What sewage sludge is and conflicts in Swedish circular economy policymaking

ABSTRACT

Recycling nutrients from renewable sources, like sewage sludge, has been promoted as a step towards a circular economy by decreasing extraction and dependency on inorganic fertilizers. Implementation, however, is often controversial. In 2018, a Swedish governmental inquiry was commissioned to propose a complete ban on land application of sewage sludge to reduce soil pollution and increase phosphorus recovery. In 2020, the inquiry suggested two pathways, one to ban all land application, and one where agricultural land use should continuously be allowed. This paper is based on interviews with experts tied to the inquiry where they reference to sewage sludge, related objects, and future management. The inquiry’s inability to propose a coherent suggestion is analysed inspired by the concept of multiple ontology. Several ontological versions of sewage sludge emerge that unveil tensions between concepts of danger and cleanliness, pollution and naturalness, often captured in previous studies of waste. Some versions of sewage sludge conflict, which can explain the difficulty to establish an ontologically singular knowledge base for a transformation of sewage sludge from waste to resource. Though most of the experts agree that circular economy and nutrient recycling are good things, policymaking is caught in an ontological conundrum.

KEYWORDS:

• Sewage sludge
• waste to resource
• nutrient recycling
• policymaking
• circular economy
• multiplicity

Introduction

In July 2018, the Swedish government initiated an inquiry called ‘Pollutant-free and circular recovery of phosphorous from sewage sludge’ with the goal to suggest a legislation that would increase the utilization of nutrients in sewage sludge, the waste product from wastewater treatment (Government Offices of Sweden 2018). Similarly, the European commission (2015) states that waste must be turned into secondary raw material replacing virgin resources as part of a circular economy; particularly highlighting recycling of phosphorus and other nutrients like nitrogen and potassium from sewage sludge to substitute non-renewable inorganic fertilizers.

Even though recycling of resources from sewage sludge is claimed to be highly desirable, the implementation of such practices has often been controversial. At the end of the 1950s, Swedish politicians settled for dumping of sewage sludge, first in proximate waterways and then, because of protests, in international waters. As times changed and ocean dumping was deemed environmentally unacceptable, agricultural use was promoted from the end of the 1960s (Sjöstrand 2014). In 1986, an environmental organization sampled Swedish sewage sludge and demonstrated worrying concentrations of heavy metals in the sewage sludge. Sequentially, the farmers’ federation imposed a nationwide ban on sewage sludge as a fertilizer (Balmer and Frost 1990). The ban was lifted after negotiations between the industrial organization of the wastewater treatment plants, the farmers’ federation and the environmental protection agency. Ten years later, however, the farmers’ federation imposed a second ban due to findings of flame retardants in the sewage sludge (Bengtsson and Tillman 2004). In the middle of the 2000s, a certification system was established in Sweden to enable sewage sludge use in agriculture (Malmqvist, Kärrman, and Rydhagen 2006).

The 2018 Swedish inquiry was the fourth in a row of inquiries aiming for increased recycling from sewage sludge (SEPA 2002, SEPA 2010, SEPA 2013). The difference now was the goal to completely replace sewage sludge land use with alternative recycling technologies. The government expressed concerns that potential pollutants were being proliferated to the environment when they instead should be contained and eliminated. Even though the levels of toxic metals in the Swedish sewage sludge have decreased significantly since the 1970s (Kirchmann et al. 2017), concentrations of for example cadmium are still higher than in the soil which leads to accumulation (Statistics Sweden 2018; Swedish Water 2020). The concentrations are lower compared to inorganic fertilizers, but scholars claim that all sources leading to cadmium accumulation should be reduced due to public health and environmental protection (Schaefer, Dennis, and Fitzpatrick 2020; Marini, Caro, and Thomsen 2020). In addition to this, the government was concerned with the thousands of chemicals used in society, which are consequently found in sewage sludge and hard to monitor (Sharma et al. 2017). Additionally, some chemicals might have toxic combination effects that cannot be assessed by testing substances one by one, and thus complicates setting up limit values (Kortenkamp, Backhaus, and Faust 2009).

