• Persistent organic pollutants (POPs) refer to chemicals that have been found to meet four criteria, namely they are persistent, bioaccumulative, toxic and are subject to long-range transport1.

• POPs have a wide range of applications and are incorporated into many consumer products therefore, contamination is widespread2-4.

• The Stockholm Convention requires all parties to destroy or irreversibly transform POPs that are present in waste streams above certain thresholds5.

• Due to their nature,POPsaredifficult to destroyand there is resistance fromwastemanagers toidentify their presence in end of life products due to increased analytical costs and a lack of versatile identificationtechniques6.

• It is essential that POPs are effectively destroyed to ensure legal compliance with international conventions and legislation (Regulation EU 2019/1021), and restrict exposure of these damaging chemicals to humans and the wider environment7.

• It is important to identify POP contaminated products so that they can be dealt with at appropriate wastemanagementfacilities.ThisalsoallowsPOPfreearticlestobeidentifiedsothattheycanbere-used or recycled thereby, reducing waste and increasing recycling rates2.

• There are currently three main classes of POP destruction technologies: thermal destruction; chemical destruction; and mechanochemical destruction. Each of these technologies can be combined with identificationandseparationtechniquestominimisetheamountofPOPswastethatmustbedestroyedand maximise recycling rates3.

• Thermal destruction techniques tend to be more established but they produce greenhouse gas emissions, create hazardous wastes and allow for very minimal recovery of material for re-use or recycling6.

• Chemical destruction techniques allow large amounts of material to be recovered or recycled. They also have lower emissions than incineration. However, more investment and research is required to optimise these techniques to make them more commercially viable3.

• Mechanochemical destruction techniques produce no gaseous emissions or hazardous by-products and POPs material can be converted into useful by-products. However, more research is required to optimise these processes to reduce reagent and energy and increase commercial viability8.

Methods for the pre-treatment and destruction of persistent organic pollutants

Evidence Statement 11 2020

evidenceSTATEMENT

Summary

ContextThe Government has committed, in their 25 Year Environment Plan for England, to increase the amount of POPs material that is being destroyed, to ensure environmental emissions are negligible by 20309. In addition to this commitment, the number of chemicals classed as POPs is increasing and efforts are beingmade by industry to improve identification in thewaste stream6. Legacy productsthatcontainchemicalsthatarenowclassifiedasPOPsareenteringthewastestreamwhen they reach the end of their life3,4,6. Consequently, the amount of POPs waste that requires destruction is also increasing.

Determining the current UK capacity for POPs disposal is a challenging task. First, capacity estimates are dependent on the type of POPs waste that requires disposal. Second, several facilities in the UK may be capable of destroying POPs but would require increased monitoring of emissions and residues6. Third, certain types of POPs waste are exported to facilities abroad so are not included in domestic capacity estimates6.

It is also difficult to accurately estimate and predict the current and future demand for POPsdestruction in the UK. Defra has commissioned a project that has attempted to estimate the current quantities of three POPs (PCBs, HBCDD, DecaBDE) in use in products and equipment and the quantities that will be sent for destruction10. The project has also predicted how the quantities in use are expected to change up to 2030, based on current policy and rates of destruction (see Table 1).

Table 1: Estimated and predicted quantities of PCBs, HBCDD and DecaBDE in 2019 and 2030

In use quantities in 2019

Amount that will remain in use in 2030

Amount sent for destruction in 2019

Amount that will be sent for destruction in 2030

4059 2 520 490 869 135

3178 1 593 423 542 068

81.18 77 472 38 402

63.56 111 614 136 990

PCB(tonnes of PCB

containing dielectric �uid)10

HBCDD(tonnes of

contaminated material)10

DecaBDE(tonnes of

contaminated material)10

This evidence statement provides a summary of established and emerging waste separation and POP destruction technologies present in the literature. It should be noted that this evidence statement has excluded some POPs (i.e. PCBs and DDTs) from the analysis based on the existence of well-established destruction techniques and their prominence in the waste stream. More details of the specific pollutants that have been included and excluded are provided in the Method Summary section. This document does not reflect government policy but will help inform policy decisions to ensure that the most effective and environmentally sustainable methods of POPs waste treatment and destruction are being used.

Pre-treatment

Several of the technologies that are available for processing and destroying POPs waste require pre-treatment of the waste. For some destruction technologies this is to ensure that POPs concentrations are below limits that are set to ensure complete destruction of the POPs3,11. Whilst, for recycling processes, such as plastics, pre-treatment is necessary to ensure that plastics containing POPs are separated out so that there is confidenceinthequalityandsafetyoftherecycledplastics3. This is a high priority given the push for the more sustainable use of natural resources and

the movement towards a more circular economy. Effective pre-treatment can ensure that the highest amounts of reusable waste fractions are retained and that only waste contaminated with POPs (above threshold values) is disposed of6.

There are several different pre-treatment technologies available and the appropriate choice will depend on the type of waste and the destruction technology being used. A summary of available pre-treatment methods has been provided below.

Dismantling and ShreddingDismantling and shredding are techniques used when a product consists of multiple components, some of which may contain POPs3. In this case, it may be economically or technologically advantageous to separate out the components that are likely to contain POPs. Dismantling is a manual process, such as when workers remove plastic casings that containflame retardants (FRs) from televisions6. Whereas, shredding is a mechanical process and is generally preferred as it is cheaper, faster and minimises worker exposure6. However, it should be noted that shredding some wastes generates large amount of airborne dust, which could pose a risk to workers and the wider environment, if not adequately abated3. Once shredding has taken place the shredded materials are separated into the non-metal shredder residue and the metal fraction, which does not contain POPs3. The non-

At present, the most readily available technique for the destruction of POPs is incineration therefore, increasing quantities of waste will need to be incinerated. This has raised several possible issues:

• The incineration capacity in the UK is volatile and subject to multiple domestic and international pressures.Atpresentitisundersignificantdemandandmaynothavethecapacitytocopewith the increased volumes of POPs waste6.

