Environmental Impacts of a Wastewater Treatment Plant – With Sidestream Deammonification

IN

DEGREE PROJECT ENGINEERING CHEMISTRY,

SECOND CYCLE, 30 CREDITS STOCKHOLM SWEDEN 2020 ,

Environmental Impacts of a Wastewater Treatment Plant

With Sidestream Deammonification MALIN EKMAN

KTH ROYAL INSTITUTE OF TECHNOLOGY

SCHOOL OF ENGINEERING SCIENCES IN CHEMISTRY,

Environmental Impacts of a Wastewater Treatment Plant

With Sidestream Deammonification

Malin Ekman

Supervisor: Nilay Elginöz Kanat Examiner: Zeynep Cetecioglu Gurol

Master of Science Thesis KTH Chemical Engineering

Chemical Engineering for Energy and Environment

SE-100 44 Stockholm

Abstract

We, the humans, give rise to wastewater everyday. Municipal wastewater is rich in carbon, nitrogen and phosphorus, of which have large impacts on the environment. Wastewater treatment is therefore a necessity to minimize the anthropogenic impacts on both nature and biodiversity. To reduce the content of these substances, the wastewater is treated in wastewater treatment plants. One of them is Himmerfjärdsverket located in Sweden that uses, among others, deammonification of which is a biological technology for treating ammonium rich wastewaters. In this thesis, a life cycle assessment is conducted in order to do an overall evaluation of the environmental profile of this entire plant during two different years, 2019 and 2015. These years also have different deammonification technologies implemented, DEMON and DeAmmon. The results are evaluated upon the following impact categories:

climate change, freshwater and marine eutrophication, human toxicity, ozone depletion and acidification.

The impact assessment is conducted in GaBi software with the database ecoinvent version 3.3

and ReCiPe as method. Results indicate that the main contributors to pollution are due to

anaerobic digestion, which is a process that stabilize sludge and also from emissions to soil

that arise from disposal of digested sludge. Other large impacts come from chemicals that are

added to the process, the effluent and other arising emissions from the different processes. It

is further concluded that there are no major differences between the two deammonification

technologies within the boundaries of this assessment.

Sammanfattning

Människan ger upphov till avloppsvatten varje dag. Kommunalt avloppsvatten är rikt på kol, kväve och fosfor, vilka har en stor miljöpåverkan. Vattenrening är i och med detta en nödvändighet för att minimera den antropogena inverkan på naturen och den biologiska mångfalden. Genom att rena vatten i avloppsreningsverk så kan halterna av dessa ämnen reduceras markant. Ett av många reningsverk är Himmerfjärdsverket som är beläget i Sverige, som bland annat använder deammonifikation vilket är en vattenreningsmetod för att rena ammoniumrikt avloppsvatten. I det här examensarbetet genomförs en livscykelanalys för att utvärdera hela reningsverkets miljöprofil under år 2019 och år 2015. Dessa två år använder sig utav två olika deammonifikationsmetoder, nämligen DEMON och DeAmmon.

Resultaten utvärderas enligt följande miljöpåverkanskategorier: växthuseffekt, övergödning i marina- och sötvattensekosystem, humantoxicitet, ozonnedbrytning och försurning.

Livscykelanalysen genomfördes i mjukvaran GaBi med ecoinvent version 3.3 som databas

och ReCiPe som metod. Resultaten tyder på att de största bidragande orsakerna till

miljöpåverkan beror på anaerob rötning av slam, vilket är en process som stabiliserar slam

och även från utsläpp till mark som uppkommer genom deponering av rötat slam. Andra

faktorer som bidrar till miljöpåverkan är kemikalier, utsläpp av det behandlade avloppsvattnet

och övriga uppkomna utsläpp från olika processer. Inom analysens gränser så dras även

slutsatsen att det inte är någon markant skillnad på de två reningsmetoderna.

Acknowledgments

First of all, I would like to express my deepest gratitude towards my supervisor at KTH Royal Institute of Technology, Nilay Elginöz Kanat for your time, guidance and expertise in life cycle assessment. Without you this thesis would not have been possible to conduct. I would also like to thank my examiner, Zeynep Cetecioglu Gurol for your help with contacts and for giving me this opportunity.