The precautionary trend is also notable among other countries in Europe (Bauer et al. 2020) and globally (Zhang et al. 2017). So, while the current EU regulation supports agricultural use of sewage sludge (EEC 1986), the implementation largely varies between member states (Wiechmann et al. 2015; Christodoulou and Stamatelatou 2016; Lupton 2017). It is even the case that the European Commission (2013) deemed the current legislation as outdated and encouraged other technologies, like incineration followed by nutrient recovery, to increase nutrient recycling while simultaneously eliminating organic pollutants – like pharmaceuticals and micro plastic – and isolating heavy metals. Banning all land application, however, would imply a radical technological shift in Sweden, where almost all sewage sludge is being applied to land. Currently, little less than a third of the sewage sludge is used in agriculture, one third for reclamation of landfills and mining sites, and one third is composted and used as garden soil (Bauer et al. 2020; Eurostat 2018).

The intention with the 2018 inquiry was to end the conflicts between stakeholders and increase sewage sludge recycling reliability by the introduction of new technology. Oberg and Mason-Renton (2018) claim that this reliance on technical solutions has been prominent in the Swedish sewage sludge management narrative, but that it will not solve the conflicts until contextual aspects, multiple lenses, and normative stances of different stakeholders are considered. So, while some writers claim that sewage sludge recycling conflict arises due to mass media misinformation (Goodman and Brett 2006) and lack of public education (LeBlanc, Matthews, and Richard 2008, 22), they do not emphasize the importance of social impact and socio-politics in the circular economy (Merli, Preziosi, and Acampora 2018; Hobson and Lynch 2016). Other scholars highlight the necessity to involve the public in political processes (Mason-Renton and Luginaah 2018; Goven et al. 2012), raise community engagement (Guzman and De Souza 2018; Pollans 2017) and acknowledge sanitary norms in the infrastructure (Margaret Del Carmen, Harris, and Öberg 2014; Gerling 2019) when enacting sewage sludge recycling.

These are all important points but, when looking at the 2018 inquiry and its predecessors, an expert panel representing diverging standpoints was attached to the investigating committee. The inquiry report was later sent out for public consultation to gather even more input from stakeholders. Simultaneously, a certification system was developed through the engagement of several societal actors. But still, the legislation has not changed, nor did the recycling of nutrients considerably increase. To understand this, Bowler (1999) might contribute with some valuable insights. He draws on actor-network theory to explain how some stakeholders in the United Kingdom mobilized support for agricultural application as the most sustainable option by establishing a common sewage sludge knowledge base. Hence, rather than to focus on different perspectives of what the world is, it would be better to study how various versions are performed by those who are engaging with it. Mol (1999) ‘suggest[s] a reality that is done and enacted rather than observed. Rather than being seen by a diversity of watching eyes while itself remaining untouched in the centre, reality is manipulated by means of various tools in the course of a diversity of practices. […] Instead of attributes or aspects, they are different versions of the object, versions that the tools help to enact’ (Mol 1999, 77). Reducing the multiple versions of sewage sludge to make it manageable lead to exclusions of versions which do not fit a distinct knowledge base. Law and Singleton (2005) write that managerialism ‘demands clarity and distinction. That which is not clear and distinct, well ordered, is othered’ (Law and Singleton 2005, 341). Delimitation of sewage sludge versions and the formation of a common knowledge base could thus be one important factor to explain the (in)ability to agree on sewage sludge management practices.

This paper uses versions as a concept to analyse what the experts of the 2018 inquiry associated and related sewage sludge with, and how these versions were related to society and preferred managerial practices. This is then discussed based on the outcome of the inquiry report published in 2020 and the consequence of the many versions of sewage sludge for policymaking.

Method

Expert interviews and the terms of reference as empirical material

The 2018 inquiry was constituted by a committee of four people and a panel of 14 experts from governmental as well as civil and private organizations. Eight were interviewed during 2019, on average for 70 minutes, with interviews audio-recorded and transcribed (except for one where notes were taken). The interviewees belonged to governmental and non-governmental organizations covering a broad spectrum of standpoints. According to Swedish legislation, there is no formal requirement of an ethical approval for a study of this kind (Swedish Ethical Review Authority 2021). Ethical considerations were, however, still regarded, as the interviewees were informed before the interview on the use of collected material (for academic publication and conference presentations) and that they had the right to withdraw. As the field of sewage sludge management is rather small in Sweden, they were promised not to be named nor associated with their organizations, as this would easily lead to identification. Thereafter they gave their consent to participate. The terms of reference (Government Offices of Sweden 2018), a document issued by the government to instruct the inquiry, was also included, as it plays a role in limiting the discussion, evoking resistance, and creating allies (cf. Prior 2011).

