PREFACE. The life cycle assessments have been performed by the following people at the Chalmers University of Technology :

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3 PREFACE Systemanalys VA is a larger project aiming at developing tools and methods for municipalities in order to facilitate their decision-making regarding choice of technologies for wastewater systems. This study was carried out using the method of life cycle assessment (LCA), but in the project other aspects of wastewater systems have also been studied such as epidemiological risk, user behaviour and economy. The LCAs were performed on planned wastewater systems in areas within three Swedish municipalities; Luleå, Västerås and Strömstad. Apart from the case studies a literature study of substitutability of nutrients in sewage compared to artificial fertilisers was performed. In addition to this report a metal flow analysis of Luleå and Västerås (Karlsson and Svensson, 1997) as well as a simplified LCA manual for wastewater systems (Svensson and Kärrman, 1997) will be published in Swedish. The Systemanalys VA project was funded by the Swedish Environmental Protection Agency, Swedish Association of Water And Sewage Works (VAV) and Swedish Association of Local Authorities (Kommunförbundet). The life cycle assessments have been performed by the following people at the Chalmers University of Technology : Gilbert Svensson, Department of Sanitary Engineering, project leader Magnus Bengtsson, Technical Environmental Planning, case study of Luleå Margareta Lundin, Technical Environmental Planning, case studies of Västerås and Strömstad Sverker Molander, Technical Environmental Planning, substitutability study Henrik Lundström, Chalmers Industriteknik, data collection and data translation for the construction part of the Västerås study The substitutability study has benefited much from the information provided by Holger Kirschmann and Kersti Linderholm. Their kind co-operation is gratefully acknowledged. The authors also gratefully acknowledge the additional viewpoints and information provided by Erasmus Otabbong who has commented on the substitutability part of the manuscript. Further the authors wish to express their gratitude to: Erik Kärrman who started the case studies, Ann-Marie Tillman for fruitful discussions and comments on the manuscript, Stefan Marklund and Bo Sundström, Luleå municipality, Torbjörn Strömberg, Gun Wallenberg and Mikael Wulf, Västerås municipality, Anders Tysklind, Strömstad municipality, VAV for the permission to use their illustration on the cover, and all other people who have contributed with valuable help in various ways. i

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5 SUMMARY The environmental performance of different types of wastewater systems has been evaluated through life cycle assessment (LCA). Three Case Studies were performed, in two of the studies conventional wastewater treatment was compared to alternative technology and in the third, two sludge treatment alternatives were evaluated. In addition to LCA, a literature study of the plant uptake of nitrogen and phosphorus in human urine and sludge was made to allow an estimation of fertiliser substitutability by spreading the nutrients in the sewage after treatment. In all studies nutrients remaining after sewage treatment were assumed to be spread on agricultural land and the reduced use of fertilisers was accounted for. The LCAs included the use of energy and raw materials, emissions to air, water and ground. In addition, the different alternatives were evaluated by three different weighting methods: EcoNV, EPS and ET long. The first of the methods was especially developed for this study. In the city district of Kronan, which is a part of Luleå, a urine sorting system was found favourable in comparison to a conventional solution when these were evaluated through LCA. This was mainly due to the following features: lower emissions of nutrients to water and a lower demand for fossil fuels, the latter also resulting in lower emissions of energy-related substances to air. However, in the urine sorting solution the emission of ammonia to air was found to be a disadvantage. For the area of Horn, in Västerås, the LCA study analysed treatment of toilet and organic kitchen waste by liquid-composting (continuous and batch operation) compared to treatment of wastewater in a small sewage plant and the compostable kitchen waste in a drum compost. In this study the environmental impact was investigated both for the construction and the operation of the systems. The Horn study showed that a liquid composting process has several environmental advantages over a wastewater treatment plant. It has the highest degree of nutrient recycling and the lowest emissions to water, especially for nitrogen but also for phosphorus. The continuous liquid composting process has the highest electricity demand, followed by the wastewater treatment plant, while the batch liquid compost process is the least electricity demanding. The small wastewater treatment plant has much higher emissions of nitrogen to water but lower emissions of ammonia to air. A disadvantage for the liquid composting process is that the construction of the system is more resource-demanding than the wastewater treatment plant. However the environmental impact during the construction phase is in all alternatives of less importance than the impact from the operation. For the islands of Koster, in Strömstad, LCA was used to analyse two sludge treatment alternatives; to treat the sewage sludge on Koster and use it as fertiliser locally or to transport it to the mainland, dewater it in the central wastewater treatment plant in Strömstad and spread it on agricultural land around Strömstad. The Koster study showed that the local sludge treatment has several environmental advantages. More nitrogen can be returned to agriculture and the emissions to water of nitrogen is lower than for the central alternative. A disadvantage is that the process requires a higher input of electricity but since transportation is avoided a lower demand for fossil fuels and lower emissions to air are the results. The study of the substitutability of nutrients in sludge compared to fertilisers concluded that it is difficult to find generally applicable data since the level of substitutability depends on a number of iii

