Search

Organic amendments are used to improve soil fertility and maintain agricultural fields in a productive state. Despite these benefits, the use of organic amendments is limited in many developing countries. The overall objective of this thesis is therefore to provide a better understanding of current waste management practices in developing countries and ensure sustainable crop production via the biotransformation of urban waste into a high-quality soil amendment. First, I aimed at determining the causes for the limited use of organic amendments in small-scale urban farming systems. I interviewed 220 urban farmers in Ethiopia and found that competition for agricultural waste between fuel, feed and soil amendment is a major cause for the limited use of organic amendments. I demonstrated that allocation of agricultural waste for soil amendment is linked with farmers’ livelihood strategies. I also studied variation in compost demand among different farmer groups, and the socio-economic variables which explained these variations. Gaseous losses of ammonia and greenhouse gas (GHG) emissions occur during composting of nitrogen-rich urban waste. Several technologies could reduce these losses. However, these technologies are inadequate to fit within the broader farming systems because they are expensive. The second aim of this thesis was to develop low-cost methods to mitigate N losses and GHG emissions from composting, while retaining its fertilising value. Composting by earthworms (vermicomposting) is proposed as a low-cost strategy for minimising N losses and GHG emissions. Using a wide range of substrate qualities (C:N ratio, labile C sources) and other factors (earthworm density, amount of input, and moisture), I showed that vermicomposting reduced N losses and GHG emissions compared with traditional thermophilic composting, but the magnitude of the earthworm effect varied between substrates. Earthworms also change the quantity and composition of dissolved organic carbon during composting. Another low-cost strategy is to delay the addition of N-rich substrates during composting. I demonstrated that addition of nitrogen-rich substrate after the thermophilic phase reduced N losses. Delayed addition of N-rich substrates increased N2O emissions, but reduced CH4 emissions. Delayed addition resulted in compost that was as stable and effective at completely eradicating weed seeds as traditional composting. In conclusion, urban waste compost should be considered as alternative source for soil amendment, particularly in developing countries with competition for agricultural waste. Technologies such as vermicomposting and delayed addition of N-rich substrate are recommended to increase or maintain the nitrogen content of compost, reduce N losses and mitigate GHG emissions.

The fifth part of this report on Circular Solutions is about the circular principle From Waste to Resource. The purpose of this study is to select promising options for the implementation of this circular principle and to elaborate these options further.

In deze studie is op basis van gesprekken met Nederlandse staandwantvissers en sleepnetvissers verkend in hoeverre het doorvaren van staandwantnetten kan leiden tot het ontstaan van zwerfvuil. Volgens de Nederlandse staandwantvissers zijn de problemen uit voorgaande decennia voorbij door de goede communicatie tussen staandwantvisssers enerzijds en sleepnetvissers anderzijds. Netten worden tegenwoordig nog doorvaren indien niet goed bekend is dat bepaalde activiteiten, zoals baggeren, gaan plaatsvinden. Doorvaren netten worden door de staandwantvissers zoveel mogelijk weer verzameld en eindigen dan niet als zwerfvuil. Door sleepnetvissers wordt aangegeven dat netten van Deense staandwantvissers regelmatig doorvaren worden, vooral gedurende de zomerperiode en binnen de 12-mijlzone. Deze netten worden losgesneden en dan òf als afval meegenomen naar wal, òf achtergelaten indien de netten zijn verankerd. Het is dan onduidelijk of de stukgesneden netten achterblijven als zwerfvuil. Op basis van de bevindingen wordt aanbevolen een betere communicatie te faciliteren tussen staandwantvissers en andere gebruikers van de kustzone.

In deze studie is op basis van gesprekken met Nederlandse staandwantvissers en sleepnetvissers verkend in hoeverre het doorvaren van staandwantnetten kan leiden tot het ontstaan van zwerfvuil. Volgens de Nederlandse staandwantvissers zijn de problemen uit voorgaande decennia voorbij door de goede communicatie tussen staandwantvisssers enerzijds en sleepnetvissers anderzijds. Netten worden tegenwoordig nog doorvaren indien niet goed bekend is dat bepaalde activiteiten, zoals baggeren, gaan plaatsvinden. Doorvaren netten worden door de staandwantvissers zoveel mogelijk weer verzameld en eindigen dan niet als zwerfvuil. Door sleepnetvissers wordt aangegeven dat netten van Deense staandwantvissers regelmatig doorvaren worden, vooral gedurende de zomerperiode en binnen de 12-mijlzone. Deze netten worden losgesneden en dan òf als afval meegenomen naar wal, òf achtergelaten indien de netten zijn verankerd. Het is dan onduidelijk of de stukgesneden netten achterblijven als zwerfvuil. Op basis van de bevindingen wordt aanbevolen een betere communicatie te faciliteren tussen staandwantvissers en andere gebruikers van de kustzone.