• Waste that does not contain POPs above destruction thresholds may be incinerated unnecessarilyduetoinadequatePOPsidentificationandsortingcapability6.

• Increased volumes of POPs waste in incinerators may increase atmospheric emissions from incineration (though the regulatory system would ensure that no significant impact to theenvironment or human health would be caused as a result)6.

• Increased concentrations of POPs in the stream of waste destined for incineration may affect the composition of the bottom ashes and air pollution control residues by increasing concentrations of ash components such as antimony. This could make recovery more challenging as waste classificationmaybealtered6.

• Incineration of large quantities of plastic waste, which contain POPs, may cause operational challengesinmunicipalwasteincineratorsgiventhehighcalorificvalue(CV)ofplasticandthe increased boiler corrosion due to halogenated substances. Energy from waste facilities arealreadyoperatingattheirCVlimitsandsomanyareunabletoacceptanymorehighCVwaste6.

metal shredder residue must undergo further processing to separate out the fractions that contain POPs. Levels of dismantling and worker exposures can be minimised by encouraging manufacturers to mark components that contain FRs3. This method has been successfully used in Japan to improve Waste Electronic and Electrical Equipment (WEEE) plastics recycling rates12. Component parts are labelled to identify parts that are manufactured from recycled plastics and parts thatcontainFRs.Thisprocessallowstheflowofmaterials to be easily traced, which has improved theefficiencyofclosed-looprecycling.

Separation technologiesThe term separation technologies covers a broad range of methods that exist to enable items that containPOPstobe identifiedandseparatedoutfrom the waste stream. Several technologies exist and the most appropriate method will depend on which POPs are likely to be present and their concentrations in the waste stream.

Hand-held devices that can detect the presence or absence of halogenated POPs can be used by recyclers to identify waste that may be contaminated. Sliding spark spectrometers operate within the optical to UV range and canbe used to detect polyvinyl chloride (PVC) andother halogenated materials3. They are primarily used to detect the presence of brominated frame retardants (BFRs) in waste and have a minimum detection limit for bromine of 0.1%. In

practice their limit is typically set at 1% bromine because contaminated plastics contain levels of BFRs between 3% and 20%3. The handheld sliding spectrometer can be combined with a near infrared detector, which allows the plastic polymer type to be determined3. This can improve the value of the recycled plastic stream as the individual polymer fractions are cleaner. X-ray fluorescenthand scanners (commonly referred to as ‘XRF scanners’ or ‘guns’) can also be used to detect plastics that contain halogenated FRs and these operate with a detection limit between 0.001% and 0.01% and can therefore, detect much lower levels of bromine than sliding spark spectrometers3. Hand held detectors have the advantage of only taking a few seconds to scan an item however, the detector must be in direct contact with the material surface and so materials with a coating must be scratched. Therefore, they are not appropriate for use in automated sorting systems. They are also unlikely to be economically feasible for small scale operations as their cost can range from £20 000 - £50 00013. Moreover in most circumstances they are not operationally feasible as it is impractical to check for POPs on an item by item basis6.

There are a number of technologies that are suitable for use on automatically sorted waste, including X-ray transmission technology. This technique uses differences in optical densities to separate materials and has been successfully used to separate plastics containing BFRs in Switzerland3. However, the ‘clean’ fractions that

are produced still contain a reduced bromine content therefore, X-ray transmission separation should be combined with further treatment, such as near infrared, to produce a marketable recycled polymer3. It should be noted that the use of near infrared is limited because it has a relatively low accuracy and is unable to identify dark coloured plastics14. Ramen spectroscopy is a promising technology that can be used in hand-held scanners and automated sorting. It has been deployed in Japan, at pilot scale, to successfully separate out plastics containing BFRs14. Direct contact with the material is not necessary and so the technology can be used as part of an automated process. The complete separation process, used in Japan, combined ramen spectroscopy with specific-gravity-separation and was able to produce plastic with a single polymer purity of 98%14.

Specific-gravity-separation, also referred to asfloatandsinktechnologyisapre-treatmentthatiscommonly used in recycling processes and uses differing densities to separate BFR contaminated plastics. The plastics are placed in a liquid media such that thebromine freeplasticsfloatand thecontaminated plastics sink3. The same technique can also be used to separate different polymers and has used been used successfully in several industrial scale plants3. However, the success of the technique is dependent on the use of an appropriate liquid media and the suitability of the input fractions. It should also be noted that over time the flotation media itself can becomecontaminated with POPs6.

A promising development of specific gravityseparation, known as the magneto-Archimedes method, has been demonstrated at laboratory scale in Japan15. The technique uses differing densities as well as the varying magnetic susceptibilities of different plastics to separate plastics containing BFRs. The study showed the potential to separate plastics with a high accuracy in a continuous process15. However, further work is required to improve the separation speed and accuracy before the technique can be deemed ready for market.

No single technique can achieve 100% separation of POPs contaminated waste therefore, there will always be residual levels of POPs in the so called ‘clean’ fraction. As such, it is often best practice to use a combination of the techniques described heretoachievethemostefficientandeconomicallyviable level of separation3.

Thermal destruction and energy recovery

Thermal technologies for the destruction of POPs waste typically fall into three broad categories: incineration; non-combustion thermal treatment; and energy recovery from waste, which generates energy using either of the two aforementioned methods6. Thermal destruction technologies can reduce the mass and volume of waste whilst reducing the fuel demand for waste disposal or generating surplus energy. However, there are significant issuesassociatedwithsomeof theseapproaches including the unintentional formation of POPs, known to occur with thermal destruction11. This occurs via incomplete destruction where

residual chlorinated organics form new chlorinated toxicants, such as dioxins or furans. A summary of the thermal destruction technologies that are available has been provided below. IncinerationIncineration is the most widely used POP destruction technique because of its high market availability, versatility and relatively low pre-treatment requirements6. Two types of incinerator can be used for the destruction of POPs waste, hazardous waste incinerators (HWIs) and municipal waste incinerators (MWIs)6. MWIs can accept a heterogeneous mix of wastes with varied

Separation Technologies Evidence Gaps• Evidence is lacking regarding which components in products are likely to have a high risk of

containing POPs. A robust database, of high risk components, would allow them to be easily identifiedandseparatedout6,16.