I am grateful to Syvab and especially to Stefan Berg and his colleagues for your cooperativeness, for all information that you have giving me and for letting me visit Himmerfjärdsverket. Also, many thanks for letting me use your pictures in this thesis.

Last, but not least, I would like to thank my family and friends for your unconditional support. Especially thanks to my grandmother for feeding me in difficult and stressful times, I appreciate this more than you will ever know.

Malin Ekman

Värmdö, July 2020

Table of Content

Glossary I

List of Figures III

List of Tables IV

1 Introduction 1

1.1 Background 1

1.2 Wastewater Treatment History in Sweden 2

1.3 Life Cycle Assessment Study 2

1.3.1 Goal 2

1.3.2 Scope 3

2 Life Cycle Assessment Methodology 5

2.1 Goal & Scope Definition 6

2.2 Life Cycle Inventory Analysis 6

2.3 Life Cycle Impact Assessment 7

2.4 Interpretation 7

2.5 Impact Categories 7

2.5.1 Acidification 8

2.5.2 Climate Change 8

2.5.3 Eutrophication 8

2.5.4 Human Toxicity 8

2.5.5 Ozone Depletion 9

3 Wastewater Treatment Methods 10

3.1 Treatment Principles 10

3.2 Wastewater Treatment in General 10

3.3 Nitrogen Removal Technologies 11

3.3.1 Nitrification & Denitrification 12

3.3.2 Nitritation & Denitritation 12

3.3.3 Deammonification 13

4 Environmental Impacts: Previous Studies 16

4.1 General 16

4.2 DeAmmon 17

4.3 DEMON 17

4.4 Impact Category Results for WWTP 18

4.4.1 Impact Category Results for Biogas & Sludge 19

5 Himmerfjärdsverkets WWTP 20

5.1 Wastewater Treatment 20

5.1.1 Mechanical Treatment 21

5.1.2 Biological Treatment 22

5.1.3 Filtration 23

5.2 Sludge Treatment 23

5.2.1 Biogas 24

5.2.2 Biodigestate 24

5.3 Reject Water Treatment 24

6 Inventory Analysis 26

6.1 Description of the System 26

6.2 LCA Modelling 27

7 Impact Assessment Analysis 30

7.1 Results & Discussion 30

7.2 Errors & Uncertainties 37

7.3 Future Potential 38

8 Conclusion 39

9 References 40

10 Appendix 1 – Detailed Flowchart 47

11 Appendix 2 – LCI 48

A2.1 Characteristics of Inflows & Outflows 48

A2.1.1 Nitrogen in Effluent 48

A2.1.2 Phosphorus in Effluent 49

A2.1.3 Suspended Solids 49

A2.2 Chemicals 50

A2.2.1 Purchased amounts 50

A2.2.2 Precipitation Chemicals 50

A2.2.3 Ekomix 50

A2.2.4 PAX 51

A2.2.5 Polymer 51

A2.2.6 Clean Water 52

A2.3 Electricity 53

A2.4 Waste 55

A2.4.1 Waste Sources 55

A2.4.2 Incineration 55

A2.5 Biodigestate 56

A2.5.1 Deposition 56

A2.5.2 Emissions by Agricultural Application 57

A2.6 Biogas 59

A2.6.1 Internal Consumption 59

A2.6.2 Avoided Emissions from Upgraded Gas 60

A2.6.3 Emissions from Internal Use 60

A2.7 Emissions from Processes 62

A2.8 Transportation 63

A2.8.1 Waste to Incinerator 63

A2.8.2 Digestate to Incinerator 63

A2.8.3 Digestate to Farmland 63

A2.8.4 Biogas 64

A2.9 Infrastructure 65

Appendix 3 – LCIA Results 66

Glossary

Abbreviations

AOB Ammonia Oxidizing Bacteria

Anammox ANaerobic AMMonium OXidation (deammonification process)

BOD Biological Oxygen Demand - measurement over the amount oxygen that aerobic organisms consume while decomposing organic matter

COD Chemical Oxygen Demand - measurement over the amount oxygen that is required to oxidize organic matter into inorganic matter

CO 2 eq Carbon Dioxide Equivalents

DeAmmon A tradename for DIB deammonification in biofilms (deammonification process)