The fifth part of this report on Circular Solutions is about the circular principle From Waste to Resource. The purpose of this study is to select promising options for the implementation of this circular principle and to elaborate these options further.

The increasing scarcity of clean water sets the need for appropriate management of available water resources. Particularly regions suffering from a lack of water urgently need integrated environmental protection and resource conservation (EP&RC) technologies in order to enable effective management of the available water resources. EP&RC-concepts focus on a minimum of consumptive use of energy, chemicals, and water and a maximum of reuse of treated wastewater and of residues produced from the pollutants present in the wastewater. Consequently, by implementing these concepts, instead of a social threat, waste(water)s like sewage and industrial effluents become an important resource for water, fertilisers, soil conditioners and to some extent also energy. In addition, a bridge is made between environmental protection and agriculture practice, stimulating (urban) agriculture in the neighbourhood of large cities. Anaerobic treatment is considered as the core technology for mineralising organic compounds in waste(water) streams. Additional technologies are required to comply with the reuse criteria. Some examples of possible EP&RC concepts, using the anaerobic treatment technology for the reclamation of domestic sewage are discussed.

The aim of this thesis is to enable taking more sustainable and cost-effective decisions on MSW management in developing cities. For this purpose, a tool named SURMAT was developed and applied using data of Ho Chi Minh City, Viet Nam (chapter 6). In order to prepare the tool for modeling of the MSW management in Ho Chi Minh City, an analysis of the current MSW management system (chapter 2), a selection of technologies (chapter 3, 4) and a costs analysis of the selected technologies (chapter 5) have been conducted. Various possible solid waste management strategies for Ho Chi Minh City for period of twenty years were elaborated and discussed focusing on minimization of costs and maximization of electricity production from wastes (chapters 6 and 7). SURMAT supports in a systematic way the optimization of logistics and choice of treatment technologies in dependence of specific situation-bound constraints, such as land availability and production of useful products from wastes. SURMAT is simple to operate and well adaptable to new situations. It can help to generate guidelines or master plans for urban solid waste management. The methodology applied to develop this decision support tool can be used to set up other tools for MSW management or for other domains.

The aim of this thesis is to enable taking more sustainable and cost-effective decisions on MSW management in developing cities. For this purpose, a tool named SURMAT was developed and applied using data of Ho Chi Minh City, Viet Nam (chapter 6). In order to prepare the tool for modeling of the MSW management in Ho Chi Minh City, an analysis of the current MSW management system (chapter 2), a selection of technologies (chapter 3, 4) and a costs analysis of the selected technologies (chapter 5) have been conducted. Various possible solid waste management strategies for Ho Chi Minh City for period of twenty years were elaborated and discussed focusing on minimization of costs and maximization of electricity production from wastes (chapters 6 and 7). SURMAT supports in a systematic way the optimization of logistics and choice of treatment technologies in dependence of specific situation-bound constraints, such as land availability and production of useful products from wastes. SURMAT is simple to operate and well adaptable to new situations. It can help to generate guidelines or master plans for urban solid waste management. The methodology applied to develop this decision support tool can be used to set up other tools for MSW management or for other domains.