The interviews were explorative, with the aim to understand how the experts thought of their work in the inquiry and what their ideas were on preferable sewage sludge management. The interview-guide aimed for free association narratives (Holloway and Jefferson 2008) and was set up to allow the interviewees to freely elaborate on a set of open topics related to their work rather than answering direct questions. The first topic was the interviewee’s role in the expert panel and how they viewed the inquiry’s terms of reference. In this way, they situated themselves in relation to the inquiry. The second topic was the work they had done so far and their ability to communicate their opinions to the group. The third topic was their thoughts on future regulation and relevant technical solutions. The initial narratives were probed with follow-up questions using the respondent’s orderings and phrases.

The analytic framework to categorize the various versions of sewage sludge

The 2018 inquiry’s terms of reference and the interviews are full of descriptions of sewage sludge through statements about what it is, by associations with similar objects, and through relating it to other objects and phenomena. This was the starting point for an abductive (Timmermans and Tavory 2012) content analysis of the empirical material where induction and deduction were iteratively used. The empirical material was initially coded for what sewage sludge was associated and related to. The focus was the framing of sewage sludge as waste and resource (Thompson 2017; Hamlin 1980). The initial coding, however, exceeded that dichotomy as sewage sludge was related to in other ways. How sewage sludge was made known, like measuring and certifying, and the political tension of how waste is made (in)determinate (Hird 2012) was therefore important to code for. The focus on determination and epistemology, however, puts the sewage sludge controversy in the realms of conflicting perspectives of different actors. This limits sewage sludge to be something which can only be ontologically positively defined. Instead, interventions with sewage sludge could be seen as enactment of various ontological versions of the object (Mol 1999).

The intention with this paper is not to produce a complete and distinct ontological description of ‘what there is’ (Woolgar and Lezaun 2013). The desire is to challenge the existence of a singular sewage sludge ontology and focus on how sewage sludge is performed in the documents, through the interviews, and through the practices which are referred to, like measurements, risk assessments, regulation, and utilization.

Moore’s (2012) review of social science waste literature provides an appropriate categorizing framework to embrace sewage sludge multiplicity, and recognize potential conflicts and possibilities. Though Moore structures concepts in academic literature, she states that ‘as is true in much social science research, [waste scholars] are reflecting the views and opinions of research subjects and their use of multiple concepts’ (Moore 2012, 783). Thus, the structure should also be applicable to everyone intervening with waste. The interviewees, however, do not deliberately formulate specific concepts like academic scholars might do in their writings. Instead, they could describe sewage sludge as having intrinsic properties as a resource, relate to a natural circulation of nutrients, while at the same time explain how an economic value depends on societal actors.

Moore (2012) organizes various concepts of waste based on the following two questions ‘(1) Can objects be defined positively – by essential characteristics inherent to them – or negatively – only in opposition to something else? (2) Do certain social processes pre-exist objects and subjects or do objects and subjects, together, help to constitute society and space’ (Moore 2012, 783). The first question results in a positive-negative divide on the essence of waste, and the second asks whether the constitutive capacities of wastes and society are dualistically separate or relationally dependent on one another.

For this study, Moore’s comprehensive diagram has been translated into a 2 × 2 matrix (see Table 1) and the single versions of sewage sludge have been grouped into broader categories of sewage sludge to give a better overview.

Table 1. The analytical framework for categorizing the versions of sewage sludge given by the interviewed experts and the terms of reference.

	Positive	Negative
Dualist	Ontologically stable and distinct from society, e.g. as a hazard and a resource.	Its nature is given in relation to other things, e.g. part of larger systems and infrastructures.
Relational	The intrinsic properties are not questioned but the emphasis is on societal relation, e.g. risk management and economic valuation.	Properties are given in relation to other objects and shapes society, e.g. causing conflict and demanding definition.

The positive-dualist corner groups versions of sewage sludge which have specific properties and are external from society. The negative-dualist corner groups versions still upholding the separation between society and sewage sludge, but where the properties are not based on physical qualities but rather on how they are related to other objects and orders. The versions found in the positive-relational corner do not question the specific properties of the sludge but rather focus on socio-cultural relations with the sludge. The fourth corner, the negative-relational, contains versions where sewage sludge and society are constitutive of one another. This entails sewage sludge as part of exerting power and raising societal barriers, forming networks with various actors, and demanding political action.

Results

The results of this study are first summarized in Table 2 and then followed by a more elaborative section for each quadrant.

Table 2. Summary of the different versions of sewage sludge and its relation to society.