6 factors such as soil type, climate, spreading conditions and type of precipitation chemical used. The loss of nitrogen depends to a high degree on how the collection, storage, transportation and spreading of urine and sludge is done. Therefore, there is a large uncertainty in the substitutability values, however, intervals and probable values of substitutability are given for nitrogen and phosphorus for human urine and sludge. These values were used in the Case Studies when the amounts of avoided fertilisers were calculated. To conclude, it has been found in the analyses that the use of an expanded system, including wastewater treatment, households and agriculture, is important for a proper evaluation of the environmental impact. The results from the Case Studies indicate that the most important factors are the emissions of nutrients to water and the avoided use of artificial fertilisers, which give decreased use of fossil fuels and emissions to air. These arguments favour the urine sorting system in the Kronan case, the liquid composting process in Horn and the local sludge treatment on Koster. iv

7 SAMMANFATTNING Miljöpåverkan från olika typer av avloppssystem har utvärderats med livscykelanalys (LCA). Tre fallstudier har utförts, i två av studierna jämfördes konventionell avloppsbehandling med alternativ teknik och i den tredje studien bedömdes olika slambehandlingsalternativ. Förutom livscykelanalyserna gjordes även en litteraturstudie av kväves och fosfors växttillgänglighet i humanurin och slam för att kunna bedöma hur mycket handelsgödsel som kan ersättas genom att sprida näringsämnena i det behandlade avloppsvattnet. I samtliga fallstudier antogs att de näringsämnen som finns kvar efter avloppsvattenbehandling sprids på jordbruksmark, vilket minskar behovet av handelsgödsel. Livscykelanalysen inkluderade användning av energi och råmaterial, emissioner till luft, vatten och mark. De olika alternativen bedömdes även med hjälp av tre olika viktningsmetoder; EcoNV, EPS och ET long. Den första av metoderna utvecklades speciellt för den här studien. I Kronan, som är en planerad stadsdel i Luleå, visade sig ett urinsorterande system vara fördelaktigt jämfört med en konventionell lösning då dessa bedömdes med LCA.. Det berodde huvudsakligen på lägre emissioner av näringsämnen till vatten och lägre behov av fossila bränslen. Det senare resulterar även i lägre utsläpp till luft av energirelaterade substanser. Ammoniakemissionerna till luft var emellertid högre i det urinsorterande systemet än i det konventionella alternativet. I det planerade villasamhället Horn i Västerås, användes LCA för att bedöma vilken typ av hantering som var att föredra ur miljösynpunkt; att behandla toalettavfall och organiskt köksavfall med våtkompostering (kontinuerlig eller satsvis drift) eller att behandla avloppsvatten i ett minireningsverk och köksavfall i en trumkompost. I Horn analyserades miljöpåverkan både för tillverkningen av de tekniska komponenterna och driften av systemet. Resultaten från Hornstudien visade att en våtkompost har flera miljömässiga fördelar jämfört med ett reningsverk. Processen ger högre recirkulation av näringsämnen och lägre emissioner till vatten, framför allt av kväve men även av fosfor. Minireningsverket hade betydligt högre emissioner till vatten, men lägre emissioner till luft av ammoniak. Den kontinuerliga våtkomposteringen har det högsta elbehovet, följt av minireningsverket, medan den satsvisa våtkomposteringen visade sig vara minst elkrävande. En nackdel vad gäller våtkomposteringen är att tillverkningen av ingående komponenter är mer resurskrävande än för minireningsverket. Emellertid är miljöpåverkan från tillverkningen i samtliga fall av mindre betydelse än från driften. För Kosteröarna i Strömstads kommun användes LCA för att bedöma två alternativa sätt att hantera slammet; att behandla slammet lokalt på Koster och sprida det som gödning där eller att transportera det till fastlandet, avvattna slammet i det centrala reningsverket för att därefter sprida det på jordbruksmark kring Strömstad. Kosterstudien visade att den lokala slamhanteringen har flera fördelar, mer kväve kan återföras till jordbruksmark och emissionerna av kväve till vatten blir lägre än för det centrala alternativet. En nackdel är att den lokala slamstabiliseringen förbrukar mer el, men i gengäld minskar transporterna vilket innebär lägre behov av fossila bränslen och lägre emissioner till luft. Studien av i vilken grad näringsämnen i slam förmår ersätta handelsgödsel visade att det är svårt att hitta generellt användbara data, eftersom ersättningsförmågan beror på en mängd faktorer som jordtyp, v

8 klimat, spridningsbetingelser och fällningskemikalie. Kväveförlusterna beror till stor del på hur uppsamling, lagring och spridning av slam och urin utförs. Det innebär att det finns en stor osäkerhet i värdena, emellertid har intervall och möjliga värden på substituerbarhet givits för kväve och fosfor i humanurin och slam. Dessa värden har sedan använts i fallstudierna när den undvikna produktionen av handelsgödsel beräknades. Sammanfattningsvis har de tre fallstudierna visat på vikten av att analysera ett expanderat system, vilket inkluderar hushåll, VA-system och jordbruk, för att man skall erhålla en mer rättvisande utvärdering av miljöbelastningen. Resultaten från fallstudierna tyder på att de viktigaste faktorerna är emissioner av kväve och fosfor till vatten samt den produktion av konstgödsel som kan undvikas genom spridning av näringsämnen från VA-systemet. Det senare innebär att användningen av fossil energi och emissioner till luft kan minskas. Dessa argument gynnar det urinsorterande systemet i Kronan, våtkomposteringen i Horn och den lokala slamhanteringen på Koster. vi

