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Substance Flow Analysis for dioxins in Denmark 5. Formation and turnover by waste treatment and disposal activities5.1 Metal scrap5.1.1 Reclamation of cable scrapReclamation of cable scrap in Denmark today 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 exists in Denmark. 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. 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 chemical 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 can be summarised as follows:
Filter dust is sent to the central Danish facility for chemical waste (Kommunekemi). Dioxin formation and disposal No measurements of dioxin emission have been undertaken at the plant or of the filter dust. In the Netherlands air emission factors of 3.7- 2280 m I-TEQ/ton scrap has been determined, based on which the investigation assumed an emission factor of 40m I-TEQ/ton scrap /Bremmer et al 1994/. The maximum figure of 2280 is, however, based on one observation only, whereas the other observations give 21 as the highest figure. The US Dioxin inventory contains one partly congener specific analysis showing that an air emission factor for scrap electrical wire recovery of between 2 and 50 m I-TEQ/ton scrap /US Dioxin Inventory 1998/. No literature data is available addressing filter dust from cable reclamation. Assuming an air emission factor of 2-2000 m I-TEQ/ton scrap, the total emission to air can be calculated as 0.005 - 5 g I-TEQ/year. Disposal of dioxin with filter dust should most likely be considered insignificant. 5.1.2 Shredder plants5 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 measurement of dioxin emission from a Danish shredder was made in 1999. The emission factor obtained was 0,0104 mg I-TEQ/ton scrap /Fyns Amt 2000/. Apart from this no measurements of dioxin related to shredder plants have been carried out in Denmark. The European Dioxin Inventory (section on Germany) states values for dioxin emission to air of 0.06 - 0.67 m I-TEQ/ton scrap /Landesumweltamt Nordrhein-Westfalen 1997/. Adopting the Danish measurement as valid to all Danish plants; the total emission from shredder plants in Denmark can be estimated at approx. 7 mg I-TEQ/year. No data on the content of dioxin in scrubber sludge and other shredder residues are available. These residues are normally directed to landfills. 5.2 Chemical waste5.2.1 Chemical waste incineration Kommunekemi that is the central facility for treatment of chemical waste in Denmark, has 3 kilns, of which 2 kilns (F3 and F4) are now equipped with dioxin filters. Hazardous waste is for the time being treated only in these two kilns. The third kiln (F1) has been used for oil and tar polluted soils but F1was closed for rebuilding in July 2000. In connection with the rebuilding F1 will also be equipped with a special dioxin filter. Before the air stream enters the dioxin filters, it is cleaned by a bag filter (one kiln) or an elector filter (the other kilns). The temperature in the bag filter and the electro-filter is around 195° C, whereas the temperature over the dioxin filters 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 chemical waste. This plant also treats clinical hospital waste. Totally the plant treats 4,700 tonnes waste/year of which 1,600 t is chemical 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. Plant activity The activity of Kommunekemi can be briefly summarised as follows:
Dusts from the dioxin filters are 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 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 kilns and flue gas cleaning systems. Also dioxin filters have been installed. In 1999 Kommunekemi used the eldest kiln F1 for incineration of different waste fractions such as polluted soil, car-fluff and liquid chemical waste. 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) have been obtained /Danish EPA 2000b/:
According to /Danish EPA 2000b/ Kommunekemi has estimated the total emission from F1 during 1999 to 2 – 2.5 g I-TEQ. For 0.2 ng/Nm3 as found in 2000 the yearly emission based on 200 million Normal m3 per year can be calculated to 0.04 g I-TEQ /year /Danish EPA 2000b/. For the two other incinerators F3 and F4 equipped with dioxin filters the following emission measurement results for dioxin (I-TEQ) have been obtained /Danish EPA 2000b/: F 3
*)Without dioxin filter F4
According to /Danish EPAb/ the total emission for F3 and F4 in 1999 can be calculated as follows: F3: Average emission 0.37 ng/Nm3, 300 million Nm3/year. Total emission 0.11 g I-TEQ /year. F4: Average emission 0.412 ng/Nm3, 300 million Nm3/Year. Total emission 0.12 g I-TEQ /year. According to the /Danish EPA 2000b/ the total emission from the ovens F1+F2+F3 can be calculated to 2.23 - 2.73 g I-TEQ /year. It is the opinion of the authors of this report that the precision expressed by these estimates and calculations is questionable. F 1 is closed down for reconstruction the next two years. When it goes in operation again it is equipped with a dioxin filter. With dioxin filters on all three kilns, an emission limit of 0.1 ng/Normal m3 limit and 300 million Nm3 stack gas from each kiln, the maximum emission from all three kilns together will be 0.09 g I-TEQ /year /Danish EPA 2000b/. Regarding emission with wastewater, Kommunekemi has estimated a total emission of 0.001 mg I-TEQ/year for 1998 /Kommunekemi 1999/. 