposit for hazardous waste. The result showed a dioxin content of 0.02 pg I-TEQ/l when the dioxin content in the blind test is deducted. /Vikelsøe, 2002/ and /the National Environmental Research Institute, 2002/. The dioxin content in leachate from Danish municipal landfills is so far maintained at the level of <0.05 g I-TEQ/year.

Tabel 5.5
Sources and quantities of dioxins assumed to be directed to landfills in Denmark

Formation of dioxins may take place by landfill fires. However, the frequency and extent of such events in Denmark is small, as it is standard procedure at Danish landfills to cover the waste with soil. Thus landfill fires can hardly be expected to be a source of any significance in Denmark, and in particular not after landfilling of combustible waste has been banned.

For combustible waste temporarily stored on landfills or other depots awaiting adequate incineration capacity to be established the situation is different. This procedure became necessary as a consequence of the Danish ban on landfilling of waste suitable for incineration. One major accident has occurred.

In July 2000 a temporary depot of 25,000 tons of waste was accidentally set on fire. The fire continued most of a week until more than 75% of the waste had burned out. A significant part of the waste consisted of wood and plastics. The wind direction changed several times during the fire. Measurements of a few soot samples taken from the most exposed areas in a neighbouring city were undertaken. 4 samples taken in distances of 380-3500m from the depot showed dioxin contents varying from 1-2 to 21 ng I-TEQ/m³. The data available are however to a few to allow for a reliable quantification of the dioxin formation and emissions occurred.

Available information indicates that a number of similar fires takes place every year in Denmark. No exact recordings of the number of fires and the amount of waste burned are made. Assuming that on average 5000 –10,000 tonnes per year of waste are consumed by such fires, and assuming the dioxin formation to be somewhat between 50 and 1000 ng I-TEQ/kg waste (as for fires in general - reference is made to section 5.3.1 and 4.1.1 – although typical PVC-products are not included in the waste, the waste should be assumed still to contain small amounts of PVC), the air emission of dioxins may be roughly estimated at 0.25 - 10 g I-TEQ/year. Assuming as for accidental fires that the amount collected and landfilled with residues from the fires comes up to 170% of the amount emitted to air, an amount of 0.4 – 17 g I-TEQ should be expected to be directed to landfills.

It is emphasised that these calculations should be taken as rough estimates likely to indicate the relevant order of magnitude of the flows in question. It is noted that the amount of waste assumed to be consumed by fires in the calculations above may well be underestimated /Hansen 2000a/.

5.6 Biological waste treatment

In 2001 450,000 tons organic garden waste was brought to composting plants /Danish EPA, 2002/. Furthermore around 200,000 tonnes of food waste and other organic materials were recycled /Teknologisk Institut, 2000/ mainly by composting and bio-fermentation processes.

Organic garden waste and food waste will contain dioxins due to e.g. atmospheric deposition.

12 measurements on organic garden waste have been carried out in 2001.The measurements come from 9 different locations. These measurements show an average dioxin content of 4.5 ng I-TEQ/kg dry matter with a minimum value of 0.5 ng I-TEQ/kg dry matter and a maximum of 15.9 ng I-TEQ/kg dry matter.

The amount of dioxin collected with organic garden waste equals 1.7 g I-TEQ/year, when the average value is used, and using a 90% confidence level the uncertainty range corresponds to 0.8 - 2.6 g I-TEQ/year.

Concerning food waste an estimate of 23 – 165 ng I-TEQ/ton waste can be developed based on table 3.6 assuming that the content of dioxin in food waste corresponds to the content of food products. Based on these assumptions the quantity of dioxins directed to biological waste treatment in Denmark can be calculated to 0.8 – 2.6 g I-TEQ/year, as the dioxin content in food waste is marginal compared to the content in the organic garden waste.

The new information on organic garden waste has developed a higher estimate than the one made in SFA 2000 /Hansen, 2000/, where the dioxin amount directed to biological waste treatment was estimated at 0.01-0.07 g I-TEQ/year.

The fate of dioxins by biological waste treatment is not well investigated. Based on a general understanding of the characteristics and behaviour of dioxins (reference is made to section 2.2 and 2.4) and design of Danish plants for biological waste treatment, little or no formation and degradation is assumed to take place. Consequently, the input of dioxins to such processes will also be present in the products produced that dominantly consist of compost and other residues used as soil improvement material and fertiliser in farming, private and public gardens and parks.