9 TABLE OF CONTENTS PREFACE... I SUMMARY...III SAMMANFATTNING...V 1. INTRODUCTION...1 The Systemanalys VA project...1 Life Cycle Assessment...2 The structure of the Case Studies...2 Recycling of nutrients...3 Electricity...3 Geographical scope...4 Multi-function activities and allocation...4 Weighting methods CASE STUDY I, KRONAN, LULEÅ...7 GOAL DEFINITION...7 Purpose...7 Compared system alternatives...7 Functional unit...7 Delimitations...8 Data sources and data quality...11 DESCRIPTION OF THE TECHNICAL SYSTEMS...12 Water treatment plant...12 Households...12 Sewage pumping...13 Wastewater treatment plant...13 Transports...16 Farming...17 Treatment chemicals...18 Artificial fertilisers...18 Electricity...18 RESULTS...19 Recycling of phosphorus...19 Energy...19 Emissions to water...24 Emissions to air...25 EVALUATION WITH INDICES...27 EPS...27 EcoscarcityNV...29 Environmental Themes, long term, Sweden (ET long)...30 Comparison and discussion...31 CONCLUSIONS CASE STUDY II, HORN, VÄSTERÅS...34 GOAL DEFINITION...34 Purpose...34 Compared system alternatives...34 vii

10 Functional unit...34 System boundaries...34 Data sources and quality...35 DESCRIPTION OF THE TECHNICAL SYSTEM...36 Households...36 Liquid Composting...37 Wastewater treatment plant...41 Spreading...44 Emissions of CH 4 and N 2 O...45 Life of system components...45 Summary of the alternatives...46 RESULTS...48 Construction...48 Operation...53 Summary of construction and operation...57 EVALUATION WITH INDICES...59 EcoscarcityNV...59 EPS...59 ET long...60 Comparison and discussion...60 CONCLUSION CASE STUDY III, KOSTER, STRÖMSTAD...62 GOAL DEFINITION...62 Background...62 Purpose and compared system alternatives...62 Functional unit...62 System boundaries...62 Data sources and data quality...64 DESCRIPTION OF THE TECHNICAL SYSTEM...65 Future system and capacities...65 Wastewater treatment plant...66 Septic tanks...67 Thickening...67 Phosphorus and nitrogen...68 Local treatment on Koster...68 Central treatment in Strömstad...69 Summary of the alternatives...70 RESULTS...71 EVALUATION WITH INDICES...76 EcoscarcityNV...76 EPS...77 ET long...77 Comparison and discussion...78 CONCLUSIONS SUBSTITUTABILITY OF FERTILISER NUTRIENTS BY PHOSPHORUS AND NITROGEN IN HUMAN URINE OR SEWAGE SLUDGE...80 INTRODUCTION...80 SHORT BACKGROUND ON PHOSPHORUS AND NITROGEN IN SOIL...81 Phosphorus...81 Nitrogen...82 Conclusion - factors affecting plant uptake and soil supply of phosphorus and nitrogen...84 AIM OF THIS STUDY AND MAIN QUESTIONS...86 viii

11 RESULTS...88 Comments on results...88 Discussion GENERAL DISCUSSION AND CONCLUDING REMARKS REFERENCES...96 APPENDICES APPENDIX A Summary Tables, Kronan, Luleå APPENDIX B Inventory data for the construction of the wastewater systems in Horn APPENDIX C Inventory data for the operation of the wastewater systems in Horn APPENDIX D Inventory data for the Koster study APPENDIX E Data on activities common to the Case Studies APPENDIX F EcoNV index for evaluation ix

12 1. Introduction The Systemanalys VA project This study has been carried out as part of a project initiated by the Swedish Environmental Protection Agency, the Systemanalys VA project. In this project various new, alternative, solutions to wastewater treatment and nutrient recycling have been studied. Different evaluation methods have been used in order to find out which are the most useful ones for local authorities wanting to evaluate projected ways of taking care of wastewater. (Here the word method is not used in a strict, scientific sense. It is used to describe different approaches trying to grasp different aspects of water, and especially wastewater, management.) These evaluation methods do not compete with each other, rather they cover different aspects of sanitary systems, and they should be seen as tools in a tool-box, each with its specific purpose. The aspects covered in the project are: User behaviour Epidemiological risk Environment Life Cycle Assessment, LCA Integrated water planning within catchment areas. This report covers the LCA part of the project, where three Case Studies have been performed. The systems studied are planned for locations in different municipalities in Sweden: Luleå, Strömstad and Västerås, and they represent rather different conditions regarding e.g. scale. All three studies are future oriented evaluations of projected systems that are, at least partly, not yet built or put into operation. * Luleå Strömstad * * Västerås Figure 1.1: The three Case Study municipalities in the LCA part of the project. 1