For many centuries urban waste management in Europe and Northern America consisted of private – to – private arrangements to remove waste from the city centre and so restrain the spread of cholera and other diseases, odour and nuisances. The agricultural and industrial value chains provided a destination and a motivation to extract and valorise rags, ashes, dust, excreta, metals, food scraps, and many other forms of secondary resources which had some value to someone. The business of recycling developed alongside of municipal waste management, and absorbed many discarded materials, but remained a separate sector with its own practices, institutions, and economic rationality. The management of solid waste management became primarily focused on dumping waste outside the city boundaries. The ‘discovery’ of the relationship between open dumping and groundwater contamination in the 1960s set the stage for a round of modernisation of waste management practices and institutions in high-income countries. The widely recognised and celebrated result was the shift from open dumping and open burning of waste to the engineered “regional sanitary landfill” as a large technical facility that concentrates waste, isolates it from population centres, protects ground-water and thus allows for safe modern disposal of increasingly complex materials. This proved to be a costly affair though, and triggered a process of ecological modernisation in solid waste management characterised by institutional and financial reforms, which elevated the cost of removal. Disposal became costly, and as cities expanded, land to dump became a scarce resource. This set the stage for incorporating valorisation into the modernised waste management landscape as an alternative to modernised disposal. The ecological modernisation process that took place in Northern Europe and North America in the 1980s and early 1990s changed the policies and practices of waste management in fundamental but seldom understood ways. Pricing of disposal in high-income countries represents a core financial reform which in turn stimulates local authorities to invest in their own recycling (composting, reuse) infrastructure as a lower-cost and environmentally attractive alternative. Municipal recycling emerges as a key modernised institution in the landscape of integrated waste management, where investment in recycling produces higher and higher recovery rates and a virtuous circle of more investment, more recovery, less waste, co-operation with the value chains which have been re-constituted as “recycling markets,” and lower system costs. In municipal recycling, the agricultural and industrial value chains function as alternative and lower-cost sinks, complementing the landfill and lowering costs for the whole waste management system. In low- and middle-income countries, in contrast, the ecological modernisation of solid waste is problematic and incomplete, and ‘recycling’ becomes a key new area of global conflict. Priced disposal does not come about, either because of low levels of disposable income or unwillingness of elected officials to impose a burden on tax- and rate-payers, or because the motivation to modernise disposal comes from global institutions and is insufficiently embedded in genuinely local policymaking. Without it the system-internal benefits of diverting materials from disposal to valorisation are missing. Municipal recycling does not emerge, and the virtuous cycle of increasing recovery ambitions and performance is replaced by a vicious cycle of interrupted private value chain transactions, declining valorisation rates, and increasing volumes of materials requiring expensive disposal. City authorities in low- and middle-income countries seeking to gain the financial benefits of selling materials compete with private (informal) waste pickers, recyclers, and livestock feeding operations, claim monopoly rights to materials, and criminalise value chain activities. But they are unable to organise effective valorisation themselves, as they lack knowledge and commercial channels to reach the value chains. The value chain actors are blamed for not buying materials, but also for exploiting poor workers in miserable working conditions. Valorisation businesses are unwilling to do business with municipalities who supply low-quality materials, so the value chain transactions fail, and both avoided costs of disposal and offsetting revenues from valorisation remain elusive. Municipalities, waste system users, and the environment lose in this situation when local authorities are unable to pay landfill operating costs, and the expensive sanitary landfill infrastructure reverts to the status of a pre-modern dumpsite, which has to handle more and more waste. Agricultural and industrial value chains also suffer, because the thousands of individual and family enterprises in waste picking, recycling, and animal feeding are at risk to lose their livelihoods, or see reduced returns on their efforts due to monopoly behaviour, criminalisation, or harassment from the formal waste system actors. Mid-level value chain enterprises get fewer materials, and increasing volumes of potentially recoverable resources end up in the dump. But there are already some examples of how changing the model can produce improved results. In a small number of cities in low- and middle-income countries, the ecological modernisation of the waste management system appears to be leading to the emergence of a new model for institutionalised valorisation, provisionally called inclusive recycling. Inclusive recycling is a model for public sector acceptance of private value chain activities of valorisation. It is a model of shared ownership, risks, and benefits, where each set of actors does what they are best at. While it builds upon the techniques for participatory planning and stakeholder engagement, as well as on technical innovations for separate collection, processing, and environmental education that characterised the development of municipal recycling in the 1980s in OECD countries, inclusive recycling does not rely on the institutional reform of priced disposal. Rather, it maintains the centre of gravity of valorisation activities in the industrial or agricultural value chains, where the knowledge and infrastructure exists to receive, process, and market materials. Instead of re-inventing recycling as a part of the municipal solid waste department’s responsibilities, inclusive recycling looks to intermediary institutions such as labour unions or recycling co-operatives to facilitate shared risks and responsibilities between local authorities and value chain actors. Inclusive recycling can be seen in some of its emerging forms in Asia and Latin America, particularly in situations where there is a tradition of co-operation between civil society and local authorities, large numbers of waste pickers at the base of the value chain pyramid, and where the paper and metal value chains are long, healthy, and deeply rooted. In place of a single municipal recycling system, inclusive recycling is a mixed system where there are many different types of actors, economic niches, and business models. The results may be high levels of recovery and diversion from disposal, making it comparable to municipal recycling as a modernised institution. Like municipal recycling, inclusive recycling contributes to the pluralism of the modernised system, with a proliferation of actors, activities, and economic niches, which qualify it as what ecological modernization scholars have called a ‘modernised mixture’. However, inclusive recycling is not municipal recycling, and in the absence of priced disposal, the risks for both local authorities and value chain actors remain high. Combining global knowledge with local control of ecological modernisation processes is one approach to keeping the risks limited and enlarging the space for the virtuous circle of inclusive recycling to take root and flourish.

