Robin Harder

Pathways and Management of Phosphorus in urban areas

Due to the finite nature of mineral phosphorus reserves, effective management of anthropogenic phosphorus flows is currently under investigation by the international research community. This article emphasizes the importance of urban phosphorus flows, which are often marginalized due to the greater magnitude of agricultural phosphorus flows. A study on phosphorus flows in Gothenburg, Sweden, points out the potential role of solid waste in nutrient management, as the amounts of phosphorus in solid waste and in wastewater were found to be equal. Importation of food commodities accounts for 50% of the total inflow of phosphorus, and food waste is a major contributor of phosphorus to solid waste. The results suggest that solid waste incineration residues represent a large underestimated sink of phosphorus. Focusing on wastewater as the sole source of recovered phosphorus is not sufficient. The Swedish national goal on phosphorus recycling, which is limited to sewage sludge, targets only a part of the total phosphorus flow that can potentially be recovered. In contrast to previous studies, agricultural flows in Gothenburg were marginal compared to flows related to the urban waste management infrastructure. We emphasize the need for debate on preferable routes for disposal of waste with a high phosphorus content. Both recovery potential and usefulness of the recovered product for agricultural purposes have to be considered. Impacts of five waste management strategies on phosphorus flows were evaluated: incineration of all the waste, comprehensive food waste separation, installation of kitchen grinders, urine diversion, and separation of blackwater and food waste.

Including pathogen risk in life cycle assessment of wastewater management. 1. Estimating the burden of disease associated with pathogens.

The environmental performance of wastewater and sewage sludge management is commonly assessed using life cycle assessment (LCA), whereas pathogen risk is evaluated with quantitative microbial risk assessment (QMRA). This study explored the application of QMRA methodology with intent to include pathogen risk in LCA and facilitate a comparison with other potential impacts on human health considered in LCA. Pathogen risk was estimated for a model wastewater treatment system (WWTS) located in an industrialized country and consisting of primary, secondary, and tertiary wastewater treatment, anaerobic sludge digestion, and land application of sewage sludge. The estimation was based on eight previous QMRA studies as well as parameter values taken from the literature. A total pathogen risk (expressed as burden of disease) on the order of 0.2-9 disability-adjusted life years (DALY) per year of operation was estimated for the model WWTS serving 28,600 persons and for the pathogens and exposure pathways included in this study. The comparison of pathogen risk with other potential impacts on human health considered in LCA is detailed in part 2 of this article series.

Including Pathogen Risk in Life Cycle Assessment of Wastewater Management. 2. Quantitative Comparison of Pathogen Risk to Other Impacts on Human Health

Resource recovery from sewage sludge has the potential to save natural resources, but the potential risks connected to human exposure to heavy metals, organic micropollutants, and pathogenic microorganisms attract stakeholder concern. The purpose of the presented study was to include pathogen risks to human health in life cycle assessment (LCA) of wastewater and sludge management systems, as this is commonly omitted from LCAs due to methodological limitations. Part 1 of this article series estimated the overall pathogen risk for such a system with agricultural use of the sludge, in a way that enables the results to be integrated in LCA. This article (part 2) presents a full LCA for two model systems (with agricultural utilization or incineration of sludge) to reveal the relative importance of pathogen risk in relation to other potential impacts on human health. The study showed that, for both model systems, pathogen risk can constitute an important part (in this study up to 20%) of the total life cycle impacts on human health (expressed in disability adjusted life years) which include other important impacts such as human toxicity potential, global warming potential, and photochemical oxidant formation potential.

Including pathogen risk in life cycle assessment of wastewater management. Implications for selecting the functional unit.