13 Life Cycle Assessment Life Cycle Assessment (LCA) is a method aiming at analysing and evaluating environmental impacts of products or services. The whole chain of activities, from cradle to grave, needed for the production of a certain product or service is taken into consideration. Both emissions of potentially harmful substances from these activities and their consumption of natural resources are analysed. In this way different technical systems, tree structures or chains of activities, producing the same utility (product or service) can be followed from cradle to grave and compared with regard to their impacts on the environment. When the term environmental impact occurs in this report, it means both emissions and use of resources. The methodology of LCA can very briefly be described as a three step procedure. These steps include: Goal and Scope definition, where the purpose of the study is defined and where the questions about what to include and what to omit are discussed. As a result of these discussions a system boundary is defined. The functional unit, i.e. the basis for comparison in the study, is also defined in this step. A flow chart which shows the relations between the different activities in the life-cycle is also produced. This chart serves as an aid in structuring the collected data. Inventory, the phase in which all information on the emissions and the resource consumption of the activities in the system under study are collected from various sources. Where no reliable data are available, assumptions may have to be made. Impact assessment, where the environmental consequences of the inventory data are assessed. Often some kind of sensitivity analysis or discussion of uncertainties is included in this step. In reality this is always an iterative process where the analyst will have to go through the different phases more than once. Often a fourth phase, interpretation, is added to the first three. This is first and foremost an analysis of possible ways to improve the environmental performance of the studied system. It should be pointed out that LCA is a method which is confined to the study of environmental impacts caused by the technical systems under study and no regard is given to the economic performance of different alternatives. The structure of the Case Studies The first part of the Case Studies presents the question and systems in focus and states more precisely the aim of the study. This is the Goal and Scooping step of the LCA methodology. Here it is made clear how the studied systems have been defined, their boundaries and their interaction with surrounding systems. The second part of the Case Studies is a relatively detailed description of the systems under study, the technical characteristics of the activities involved, their consumption of resources and their emission of substances which might be harmful for humans or the environment. This is the inventory. Since the systems studied are fictitious much uncertainty is involved in these descriptions, and assumptions have been made concerning some of the characteristics of the activities. The descriptive parts are followed by more analytical parts where various aspects of the impacts on the environment of the alternatives are assessed. Different methods are used for this assessment in order to give a richer picture of the problems caused by the systems. Different sets of assumptions have been 2

14 used in a form of simplified sensitivity analysis. For some vital and uncertain parts of the systems, a kind of flip-over analysis has also been performed, where it has been calculated to what extent the value of a certain parameter has to differ from the basic assumption for the ranking of the alternatives to change. The last part of each Case Study is a brief conclusion and discussion of the results presented in earlier chapters. The validity and the sources of uncertainty of the results are dealt with as well as a short part on possible improvements of the alternatives. Recycling of nutrients The bringing of macro nutrients such as phosphorus and nitrogen to agricultural land affects the environment in two different ways. Firstly, the nutrients that are made available to plants reduce the need for commercial fertilisers. Secondly, bringing the nutrients to soil so that they can be fixed in plants means that emissions to air and water are reduced. Another important macro nutrient is potassium, which, however, has been excluded in these studies. Earlier studies A study of sanitary systems using life cycle assessment methods was conducted in 1996 by Tillman et al. The aims of the LCA-study encompassed the estimation of environmental impacts caused by two different conventional sanitary systems as compared to two alternative ways of treatment, a local treatment and a urine sorting system. To achieve a comprehensive comparison between the different systems with regard to the recycling of plant nutrients to agriculture the delimitation of the systems included a subpart of the agricultural system, namely the addition of fertiliser to agricultural land. The comparison was made in an indirect way since the addition of plant nutrients from the sanitary system was viewed as avoided addition of fertiliser. Therefore, an important question needing a quantitative answer in the LCA was the degree of substitutability between plant nutrients from the sanitary system and the same from commercial fertilisers. If the degree of substitutability could be estimated, then the environmental impacts of fertiliser and sludge additions could be compared. Fertiliser substitutability As part of this LCA-study it was decided to undertake a further investigation into the comparison of plant nutrients supplied as fertiliser or in flows from the sanitary system trying to reach better estimates of the substitutability than Tillman et al. (1996) used. The initial commission included only a short investigation of the availability of phosphorus in sewage sludge but it was soon discovered that nitrogen also should be incorporated as well as the substitutability between human urine and fertiliser. The question in focus for this study was the degree of substitutability of these substances compared to artificial fertiliser, i.e. how much fertiliser can be substituted for by the spreading of substances from the sanitary systems. The results of this investigation have been used in the Case Studies and they are presented in a more comprehensive way in a separate chapter after the LCA Case Studies. Electricity Electricity has been treated as the present Swedish average mix, i.e. mainly a mixture of nuclear energy (49%), water power(44%) and combined power and heating plants (6.6%). In theory, it would have been more correct to use estimates of what will be the marginal electricity source in years time, but since such estimates are almost impossible to do with any accuracy, today s average was 3