DEMON DEamMONification (deammonification process) DM Dry Matter

FEP Freshwater Eutrophication Potential FU Functional Unit

HRT Hydraulic Retention Time HTP Human Toxicity Potential LCA Life Cycle Assessment LCI Life Cycle Inventory

LCIA Life Cycle Impact Assessment GHG GreenHouse Gases

GSBR Granular Sludge Blanket Reactor GWP Global Warming Potential MBBR Moving Bed Biofilm Reactor MEP Marine Eutrophication Potential NOB Nitrite Oxidizing Bacteria ODP Ozone Depletion Potential PAX Polyaluminiumchloride PE Population Equivalents SBR Sequencing Batch Reactor

SHARON Single reactor system for High activity Ammonium Removal Over Nitrite

SRT Solid Retention Time

Swedish EPA Swedish Environmental Protection Agency (SWE: Naturvårdsverket) TAP Terrestrial Acidification Potential

tkm Tonne-kilometer WWT WasteWater Treatment WWTP WasteWater Treatment Plant

Chemicals & Chemical Formulas

1,4-DB 1,4-dichlorobenzene

C Carbon

CFC Chlorofluorocarbon

CH 4 Methane

CO 2 Carbon dioxide

H ⁺ Hydrogen ion

H 2 O Water

HCFC Hydrochlorofluorocarbon HCO 3 - Bicarbonate

N Nitrogen

N 2 Nitrogen gas

N 2 O Nitrous oxide NH 4 + Ammonium NO 2 - Nitrite NO 3 - Nitrate

O 2 Oxygen gas

OH ^- Hydroxide

P Phosphorus

SO 2 Sulfur dioxide

Geographies GLO Global RER Europe

RoW Rest-of-World

SE Sweden

List of Figures

Figure 1.1: Block diagram with unit processes and system boundary for the LCA study. ... 4

Figure 1.2: Framework of LCA ... 5

Figure 3.1: Three different pathways for nitrogen removal. ... 11

Figure 3.2: Anammox bacteria in suspended biofilm (© Syvab). ... 14

Figure 3.3: Plastic carrier with some biofilm on the interstitial surface. ... 14

Figure 5.1: The tunnel system that moves the water from the connected municipalities to the plant (© Syvab). ... 20

Figure 5.2: Overview of Himmerfjärdverket treatment plant (© Syvab). ... 21

Figure 5.3: Presedimentation basin (© Syvab). ... 22

Figure 5.4: Aeration basin (© Syvab). ... 22

Figure 5.5: Intermediate and final sedimentation basins (© Syvab). ... 22

Figure 5.6: Fluidizing bed (© Syvab). ... 23

Figure 5.7: Biodigestate (© Syvab). ... 24

Figure 5.8: Reject water treatment facility with DEMON in foreground with the water treatment basins in the background (© Syvab). ... 25

Figure 6.1: Modeling of the plan in GaBi software ... 28

Figure 7.1: Comparison of impacts for the whole treatment plant in the operation phase, which is divided into water line, sludge line and deammonification unit ... 31

Figure 7.2: Comparison of impacts from units in the water line; screen, primary sedimentation, aeration, intermediate and final sedimentation, fluidizing bed and filter together with effluent, electricity and waste disposal ... 32

Figure 7.3: Comparison of impacts by inputs and outputs from the water line; chemicals, electricity, emissions to air and water and handling of produced waste ... 33

Figure 7.4: Comparison of impacts from units in the sludge line; flotation, thickener, anaerobic digester and dewatering together with electricity, biogas handling and digested sludge ... 34

Figure 7.5: Comparison of impacts by inputs and outputs from the sludge line: chemicals, electricity, handling of produced biogas, handling of digested sludge and treatment of sludge ... 34

Figure 7.6: Comparison of impacts from deammonification unit; emissions to air and electricity. ... 35

Figure 7.7: Comparison of impacts from added chemicals to the whole treatment plant. ... 36

Figure A1.1: Detailed flowchart over Himmerfjärdsverket WWTP ... 47

List of Tables

Table 2.1: Impact categories used in this assessment ... 8

Table 4.1: Impact categories for five WWTPs ... 18

Table 6.1: Inventory data for Himmerfjärdsverket WWTP for year 2019 and 2015 ... 27