For many centuries urban waste management in Europe and Northern America consisted of private – to – private arrangements to remove waste from the city centre and so restrain the spread of cholera and other diseases, odour and nuisances. The agricultural and industrial value chains provided a destination and a motivation to extract and valorise rags, ashes, dust, excreta, metals, food scraps, and many other forms of secondary resources which had some value to someone. The business of recycling developed alongside of municipal waste management, and absorbed many discarded materials, but remained a separate sector with its own practices, institutions, and economic rationality. The management of solid waste management became primarily focused on dumping waste outside the city boundaries. The ‘discovery’ of the relationship between open dumping and groundwater contamination in the 1960s set the stage for a round of modernisation of waste management practices and institutions in high-income countries. The widely recognised and celebrated result was the shift from open dumping and open burning of waste to the engineered “regional sanitary landfill” as a large technical facility that concentrates waste, isolates it from population centres, protects ground-water and thus allows for safe modern disposal of increasingly complex materials. This proved to be a costly affair though, and triggered a process of ecological modernisation in solid waste management characterised by institutional and financial reforms, which elevated the cost of removal. Disposal became costly, and as cities expanded, land to dump became a scarce resource. This set the stage for incorporating valorisation into the modernised waste management landscape as an alternative to modernised disposal. The ecological modernisation process that took place in Northern Europe and North America in the 1980s and early 1990s changed the policies and practices of waste management in fundamental but seldom understood ways. Pricing of disposal in high-income countries represents a core financial reform which in turn stimulates local authorities to invest in their own recycling (composting, reuse) infrastructure as a lower-cost and environmentally attractive alternative. Municipal recycling emerges as a key modernised institution in the landscape of integrated waste management, where investment in recycling produces higher and higher recovery rates and a virtuous circle of more investment, more recovery, less waste, co-operation with the value chains which have been re-constituted as “recycling markets,” and lower system costs. In municipal recycling, the agricultural and industrial value chains function as alternative and lower-cost sinks, complementing the landfill and lowering costs for the whole waste management system. In low- and middle-income countries, in contrast, the ecological modernisation of solid waste is problematic and incomplete, and ‘recycling’ becomes a key new area of global conflict. Priced disposal does not come about, either because of low levels of disposable income or unwillingness of elected officials to impose a burden on tax- and rate-payers, or because the motivation to modernise disposal comes from global institutions and is insufficiently embedded in genuinely local policymaking. Without it the system-internal benefits of diverting materials from disposal to valorisation are missing. Municipal recycling does not emerge, and the virtuous cycle of increasing recovery ambitions and performance is replaced by a vicious cycle of interrupted private value chain transactions, declining valorisation rates, and increasing volumes of materials requiring expensive disposal. City authorities in low- and middle-income countries seeking to gain the financial benefits of selling materials compete with private (informal) waste pickers, recyclers, and livestock feeding operations, claim monopoly rights to materials, and criminalise value chain activities. But they are unable to organise effective valorisation themselves, as they lack knowledge and commercial channels to reach the value chains. The value chain actors are blamed for not buying materials, but also for exploiting poor workers in miserable working conditions. Valorisation businesses are unwilling to do business with municipalities who supply low-quality materials, so the value chain transactions fail, and both avoided costs of disposal and offsetting revenues from valorisation remain elusive. Municipalities, waste system users, and the environment lose in this situation when local authorities are unable to pay landfill operating costs, and the expensive sanitary landfill infrastructure reverts to the status of a pre-modern dumpsite, which has to handle more and more waste. Agricultural and industrial value chains also suffer, because the thousands of individual and family enterprises in waste picking, recycling, and animal feeding are at risk to lose their livelihoods, or see reduced returns on their efforts due to monopoly behaviour, criminalisation, or harassment from the formal waste system actors. Mid-level value chain enterprises get fewer materials, and increasing volumes of potentially recoverable resources end up in the dump. But there are already some examples of how changing the model can produce improved results. In a small number of cities in low- and middle-income countries, the ecological modernisation of the waste management system appears to be leading to the emergence of a new model for institutionalised valorisation, provisionally called inclusive recycling. Inclusive recycling is a model for public sector acceptance of private value chain activities of valorisation. It is a model of shared ownership, risks, and benefits, where each set of actors does what they are best at. While it builds upon the techniques for participatory planning and stakeholder engagement, as well as on technical innovations for separate collection, processing, and environmental education that characterised the development of municipal recycling in the 1980s in OECD countries, inclusive recycling does not rely on the institutional reform of priced disposal. Rather, it maintains the centre of gravity of valorisation activities in the industrial or agricultural value chains, where the knowledge and infrastructure exists to receive, process, and market materials. Instead of re-inventing recycling as a part of the municipal solid waste department’s responsibilities, inclusive recycling looks to intermediary institutions such as labour unions or recycling co-operatives to facilitate shared risks and responsibilities between local authorities and value chain actors. Inclusive recycling can be seen in some of its emerging forms in Asia and Latin America, particularly in situations where there is a tradition of co-operation between civil society and local authorities, large numbers of waste pickers at the base of the value chain pyramid, and where the paper and metal value chains are long, healthy, and deeply rooted. In place of a single municipal recycling system, inclusive recycling is a mixed system where there are many different types of actors, economic niches, and business models. The results may be high levels of recovery and diversion from disposal, making it comparable to municipal recycling as a modernised institution. Like municipal recycling, inclusive recycling contributes to the pluralism of the modernised system, with a proliferation of actors, activities, and economic niches, which qualify it as what ecological modernization scholars have called a ‘modernised mixture’. However, inclusive recycling is not municipal recycling, and in the absence of priced disposal, the risks for both local authorities and value chain actors remain high. Combining global knowledge with local control of ecological modernisation processes is one approach to keeping the risks limited and enlarging the space for the virtuous circle of inclusive recycling to take root and flourish.