15 chosen. This choice was made following Ekvall (1997). As will be seen later in the report, the differences between the alternatives in this respect are very small, and therefore this choice of electricity mix, will not be of major importance to the ranking of the alternatives according to their environmental consequences. Geographical scope The pollutants from the activities studied have effects on different geographical scales, CO 2 on a global scale and BOD on a local scale for instance. These differences have to some extent been taken into consideration in the impact assessment part of the study. In the evaluation with indices, the ET long and EcoNV methods are calculated for average Swedish conditions, whereas the EPS is developed for global data. No further adaptation to local conditions has been made in these evaluations. Multi-function activities and allocation In LCA, multi-function activities are sometimes difficult to handle, since in many cases there is no clear rule stating how much of the environmental impact should be attributed, or allocated with an LCA term, to the one product/service and how much to the other. In this study the extra benefit of nutrients being brought to agricultural land has been treated as a reduced need for artificial fertiliser. With a reduced need for such substances comes reduced production and consequently reduced emissions and resource consumption. Also the transports of these amounts of fertilisers are avoided. This way of looking at the systems has the advantage that the benefit of the nutrients is seen as a reduced environmental impact (which can more easily be compared to the other environmental impacts caused by the systems) and not as another function of the systems. For a more thorough discussion of the thoughts underlying this kind of analysis, see e.g. Tillman et al., 1994). Weighting methods In order to say something about the total environmental performance of the systems studied, there is a need for a way of weighting different types of emissions and other types of impact on the environment. This weighting is supposed to indicate what emissions are the most harmful ones and which are less significant. In the results chapters of the Case Studies different aspects of the environmental impacts of the alternatives are investigated. In the evaluation with indices chapters attempts are made to combine these aspects with three different weighting methods. This is done both in order to give an understanding of which alternative is the least environmentally harmful and to show what emissions etc. that cause the major part of the environmental impact. It should be stressed that different methods take different parameters into account and treat them in different ways. In order to facilitate the interpretation of the results from these evaluation methods, a table that shows what emissions and resource demands are included in the respective methods is provided in Table 1.1. The evaluation of the construction phase in the Case Study of Horn also comprises a number of other parameters. For the EPS method the emissions of Ni, Pb, Zn, Cr, Cu, Cd and Hg are included. For ET long are, apart from these metals, also the following parameters included: emissions of As, Mn, Co, HCl and formaldehyde, and generation of industrial waste, ashes and hazardous waste. 4

16 Table 1.1: Parameters covered by the different evaluation methods. Parameter EPS EcoNV ET long CO 2 X X X CO X X NO x X X X N 2 O X X SO 2 X X X CH 4 X X HC X X VOC X X X PAH X X Particles X X NH 3 X X X P-tot X X X N-tot X X X BOD X X COD X X Phenol X Oil (as resource) X X Fossil gas (as resource) X X Diesel (as resource) X X Iron (as resource) X Phosphorus (as resource) X EPS EPS is a Swedish set of indices, building primarily on the willingness-to-pay for the protection of five safeguard subjects; biological diversity, human health, production capacity of ecosystems, nonrenewable resources and aesthetic values. The environmental impact is expressed in Environmental Load Units (ELU). EPS tends to put a lot of attention to global environmental threats, especially to climate change, and to the use of resources. The EPS method was first presented in Steen & Ryding (1992). The set of indices used here comes from the latest up-date of the method (Steen, 1996). ET long, Sweden The environmental themes methods was originally developed in the Netherlands (McKinsey & Company, 1991). The indices are calculated in two steps. In the first step the various substances are grouped into themes (or environmental threats to use another term), like for instance eutrophication. The contribution of each substance to each theme is described in quantitative terms. In the next step, the different themes are compared and weightted in relation to each other. In the case of ET long this weighting was done on the basis of assumed long-term critical loads (Baumann et al, 1993). EcoNV EcoscarcityNV (or in short: EcoNV) is a new index developed especially for the Systemanalys VA project. It is based on the principle of distance-to-target, i.e. it uses the relation between a fixed target and the state of today to determine the weight of different environmental impacts. The guiding targets in this case has been the environment targets set up by the Swedish EPA in the Miljömål 2021 study. Since the reduction targets in this report are expressed only for a limited number of substances, 5

17 the coverage of this set of indices is not as broad as for the other methods. It is however based on very new targets that can be expected to reflect the latest knowledge in the area of environmental impact of emissions from human activities. For a short description of how these indices were calculated, see Appendix F. N.B. that the EcoNV method does not account for the use of resources, only emissions are included in the evaluation. 6