	Positive	Negative
Dualist	It comprises not one but many resources, such as phosphorus, nitrogen, humus, and methane. It can be dangerous because of heavy metals, microplastics, and other substances.	It links the eco-cycle between humans and food production. It is the polluted residue of wastewater treatment.
Relational	It is a risk that should be handled with precaution or balanced with potential benefits. Its economic value depends on market actors.	It is part of a socio-technical system for disposal of waste. It leads to conflicts and exclusion. It demands political determination.

Positive-dualist: sewage sludge between resources and hazards

The inquiry’s terms of reference claims that sewage sludge contains large amounts of phosphorus, a vital nutrient for agriculture. Therefore, recovery is urgently needed to secure access to the mineral (Government Offices of Sweden 2018, 1). This concern is shared by many of the interviewees. One says that phosphorus security ‘is a problem which the whole world is struggling with. The access to phosphorus, which is not crap, is a challenge. So, we need to recirculate it’. They refer to peak phosphorus (see Cordell and White 2011) and the fear that food security is threatened due to near future depletion of mined phosphorus, or at least restricted to low quality supplies in a few countries.

The terms of reference also states that nutrients other than phosphorus could be of interest to recover from the sludge if possible. However, one interviewee says that other nutrients than phosphorus are being downplayed, ‘if we look at what enters the wastewater, then we have around 60,000 tonnes of nutrients, of which phosphorus is somewhere around five to six tonnages, that is around 10%, extracting 100% of the phosphorus from sludge through incineration only gives 10% of the nutrients. Hey, that is not circular economy’. Phosphorus as the sole motivation for sewage sludge as a resource is thereby challenged. Nitrogen and organic matter are mentioned by several as important substances in the sewage sludge and that these should also be considered resources.

Sewage sludge is generally framed as a resource for food production by the interviewees, but there are other areas of utilization. The terms of reference states that ‘suggestions [in the final report] must not hinder the extraction of biogas from sewage sludge through anaerobic digestion’ (Government Offices of Sweden 2018, 1). The interviewees do generally not see any problem in combining nutrient recycling and methane extraction. One relates to a parallel governmental inquiry where ‘they are supposed to find the prerequisites for biogas marketization and stimulation of production. In our terms of reference, we are required not to obstruct this’. By referring to biogas, sewage sludge becomes a source of renewable energy.

Sewage sludge utilization as climate friendly leads one interviewee to say that spreading the sludge in agriculture ‘saves energy which leads to benefits for the climate in many ways, it is a carbon sink, and nitrogen contributes as well’. The interviewee adds that if the sludge has been dried using energy, then it might make sense to incinerate it and extract phosphorus from the ashes, ‘the difficult part is dewatering, drying, [… so if you make] all of that effort, then it is better to go the whole way’. Some interviewees mention natural gas dependent nitrogen fertilizer production and connect sewage sludge to energy and climate change.

Sewage sludge is not only resources but also hazard. The terms of reference states that avoiding dangerous substances like heavy metals, pharmaceuticals, and microplastics is urgently needed as these hardly degrade and are proliferated in the environment. One of the interviewees highlights cadmium, which ‘has been discussed as one of the substances of which we can see health impacts today. There are not that many other substances or studies for which we have this much knowledge’. The interviewee also refers to other substances such as PFAS, a group of organic compounds potentially toxic, which stayed undetected until recently.

The terms of reference portrays a conflict between avoiding environmentally dangerous substances while simultaneously increasing the recovery of phosphorus. The interviewees on the other hand highlight the multiplicity of resources and hazards and give the sewage sludge specific properties that are intrinsic and not constitutive of society.

Dualist-negative: sewage sludge as eco-cyclical link or societal liver

The dualist-negative dimension encompasses versions of sewage sludge where properties are relativized, and sewage sludge becomes part of a dualistic dis/order where society and sewage sludge are mainly kept separate. The terms of reference states that the long-term Swedish ambition is to transform society into a circular economy where waste becomes a resource. It is argued that recycling of the nutrients in sewage sludge to agriculture is part of an eco-cycle where plants provide nutrition for humans and animals as food, who after digestion ought to return the nutrients to the plants.

The word eco-cycle is frequently used by the interviewees. According to one, the eco-cycle means returning sewage sludge to agriculture, as it ‘is there where the eco-cycle can be motivated. That cannot be done if it is thrown in the forest or a landfill. That is not an eco-cycle’. Sewage sludge is thereby related to other objects in the eco-cycle where nutrients should be circulated from food to humans, back to the soil, and subsequently to food again. Even interviewees sceptical of agricultural use of sewage sludge might still consider human waste as fertilizer to be hypothetically preferable. One says that earth-closets may be the preferred long-term solution, where excrements are returned to the eco-cycle but that extracting pure phosphorus ‘is a potential sub-solution, or solution on the way, where we can say that at least you get this pure phosphorus back to your agriculture, back to your eco-cycle, while we continue thinking of what we can do with the rest’.