I the context of wastewater management, microbial hazards are often addressed in risk assessment (RA) studies but are at present not routinely included in life cycle assessment (LCA) studies. A recent attempt to include pathogen risk in LCA of wastewater management explored the application of quantitative microbial risk assessment (QMRA) with the intent to compare pathogen risk with other potential impacts on human health. When presented together in an LCA framework, the pathogen risk is treated as an LCA impact category (i.e., category of environmental impact, such as global warming or acidification). This requires that the results obtained through QMRA be scaled to a functional unit, which is not the case in RA studies. The functional unit defines how results are reported using a consistent temporal scale and other assumptions (e.g., carbon dioxide equivalents released per treatment of 10 000 m wastewater per day during 1 day). In our opinion, the choice of the functional unit for an LCA study that includes a QMRAbased impact category should be carefully considered, as we believe that some functional units are preferable to others. Let us consider a municipality intending to build a new wastewater treatment plant to serve 30 000 persons and treat 10 000 m wastewater per day on average. An LCA study could be performed in order to identify the wastewater management option with the best environmental performance, thereby also accounting for the overall pathogen health burden associated with the wastewater treatment operations. The input for life cycle impact assessment (LCIA) traditionally consists of emissions from different processes at different locations, which are aggregated and scaled to a functional unit. In conventional LCA impact categories, the emission inventory usually only represents a fraction of the emissions of the contributing processes, and the mathematical relationships usually are linear. However, the pathogen doses in typical QMRA are total doses and the mathematical relationships are nonlinear. Do these differences preclude scaling a QMRA-based impact category to a functional unit? Let us assume that the QMRA-based impact category for pathogen risk amounts to a total health burden of 3.65 disability-adjusted life years (DALY) per year for a conventional municipal wastewater treatment plant based on all exposure pathways considered. This result, we believe, can very well be scaled to for example 0.01 DALY per treatment of 10 000 m wastewater per day during 1 day, if this were the functional unit of the LCA. In contrast to conventional LCA impact categories, where scaling to a functional unit usually takes places before impact assessment, scaling to a functional unit for the QMRAbased impact category must take place after impact assessment. In other words, irrespective of the functional unit, the underlying calculation of pathogen risk (expressed as health burden) must always be based on the relevant population of people exposed, the pathogen emissions from the full-scale plant, and during the time scales applied in the respective calculation model (QMRA). But, are some functional units preferable to others? In both water and wastewater management, a QMRA is usually set up with a year as the temporal scope to capture the natural variation in pathogen exposure. A temporal scope of at least a year is also important if cross-connection events that influence the quality of water occur only a small fraction of the time, but have a large overall impact on the annual health burden. Say the municipality considers a new type of wastewater treatment system with a pathogen health burden of 10−3 DALY per year, but with all of the exposure occurring during one event with duration of only 1 day, which affects only a small subset (100 people) of the wastewater service population (30 000 people). If the pathogen health burden were scaled to match a “per day” functional unit, the health burden would be reported as 2.7 × 10−6 DALY per day of operation. However, for the individuals exposed, the associated health burden is zero for 364 days of the year, while for the remaining day, it is 10−3 DALY per day of exposure. A “per

Quantification of Goods Purchases and Waste Generation at the Level of Individual Households

Quantifying differences in resource use and waste generation between individual households and exploring the reasons for the variations observed implies the need for disaggregated data on household activities and related physical flows. The collection of disaggregated data for water use, gas use, electricity use, and mobility has been reported in the literature and is normally achieved through sensors and computational algorithms. This study focuses on collecting disaggregated data for goods consumption and related waste generation at the level of individual households. To this end, two data collection approaches were devised and evaluated: (1) triangulating shopping receipt analysis and waste component analysis and (2) tracking goods consumption and waste generation using a smartphone. A case study on two households demonstrated that it is possible to collect quantitative data on goods consumption and related waste generation on a per unit basis for individual households. The study suggested that the type of data collected can be relevant in a number of different research contexts: eco-feedback; user-centered research; living-lab research; and life cycle impacts of household consumption. The approaches presented in this study are most applicable in the context of user-centered or living-lab research. For the other contexts, alternative data sources (e.g., retailers and producers) may be better suited to data collection on larger samples, though at a lesser level of detail, compared with the two data collection approaches devised and evaluated in this study.

Including pathogen risk in life cycle assessment: the effect of modelling choices in the context of sewage sludge management

PurposeRecent attempts to include adverse effects of pathogens on human health in life cycle assessment (LCA) have focused on integrating results obtained through quantitative microbial risk assessment (QMRA) as an impact category in LCA. This study aimed to investigate whether the use of QMRA can be an adequate way of integrating pathogen impact potential in LCA and to quantify how pathogen impact potential is affected by choices regarding model structure and mathematical relationships used.MethodsThis study was performed for the context of sewage sludge management and is based on pathogen concentrations in treated sludge reported in the literature. Eight reference pathogens were included in order to address important microbial groups. The pathogen impact potential associated with land application of sewage sludge was quantified based on a QMRA model for eight distinct exposure pathways. The modelling choices investigated were linearisation of dose-response and severity assessment and different modelling approaches and parameter choices in fate and exposure assessment.Results and discussionThe linearisation of effect and severity assessment had a minor impact on the results for exposure pathways where pathogen doses were low but had a major impact where pathogen doses were high. The assumptions regarding fate and exposure conditions, such as pathogen decay time, number of individuals exposed and frequency of exposure, had a significant effect on overall pathogen impact potential. If pathogen impact potential is to be integrated in LCA, a range of different parameterisations for each exposure event may be warranted rather than only the one with the highest risk per individual exposed as commonly reported for QMRAs. This is also in line with the ordinary LCA practice of focusing on average rather than extreme conditions.ConclusionsThis study suggests that the use of QMRA can be an adequate way of integrating adverse effects of pathogens on human health in LCA. However, analysts should be careful when choosing model parameters such as the number of people exposed or the frequency of exposure, as LCA may require a different parameterisation than an ordinary risk assessment (RA). Therefore, a direct integration of the results of a QMRA study into LCA may be problematic. Also, in order to avoid potential bias, analysts should carefully consider whether or not pathogen impact potential and human toxicity potential need to be estimated based on a similar set of exposure pathways.