18 2. Case Study I, Kronan, Luleå GOAL DEFINITION Purpose The study has been made in order to find out the environmental consequences of two different sewage treatment alternatives for the projected housing area Kronan in the city of Luleå. Kronan is planned for 2700 inhabitants and places of work for about 1000 people. The major difference between the alternatives studied is that in one case the urine will be taken care of separately, while in the other the urine will be treated together with the rest of the sewage in a conventional way. Compared system alternatives Here the two alternatives are presented briefly to give a basic understanding of the systems and the differences between them. In the first alternative, hereafter called the conventional alternative, all sewage will be treated in a conventional manner in the existing Uddebo Wastewater Treatment Plant (WWTP). The sludge from the treatment plant will be transported to farms near Luleå and applied as fertiliser. In the second alternative, hereafter called the sorting alternative, urine sorting WCs will be installed. The urine water will be taken care of separately and stored in tanks before being transported to farms. The remaining fractions of the sewage (faeces and wastewater from kitchens, bathing and washing) will be treated at Uddebo similar to the first alternative. Both the urine and the sludge will be used as fertilisers. Figure 2.2 shows the system for the sorting case. The only difference between the alternatives on this level of detail is the link with urine from household to farming, which does not exist in the conventional case. Functional unit In order to compare the two alternatives, all emissions and all resources have been related to a functional unit, i.e. the major function performed by the systems. This unit has been defined in the following manner: Treatment of the sewage from one person-equivalent during one year. The person-equivalent in this study is a fictitious person who spends all his or her time in Kronan. This choice of functional unit focuses on the wastewater treatment, while the recycling of nutrients is seen as an extra benefit. 7

19 Production of chemicals Water Fertiliser production Transport Water treatment Transport Pumping Transport Farming Household Faeces Other Urine Collection Transport Pumping Sewage Treatment Plant Uddebo Sludge Production of chemicals Transport Figure 2.2: Effluent water Flow chart of the wastewater treatment system in the case where urine is sorted. The parts indicated by dotted lines refer to the urine sorting alternative only. Delimitations Only the operation is studied In all studies, choices have to be made about what to include and what to omit. In this study, one important delimitation is made, namely that only the operation of the systems has been analysed. No consideration has been given to the energy and natural resources needed to build the systems. This delimitation was, however, made with the findings of earlier studies of sanitary systems in mind. Tillman et al (1996) showed in a study of the sewage treatment in Bergsjön (a part of the city of Gothenburg) that the environmental impact of the construction phase did not differ much between the different scenarios, so that the ranking of the alternatives was not affected by the inclusion of this phase. The environmental impact of the construction phase was, however, not negligible in comparison to the operation, it was just not of decisive importance to the comparison and ranking of the different alternatives. In the case of Kronan it is quite easy to see that the differences in the construction phase between the two scenarios are not very large. The difference would merely consist of some plastic pipes and a number of tanks for storing the urine water; the majority of the building components used would be common to both alternatives. Time This is a prospective, forward-looking, study trying to find out the consequences of systems that do not yet exist. For the analysis, a point in time has been chosen, where the operation of the systems is assumed to be stable. This has been characterised in the following manner: 1. The Kronan housing area is built and all the inhabitants have moved in. 8

20 2. The Uddebo WWTP is extended with a step for biological treatment, and this new step is running in steady state. 3. Systems and routines for bringing the major part of the urine and the sludge to agricultural land are established. Sanitary systems are long-lived structures; most components last for at least twenty years and some of them much longer. This fact makes the environmental assessment of such systems more difficult than analyses of products with shorter lives. In this particular case, in order to assess the environmental impacts of the alternative systems, assumptions have to be made about conditions that lie decades into the future. In general, this study is based on the assumption that no dramatic changes will occur in the society that surrounds the systems under study. This makes the value of the study small, when it comes to really long-term effects. The ambition in this study is to present results that can still be valid after approximately a decade from now. Trying to look further into the future would only lead to very vague conclusions. So the purpose of the study is not to make a full assessment of the total lives of the systems, but rather to look into the environmental impacts that lie in a foreseeable and reasonably predictable future. Geographical boundaries The greater part of the inventory data are collected from the systems and the area under study, they are what can be called site specific data. In some cases, however, more general data have been used, mostly when no site specific data have been available or when the general data sets have been regarded as representative also for Luleå, like for instance data on the amounts of various substances in household sewage. Delimitations in the technical systems The general principle used has been to include only the activities where differences between the alternatives are likely to occur. The heating of water has not been included in the analysis since it has been assumed that there will be no difference between the alternatives in the consumption of hot water. For the sake of making a complete description of the technical systems and an analysis of the environmental impact of these systems, it might have been included. In the analysis only the environmental impacts the households cause via the sanitary systems have been regarded. Other environmental impacts of the households have been regarded as irrelevant in this study. The treatment of storm water has not been included in the study. In both alternatives, storm water will be taken care of separately and, consequently, it will not affect the flows of sewage and urine. The flows of heavy metals in the storm water from Kronan have been investigated by Karlsson (1997). The scale of the studied systems As it has been mentioned above, this study investigates the consequences of the choice between urine sorting versus conventional treatment for a specific housing area, Kronan. The sewage system in 9