Operational and cargo related wastes from ships are an important source of litter in the marine environment in the southern North Sea and cause serious economical and ecological damage. Inadequacies in the ship to shore waste delivery procedures are considered a major factor in illegal discharges. The European Union therefore addressed the problem with the Directive on Port Reception Facilities (Directive 2000/59/EC). Obligatory waste delivery to shore and indirect financing of the costs are key-elements of the Directive to stimulate and enforce proper disposal of shipwaste in harbours. Monitoring the effect of the EU Directive is required. In the Netherlands, the Ministry of VenW commissions regular updates of Dutch data in the Fulmar-Litter monitoring database maintained by IMARES.

Operational and cargo related wastes from ships are an important source of litter in the marine environment in the southern North Sea and cause serious economical and ecological damage. Inadequacies in the ship to shore waste delivery procedures are considered a major factor in illegal discharges. The European Union therefore addressed the problem with the Directive on Port Reception Facilities (Directive 2000/59/EC). Obligatory waste delivery to shore and indirect financing of the costs are key-elements of the Directive to stimulate and enforce proper disposal of shipwaste in harbours. Monitoring the effect of the EU Directive is required. In the Netherlands, the Ministry of VenW commissions regular updates of Dutch data in the Fulmar-Litter monitoring database maintained by IMARES. Operationeel en aan lading gerelateerd scheepsafval is één van de belangrijke bronnen van zwerfvuil in de zuidelijke Noordzee. Zulk afval heeft ernstige economische en ecologische gevolgen. Tekortkomingen in afgifteprocedures in havens zijn een belangrijke achtergrond bij het illegaal overboord zetten van afval. De EU heeft dit probleem aangepakt met de ‘Richtlijn betreffende havenontvangstvoorzieningen’ (Richtlijn 2000/59/EC; de zogenaamde ‘HOI-Richtlijn’). Verplichte afgifte van afval en indirecte financiering van de kosten vormen de kern van de maatregelen waarmee de Richtlijn correcte afvalafgifte wil stimuleren en afdwingen. Het monitoren van de effecten van de HOI-Richtlijn is noodzakelijk. Het Ministerie van VenW is voor IMARES de opdrachtgever voor de Nederlandse stormvogel graadmeter.

Chemische hulpmiddelen zijn onmisbaar voor een goede reiniging en een klein residu zal er altijd zijn. Daarom werd door het PR een oriënterend onderzoek uitgevoerd om de niveaus in de praktijk te bepalen.

Table of contents: 1. Solid waste segragation at source in Ho Chi Minh City. 2. Survey of technical efficiency and economic viability of existing composting ventures and survey of the institutional and regulatory framework regarding composting in Vietnam. 3. Demand analysis of urban waste compost. 4. Stakeholder dialogue. 5. Urban biowaste treatment and reuse in Vietnam with emphasis on Ho Chi Minh City. 6. Identifying mechanisms to achieve a viable and manageable biowaste reuse chain in Ho Chi Minh City.

Table of contents: 1. Solid waste segragation at source in Ho Chi Minh City. 2. Survey of technical efficiency and economic viability of existing composting ventures and survey of the institutional and regulatory framework regarding composting in Vietnam. 3. Demand analysis of urban waste compost. 4. Stakeholder dialogue. 5. Urban biowaste treatment and reuse in Vietnam with emphasis on Ho Chi Minh City. 6. Identifying mechanisms to achieve a viable and manageable biowaste reuse chain in Ho Chi Minh City.