• Evidence is lacking regarding viable technical solutions that could be standardised across industry to ensure manufacturers mark components with the chemicals that were used to manufacture them. Such a solution would allow waste management facilities to easily identify items that contain chemicals, which may be classed as POPs in the future6.

• Evidence is lacking in regards to whether the use of recycled plastics in sensitive products, such as food packaging or children’s toys, is appropriate as in some cases POPs concentrations may not be below acceptable thresholds17.

• Evidence is lacking in regards to the overall chemical burdens that workers in dismantling and recycling plants are exposed to and the possible health impacts of this exposure3,6.

• Evidence is lacking in regards to the potential environmental impact of dismantling activities6.

concentrations of POPs3. However, not all POPs can be successfully destroyed in MWIs because they typically operate at a minimum temperature of 850 °C, which is lower than the required temperature to ensure complete destruction of some POPs11. Therefore, not all POPs waste can be destroyed using MWIs, some must be sent to HWIs18.

Whilst, incineration is a well-established, widely available, mature technology that requires low levels of pre-treatment there are practical issues associated with both incineration types in the UK6. HWIs are a high cost treatment and only three facilities currently exist in the UK (Fawley near Southampton, Ellesmere Port near Liverpool and Sandwich in Kent)19. Most HWIs are not equipped with energy or resource recovery solutions therefore, energy efficiency is not optimised.Furthermore, some incinerators do not reprocess their bottom ash and air pollution control residue so valuable products in the waste, such as antimony or bromine, are not always recovered andinsomecasestherecoveryisinefficient3,6. In addition, incineration releases greenhouse gases

Table 2: Estimates of emissions from municipal waste incinerators

and creates hazardous by-products that must be dealt with such as air pollution control residue and unintentionally formed POPs (see Table 2)18.

Destructionefficiencyisheavilydependentontheincinerator temperature but it is also affected by the concentration and type of POPs present11,18 (see Table 3). Higher temperatures are advised when large amounts of POPs are present and are always favourable to ensure the complete destruction of POPs19. However, some countries have raised concerns about the lack of detail, provided in the Basel Convention, regarding which temperatures are required to destroy different POPs21. To address this concern the Swedish Environmental Protection Agency carried out an evidence review to determine destruction levels for POPs at different incineration temperatures18. Theyfoundsignificantgapsintheevidencesuchthat the destruction of PBDEs and PFOS in MWIs couldonlybestatedwithalowlevelofconfidence18. Similarly, the destruction of HBCD could only be confirmedwithamediumlevelofconfidencewhilst,therewasahighlevelofconfidencethatPCDD/Fswere destroyed in MWIs18. The study concluded

Table 3: Recommended incineration temperatures for destruction of selected POPs

PyrolysisPyrolysisisdefinedasthethermaldecompositionof waste in the absence of air3. High temperatures (>300 °C) are used to irreversibly convert waste into gases, water, oil, tar and char. Pyrolysis can be used as a standalone treatment or in combination with incineration25. Studies have found pyrolysis compares favourably with MWIs as it has lower emissions, requires lower temperatures and has better levels of energy and resource recovery25-26. For example, it has been shown that pyrolysis can be used to convert brominated plastic waste into valuable hydrocarbon products, such as methane and pyrolysis oil (a synthetic fuel), using only 10% of the energy content of the waste27.

However, there are very few successful implementations of pyrolysis because there are often technical issues associated with

that levels of destruction are highly dependent on temperatures, turbulence and residence times being optimised18. Shut down and start up were identifiedasmajorsourcesofunintentionalPOPsand should therefore be minimised. It was also noted that waste should be relatively homogenous and have consistent POPs concentrations because the unintentional formation of POPs is strongly dependent on the ratio of chlorine and bromine in the waste mixture18. Moreover, high levels of halogens should be avoided in the waste stream as these can form corrosive materials that damage incinerators thereby increasing the risk of unintentional POPs formation and maintenance costs3,18,22.

Incineration with energy recoveryAs has already been mentioned one of the major drawbacks of hazardous waste incineration is the lack of energy recovery as this does not align with priorities to improve the sustainability of waste disposal6. Although, it should be noted that HWIs notcurrentlyrecoveringenergycouldbemodifiedto do so in the future6. It has been argued that rather than investing in improved separation techniques to increase recycling rates and improve the quality of recycled materials that it may be better to incinerate POPs waste and recover its energy value in waste to energy plants23. However, for this to be successful incineration plants will need to ensuretheyhavesufficientairpollutionabatementequipment in place to cope with the increased demand. There is currently only one hazardous

waste incinerator in the UK operating with a limited amount of energy recovery but there are 50 operational municipal waste energy recovery plants in operation in the UK, which generate large amounts of electricity6. However, they have been met with objections from environmental groups that argue against incineration because of its claimed negative impact on recycling rates and greenhouse gas emissions24. Nonetheless, it is important to note that in the absence of other waste disposal facilities the current alternative to incinerationwouldbelandfill,whichisalsolikelytobe met with objections from the public6.

the technology. Pyrolysis plants have high maintenance costs, compared with incinerators, because the plants have a higher level of complexity22. Furthermore, the char recovered from the process can contain levels of brominated POPs such that it is characterised as hazardous waste in some EU member states and has limited market value3. In addition, the pyrolysis oil, can have high levels of contamination, limiting its use and value3. Therefore, levels in the oil must be monitored to ensure it can be used and is within the limits set out by the Stockholm Convention1. It is also difficult to generate energy from thegases produced by pyrolysis as they contain high concentrations of tars therefore, the gases must be cleaned prior to use3. Pyrolysis systems also typically require high levels of pre-treatment to ensure the waste can be fed in to the reactors22. Finally, some pyrolysis plants use unsustainable fuel sources, such as fossil fuels, to create the high temperatures that are required, resulting in high amounts of greenhouse gas emissions6.