Table 6.2: Processes and its associated geographies used in ecoinvent v3.3. ... 29

Table 7.1: Characterized impact scores in total for Himmerfjärdsverket WWTP ... 30

Table 7.2: Reduction of ammonium in reject water for DEMON in 2019 and DeAmmon in 2015 ... 35

Table 7.3: Reduction of nitrogen and phosphorus for 2019 and 2015 ... 35

Table A2.1.1: Characteristics of influent and effluent wastewater for Himmerfjärdsverket WWTP, based on a functional unit of 1 m ³ wastewater inflow for year 2019 and 2015. 48 Table A2.1.2: Percentage of nitrogen species in effluent wastewater in an average. ... 48

Table A2.2.1: Polymer flows added to different units within the plant. ... 51

Table A2.2.2: Calculated percentages of purchased polymer to different units along with calculated amounts for the flows per FU. ... 52

Table A2.2.3: Clean water inflow to Himmerfjärdsverket WWTP. ... 52

Table A2.3.1: Electricity consumption at Strass WWTP ... 53

Table A2.3.2: Electricity consumption for the sludge line. ... 53

Table A2.5.1: Dewatered sludge quality for Himmerfjärdsverket WWTP per FU for year 2019 and 2015. ... 56

Table A2.5.2: Dewatered and dried sludge deposition for Himmerfjärdsverket WWTP for year 2018 and 2015. ... 56

Table A2.5.3: Dewatered and dried sludge deposition from Himmerfjärdsverket WWTP per FU for year 2019 and 2015 ... 57

Table A2.5.4: Division of nitrogen in digestate for agricultural application ... 57

Table A2.5.5: Calculated nitrogen-based air emissions from digestate that is spread on farmland. ... 58

Table A2.6.1: Gas usage at Himmerfjärdsverket WWTP per FU for year 2019, 2018 and 2015. ... 59

Table A2.7.1: Calculated amounts of air emissions from the treatment process, based on numbers from Strass WWTP ... 62

Table A2.9.1: Influent flow to Himmerfjärdsverket for the last ten years ... 65

Table A3.1: Characterized impact scores for Himmerfjärdsverket WWTP in year 2019 ... 66

Table A3.2: Characterized impact scores for Himmerfjärdsverket WWTP in year 2015 ... 66

Table A3.3: Characterized impact scores from products at Himmerfjärdsverket WWTP in year 2019 ... 67

Table A3.4: Characterized impact scores from products at Himmerfjärdsverket WWTP in year 2015. ... 67

Table A3.5: Characterized impact scores from chemicals at Himmerfjärdsverket WWTP in year 2019 ... 67

Table A3.6: Characterized impact scores from chemicals at Himmerfjärdsverket WWTP in

year 2015 ... 68

1 Introduction

In this chapter, background, goal and scope of this study are presented.

1.1 Background

Wastewater treatment (WWT) is a relatively new invention. Approximately 90 years ago Sweden did not have any wastewater treatment plants (WWTPs) at all. A lot have happened during these years, but more can be done in the future (Stockholm vatten, 2011). The main reason for treatment of wastewater is to protect aquatic ecosystems and human health.

However, recently WWT is not only about purifying the wastewater, but also a way of collecting and produce resources like nutrients and energy. Moreover, life cycle assessment (LCA) within WWT was initially used for evaluation of energy and resource consumption.

Today LCA is also used to evaluate environmental impacts like global warming potential (GWP) and toxicity impacts as well as for comparison between different trade-offs of not yet implemented alternative systems (Larsen, 2017).

Water pollution occurs when the water quality gets impaired or when the ecological balance is disrupted. The greatest source of pollution comes from organic materials that end up in the freshwater systems (Nilsson et al., 2007). Living and dead plants and animals are natural sources of organic materials in the waters, but human activity increases these numbers by, for example, industries, sewage systems and agriculture. Organic materials are biodegradable, meaning that microorganisms decompose the material in the waters. Aerobic microorganisms consume dissolved oxygen and thereby lowering oxygen levels that in turn can give rise to hypoxia (oxygen deficiency) (Naturvårdsverket, 2019). Biological oxygen demand (BOD) is a way to measure the amount oxygen the microorganism consumes while they degrade organic materials (Nilsson et al. 2007).