Van twee typen verdachte categorieën dempingen zijn parameters voor de kansverdeling van het landbouwkundig risico afgeleid uit gemeten bodem- en grassamenstelling. De noodzakelijke steekproefomvang voor het toekomstig onderzoek bij een zekerheid van 90␎n een absolute fout van 5␒s 100 steekmonsters per dempingcategorie en 25 bij een fout van 10ÐDeze aantallen zijn 60 en 15 bij een absolute fout van respectievelijk 5␎n 10␒n de berekende landbouwkundige risico's en een zekerheid van 80ÐBehalve voor cadmium en zink is geen relatie gevonden tussen gehaltes in gras en de bodem. Kwik en lood spelen een rol bij shredder; voor bouw en sloopafval zijn dat cadmium en lood. Het kopergehalte is incidenteel problematisch voor schapen maar niet voor rundvee. Aanbevolen is om landbouwkundige risico's te toetsen aan zowel de veevoerdernorm als de warenwetnorm. Verdacht dempingmateriaal wordt in het algemeen niet verwijderd, maar afgedekt met een laag schone grond, afkomstig uit het gebied zelf. De samenhang tussen herverontreiniging vanuit verdacht dempingmateriaal als gevolg van capillaire opstijging, bioturbatie, vertrapping van de zode door vee en insporende werk- en voertuigen en de dikte van de afdeklaag is bepaald met een daartoe ontwikkeld model en aan literatuur ontleende parameters. Geconcludeerd is dat een afdeklaag (leeflaag) van 0,3-0,35 m grond toereikend is, onder voorwaarde dat het organischestofgehalte in de bodem niet afneemt.

The production, use and disposal of many compounds inevitably leads to their presence in the environment as organic trace pollutants. Although their concentration may be low, these trace compounds can present an environmental hazard associated with their toxicity for human beings, their potential to accumulate in biota and ecosystems and in some cases their function as a catalyst in the destruction of the ozone in the stratosphere.In many cases these organic trace compounds enter the sewage system and will finally appear in municipal activated sludge plants. Several processes determine their distribution in these plants. Hydrophobic compounds can partition to the sludge and in this manner may create a potential hazard associated with sludge disposal. Volatile organic compounds are amenable to air stripping and surface desorption and therefore are frequently found in the off-gas of activated sludge plants. Whereas sorption and volatilisation merely rearrange the distribution of compounds among the different environmental compartments (sludge, air and water), only a destructive process such as biodegradation can actually remove them from the environment.During the last two decades several activated sludge fate models have been developed. These models are used (i) to predict the environmental exposure to specific organic trace compounds expected to appear in municipal wastewater's, (ii) to optimise the design and control of treatment plants with respect to the removal of these pollutants and (iii) to establish limits on treatment plant influent loads based upon allowable effluent loads. The reliability of these models only has been demonstrated to a limited extent and therefore their applicability remains uncertain. A validation study may help to gain some confidence in these models, but also can reveal some of their shortcomings.Based on an extensive literature review such a validation study was set-up. The fate of three test trace compounds in a pilot-scale municipal activated sludge plant was investigated: the C 12 -homologue of linear alkylbenzene sulfonate (LAS-C 12 ), nitrilotriacetic acid (NTA) and toluene. The sludge retention time (SRT) of the plant and influent concentration of the trace compounds were varied. In addition, for each of the test compounds their biodegradation kinetics by activated sludge were assessed with a method which was specifically developed for this purpose. The results showed that existing models do not yield accurate predictions, in particular because the biodegradation kinetics they employ are incorrect. A generic assessment of the fate of organic trace compounds in activated sludge plants therefore should not rely on model calculations alone. Still, existing models can be used for a first screening of new priority compounds or to design field monitoring studies for existing priority compounds. More accurate models can only be developed if more fundamental research is directed towards biodegradation of mixtures of organic substrates by mixed microbial cultures such as activated sludge.Keywords : activated sludge, organic trace pollutants, fate modelling, wastewater

The production, use and disposal of many compounds inevitably leads to their presence in the environment as organic trace pollutants. Although their concentration may be low, these trace compounds can present an environmental hazard associated with their toxicity for human beings, their potential to accumulate in biota and ecosystems and in some cases their function as a catalyst in the destruction of the ozone in the stratosphere.In many cases these organic trace compounds enter the sewage system and will finally appear in municipal activated sludge plants. Several processes determine their distribution in these plants. Hydrophobic compounds can partition to the sludge and in this manner may create a potential hazard associated with sludge disposal. Volatile organic compounds are amenable to air stripping and surface desorption and therefore are frequently found in the off-gas of activated sludge plants. Whereas sorption and volatilisation merely rearrange the distribution of compounds among the different environmental compartments (sludge, air and water), only a destructive process such as biodegradation can actually remove them from the environment.During the last two decades several activated sludge fate models have been developed. These models are used (i) to predict the environmental exposure to specific organic trace compounds expected to appear in municipal wastewater's, (ii) to optimise the design and control of treatment plants with respect to the removal of these pollutants and (iii) to establish limits on treatment plant influent loads based upon allowable effluent loads. The reliability of these models only has been demonstrated to a limited extent and therefore their applicability remains uncertain. A validation study may help to gain some confidence in these models, but also can reveal some of their shortcomings.Based on an extensive literature review such a validation study was set-up. The fate of three test trace compounds in a pilot-scale municipal activated sludge plant was investigated: the C 12 -homologue of linear alkylbenzene sulfonate (LAS-C 12 ), nitrilotriacetic acid (NTA) and toluene. The sludge retention time (SRT) of the plant and influent concentration of the trace compounds were varied. In addition, for each of the test compounds their biodegradation kinetics by activated sludge were assessed with a method which was specifically developed for this purpose. The results showed that existing models do not yield accurate predictions, in particular because the biodegradation kinetics they employ are incorrect. A generic assessment of the fate of organic trace compounds in activated sludge plants therefore should not rely on model calculations alone. Still, existing models can be used for a first screening of new priority compounds or to design field monitoring studies for existing priority compounds. More accurate models can only be developed if more fundamental research is directed towards biodegradation of mixtures of organic substrates by mixed microbial cultures such as activated sludge.Keywords : activated sludge, organic trace pollutants, fate modelling, wastewater