A promising area of research in the use of pyrolysis for POPs waste disposal is the combined treatment of halogenated plastic waste alongside electric arc furnace dust (EAFD)28. The combined pyrolysis ofBFRsandPVC, present in the plasticwaste,produces acids (HCl and HBr)28. These acids react with the metal oxides in EAFD to form metal halides, which can be separated out easily. Using EAFD, which is a waste product, as opposed to using metal oxides additives reduces the cost of

the process and increases the amount of waste that is treated28. The presence of EAFD also minimises the unintentional formation of halogenated organic compounds as they are captured during the process. The combined treatment also allows the valuable and finitemetals present in the EAFD,such as zinc and lead, to be recovered28. Bromide containing materials can also be recovered as part of the process. However, there are currently no pilot or industrial scale plants in existence28. Therefore, further research needs to be carried out to better understand the process and determine whether it is appropriate for use at an industrial scale.

Supercritical Water Oxidation Supercritical water oxidation (SCWO) is primarily used commercially to treat aqueous organic wastes that are too dilute to be handled by incineration plants29. Water exhibits unique organic solvent like properties under supercritical conditions whereby the organics and an oxidant, such as air or oxygen, mix with the water and the waste is oxidised to form carbon dioxide and water3. The treatment is less complex if wastes only contain carbon, hydrogen, oxygen and nitrogen because other elements, such as chlorine or fluorine, produceacidsorsaltsthatcanleadtodifficultiesbecauseof corrosion and salt precipitation3. Several full-scale SCWO plants are currently in existence with plants located in Sweden, China and the USA3,30. However, large amounts of research and development are being carried out to maximise efficiency and minimise levels of corrosion and

facilitates energy recovery by forming syngas, which can be used to produce chemical products or burned to produce energy2. The main advantage ofgasificationasadestructiontechnologyarethatit creates a valuable product in the form of syngas. Moreover, the formation of other POPs can be controlled to a very low level2.Gasificationhasahigherdebrominationefficiencythanpyrolysisbutrequires a greater amount of energy2. Life cycle assessment has found that staged-gasificationis an eco-efficient technology for the disposalof WEEE plastics2. However, data on the long term operation of gasification plants, includinginformation on efficiency, emissions and costs,is lacking3. The main challenge for gasificationtechnology is ensuring that the syngas is of high enough quality for use. To ensure the quality of the product gas high levels of maintenance and gas purificationare required,which increasesoverallcosts2. Furthermore, the gas quality is dependent onsufficientcharacterisationandpre-treatmentofthe waste2.

Gasification has been used in combination withpyrolysis to develop a process that destroys POPs in plastics with a completely closed bromine loop, thereby allowing valuable resources to be recovered27. The process uses pyrolysis to break down the plastic into its petrochemical feedstock components.Gasificationisthenusedtoconvertthe hydrocarbons into syngas27. Following this, the metals are recovered from the pyrolysis slag in a molten metal bath and the remaining carbon fraction is used to heat the bath27.The flue gasand hydrogen bromide are then converted into their salts and hydrobromic acid is sometimes produced at this stage27. The bromine residues and salts can then be used industrially to manufacture commercial bromine-based products27. This process avoids potential releases of harmful bromine substances and enables the sustainable production of other bromine products27.

Catalytic DecompositionCatalytic decomposition is defined as thedecomposition of POPs waste with the aid of one or several catalysts3. There are two main classes: base catalytic decomposition and thermal catalytic dechlorination.

Base catalysed decomposition (BCD) uses sodium hydroxide, catalysts and a hydrocarbon reagent mixture to treat both liquid and solid POPs waste11. The process generates hydrogen at high

salt precipitation so that more heterogeneous waste can be treated efficiently3. Supercritical water oxidation is a promising technology as it has beenproventohavehighdestructionefficiencies,low gas emissions and low amounts of solid by-products30. Moreover, the process does not result in the unintentional formation of other POPs. However, plants tend to have small capacities and high levels of pre-treatment are required for solid wastes so that they can be pumped as fine slurries3. Therefore, other technologies may be more suitable for halogenated wastes, such as plastics and foams, due to corrosion and maintenance requirements and the requirement of relatively homogenous streams3.

GasificationGasification is a process that uses hightemperatures (>700 °C) in the presence of oxygen or steam to convert waste into synthesis gas, which is primarily composed of carbon monoxide, carbon dioxide, hydrogen, nitrogen and some hydrocarbons29. The process may also produce small amounts of other gases and tars. The process

temperatures (300 °C), which breaks down the chemical bonds in the POPs. This process can be used to treat waste with high concentrations of halogenated compounds. The waste requires pre-treatment to ensure it is within acceptable PH and moisture limits3. Thermal desorption is also required prior to treatment whereby, heat is used to increase the volatility of contaminants so they can be removed from the solid matrix. The technology is currently available commercially via established vendors and there are several facilities worldwide3. There is also no possibility for POPs to be formed unintentionally because oxidation does not take place. However, plant construction has a high capital cost and the systems are moderately complex22. The process also produces by-products that may contain chlorinated hydrocarbons and would therefore require appropriate disposal.

Similar to BCD, thermal catalytic dechlorination requires relatively lower temperatures than other treatments31.Highdechlorinationefficiencieshavebeen achieved using metal oxides as catalysts to treatflyash.Forexample,thecompleteremovalofHCBfromflyashhasbeenachievedinunder30 minutes at relatively low temperatures (300-400 °C), in comparison to other thermal treatments31. Furthermore, the use of noble metals allows dechlorination to take place under even milder conditions (50-60 °C) without any unintentional formation of other POPs31.