Oppositely, sewage sludge becomes concentrated pollution when related to wastewater treatment plants. One interviewee says that ‘[i]n the sludge, nutrients are collected but also several dangerous substances. […] For me it is obvious that here we have a possibility to really isolate these substances from the eco-system’. The pollutants in the sludge disrupt the natural order and should not be returned to the eco-cycle. The terms of reference states that it is desirable to avoid the proliferation of dangerous substances into the eco-cycle and rather steer towards a pollutant-free and resource-efficient recycling of phosphorus. The sewage sludge itself is thus not a part of the eco-cycle but the different substances in the sludge are either included or not. Hence, phosphorus is part of the eco-cycle, while dangerous substances are not.

Whether the nutrients can be considered resource or hazard is challenged by some interviewees. One relates sewage sludge to other sources of nutrients and questions, ‘[h]ow important is this phosphorus resource found in the sludge, compared to other phosphorus sources in this country like for example mining waste and dredged materials?’ Another says that ‘shortly after our inquiry was initiated, [a mining company] and [a recycling company] presented a method for extracting phosphorus from the slag heaps. […] This slightly changed the agenda of phosphorus as a limited resource in Sweden and Europe’. On the other hand, interviewees compare the risk of using sewage sludge to other more accepted objects like manure, pesticides, and food waste compost (bio-fertilizer). One says, concerning the focus on sewage sludge in the terms of reference, ‘I think that by not including bio-fertilizer, something is lost. […] From a societal perspective, it would be reasonable to include that as it contains more or less the same substances’. The interviewee claims that bio-fertilizers are sometimes more polluted than sewage sludge. Another says that the ‘levels we accept of different substances in [tap water] cannot be less restrictive than those for sewage sludge’. They argue that having tighter regulations for sludge than for bio-fertilizers and tap water is unreasonable as they should be regarded in relation to sewage sludge.

The negativity of sewage sludge is expressed by the interviewees through the many comparisons to other objects and the definition of the eco-cycle. Hence, sewage sludge can be a waste of resources when just a few nutrients are recovered, or a waste by returning dangerous substances, which have been isolated at the wastewater facility, to the eco-system.

Positive-relational: risks and economic value

The intrinsic properties of the sewage sludge are not questioned in versions sorted under the positive-relational dimension. Instead, sewage sludge becomes something that the society has to act upon, exemplified here by looking at risks and potential economic value.

Sewage sludge as risk

The composition of sewage sludge is sometimes referred to as a mirror of the society, and thus the composition of it changes depending on consumption habits, connected businesses, and treatment processes. Many of the substances which are released into the wastewater might have unknown effects on the environment, could have combination effects, and might not be measurable. This leads to uncertainty regarding potential risks. Some interviewees argue that this uncertainty demands society to take a precautionary stance, ‘it is a sludge which we do not know anything about, how many substances it contains. We know the effects of some so-called particularly dangerous substances which can be found in the sludge. […] But then we also have a load of other substances, thousands of substances, which we know very little of and whose combined effects are very little known. […] It is very hard to make any risk assessments as we do not have the methods, […] particularly on all those substances which we do not know if they exist or what effects they have’. Another interviewee says, ‘when can I feel safe? I don’t know if anyone ever wants to say that? Who can actually assure that something in society is safe and on what time-horizon? But if we turn it around, pure phosphorus can potentially be a part solution’. These interviewees state that a society cannot assure safety to its population if the sewage sludge cannot be fully evaluated. Therefore, incineration and the isolation of phosphorus could be a way to reduce the potential risks.

Another way to handle the uncertainty, rather than referring to the precautionary principle, is to accept some potential risk. One interviewee says, ‘I see the spreading of sludge as taking responsibility. It is very easy to say no, that is the simple way out, but it is more difficult to deal with the problem instead”. Another questions the proponents of the precautionary principle, ‘they point to the precautionary principle, and now many talk more and more about nano-plastics, that those might be the problem. But it remains, as I said, to be proven’. When asked about how science can be incorporated despite ambiguous results, the answer is ‘in the best of worlds we could have done it in one way, […] but sometimes one must do certain things which involves some risks, but which are economically much better for society’. The interviewee argues for evidence-based knowledge, but as science might not give clear-cut answers, they advocate an economic assessment to balance eventual risks.