Estimating human toxicity potential of land application of sewage sludge: the effect of modelling choices

PurposeMany municipalities are facing increasing pressure to adapt solid waste and wastewater management infrastructures in order to better close nutrient cycles. The focus of this study is on the estimation of the human toxicity potential associated with chemical contaminants released upon the application of sewage sludge to agricultural land. More specifically, this study investigated the effect of modelling choices regarding fate and exposure assessment.MethodsMonitoring data were collected for contaminants present in the sewage sludge from the wastewater treatment plant in Gothenburg and from other municipal wastewater treatment plants in Sweden. Based on these monitoring data, an overall burden of disease was estimated using characterisation factors taken from the USEtox models (versions 1.01 and 2.0). For the exposure through vegetables, an alternative life cycle impact assessment (LCIA) model was developed. The intake fractions thus obtained were used in combination with human health effect factors taken from the USEtox 2.0 database. The model results were compared with the USEtox models, and whether these two versions of the USEtox model provide significantly different results was also examined. The potential relevance of accidental ingestion of sludge was also considered.Results and discussionThe different LCIA models provided burden of disease estimates that differed from one another for individual contaminants (up to five orders of magnitude). The aggregated burdens of disease (i.e. sum for all contaminants considered in this study) estimated through different model variants, however, were of the same order of magnitude. For both metals and organic contaminants, only a small set of contaminants was found to make significant contributions to the aggregate burden of disease. However, it is uncertain whether the 15 metals and 106 organic contaminants covered by this study are those of greatest health significance of all contaminants potentially present in sewage sludge.Conclusions and recommendationsThe results of this study indicate that the technical information provided by the various approaches to modelling human toxicity in life cycle assessment (LCA) in the context of land application of sewage sludge management is consistent on the whole. However, given the uncertainties associated with the assessment of human toxicity in LCA, it is important to also contemplate the extent to which LCA in general is capable of informing the sewage sludge debate when it comes to human toxicity and possibly also other indicators. Future research could focus on identifying which types of questions of interest in the context of sewage management can be answered by LCA and which cannot.

Automatic classification of municipal call data to support quantitative risk analysis of urban drainage systems

Quantitative analyses of urban flood risks are often limited by lack of data on flood incidents. Call data are a valuable source of information about urban flood incidents, yet the unstructured nature of call information results in large time investments to prepare the data for application in quantitative analyses. Consequently, the existing call databases are not used for this purpose. If automatic classification routines can be applied to transfer unstructured call data into a quantitative data source, large stores of currently unused data can be made available for quantitative risk analysis of urban infrastructure systems. This article aims to assess whether automatic classification of calls from municipal call centres can reach sufficient accuracy to allow for use of the results in quantitative risk analysis. This is illustrated by the application of automatic classification results in quantitative fault tree analysis for urban flooding, for two cases with datasets of approximately 6000 calls. The results show that the obtained classification accuracy is sufficient to correctly rank failure mechanisms according to their contributions to the overall failure probability. This is a promising first result that shows the potential of automatic call classification to obtain data about failure incidents that are otherwise hard to find.

Life cycle assessment of sludge management with phosphorus utilisation and improved hygienisation in Sweden

To provide input to sewage sludge management strategies that address expected new regulations in terms of hygienisation and phosphorus recovery in Sweden, an environmental life cycle assessment (LCA) was made. The LCA identified environmental hot spots for methods that may permit sludge or phosphorus from sludge to be applied on agricultural land. In particular, thermophilic digestion, pasteurisation, thermal hydrolysis, urea treatment and mono-incineration with phosphorus recovery were compared. In addition, a sludge management system involving drying of sludge before use in forestry was investigated. The results showed that some major impacts are related to large uncertainties, such as those related to emissions from sludge storage. It also showed that large gains can be achieved when products from the systems replace other products, in particular when biogas is used to replace natural gas in vehicles, but also when sludge is used in agriculture and forestry. In general, there are small differences between the sludge management methods. Retaining the sludge matrix to allow for its utilisation in agriculture may conflict with keeping emissions to air and water from the sludge matrix low. It is recommended that any sludge management option minimises emissions from sludge to air and water and that resources are recovered and used, in line with the principles of a circular economy.

Perspectives on quantifying and influencing household metabolism

Household metabolism is a concept that is concerned with the analysis of stocks and flows of energy, matter, and information at the household scale. This paper starts by providing a brief overview of the concept of household metabolism. Rather than attempting an in-depth review and analysis of this field, the article subsequently maps the contributions and perspectives of a broad variety of research traditions that have an interface with the concept of household metabolism. Next, this paper highlights a number of controversial issues connected to household metabolism, and studies at the interface of household metabolism. Finally, this paper argues that the concept of household metabolism can provide valuable help in diagnosing misalignments between enacted system dynamics and expressed societal goals, and can help to design research that facilitates their alignment.