Plasma arc technologyPlasma arc technologies convert waste to syngas, metals and an inorganic slag using an electric arc and an ionised gas heated to very high temperatures (up to 10 000 K)3,29. The main advantage of plasma technology is thatthe chemistry in the furnace can be

closely controlled to suit the feedstock. High temperatures (in excess of 1500 °C) can be achieved in inert conditions without the need for combustion chemistry allowing the production of syngas, which can be used to generate energy3,22. Plasma technology systems have demonstrated highdestructionefficienciesthatsatisfyregulatoryrequirements and there are several plants that typically use plasma technology alongside gasificationtotreatwaste5. In this case plasma is typically used as a ‘polishing’ system to ensure the destruction of long chain hydrocarbons, produced fromgasification,andcomplexPOPs5. Plasma arc systems have been used to recover energy from a wide range of waste streams including incinerator fly-ash and air pollution control residues3,22. However, it should be noted that high levels of pre-treatment may be required to alter the chemistry of the feedstock to prevent damage to the furnace6.

in the cement kiln dust6. Therefore, waste streams may need to be blended to reduce these risks6. Smaller capacity cement kilns tend to be under batch operation6. This can lead to quality issues in ash and suboptimal performance, which may be important if POPs wastes are used as co-incineration fuel as this could affect emissions and the quality of the cement produced6.

Cement kilns are an appealing technology for POPs destruction as they have high destruction efficiencies, generate energy from the waste,require minimal pre-treatment and are a mature and well established technology22. Moreover, the UK has several cement kilns (although not all are permitted to burn hazardous waste) so there is potential for large capacity in the UK6. However, there is a risk that POPs are unintentionally formed. Therefore, it is important that halogen levels are sufficiently monitored to ensure emissions arewithin acceptable limits and that cement quality is not compromised6. At present, fuel replacement by chlorinated hazardous waste is limited to 40%6. Beyond this level cement kilns are no longer considered to be co-incinerators and are instead classified as waste incinerators with differentregulatory requirements6. It should also be noted that the replacement of fuel with hazardous waste may be perceived negatively by the public.

Metal SmeltersThe destruction of some POPs has been demonstrated using metal processing technologies3,11. Technologies such as smelters

As is typical of all high temperature processes, plasma systems also have the potential to unintentionally produce POPs22. They also have high energy demands, produce high levels of emissions and have high levels of complexity, which require specialised staff22.

Cement Kilns The co-processing of hazardous waste in cement kilns is a long established practice6. Tests have shown that provided the process and inputs are appropriately controlled there are no differences in product quality or emissions when parts of the fuel are replaced with hazardous waste3. Cement clinker is typically manufactured in large rotary kilns at temperatures (1500 °C) and residence times (>2s) that are sufficient todestroyPOPs3. Cement manufacturing is an energy intensive process and so the replacement of fuel with hazardouswaste increases the efficiency of theprocess and allows for energy to be recovered from the waste3. The destruction efficiency andunintentional formation of POPs are dependent on the feeding points, temperatures and residence times therefore, it is important to ensure the configurationiscorrect18.Thedestructionefficiencyis also heavily dependent on the halogen content of the waste18. To assess whether the plant can be used for routine disposal the POPs content of emissions, products and bypass stack need to bequantified6. If POPs percentages in the waste stream are too high this can reduce the quality of the cement, increase ash formation, clog the fuel injection zone and increase POPs concentrations

Thermal Destruction Evidence Gaps• More data are needed on the emissions of POPs from thermal destruction processes using

complex, heterogeneous waste streams as opposed to model compounds8.• More data are needed on the residence times, turbulence and temperatures required to maximise destructionefficienciesinMWIs,usingreal-worldwastestreamswithvariedcompositionsofPOPs8,18.

• Lessestablishedtechnologiessuchaspyrolysisandgasificationrequiremorecomprehensiveresearch to understand how they perform with waste streams containing different compositions of POPs and how to optimise these processes to maximise energy recovery, destruction efficiencyandminimiseemissions3,6.

• More data are needed emissions from on cement kiln emissions from wastes that contain varied halogen contents6.

• More research is needed to develop cheaper catalysts for thermal catalytic destruction that work at lower temperatures and suppress the formation of toxic by-products31.

• More research is required on how to minimise halogen corrosion to reduce failures and maintenance costs3.

• More data are needed, at both pilot and full scale, on less established technologies6.• More research is needed to better understand how to combine different technologies to maximiseefficiency6.

and electric arc furnaces can integrate some materials that contain halogens with primary or secondary materials such as ore concentrates, catalysts and industrial residues3,6. However, limited information exists on the effectiveness and environmental impacts of these technologies to destroy halogenated POPs8.

Smouldering CombustionSmouldering combustion has been demonstrated to be a promising technology for the remediation ofmediacontaminatedwithPFASsspecifically32. During the process the PFASs are absorbed onto a solid fuel, such as granular activated carbon (GAC)32. The GAC is then subjected to smouldering combustion at temperatures >900 °C32. In laboratory conditions, concentrations in post treatment residues were demonstrated to be below detection limits but some PFASs were emitted as part of the process32. However, it was proposed that these could be scrubbed using GAC in an off-gas treatment32. This method has yet to be scaled beyond the laboratory but if it successfully developed at an industrial scale it could be used to destroy PFASs emitted from incinerators or PFASs dissolved in chemical recycling processes32.

Chemical Destruction and RecyclingChemical processes can be broadly categorised into those that destroy POPs via dehalogenation and those that separate POPs via dissolution or solvent extraction. The separation of POPs creates a clean waste stream that can be recycled and a separate stream, which can be treated to destroy the POPs3. This reduces the amount of POPs waste that needs to be destroyed and increases recycling rates thereby, aligning with priorities to create a more circular economy6. Solvent extraction processes use solvents that only dissolve the selected target polymer and leave the non-target polymers intact, allowing efficient separation in single polymer streams6. This process can be challenging depending on the complexity of the different polymers present in the waste stream.