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, if any, are not available either. The fly ash and slag are deposited on Kommunekemi's own landfill at Klintholm. 5.2.2 Incineration of waste oilApart from the waste oil received and incinerated at the central Danish facility for chemical 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 1997 around 22,600 tonnes waste oil was incinerated at district heating plants /Danish EPA 1999d /. Measurements of the air emission of dioxins caused by incineration of waste oil at district heating plants have been carried out in Denmark on one plant during spring/summer 2000. The plant 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 ranging between 295 and 1,476 ng I-TEQ/m3 waste oil were reported /dk-TEKNIK 2000/. Assuming a density of 0.9 ton/m3 these emission factors correspond to a total dioxin emission to air in Denmark from waste oil incineration of 0.006 - 0.03 g I-TEQ/year. As the plant is using unrefined waste oil and is equipped with a scrubber, it is likely representative to other waste oil based district heating plants in Denmark. Adopting an air emission factor of 2 µg I-TEQ/ton waste oil as in /Jensen 1997/, who was quoting /Bremmer et al 1994/ leads to an estimated emission of 0.045 g 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 waste5.3.1 IncinerationSolid 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 5.1) 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 5.1
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. As per spring 2000 only 7 plants has established special dioxin filters for treatment of the flue gas besides the normal flue gas cleaning equipment. 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 waste incinerated in Denmark comes up to approx. 2.6 million tonnes per year (1998 - figure /Teknologisk Institut 2000/). In table 5.2 is indicated the knowledge available as per spring 2000 regarding installation of special dioxin filters and for plants without such filter 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 5.2. As shown the total emission may as best estimate be stated as approx. 21 g I-TEQ/year, with a likely min./max. range of 11 – 42 g I-TEQ/year. To the best of knowledge none of the measurements undertaken is based on a sampling time exceeding 6 hours. A Belgian study indicates that continuos 14 days sampling – thus capturing deviating operating conditions – detects dioxin emissions 3 - 50 larger than detected by 6 hour sampling /De Fré & Wevers 1998/. Details in this study may be discussed, and it is not known whether the observations may be valid also to Danish conditions. The study, anyway, is raising the question of the importance of deviating process conditions and their significance to the total dioxin emission. No other studies addressing this question exist. The available Danish measurements (data is collected early 2000) is summarised in table 5.2. 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 5.2
For plants without dioxin filter it seems that the type of flue gas cleaning process employed to some extent determines the dioxin emission, and that dry processes are better than wet and semidry processes. However, the data available are limited and do not allow for solid conclusions. With respect to uncontrolled burning of waste recent American investigations have revealed that such 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. Residues The available knowledge regarding dioxin content in residues from Danish waste incineration plants is indicated in table 5.3. As shown the total quantity may be estimated at 63 – 495 g I-TEQ/year. Of this quantity around 97% is collected with flue gas cleaning residues. Table 5.3
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/. Whereas clinker will partly be landfilled and partly be utilised for civil works (in this context also regarded as landfilling), flue gas cleaning residues will be directed to landfilling only. However, around 38,000 tonnes of flue gas cleaning residues (1998-figure /Teknologisk Institut 2000/) assumed to correspond to 28 – 220 g I-TEQ/year are exported for landfilling abroad. 5.4 Healthcare risk wasteThe 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 chemical waste and partly healthcare risk waste is in operation. This plant treats approx. 4,000 tonnes waste per year. The plant is equipped with bag filter, but has no special dioxin filter. 2 measurements from 1999 gave results of 1.4 and 5.8 ng N-TEQ/Nm3 respectively. Assuming 6 Nm3/kg waste and that an N-TEQ may be considered equal to I-TEQ, the yearly emission to air can be calculated as 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 landfillsThe 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 which is suitable for incineration. Included in this quantity will be around 37 - 415 g I-TEQ/year of dioxins as detailed in table 5.4. 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. Tabel 5.4