5.7 Wastewater and sewage sludge

5.7.1 Wastewater treatment

The total amount of wastewater discharged from Danish wastewater treatment plants sums up to approximately 770 million m³ as an average for the years 2000 and 2001. The storm water systems furthermore discharges an extra 190 million m³ in a normal year and from separate industrial sources the average discharge has been approximately 70 million m³ during 2000 and 2001./Danish EPA, 2002a / and /Danish EPA, 2001a/.

In the SFA 2000 /Hansen, 2000/ 3 samples from 1995 from a single Danish treatment plant were reported which showed dioxin levels of 0.4-1.4 ng I-TEQ/m³ in the outlet from the plant /Vikelsøe 2000/. More measurements from outlets of waste water treatment plants have been made available from the period 2000 -2002 due to analytical work undertaken by the National Environmental Research Institute on behalf on clients. However, the origin of the samples is in most cases poorly described making data interpretation difficult. In total 26 measurements are available, of which 3 originates from a semilarge treatment plant (the one described above), 3 measurements originates from an industrial textile processing plant and 3 from other industrial plants. The origin of the remaining 19 measurements is not stated and they must be assumed to represent a mix of municipal and industrial waste water treatment plants.

Considering all measurements available from Denmark, they can be described as ranging within 0 - 3 ng I TEQ/m³, and an average value of 0.5 ng I-TEQ/m³ with a 90% confidence level that ranges from 0.23 - 0.75 ng I-TEQ/m³ /Vikelsøe, 2002/. No measurements of dioxin in water from storm water drainage systems have so far been carried out in Denmark.

Based on the data available the emission of dioxin with waste water and storm water to Danish water recipients may roughly be estimated as follows:

Municipal waste water: 770 million m³ with 0.4-1.4 ng I-TEQ/m³ corresponds to 0.31-1.08 g I-TEQ yearly.

Industrial waste water: 70 million m³ with 0.23-0.75 ng I-TEQ/m³ corresponds to 0.02-0.05 g I-TEQ yearly.

Storm water- direct discharges: 190 million m³ with 0.4-1.4 ng I-TEQ/m³ corresponds to 0.08-0.27 g I-TEQ yearly.

Total emission: 0.4-1.4 g I-TEQ yearly.

This emission should be considered equal to the previous estimate for year 2000 of 0.3 - 1.4 g I-TEQ/year /Hansen, 2000/.

It is noted that the dioxin concentrations assumed for storm water should be regarded as a best estimate only, as the concentration of dioxin in storm water could well be higher than in municipal waste water, as storm water will be a carrier of dioxin originating from atmospheric deposition which seemingly is the dominating source of dioxin to the waste water and storm water system.

The sources of dioxin in wastewater and storm water may be outlined as indicated in table 5.6.

Table 5.6
Sources and quantities of dioxins assumed to be directed to wastewater and storm water drainage in Denmark

The calculated total contribution of 0.4 - 4.8 g I-TEQ/year should be taken as comparable to the estimated total content in discharged waste and storm water of 0.4 - 1.4 g I-TEQ/year (see above) and the calculated total content in sewage sludge of 1.2 - 2.3 g I-TEQ/year (reference is made to section 5.7.2) indicating that the contribution to waste water treatment plants in Denmark is at least 1.6 - 3.7 g I-TEQ/year. These observations indicate that the deposition level stated in chapter 6 is a realistic estimate.

It is, however, not possible based on the existing data to discuss the fate of dioxins in wastewater treatment plants. /Vikelsøe, 2002/ points out that observed congener profiles for dioxins in sewage sludge only partly are correlated to profiles for air deposition. Some correlation to congener profiles for textiles may also be argued. Any definite conclusions on sources for dioxins in wastewater and sewage sludge should so far be considered premature. For a more detailed review of existing international experience related to the fate of dioxins by wastewater treatment and sludge treatment and disposal reference is made to /Jensen 1997/ and /Jones & Sewart 1997/.

It should be noted, that sewage systems as well as storm water systems contain a number of sinks for dioxins e.g. sediment traps as well as the sewage hide inside the sewage pipes. In sediment from sediment traps on storm water systems in the Copenhagen area has e.g. been registered 1.2 - 1.9 ng N-TEQ/kg dry matter (2 samples, 1996 - /Kjølholt et al 1997/). Thus, it seems quite reasonable that the contribution from sources exceeds the amount registered by analysis of wastewater samples and sewage sludge. The content of sediment traps, when cleaned, should be expected to be directed to landfills. It is, however, not possible to estimate the amount of dioxins directed this way.