21 Kronan will be connected to the existing system in Luleå and the existing WWTP at Uddebo. It has been assumed that this plant has the capacity to take care of the sewage from Kronan. Since it is only a small part of a larger system that is studied, the analysis should be regarded as a marginal analysis. Hence, the results of the study are only relevant for minor changes like the ones here studied and not for more extensive changes. If, for example, a majority of the households in Luleå were to install urine sorting WCs the consequences might be different from what is shown in this study. This delimitation in scale is important and it has to be considered when the results are interpreted. Inventory parameters In the inventory of the systems under study, the parameters (substances etc.) presented in Table 2.1 are the ones that have been chosen. Other substances than the ones mentioned above do appear in the study, but the inventory has, however, primarily concentrated on finding information on these. Table 2.1: Categories and parameters used in the inventory. Resources used Energy (Oil, Fossil gas, Diesel, Electricity) Raw materials (Raw Phosphate, Iron ore) Emissions To air Carbon dioxide, Carbon monoxide, Nitrogen oxides, Sulphur oxides, Methane, VOCs, Particles Waste To water Nitrogen, Phosphorus, Oxygen demanding substances Heavy metals have not been included in the study. A separate study is carried out in parallel to this one, and it is focusing especially on the flows of heavy metals in the case of Kronan (Karlsson, 1997). Apart from these flows of substances that pass between the imagined boundary between the technical systems studied and nature, other flows go to other technical systems. Some of these flows have been treated using the kind of approach mentioned in the Introduction, trying to describe the flows as reduced needs for substitutable activities and environmental impacts. Other flows have simply not been followed back to the cradle or to the grave in nature. Such flows have been accounted for and included in the inventory, but they are not regarded in the evaluation. In accordance with LCA practice, the ambition has been to leave as few flows as possible un-traced in this manner. Electricity The electricity demands of the different activities in the systems studied are reported in the results chapter. In the impact assessment and evaluation, however, the electricity has been followed to its cradle, using the average mix as described in the Introduction. The summary tables for the alternatives, which can be found in Appendix A, are based on the average mix, so here electricity is 10

22 expressed in terms of the resource uses and the emissions from the electricity production associated to the systems studied. Data sources and data quality Most data used in the study are of a site-specific character. These have been provided by the local authorities in Luleå, and should have high accuracy and relevance. Nonetheless, many assumptions have been made about the performance of the systems studied. Data of a more general character, e.g. energy demand in fertiliser production, have to a large extent been taken from Tillman et al. (1996). These data are usually based on averages for an industry, a country etc. For issues not covered in these reports, like for instance detailed data concerning agriculture, the information has been collected from literature and through interviews with experts in the respective fields. The fact that the systems under study are not yet built introduces a great deal of uncertainty into the analysis. In some cases well grounded assumptions about future conditions have been possible to make, while in others, like for instance with the electricity mix, the analysis rests on present figures. When of importance for the ranking of the alternatives this uncertainty is discussed. 11

23 DESCRIPTION OF THE TECHNICAL SYSTEMS In this section the technical systems are described and data and assumptions made about the activities in the systems are presented. The results of the study is to a high degree depending upon these assumptions. The information in this section is to the larger part provided by the municipality of Luleå (Luleå, 1997 and Marklund, 1997). Water treatment plant For the Gäddvik water treatment plant, the figures in Table 2.2 have been used. These are based on the present operation of the plant. No major changes are projected for the near future. Figures are given per year. Table 2.2: Production and resource demand for the Gäddvik water treatment plant (per year). Water production m 3 Electricity demand kwh Chemicals used Slaked lime 266 tonnes Carbon dioxide 288 tonnes Chlorine gas 1.67 tonnes The electricity figure includes both the demand at the plant and what is needed for the distribution of the drinking water. Households For the households it has been assumed that the machines and equipment will be highly modern and water saving. It is thus not too optimistic to assume that the water consumption will be around 160 l per person and day, i.e. 58 m 3 per year. In the urine sorting alternative, it has been estimated that this figure will be somewhat lower due to the smaller amount of water used for flushing in this type of WCs, hence a water consumption of 150 l, i.e. 55 m 3 per year. has been chosen. The volume of urine and flushing-water has been estimated to 0.9 m 3 per person and year. For the amounts of nutritive substances in the sewage the standard values from the Swedish EPA has been used. These figures are presented in Table 2.3. Table 2.3: Amounts of nutrients in different fractions from households, grams per person and year. Swedish average values (SNV, 1995 and Sundberg, 1997). Urine Remaining Total Substance fraction Phosphorus Nitrogen The figures for phosphorus represent average Swedish consumption of low-phosphorus detergents and washing powder. The inflow of substances from the households has been assumed to be equal in both alternatives. 12