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 in 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 the 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 tonnes of waste was accidentally set on fire. The fired 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 (regarding 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 2000/. 5.6 Biological waste treatmentIn Denmark in 1998 around 550,000 tonnes of organic garden waste (branches, leaves and grass) together with 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. No dioxin measurements of raw materials nor products and residues from biological waste treatment have been undertaken in Denmark. Thus, the amount of dioxins present in the materials directed to biological waste treatment may only be estimated as follows: It is assumed that the content of dioxins in organic garden waste is in the range of 10 – 60 ng I-TEQ/ton materials corresponding to the estimates made for grass, silage, hay and root crops (reference is made to table 3.4 in section 3.4.4). Concerning food waste an estimate of 23 – 165 ng I-TEQ/ton 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 as 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 sludge5.7.1 Wastewater treatmentThe total amount of wastewater discharged from Danish wastewater treatment plants sums up to approx. 770 million m3 as an average for the years 1989 - 1996, whereas storm water systems discharges an extra 200 million m3 in a normal year /Danish EPA 1997/. Only few measurements of dioxins in wastewater are available from Denmark. 3 samples from a single plant showed dioxin levels of 0.4-1.4 ng I-TEQ/m3 in the outlet from the plant /Vikelsøe 2000/, whereas no measurements are available for inlets. Assuming this level to be valid to all Danish wastewater, the amount of dioxins discharged from Danish wastewater treatment plants can be estimated at 0.3 – 1.1 g I-TEQ/year. No measurements of dioxin in water from storm water drainage systems are available from Denmark. Assuming the same content of dioxins as in wastewater would correspond to a total quantity of 0.08 – 0.3 g I-TEQ/year, assumed to be emitted directly to the water environment. As the number of measurements are very few, the estimate should be considered very uncertain. Based on the knowledge presented in this report the sources of dioxin in wastewater and storm water may be outlined as indicated in table 5.5. The calculated contribution of 1- 8.7 g I-TEQ/year should be taken as comparable to the estimated total content in discharged waste and storm water of 0.3-1.4 g I-TEQ/year (see above) and the calculated total content in sewage sludge of 2.1 g I-TEQ/year (reference is made to section 5.7.2) paying respect to the uncertainties related to these estimates and calculations. However, it is not possible based on these data to discuss the fate of dioxins in wastewater treatment plants. /Vikelsøe 2000/ points out that observed congener profiles for dioxins in sewage sludge is correlated far better to congener profiles for textiles than to profiles for air deposition. Any definite conclusions on sources for dioxins in wastewater and sewage sludge should thus 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. Table 5.5
5.7.2 Treatment and disposal of sewage sludgeIn 1997 the total production of sewage sludge from municipal wastewater treatment plants was 1,160,768 t wet weight corresponding to 151,159 tonnes of dry matter /Danish EPA 1999a/. The sludge is applied to farmland as well as to special sludge incineration plants and landfills as detailed in table 5.6 below. The content of dioxins in Danish sewage has been thoroughly investigated during the recent years. 38 samples of sewage sludge covering city areas as well as rural districts have been analysed during the years 1996 - 98. The average content of dioxins was determined as 13.8 ng I-TEQ/kg with min./max. values of 1.9/80.0 ng I-TEQ/kg /Vikelsøe 2000/. Based on the value of 13.8 ng I-TEQ/kg, the total quantity of dioxins collected in sewage sludge i Denmark can be calculated to 2.1 g I-TEQ/year. The distribution of this dioxin on the relevant disposal routes is also indicated in table 5.6. Table 5.6
Incineration of sewage sludge takes place at 5 plants in Denmark (reference is made to table 5.7). 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 will e.g. be equipped with dioxin filter /Stads- og havneingeniøren 1999/. 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 5.7
Based on an air flow of 180 million Nm3/year and dioxin content of 0.007 ng I-TEQ/Nm3 (as found by measurement per November 1999 /Lynetten 2000/ Yearly emission is estimated at 68 mg I-TEQ based on measurements from 1996 /Spildevandscenter Avedøre 1999/. Other minor sludge incineration plants include Køge, Bjerringbro and Brønderslev. However, for around 5000 tonnes dw the plants used for incineration are not indicated by /Danish EPA 1999a/. They could be municipal waste incineration plants. The estimated emission is based on the emissions factors from Lynetten and Avedøre. 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 (0.07-0.15 + 0.05-0.09 + 0.5 = 0.62-0.74) 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 (unknown – reference to section 5.7.1). 5.8 SummaryThe 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 5.8. Table 5.8
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