Sewage sludge as economically valuable

Assessing an economic value to sewage sludge and a demand for potential products seems to be a challenge. The terms of reference states that sewage sludge is a source of scarce phosphorus which should be returned to society. One interviewee questions this, ‘the terms of reference and the tasks we should do is not about returning, but about recycling and recovering. I mean returning is actually a market aspect. How will the phosphorus that we recover be turned into a product? And how will that be accepted by the market? At what price? […] Even if we get the best phosphorus by incinerating the sludge and recover the phosphorus, perhaps no one wants it. Those from the food industry might still say that it comes from sewage sludge and that consumers are not interested?’

Some interviewees see the food industry as a key actor in giving sewage sludge an economic value. One states that the food industry demands ‘a functioning system, that removes the risk […] and does not cost them anything. That would be the dream. But if I say it like this, if there wasn’t any financial risk then they would have bought the produce’. Another says that ‘most important right now is actually the food industry and their stance. [… Their hesitancy] may not be based on scientific research in the first place, but they want to protect their brands. […] There is simply too little at stake and too little to gain from being positive to the use of sewage sludge’. Yet another says that the food industry ‘has a clear standpoint, it is not on the map that they will allow sewage sludge fertilized crops in parts of their production, like flour or foodstuff, they have too much to lose’.

Phosphorus recovery could be a way to enable reuse of nutrients but might not be the most valuable resource in monetary terms. One interviewee criticizes the narrow focus of the terms of reference and compares phosphorus to other nutrients, ‘value-wise [phosphorus] has the smallest value, and if we look at how long it will last in the form that it is being extracted and made available to crops, then phosphorus will last the longest. So, from an eco-cycle perspective, talking about the circular economy, the terms of reference is rather strange’. Another interviewee is upset regarding an initial draft of the terms of reference where agricultural application ‘was stated […] as an issue of disposal, saying that most farmers get paid for sewage sludge, something which is not at all true’.

Whether sewage sludge is a waste desired by none unless they get paid, or valuable if the food industry was less reluctant, are conflicts of valuation between societal actors. Giving sewage sludge an economic value is not only an issue of estimating the monetary worth of the demanded resources. It involves weighing a potential benefit against eventual costs and risks, comparing different resources in the sludge and the willingness to pay by different actors.

Negative-relational: sewage sludge demanding political action and causing conflict

In this section sewage sludge and society are mutually constitutive of social relations and material properties. The sewage sludge is formed in relation to humans and infrastructures, but also forms their relations. Some interviewees stress the performativity of the sanitary infrastructure, which generates a need to dispose of the sewage sludge. One says, ‘seen from a disposal perspective, I mean the old sludge-thinking, then there is a logic; if there is a sludge, then we should extract phosphorus and other valuables, of course’, and claims that the old managerial thinking has its rationale which makes the sewage sludge into a disposable object. Another says regarding the terms of reference that ‘we are not supposed to problematize the contemporary sewage system and the way to handle it. I mean the reason we have a sludge comes from choosing a certain type of management […] In the best of worlds, one should look at the sewage system from a broader perspective to see what the future sewage systems should look like’. The interviewee asks if a technology, built for sanitary purposes, can be transformed into a recycling facility, without changing the technology itself. However, other interviewees say that building an infrastructure for separation and recycling might not be sufficient to increase the utilization of the effluent, as the relationship goes further than the infrastructure.

The sewage sludge can cause conflicts between individuals and organizations. One interviewee says, ‘I have some issues with the terms of reference as it is defined, which I had from the beginning, and have received a lot of crap as some think that I am against eco-cycling. But it is the exact opposite, I am very concerned’. The interviewee endorses a reconstruction of wastewater treatment plants into eco-cycling plants that recycles both sewage sludge and reject water. Questioning phosphorus recovery is criticized as opposing recycling altogether. Another interviewee sighs and says, ‘we have had, what should I call it, a deviating opinion, and this also differentiates us from many other [actors], it is like, ahh, it is a little, I wouldn’t say acrimonious, but a sensitive issue’. The interviewee’s scepticism towards the utilization of sewage sludge has caused conflicts with other organizations and authorities.