Living organisms are dependent on nutrients as well. However, too much nutrients in waters can be seen as a source of pollution since they give rise to excessive growth of cyanobacteria, or better known as algae. Nitrogen and phosphorous are the two most mentioned nutrients when it comes to water quality (Nilsson et al., 2007). This is because excessive levels of them give rise to the greatest environmental problem that the Baltic Sea has today, namely eutrophication (BalticSea2020, 2020).

Municipal wastewater is water and pollutants that arise from households, for instance

laundry, cooking and toilets. It also consists of storm water and water from industries and

hospitals. Municipal wastewater contains BOD, nutrients (mainly nitrogen and phosphorous),

persistent chemicals, metals and oil. Municipal wastewater treatment plants often compile the

influent water by BOD, chemical oxygen demand (COD), suspended solids and amount of

nitrogen and phosphorus (Persson, 2011).

The Swedish Environmental Code and EU legislation regulates which emissions and to what amount they can be emitted into the environment. The two most important EU directives for WWT is directive 91/271/EEG concerning urban WWT and the water framework directive 2000/60/EG (Naturvårdsverket, 2016). This forces the development of improvement and innovations regarding techniques in order for WWTPs to be able to meet new requirements.

1.2 Wastewater Treatment History in Sweden

Sweden’s first municipal WWTP, Ålstensverket, were built in 1934 in Stockholm due to sanitary problems, bad smells, dirty and closed bathing waters due to bad water quality in the city. Before this, wastewater was discharged untreated directly into nearest watercourse (Stockholm vatten, 2011). Over time this caused hypoxia, mortality of fish and waterborne epidemics. It was not until 1960s that eutrophication of waters gained attention and with this, treatment plants were further developed (Naturvårdsverket, 2016). From only treat the water mechanically to also use biological treatment methods in order to reduce BOD and to deal with this problem. In the late 1960s, the Swedish Environmental Protection Agency (Swedish EPA) was formed and thus the focus of environmental protection work changed to deal with compounds that have a large impact on the environment in time and space. Because of this, in the 1970s chemical treatment methods were introduced to deal with phosphorus. From now on phosphorus could be precipitated by addition of a precipitation chemical in the system and then removed by sedimentation. It took until 1990s before nitrogen compounds could be treated and reduced from wastewaters (Persson, 2011). A reason for this is that methods for nitrogen reduction require extensive expansions of the facilities, unlike what is necessary for phosphorus reduction (Lännergren, 2015).

1.3 Life Cycle Assessment Study

The purpose of this study is to do an attributional LCA over a WWTP. The plant in this study is Himmerfjärdsverket, located in Botkyrka, Sweden, see chapter 5 for a more detailed description over the plant. This thesis is a contribution to the MENToR (Methodology for environmental sustainability assessment in the early design stage of a resource recovery system) project, which is carried out by KTH and IVL (Swedish Environmental Research Institute). A focus regarding deammonification methods for purifying reject water will be held throughout this study. Deammonification is a biological technology that reduces ammonium in ammonium rich water streams.

1.3.1 Goal

The goal of this study is to compare two different years regarding municipal WWT at

Himmerfjärdsverkets WWTP, along with environmental burdens arising from the whole plant

considering a LCA perspective. Meaning that the performance of all activities and products

connected to this plant will be investigated and evaluated with respect to their environmental

impacts. The main difference between these two years is that they have different

deammonification methods (see section 3.3.3) of purifying reject water mainly from nitrogen

in the form of ammonium. Because of this, the two years are divided into two cases where the first case uses a method called DEMON and the second case uses DeAmmon. What distinguishes these two methods is that they have different reactors that are controlled in different ways and the biological growth is different.

To fulfill the goal of this thesis, the following research questions have been established:

1. Which processes at Himmerfjärdsverkets WWTP are the main contributors to the environmental impacts for each year, and why?

2. Are there any differences between the two deammonification methods DEMON and DeAmmon considering a LCA perspective at Himmerfjärdsverket? If so, specify them.

1.3.2 Scope

In this section the scope of the LCA assessment conducted in this study is described, which includes the system definition, functional unit (FU) and system boundaries.