5.7.2 Treatment and disposal of sewage sludge

In 1999 the total production of sewage sludge from municipal wastewater treatment plants was 1,442,930 t wet weight corresponding to 155,622 tonnes of dry matter /Danish EPA 2001b/. The sludge is applied to farmland as well as to special sludge incineration plants and landfills as detailed in table 5.7 below.

The content of dioxins in Danish sewage has been thoroughly investigated during the recent years. 95 samples of sewage sludge covering city areas as well as rural districts have been analysed during the years 1995 - 2002. The average content of dioxins has been determined as 11.4 ng I-TEQ/kg dry matter with min./max. values of 0.7/201.3 ng I-TEQ/kg dry matter/Vikelsøe 2002/. The measurements correspond to an average annual quantity of dioxin collected with sewage sludge of approximately 1.8 g I-TEQ/year. The estimated uncertainty is 1.2 - 2.3 g I-TEQ/year, when a 90% confidence level is used.

The distribution of this dioxin on the relevant disposal routes is also indicated in table 5.6.

Table 5.7
Disposal of sewage sludge and dioxins contained in sewage sludge in Denmark 2000-2002.

In SFA 2000 /Hansen, 2000/ the total amount of dioxin in sewage sludge was estimated at 2.1 g I-TEQ/year. The reduction is caused by slightly decreasing concentrations of dioxins in sewage sludge, as the total amount of dry matter has increased by approximately 3% compared to the figures from 1997, used in SFA 2000 /Hansen, 2000/.

Incineration of sewage sludge takes place at 5 plants in Denmark (reference is made to table 5.8). Of these Lynetten and Spildevandscenter Avedøre are the two major plants. The emission from Lynetten and Avedøre will be reduced in the coming years because of new installations at the two plants. Avedøre has been equipped with dioxin abatement. As the temperature in the incineration chamber exceeds 1000ºC, it seems justified to assume that all or at least most of the dioxins present in sludge will be destroyed by the process.

Table 5.8
Dioxin emission to air in Denmark from incineration of sludge.

The new measurements at sludge incineration plants result in a reduction of the estimated level of the dioxin emission from sludge incineration, compared to SFA 2000 /Hansen, 2000/.

The resulting ash from burning of sludge constitutes between 25-45% of the dry matter, and 8,000-15,000 tonnes of ash yearly are currently being directed to landfills. As part of the flue gas cleaning system – at least at the major plants – also a scrubber system is employed. The scrubber water is normally directed to the wastewater treatment plant and mixed with the raw wastewater. No recent measurements of the dioxin content in ash and scrubber water from sludge incineration from Denmark are available. The only available measurements date back to 1989, at which time measurements at Lynetten showed a dioxin content of bottom ash of 6.3 ng N-TEQ/kg and of scrubber water of 0.28 ng N-TEQ/l /Jensen 1997/.

Assuming the data for bottom ash still to be valid and relevant to all sludge incineration plants in Denmark, and furthermore assuming N-TEQ to equal I-TEQ, the quantity of dioxins collected by bottom ash and directed to landfills can be calculated as 0.05 – 0.09 g I-TEQ/year. Concerning scrubber water it may, based on data from Lynetten /Lynetten 2000/ and assuming that all air emissions from sludge incineration in Denmark is treated by scrubber, be estimated that the total amount of scrubber water comes up to approx. 1.8 million m³/year. A content of 0.28 ng I-TEQ/l will correspond to a total quantity of 0.5 g I-TEQ/year. The dioxin formation by sludge incineration plants can thus be summed up to (0.0018 + 0.05 - 0.09 + 0.5 = 0.55 - 0.59) g I-TEQ/year. The amount of dioxins collected by the scrubber water and redirected to wastewater treatment will to some extent be included in the figure for discharges from wastewater treatment plants (reference to section 5.7.1).

5.8 Summary

The assessments and estimates related to formation and turnover of dioxins by waste treatment and disposal activities in Denmark by the end of the nineties and presented in section 5.1 to 5.8 are summarised in table 5.9.

Table 5.9
Summary of formation and turnover of dioxins by waste treatment and disposal activities in Denmark