Alcoholysis Alcoholysis is a separation process that has been used to separate POPs in foams commonly found in soft furnishings3. The foams are heated to high temperatures with an alcohol and catalysts to depolymerise the polyurethane and form the component polyols and amines. Depolymerisation percentages over 90% have been reported making this technique an efficient method to recyclepolyols3. However, limited data exists on the extent of dehalogenation of BFRs that takes place during alcoholysis therefore, there are likely to be BFRs present following depolymerisation3.Purificationisfeasible but is currently an expensive process and is yet to be optimised3. Therefore, alcoholysis is not yet an appropriate solution for the environmentally sound destruction of POPs.

Solvent Extraction Solvents can be used to extract POPs from various types of waste. Solvent based extraction has been used at an industrial scale in plants to extract PVCs and BFRs from waste3. The technique hasalsobeenused to removeflameretardants,foaming agents and chlorofluoroalkanes frompolyurethane foams3. These foams are commonly used as sampling traps to analyse air samples for FRs therefore, effective solvent extraction methods with high recovery rates have been developed3. However, this technique has yet to be applied to the removal of BFRs from foam present in industrial waste3. Hence, more research is required to understand whether this technology could be applied in this way to more heterogeneous waste streams.

One of most promising solvent based extraction processes that has been developed recently is CreaSolv®11,33. The process uses specificallydevelopedproprietarysolvents tocreatepurifiedpolymers that comply with the Restriction of Hazardous Substances Directive and can be used to manufacture new polymers3,33. The BFRs that are removed as part of the process are destroyed separately, typically via HWI36. The solvents used in the process are not hazardous or classed as volatile organic compounds36. Therefore, they can be reused in the process.

The Creasolv® process can accept mixed waste streams and the propriety company state that it can be used to recycle plastic packaging, expanded polystyrene (EPS), waste electrical and electronic equipment (WEEE), end of life vehicles and plastic composites33. Tests have demonstrated that hexabromocyclododecane (HBCDD) can be removed from EPS insulation

panelswithanefficiencyof>99.7%andthat therecycled polystyrene can be used to make new EPS as it contains levels of HBCDD <100ppm36. The process is currently being used at a pilot plant in Indonesia to recycle polyethylene sachets in a closed loop36. A demonstration plant is also being built in the Netherlands with the support of the Basel Convention36. Creasolv® has now been listed as a recommended technology for the environmentally sound management of POPs waste in the Convention11. The plant is being built alongside a bromine recovery unit so that the bromine from the extracted HBCDD can be recovered and used in other chemicals11.ThedestructionefficiencyofHBCDD has been reported as 99.999% and life cycle analysis has shown that CreaSolv® has a lower environmental impact than incineration with energy recovery36. The CreaSolv® process has been shown to consume only 20% of the energy that is required to manufacture virgin polymers27.

However, there are some issues associated with the process that need to be addressed before it can be deemed to be an economically feasible solution. The recycled polymers that are produced must be carefully monitored to ensure they are compliant with regulatory limits and can be used to manufacture new products13. To mitigate the risk from contaminated plastics, the concentrations of POPs in recycled polymers should be closely monitored if they are to be used in sensitive applications such as toys or food packaging13. The process also requires relatively high levels of pre-treatment because the waste must be shredded, compacted and sieved to remove any metals13. The advantage of this is that metals can be recovered, thereby increasing the sustainability of the process. Commercial viability of the process in the UK has been assessed such that the extraction of BFRs from WEEE would be viable with a throughput of 10 000 tonnes/year13. However, commercial viability could be vastly improved following more research to optimise and develop the process13.

Mechanochemical DestructionThe field of mechanochemistry is rapidlydeveloping and is the focus of large amounts of new research. It is typically used for the preparation of new materials, however, mechanochemical (MC) destruction is a promising technology for the destruction of POPs. Special high energy mills are used to carry out chemical transformations that are initiated or accelerated by mechanical forces8.

One of the main advantages of MC technology is that it is more environmentally friendly than other methods of destruction8,31. It is a non-combustion technology so no off-gas treatment is required and the milling process is carried out at relatively low temperatures and pressures8,31. MC destruction emits less CO2 than combustion, has a lower energy requirement and the risk of the unintentional formation of other POPs is very low8,31. MC destruction does not require the use of solvents and in some cases the reactions can be carried out without the addition of any co-reagents8,31. However, the use of alkali earth oxides and metals iscommonlyemployedtoincreaseefficiency8,31.

The mills used in MC destruction have a low levelofcomplexityanddonotposeasignificantenvironmental risk because of the modest reaction conditions and the lack of hazardous reagents or by-products29.Theproductsofthereactionarefinelymilled inorganic mixtures that contain, carbon, CO2, water and inorganic halides8. Research studies have demonstrated that MC destruction can effectively destroy several halogenated pollutants8. However, different compounds may require different co-reagents to ensure maximum

Chemical Destruction Evidence Gaps• More research is required to develop

solvent based recycling technologies that have been demonstrated to be feasible at the laboratory and pilot scale into large scale chemical recycling plants6.

• More research is required to optimise the recovery of rare earth metals, such as antimony, because their high market value would increase the economic viability of these technologies6.

levels of destruction are achieved8. MC destruction technology is now recognised as a viable non-combustion method for the destruction of POPs and can be used to treat several types of solid wastefrompurestockpiledPOPstoflyash8.

There are currently three existing pilot and full-scale MC technology plants in New Zealand, Japan and Germany3. However, further research is required to optimise the process before it can be deployed industrially in a safe and economically viable manner. The current process requires high quantities of reagents and several hours of milling, which results in high costs and high energy demands34. Research has shown that more expensive co-milling reagents can achieve complete destruction at stoichiometric ratios34. The increased reagent cost can be mitigated by choosing reagents that produce high value materials34. This has been demonstrated in the case of destruction of brominated POPs where selected reagents completely converted the pollutants to their corresponding oxybromides, which have many potential applications35.