24 For the sorting alternative the analysis is based on the assumption that all urine and all faeces are correctly sorted. In reality, it might be a problem that this is not the case (contamination of urine etc.), but since this study is focusing primarily on the quantitative aspects of the flows of nutritive substances, the divergence from the assumption made cannot possibly be so large that it has any great influence on the results. Sewage pumping During the transport from the household to the sewage treatment plant, a considerable amount of water comes into the pipes from the surrounding soil. It has been roughly estimated that this will add 40% to the volume, so that the volume of incoming sewage to the treatment plant will be approximately 80 m 3 and 77 m 3 for the two alternatives respectively. (Approximately the same amount of incoming water in both cases, 40% of 55 m 3 = 22 m 3.) The energy demand for pumping the sewage from Kronan to the treatment plant at Uddebo has been estimated to 11 kwh per person and year, given a specific sewage-flow of 380 l per person and day. In the alternatives under study, the volumes will be smaller, and assuming a linear relation between energy consumption and volume, the energy consumed in the alternatives has been calculated to 6.3 kwh and 6.1 kwh per person and year, respectively. Wastewater treatment plant The wastewater treatment plant at Uddebo is run by the municipality and it serves some person-equivalents (1995). Today the operation is confined to chemical treatment, but the plant will be extended with a biological step in This means that when Kronan is completed, the plant will have both chemical and biological treatment steps. Even though the bio-step is not yet erected, it has been possible to make good assumptions about its performance since this treatment technology is well-known from existing plants located elsewhere. At the Uddebo WWTP the flows from the systems studied is treated together with large volumes of wastewater from other parts of Luleå. Therefore, it has been necessary to assess how much of the energy, chemicals etc. used at the plant that should be allocated to the systems studied. It has been found reasonable to allocate the precipitation chemicals according to how much phosphorus there is in the different flows. Energy consumption has, on the other hand, been allocated according to the treated volumes. For the production of sludge the following figures have been chosen (Gujer, 1996): 80 g TS per person and day, conventional case. 70 g TS per person and day, sorting case For a sludge of 20% TS this would be equivalent to the following amounts per person and year: 146 kg, conventional case. 128 kg, sorting case 13

25 The flow of phosphorus through the treatment plant in the sorting case is illustrated in Figure 2.3 below. Here a reduction of 95 percent has been assumed. 347 Uddebo WWTP Figure 2.3: Sludge To receiving water to farming Flow of phosphorus through the wastewater treatment plant at Uddebo in the urine sorting case, g/pe y. For the conventional case, the corresponding flows would be like in Figure 2.4: 712 Uddebo WWTP Figure 2.4: Sludge To receiving water to farming Flow of phosphorus through the wastewater treatment plant at Uddebo in the conventional case, g/pe y. Also for oxygen demanding substances a reduction factor of 95% has been chosen. Since there is no step for nitrogen removal at the plant it has been considered reasonable to assume a 30% reduction of nitrogen. The contents of nitrogen in the sludge is analysed regularly. In 1994 the total amount of nitrogen in the sludge was 54.8 tonnes. Here it has been assumed that the percentage of the nitrogen that is caught in the sludge will be the same in the future as it is today people are connected to the plant, and if they all produce 4.9 kg of nitrogen per year and person, this would mean that the plant takes care of approximately 300 tonnes. This means that about 18% of the nitrogen (54.8/300) is caught in the sludge. In the case of this study this would result in 882 g/pe y being caught in the sludge in the conventional case and 164 g/pe y in the sorting case. Table 2.4 summarises the figures for consumption of energy and chemicals, the flows etc. at the Uddebo plant during one year. Some of the figures refer to the 1995 situation, others are estimates on how the plant will operate with the new biological treatment step. 14

26 Table 2.4: Data describing the WWTP at Uddebo. Person-equivalents served (1995) Persons connected (1995) Inflow of wastewater m 3 /year (1995) Inflow of phosphorus 55 tonnes/year (1995) Sludge produced m 3 (20% TS) (1995) Chemicals consumption Ferrous precipitation chemical 1300 tonnes/year Estim. Polymer 8 tonnes/year Estim. Electricity consumption Machinery kwh/year Estim. Pumping kwh/year Estim. Heating kwh/year Estim. TOTAL kwh/year The plant also has a production of biogas, which will partly be used internally. This is a fairly new practice at Uddebo and it is therefore not yet fully known how it is going to operate. Plans are, however, to digest all sludge in the future and using as much of the gas that is necessary for internal use (heating of the digester and some premises). The gas that is not used for these purposes will either be flared or sold for external use. It has been estimated that the amount of gas that will be produced when the digester takes care of all the sludge is going to equal about MWh per year. According to the municipality about 50% of this gas can be used at the plant (average figure for the whole year). The emissions from the burning of this gas have to be taken into account in this analysis as an impact. How the remaining 50% should be treated is less obvious. If it is flared, the exhausts should be treated as any emission and included in the analysis as an impact to the environment. If it is used for other purposes, such as fuelling buses, thereby reducing the demand for other fuels (diesel or fossil gas in the case of buses), it is reasonable to treat the gas in the same manner as is done with the nitrogen and the fertiliser, i.e. to include also the avoided production and burning of diesel. Since it is not known what will happen with this remaining amount of gas, it is hard to decide how it should be treated in the analysis. For the comparison of the alternatives under study, this is irrelevant, but it is nevertheless an important part of the environmental performance of the systems and therefore a point that ought to be regarded when the systems are evaluated from an environmental perspective. In the LCA inventory, the excess gas will be accounted for as a by-product, biogas, and it will not be treated further in the evaluation. The emissions from the burning of biogas have been approximated with figures for fossil gas, only with the modification that the emissions of CO 2 have been omitted (since these are not of fossil origin and therefore are not considered as contributions to the CO 2 concentration in the atmosphere) and the emissions of SO 2 have been halved. The figures have been taken Tillman et al. (1996). Emissions from the gas that is used internally are presented in Table 2.5. Table 2.5: Emissions from the burning of biogas for internal use at Uddebo WWTP. Substance Emissions per year CO 14 kg HC 220 g NO x kg 15