Sewage sludge indeterminacy can also demand political action. One interviewee says that ‘the wastewater treatment plants […] have a need to get rid of their sludge, and do not want a high cost for this. But at the same time, I think, what they really want is clarity. We have now kept on discussing this for many years. Inquiry after inquiry has been initiated. I think they want someone to put one’s foot down’. The interviewee claims that the uncertainty of what sewage sludge is and how it should be governed persists. Hence, there is a need to stabilize one version and limit the discussion. Sewage sludge is not just formed by society according to the interviewees but can be a source of conflicts and exclusion. It is something which avoids easy classification and raises demands for firm political decisiveness to be governable.

Discussion

In early 2020, the inquiry’s committee finished the report and presented two opposing suggestions ‘(1) a complete ban on spreading with very limited exceptions, or (2) a ban on spreading [… where] exceptions are permitted for sanitized and quality-assured sludge to be spread on productive farmland’ (Government Offices of Sweden 2020, 33). Though the inquiry’s mandate was limited by the government to suggest a legislative ban on all land application and supportive structure for recovering technologies, the committee chose to defy the government and recommend the continuation of agricultural application.

Two parts of this ambivalent outcome will be addressed in this section. First, the inability to suggest one management for sewage sludge nutrient recycling. Second, the ability to give a unified suggestion regarding the non-agricultural used sewage sludge. The discussion ends with some thoughts on the usefulness of regarding sewage sludge as ontologically multiple rather than subject to various perspectives.

Agricultural use or not

Whether sewage sludge should be used in agriculture, or not, evokes a classic conflict between reusing waste and eliminating pollution (Brunner 2010; Gerling 2019; Johansson, Velis, and Corvellec 2020). Previous literature emphasizes the importance of involving various stakeholders and building trust to bridge that gap. Involving the expert panel, however, did not help to close that divide. Instead, the report suggested a binary choice between banning or allowing agricultural use. One practice, enforcing that divide, is the establishment of limit values. This is illustrated with the certification system established in the mid 2000s imposing stricter regulation for agricultural application than the Swedish legislation. One interviewee explains that it ‘was a reaction from the farmers’ federation, the food industry and the wastewater operators. They thought that we cannot have this old legal framework’.

Most agricultural applied sewage sludge comes from certified wastewater treatment plants and is seen as good quality, even by the more critical experts: ‘there might not be any acute problems from eating the produce from fields fertilized with sludge within the next two to five years. That can be done if we use the best sludge, which is the one which is used today, but it is not a wise long-term solution’. The certification induces a border between good and bad sludge and one interviewee says, ‘the sludge is extremely sampled and measured. It is much more sampled than all our import of food and […] all forms of waste’. Another interviewee also delegitimizes agricultural application with sewage sludge from non-certified facilities by calling it illicit spreading, though it is legal according to Swedish law.

Sewage sludge as a risk, which requires action from society, is performed through the practice of measuring and sampling, negotiation, and the establishment of certificates, and a following distinction between good and bad sludge. Sewage sludge is both resource, which should be used in agriculture, and hazard, which needs to be limited, involving actors in an economic value chain. The above example shows what Mol (1999) calls collaboration. The various versions of sewage sludge, as presented in this paper, partly overlap. On the other hand, sewage sludge as the societal liver with unmeasurable risks that must be disposed of is difficult to harmonize. The conflicting versions evolves from the practice to ensure clean effluents generating a relation between the infrastructure’s purifying purpose and the sewage sludge (Burgman and Wallsten 2021). This sewage sludge is not tameable by limit values as these are subject to uncertainty and stakeholder negotiation. Instead, the versions are set into a sequence (Mol 1999, 84), where precaution and safe effluents have priority, and nutrient recycling is subordinated. Incineration followed by phosphorus recovery, a technology often referred to by the interviewees, could enable such a sequence but rests on sewage sludge as a source of phosphorus, rather than many nutrients.

The persistence of sewage sludge as a source of nutrients

What is also remarkable, apart from the persistent conflict regarding sewage sludge as fertilizer, is the consensus that all other land application should be banned. While agricultural use corresponds to around a third of the total amount of Swedish sewage sludge, other uses equate to almost 70%. Hence, composting and land reclamation are deemed wrong, and a strong metabolic relationship to the sludge enforces sewage sludge as a nutrient resource for food production (Burgman and Wallsten 2021).