$20 000 - 50 000 per device3

Established

Established

CountriesRunning costsCapital costsCurrent feasibility

Established

Established

EstablishedEstablished

Established

Established

N/AN/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

ND

ND

ND

ND

ND

NDND

NDND

N/A

ND

NDND

£5 million36

$200-5000/tonne29

$1.2-1.5 million29

$1million

$250-1000/tonne29

$1200/tonne29

£0.7 million/year36

Established

$1-5/kg22

ND

Japan & France2

Japan15

Global22

Global

Global

Global

Global22

Global22

Global22

The Netherlands, Indonesia33

New Zealand, Japan, Germany8

$200-500/m3 for soils22$2-6 million22

High22

Not successfully implemented for

POPs waste2

Not considered a proven technique

for BFR waste

Established/more data needed for large volumes of

solid plastic waste

Established/more treatment data for

FRs

Experimental/pilot scale for POPs15

Experimental/pilot scale32

Established/more data needed for

some POPs

Not feasible does not remove POPs

Dismantling

Hand-held devices

Speci�c-gravity separation

Magneto-Archimedes separation

Incineration

Pyrolysis

Supercritical water oxidation

Gasi�cation

Catalytic decomposition

Plasma arc technology29

Cement kilnsMetal processing

Smouldering combustion

Alcoholysis

Solvent andsupercritical �uid

extractionMechanochemical

destruction

Pre-

trea

tmen

tTh

erm

al d

estr

ucti

on a

nd e

nerg

y re

cove

ryCh

emic

al

dest

ruct

ion

and

recy

clin

g

Mechanochemical Evidence Gaps• Research should be carried out to

optimise reagent choice to reduce costs and energy demands by improving reaction kinetics and lowering reagent to pollutant ratios8,35.

• Research should be carried out to optimise milling devices to reduce costs and energy demands by improving reaction kinetics and reducing milling duration8,35.

• Research should be carried out to improve the understanding of reaction mechanisms for different compounds and reagents under different conditions to optimise the process8,35.

• Research should be carried out to improve the understanding of the technology’s effectiveness on complex solid waste matrices to ensure the presence of inorganic components does not increase the risk of unintentional formation of POPs8,35.

Summary of current feasibility and estimated costs for each technology (estimates do not incorporate the cost of packing, shipping or any pre-treatment needed)

References1. UNEP. The Stockholm Convention on persistent organic pollutants. 2017*2. Wang R, Xu, Z. Recycling of non-metallic fractions from waste electrical and electronic equipment (WEEE): a review. Waste Management 2014; 34:1455-14693. Lucas D, et al. Methods of responsibly managing end-of-life foams and plasticscontainingflameretardants:PartI.EnvironEngSci2018;35:573-5874. United Kingdom of Great Britain and Northern Ireland, The national implementation plan for the Stockholm Convention on Persistent Organic Pollutants; NIP UK: 2017*5. Secretariat of the Basel Convention, Basel convention on the control of transboundary movements of hazardous wastes and their disposal. 2018;1471-68956. Personal Communication with Evidence Statement Steering Group Members. 20197. EU. Regulation (EU) 2019/1021 of the European Parliament and of the Council.OfficialJournaloftheEuropeanUnion20198. Cagnetta G, et al. Mechanochemical destruction of halogenated organic pollutants: A critical review. J Hazard Mater 2016;313:85-1029. Defra. A Green Future: Our 25 year plan to improve the environment. 2018*10. Defra. Further update of the UK’s persistent organic pollutants multi-media emissions inventory ECM_55296. 2019.11. UNEP. General technical guidelines on the environmentally sound management of wastes consisting of, containing or contaminated with persistent organic pollutants. UNEP 201812. The national implementation plan of Japan under the Stockholm Convention on Persistent Organic Pollutants; NIP 201613. FreegardK, et al. Develop a process to separate brominated flameretardants fromWEEEpolymers:final report.Waste&ResourcesActionProgramme; 2006;PLA-37 14. Kawazumi H, et al. High-performance recycling system for waste plastics using raman identification. In Progress in Sustainable EnergyTechnologiesVolII2014:519-52915.MisawaK,etal.Separationofflameandnonflame-retardantplasticsutilizing magneto-archimedes method. J Phys Conf Ser 2017;871:01210316. Stubbings W A, Harrad S. Extent and mechanisms of brominated flameretardantemissionsfromwastesoftfurnishingsandfabrics:acriticalreview. Environ Int 2014;71:164-17517. Guzzonato A, et al. Evidence of bad recycling practices: BFRs in children’s toys and food-contact articles. Environ Sci: Process Impacts 2017;19:956-96318. Lundin L, Jansson S. A desktop study on the destruction of persistent organic compounds in combustion systems Keminska Institutionen 2017