1.3.2.1 System Definition

In this assessment the construction and operation phase of the plant was investigated. The modeling was done in GaBi software using ecoinvent v3.3 as database with ReCiPe 2016 v1.1 as method for the life cycle impact assessment (LCIA). Moreover, data used for the life cycle inventory (LCI) are mainly obtained from the investigated plant, which in turn comes from sensors, business partners or, a minor part, from calculations. Data that could not be obtained directly from the plant come from the database, environmental reports, peer reviewed scientific articles or calculations based on known numbers.

1.3.2.2 Functional Unit

The function of the system is treatment of municipal wastewater at Himmerfjärdsverket WWTP. Every calculation and every modeled flow in the system will be normalized with respect to the FU. For this study, the FU is treatment of 1 m ³ wastewater influent.

1.3.2.3 System Boundaries

The system that is analyzed in this assessment is the construction and operation phase of

Himmerfjärdsverkets WWTP. Operation phase includes treatment of municipal wastewater,

starting from the influent input into the first unit of the system until the discharging of the

effluent, products, solid waste and their contributing emissions. Transportations for material,

inputs and outputs are taken into account, as well as their impacts. Additionally, in this case

there exist two pump stations for the tunnel system that the wastewater travels in before it

arrives to the plant, of which are outside of the system boundary. Demolition of

infrastructure, material for the tunnel system and secondary waste (waste other than what is

collected from the treatment process) is not accounted for. In figure 1.1 the system boundary

can be seen. Unit processes within the boundary are further described in chapter 5.

Figure 1.1: Block diagram with unit processes and system boundary for the LCA study.

The lifespan of the plant is approximated to be 30 years while the assessment is based on yearly data from the two years 2019 and 2015. DeAmmon was implemented year 2007 and DEMON replaced it in 2017, which means that data from 2019 are used for case 1 and data from 2015 are used for case 2.

1.3.2.4 Geographical Boundaries

Focus will be on Sweden since the investigated plant is located there and will therefore be used to the greatest possible extent. However, most of the processes in the database that are applicable on this assessment only exist in larger geographical areas, such as Europe or worldwide.

Screen &

grit chamber

Primary

sedimentation Aeration Fluidizing bed ^Filter

Sludge thickener

Flotation Digester Sludge

dewatering

Deammonification

Gas engine Gas to

upgrading Torch

Effluent

Dewatered sludge

Vehicle gas Influent

Heat furnace

Intermediate

& final sedimentation

Chemicals Electricity Infrastructure

Emissions Transportation

Transportation Avoided production

2 Life Cycle Assessment Methodology

Analytical tools can be used as guidance for stakeholders and decision makers regarding environmental decisions. LCA is only one of these many powerful tools that can be used. A feature that LCA has is cradle-to-grave approach, meaning that it includes every chain in the evaluated process, product or service during its physical lifetime. From the resource extraction (cradle) to the manufacturing, the usage phase until its end of life (grave) and the transportation in between the steps is taken into account. By taking this approach it is possible to find the environmental impacts and thereby see where in the system there is an issue or detect side effects. When the hotspot is found, further investigations can be made regarding how to improve or optimize that part in the chain. Different options can also be weighted against each other to come up with the best solution. By doing so, the problem is not replaced by the first option; instead it is replaced by the best possible solution with respect to the environment (Wrisberg et al., 2002).

LCA have a holistic approach were every step in the chain can be quantified both direct and indirect with respect to the environmental impact it contributes with (Sadhukhan et al., 2014).

Moreover, shifting of burdens can be avoided since LCA is a comprehensive method that takes many different environmental problems into account. This is because when one type of problem is lowered, another type of problem can increase in another place in the chain. By looking at the whole picture, these problems could be detected and thus avoided (Bjørn et al., 2018a).

ISO 14040-series gives a framework to proceed from when conducting an LCA. ISO 14040 and ISO 14044 are the core standards that describe the principles followed by the requirements and guidelines (Heinrich, 2014). Even though ISO standards gives a framework to work from, Curran (2014) argues that the framework is somewhat vague since there are no strict rules and hence gives room for interpretation by the one who is conducting the assessment. This implies that the results from the assessment could be evaluated differently depending on whom the person is that does the research.