Van twee typen verdachte categorieën dempingen zijn parameters voor de kansverdeling van het landbouwkundig risico afgeleid uit gemeten bodem- en grassamenstelling. De noodzakelijke steekproefomvang voor het toekomstig onderzoek bij een zekerheid van 90␎n een absolute fout van 5␒s 100 steekmonsters per dempingcategorie en 25 bij een fout van 10ÐDeze aantallen zijn 60 en 15 bij een absolute fout van respectievelijk 5␎n 10␒n de berekende landbouwkundige risico's en een zekerheid van 80ÐBehalve voor cadmium en zink is geen relatie gevonden tussen gehaltes in gras en de bodem. Kwik en lood spelen een rol bij shredder; voor bouw en sloopafval zijn dat cadmium en lood. Het kopergehalte is incidenteel problematisch voor schapen maar niet voor rundvee. Aanbevolen is om landbouwkundige risico's te toetsen aan zowel de veevoerdernorm als de warenwetnorm. Verdacht dempingmateriaal wordt in het algemeen niet verwijderd, maar afgedekt met een laag schone grond, afkomstig uit het gebied zelf. De samenhang tussen herverontreiniging vanuit verdacht dempingmateriaal als gevolg van capillaire opstijging, bioturbatie, vertrapping van de zode door vee en insporende werk- en voertuigen en de dikte van de afdeklaag is bepaald met een daartoe ontwikkeld model en aan literatuur ontleende parameters. Geconcludeerd is dat een afdeklaag (leeflaag) van 0,3-0,35 m grond toereikend is, onder voorwaarde dat het organischestofgehalte in de bodem niet afneemt.

De gemeente De Ronde Venen ligt in het gebied de Venen in het Groene Hart. De veengronden in dit gebied zijn vanaf de achttiende eeuw regelmatig opgehoogd met stadsafval om hun draagkracht en vruchtbaarheid te verbeteren. De opgebrachte laag wordt toemaakdek genoemd. In dit toemaakdek komen hoge concentraties zware metalen en PAK voor. Om de ecologische risico's van deze verontreinigingen in kaart te brengen is onderzoek gedaan naar de concentraties van de afzonderlijke verontreinigingen en de effecten die deze verontreinigingen hebben op bodemorganismen en daarvan voor hun voedsel afhankelijke vogels en zoogdieren.