19. Fera. Recycling of home and garden pesticide containers: Incineration (HSE1101). Evidence Project PS2808; 201320. Sabbas T, et al. Management of municipal solid waste incineration residues. Waste Management 2003;23:61-8821. The national implementation plan for the Stockholm Convention on Persistent Organic Pollutants for Sweden; NIP 201722. STAP. Selection of persistent organic pollutant disposal technology for the global environment facility. Scientific and Technical Advisory Panel;Global Environment Facility; 201123. Fisher M, et al. Sustainable electrical and electronic plastics recycling. IEEE International Symposium on Electronics and the Environment 2004:292-29724.VaughanA.Waste incineration set to overtake recycling inEngland,Greens warn. The Guardian, 16th July 2018 25. Lamers F, et al. ISWA White Paper on alternative waste conversion technologies. ISWA 201326. Quicker P, et al. Status of alternative techniques for thermal waste treatment. Expert report for the Federal Ministry for the Environment Project Z 6-30 345/18; 201527. Nnorom IC, Osibanjo O. Sound management of brominated flameretarded (BFR) plastics from electronic wastes: State of the art and options in Nigeria. Resour Conser Recy 2008;52:1362-137228. Al-harahsheh M, et al. Treatments of electric arc furnace dust and halogenated plastic wastes: A review. J Environ Chem Eng 2019;7:10285629. UNEP. Destruction and decontamination technologies for PCBs and other POPs wastes under the Basel Convention—a training manual for hazardous waste project managers 200230. Wang S, Li Y. Supercritical water oxidation for environmentally friendly treatment of organic wastes. In Advanced Supercritical Fluids Technologies. IntechOpen 201931. Tong M, Yuan S. Physiochemical technologies for HCB remediation and disposal: a review. J Hazard Mater 2012;229-230:1-1432. Major DW. Demonstration of smoldering combustion treatment of PFAS impacted investigation-derived waste. Geosyntec Consultants, SERDP Project ER18-1593 201933. Fraunhofer. The CreaSolv® Process. Fraunhofer Institute for Process EngineeringandPackagingIVVhttps://www.ivv.fraunhofer.de/en/recycling-environment/recycling-plastics.html#creasolv (28/11/2019)34. Zhang K, et al. Mechanochemical destruction of decabromodiphenyl ether into visible light photocatalyst BiOBr. RSC Advances 2014;4:14719-1472435. Cagnetta G, et al. Mechanochemical conversion of brominated POPs into useful oxybromides: a greener approach. Scientific reports2016;6:2839436.DohertyJ.RecyclingtechnologiesfirmsupplansforScottishpyrolysisplant. letsrecycle.com 13th March 201837. International POPs Elimination Network, Civil Society Works to Eliminate Persistent Organic Pollutants (POPs)

This Evidence Statement was written by Rosie Williams in a collaboration between Defra’s Chief ScientificAdviser’sOfficeandDefra’sChemical,PesticidesandHazardousWaste team.AliceMilner provided oversight and methodological guidance. Liz Lawton provided subject-specificadviceandchairedthesteeringgroup.Thesteeringgroupprovidedsubject-specificadviceandreviewed the Evidence Statement. Production was by Malcolm Kelsey and Jen Thornton. The work was funded by the London NERC DTP. Contact: alice.milner@rhul.ac.uk, liz.lawton@defra.gov.uk or max.folkett@defra.gov.uk

Evidence Statements

Evidence Statements are succinct summaries of evidence from published literature in a definedpolicy setting that are written for senior policy officials and a general non-expert audience tosupport decision making. No attempt has been made to make recommendations, but only to summarise the evidence. Evidence Statements are developed using systematic approaches to improve the reliability and confidence in thefindings, and improve the ease with which theyare updated in light of new evidence. Evidence Statements are therefore designed to be “living” documents that are updated regularly based on consultation with the expert community and when new evidence appears.

Method summary

The following search string was used to findpublished evidence related to the primary question of the Evidence Statement (What methods are currently available for the pre-treatment and destruction of persistent organic pollutants?):

TITLE-ABS ((“persistent organic pollutants”OR37ORBFRsOR“brominatedflameretardants”

OR “decabromodiphenyl ether” OR “c-decaBDE”OR decaBDE OR heptabromobiphenyl*

OR hexabromobiphenyl* OR “Foremaster BP-6”OR “Firemaster FF-1” OR hexabromocyclododecane

OR HBCDD OR hexaBDE OR heptBDEOR hexachlorobenzene OR HCB

OR hexachlorobutadiene OR HCBD OR lindaneOR gamma-HCH OR pentachlorobenzeneOR PeCB OR pentachlorophenol OR PCP

OR“perflurooctanesulfonicacid”OR“perfluooctanesulfonylfluoride”

OR PFOS OR “polychlorinated napthalenes”OR PCNs OR “chlorinated napthalenes”

OR“short-chainchlorinatedparaffins”ORSCCPsOR“chlorinatedparaffins”OR“tetrabromodiphenyl

ether” OR “pentabromodiphenyl ether”

OR“pentadecafluorooctanicacid”ORPFOAOR“perfluorohexanesulfonicacid”ORPFHxS

OR “dechlorane plus”) AND (disposal OR remediat*OR destr* OR noncombustion OR “irreversibl*

transform*” OR pre-treatment) AND NOT( popping OR music OR biomonitor))

AND NOT TITLE (soil OR microplastic OR sedimentOR groundwater OR wastewater OR occurrence)

AND NOT TITLE (“polychlorinated biphenyls”OR PCBs OR DDTs

OR Dichlorodiphenyltrichloroethane OR mercuryOR aldrin OR “alpha hexachlorocyclohexane”

OR “alpha-HCH” OR “beta hexachlorocyclohexane”OR “beta-HCH” OR chlordane OR chlordecone

OR dieldrin OR *endosulfan OR endrin OR heptachlorOR mirex OR “polychlorinated dibenzo-p-dioxins”

OR PCDD OR “polychlorinated dibenzofurans”OR PCDF OR toxaphene OR dicofol OR methoxychlor))

Search date: 07/11/19 Database: Scopus

The search was restricted to review articles written in English and published between 2005-2019, i.e. after the Basel Convention review in 2005. POPs and waste streams types (soil, groundwater, wastewater and sediment) less relevant to the current waste disposal issues in the UK were excluded from the search. The search resulted in 112 articles, of which 11 provided information on the pre-treatment or destruction/decomposition of POPs and were included in the Evidence Statement. Additional grey literature reports and scientificpaperswereprovidedbymembersofthesteering group and from a Google search using the terms “persistent organic pollutants irreversible transformation”. These articles are marked with an asterisk in the reference list. The Evidence Statement was reviewed by a steering group of experts from Defra (Liz Lawton, Max Folkett, GraemeVickery,AdilShabbir) theEnvironmentAgency (Bob McIntyre, Ben Freeman, Alan Owers, Richard Hawkins), the University of Lancaster (Andrew Sweetman) and the Water Research Centre Ltd (Jane Turrell). The work was completed between 15/10/19 and 24/01/20.