It is notable, perhaps, that land reclamation is labelled as ‘other’ by Eurostat (Eurostat 2018). Is the non-fertilizing sewage sludge an other sludge? Sewage sludge as a mine cover is not an economically interesting product for farmers, a nutrient, part of an eco-cycle, nor a societal liver. However, ‘what is “other” is also within’ (Mol 1999, 85). Sewage sludge as non-fertilizer is not separable from other versions, despite practices of establishing limit values and legislative bans; it is still sewage sludge. Some interviewees support composting but say that fighting for agricultural use is already stretching the limits of the inquiry. The managerial desire to limit sewage sludge ontology generates a bad sludge that fails to be contained (Hird 2012). The apparent consensus is thus not only a result of the strong support for sewage sludge as nutrient, but also a performance of obedience towards the terms of reference and the desire to form a coherent national legal framework.

Sewage sludge’s multiple ontology

Arguing for sewage sludge multiple ontology, rather than actors’ different perspectives on a singular sewage sludge, has some consequences. It is not to make claims about the true nature of sewage sludge, to say ‘what there is’ (Woolgar and Lezaun 2013) or that these ontological versions are fixed and stable. Instead, it challenges a position where sewage sludge has a distinct nature which should lead to a certain management, where more research should enhance the possibilities to find the optimal solution. Attempts to reduce misinformation from mass media (Goodman and Brett 2006) or improve public education (LeBlanc, Matthews, and Richard 2008, 22), relies on the assumption that sewage sludge is a fertilizer which should be used for agriculture and that most scientific studies support this. But that ignores the dependency on the enforcing practices of this nature, for example the establishment of good and bad sludges (see Goldfarb, Krogmann, and Hopkins 1999 on the discussion of sewage sludge and biosolids). The paper also challenges the common view that conflicts arise due to the exclusion of stakeholders (Morone and Imbert 2020); the main argument is that policymaking should not solely rely on evidence-based science but on the inclusion of multiple lenses to get a more complete picture (Oberg and Mason-Renton 2018). This, however, assumes that various perspectives add up to a more complete picture of reality. A multiple ontology would complicate this, as the sum of many versions would not be closer to a singular true nature of sewage sludge. Instead, the emphasis is on the tensions of performing a common knowledgebase and the practices to achieve this. This could be done through community engagement (Goven et al. 2012; Guzman and De Souza 2018), but also through alliances of some stakeholders (Bowler 1999).

Rather than viewing sewage sludge controversies as the result of deviating opinions, the issue could be understood as the inability to make the various versions of sewage sludge collaborate. Mol (1999) also emphasizes the interference between the versions of the object and other realms. The political decision on which management to support will rely on how sewage sludge is enacted, but the decision will also affect what sewage sludge becomes. And due to the relations to other objects (Burgman and Wallsten 2021), like bio-fertilizers or peak phosphorus, it can have a repercussive effect on the ontology of these.

Conclusion

This paper has used the recent Swedish attempt to change the legislation on sewage sludge from agriculture application to phosphorus extraction as an example of the difficulties to turn waste into resource. Utilization of sewage sludge has a long and controversial history. This paper argues that the conventional way to describe these conflicts, as the results of incomplete and conflicting perspectives, cannot fully explain why the recent inquiry did not come with one policy recommendation but two. Thinking instead of sewage sludge as ontologically multiple means that there is not one singular reality which can be uncovered with more research nor solved with one universal optimal technical solution. Different sewage sludge versions emerge through the interaction with sewage sludge, both rhetorically and physically, and what sewage sludge becomes is equally important as the discussion of potential technological changes. While waste-to-resource management, as suggested by the inquiry, can both be the extraction of phosphorus and the return of sewage sludge to agriculture, there are more alternatives such as garden soil production. Hence, thinking with multiplicity could open new possibilities beyond the classic dichotomy of agricultural use and nutrient recovery. Therefore, splicing the many versions of sewage sludge becomes a persistent conundrum for which policymakers and researchers need to exist and take decisions along rather than seek to solve once and for all. How this is done is beyond the scope of this study but should be the topic for future research on sewage sludge utilization and its consequences.

Acknowledgements

This work has been read with endurance and supported with valuable comments by Harald Rohracher and Björn Wallsten at Linköping University. The research group Socio-technical research of infrastructures, politics and the environment (STRIPE) at Linköping University, the participants at the Nordic STS pre-conference 2019 in Tampere and the panel on sewage sludge at the Re-Opening the bin 2021 conference in Gothenburg have provided important feedback to earlier drafts.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was funded by the Swedish Energy Agency (46028–1).

Notes on contributors

Linus Ekman Burgman

Linus Ekman Burgman has a MSc in Economics from University of Copenhagen and is currently a PhD-student in an interdisciplinary research group working on sewage sludge and recycling through thermal treatment. He has previously done research on food waste behaviour, parallel currencies in Palestine, and nationalist women.