In the Netherlands, recycling of solid organic waste streams as compost only becomes possible if the compost complies with the heavy metals standards of the BOOM decree. This dissertation focuses on the removal of heavy metals from biowaste, i.e. the source separated organic fraction of municipal solid waste. Biowaste is referred to as an organic waste stream but surprisingly it was found that a large part of biowaste is composed of inorganic material, i.e. sand, silt and clay minerals. The inorganic part of biowaste originates from the collection of garden waste. Comparison of the natural background content of heavy metals in the original constituents of biowaste with the heavy metal content of biowaste showed that biowaste is not contaminated with heavy metals. Based on these results it can be stated that there is a conflict between two government policies of (1) preventing the accumulation of heavy metals in the soil (BOOM decree) and (2) promoting the recycling and reuse of organic waste streams (National Environmental Policy Plan). It is recommended that the different legislations concerning the dosage of various organic and artificial fertilisers have to be combined in a single legislative framework.An analytical fractionation scheme was presented to determine the physico-chemical distribution of heavy metals in biowaste. The fractionation scheme was used to assess the application of physical separation and chemical extraction to reduce the heavy metal content of biowaste. On the basis of the results of the physical distribution of heavy metals in biowaste, a physical separation process was designed to valorise biowaste. A pilot plant study showed that physical separation of the biowaste is possible by a combination of physical wet separation units operated under wet conditions. The process results in (1) an organic fraction which can be converted to clean-compost, (2) a sand fraction which can be re-used in road and building construction and (3) a fraction high in humus and lutum which would make an excellent soil improver but which cannot be re-used because the heavy metal levels are too high. From a discussion of the advantages and disadvantages of the chemical extraction by inorganic acids and complexing agents it was concluded that these extracting reagents are not applicable on a practical scale due to the costs of the process and the negative environmental impacts of the discharged solid and liquid waste streams. Citric acid was proposed as an alternative extracting reagent which does not have these drawbacks.Mechanistic models were developed in order to gain more insight into factors controlling the extraction efficiency and rate of extraction of heavy metals from biowaste. Chemical equilibrium modelling was used to calculate the speciation of heavy metals in biowaste. The NICA-Donnan model taking into account the complex binding characteristics of organic matter, i.e. polyfunctional and polyelectrolytic behaviour was applied to interpret the proton and Cu(II) binding to particle-sized organic particles of biowaste. The results indicate that the humic acid content of biowaste regulates the speciation of heavy metals in biowaste. Moreover, a mechanistic model was developed which describes the course of the acid extraction of heavy metals from solid organic particles of biowaste. The extent of the proton-metal exchange is determined by the competition between the heavy metal ion and the proton for the reactive sites of the organic particles. Diffusion of the ions in the film layer and inside the particles was described by the Nernst-Planck equations. This model is able to give a qualitatively interpretation of the acid extraction of Cu(II) from the isolated particle-sized organic fractions in biowaste and the model can also explain the anomalies observed during the acid extraction of Cd, Cu and Zn from sewage sludge.

In the Netherlands, recycling of solid organic waste streams as compost only becomes possible if the compost complies with the heavy metals standards of the BOOM decree. This dissertation focuses on the removal of heavy metals from biowaste, i.e. the source separated organic fraction of municipal solid waste. Biowaste is referred to as an organic waste stream but surprisingly it was found that a large part of biowaste is composed of inorganic material, i.e. sand, silt and clay minerals. The inorganic part of biowaste originates from the collection of garden waste. Comparison of the natural background content of heavy metals in the original constituents of biowaste with the heavy metal content of biowaste showed that biowaste is not contaminated with heavy metals. Based on these results it can be stated that there is a conflict between two government policies of (1) preventing the accumulation of heavy metals in the soil (BOOM decree) and (2) promoting the recycling and reuse of organic waste streams (National Environmental Policy Plan). It is recommended that the different legislations concerning the dosage of various organic and artificial fertilisers have to be combined in a single legislative framework.An analytical fractionation scheme was presented to determine the physico-chemical distribution of heavy metals in biowaste. The fractionation scheme was used to assess the application of physical separation and chemical extraction to reduce the heavy metal content of biowaste. On the basis of the results of the physical distribution of heavy metals in biowaste, a physical separation process was designed to valorise biowaste. A pilot plant study showed that physical separation of the biowaste is possible by a combination of physical wet separation units operated under wet conditions. The process results in (1) an organic fraction which can be converted to clean-compost, (2) a sand fraction which can be re-used in road and building construction and (3) a fraction high in humus and lutum which would make an excellent soil improver but which cannot be re-used because the heavy metal levels are too high. From a discussion of the advantages and disadvantages of the chemical extraction by inorganic acids and complexing agents it was concluded that these extracting reagents are not applicable on a practical scale due to the costs of the process and the negative environmental impacts of the discharged solid and liquid waste streams. Citric acid was proposed as an alternative extracting reagent which does not have these drawbacks.Mechanistic models were developed in order to gain more insight into factors controlling the extraction efficiency and rate of extraction of heavy metals from biowaste. Chemical equilibrium modelling was used to calculate the speciation of heavy metals in biowaste. The NICA-Donnan model taking into account the complex binding characteristics of organic matter, i.e. polyfunctional and polyelectrolytic behaviour was applied to interpret the proton and Cu(II) binding to particle-sized organic particles of biowaste. The results indicate that the humic acid content of biowaste regulates the speciation of heavy metals in biowaste. Moreover, a mechanistic model was developed which describes the course of the acid extraction of heavy metals from solid organic particles of biowaste. The extent of the proton-metal exchange is determined by the competition between the heavy metal ion and the proton for the reactive sites of the organic particles. Diffusion of the ions in the film layer and inside the particles was described by the Nernst-Planck equations. This model is able to give a qualitatively interpretation of the acid extraction of Cu(II) from the isolated particle-sized organic fractions in biowaste and the model can also explain the anomalies observed during the acid extraction of Cd, Cu and Zn from sewage sludge.