Figure 1.2: Framework of LCA, modified from the ISO 14040 standard.

Impact assessment Goal and Scope

definition

Inventory

analysis Interpretation

Life Cycle Assessment Framework

In accordance to the ISO 14040-series a LCA is divided into four phases: Goal and scope definition, LCI analysis, LCIA and interpretation, see figure 1.2.

2.1 Goal & Scope Definition

There are two methods to choose between when conducting a LCA: consequential or attributional. The former have a focus on the future and the latter on the present.

Consequential, as the name implies, handles the consequences a change in the chain can give rise to. By doing this, different options can be weighed against each other before a change is made. Attributional on the other hand handles burdens that the process gives rise to, often based on data from the past. This method finds the hotspots and the environmental footprint of today. Further, this can help decision makers decide if a change regarding a hotspot should be made or not (Finnveden & Potting, 2014).

The first step when conducting a LCA is to define the goal and scope. According to Sadhukhan et al. (2014) this step could be divided into the following:

1. Functional unit 2. System definition 3. System boundaries

Firstly, the FU has to be defined. This is the unit that the whole assessment is based on. A functional unit should include a function and a quantity for that function of the study, like 1 kg produced bioethanol, among others. The functional unit is of great importance when it comes to comparison. If different alternatives or studies should be compared with the assessment, the basis, namely the functional units, must be comparable. If this is not the case no reliable comparison can be made between the alternatives. Secondly, the system needs to be well defined regarding data quality and availability, assumptions and justifications.

Thirdly, boundaries about the system assessed have to be defined. The system boundaries delimit which processes to look at and refers to both geographical and temporal boundaries.

2.2 Life Cycle Inventory Analysis

The second step is to collect data needed based on the goal and scope and the requirements that follows with them. First the main and the most important process should be identified.

From this, other processes, both upstream and downstream, should be identified in

descending order. The next step is to plan and collect data for these identified processes. This

is done iteratively for the avoidance of collecting data with none or low relevance for the

process since it is time consuming. Moreover, when the data is collected the LCI model can

be constructed with the help of some LCA software, such as SimaPro or GaBi (Bjørn et al.,

2018b).

2.3 Life Cycle Impact Assessment

LCIA is the third step when conducting a LCA. Here, elementary flows from the LCI analysis are converted into their potential environmental impacts for better understanding the magnitude and significance of the result. This is done because elementary flows are not comparable with each other since their impacts are not accounted for. For clarification, elementary flows can have the same emitted amount but since the flows consist of different substances they also have different impact on the environment. For example, two different greenhouse gases (GHG) affect the climate differently even though the same amount is being released (Rosenbaum et al., 2017). This is because they have different GWPs. Methane (CH 4 ) is 25 times stronger than carbon dioxide (CO 2 ), while nitrous oxide (N 2 O) is 298 times stronger than CO 2 (Forster et al., 2007).

According to the ISO 14040-series category impact, classification and characterization are mandatory steps in a LCIA. Classification implies that flows from the LCI should be assigned an impact category i.e. a type of environmental issue. The substance in a flow can give rise to environmental problems so the substance gets paired with one or several impact categories of which the substance contributes to. For example, CO 2 gets paired with GWP while sulfur dioxide (SO 2 ) can be paired with both acidification and human toxicity. Characterization is to quantify the impact categories in classification, which is done with the help by a characterisation factor. For instance, GWP for any GHG are related to CO 2 eq and thus the characterization factor of CO 2 is 1 and 25 for CH 4 (Rosenbaum et al., 2017; Sadhukhan et al., 2014).

2.4 Interpretation

The fourth and last step in a LCA is interpretation. Here the results from the earlier steps should be analyzed regarding the data, assumptions and everything that can affect the outcome and final result from the assessment. Further, a sensitivity and consistency analysis can be made which gives a prediction about the uncertainty level in the LCA and if the assessment is consistent towards the goal. The outcome from the LCA should be clearly presented together with its uncertainties (Hauschild et al., 2017).

2.5 Impact Categories

Impact categories that are going to be used in this assessment are acidification, climate

change, eutrophication, human toxicity (non-cancerogenic) and ozone depletion. See table

2.1. The chosen impact categories are briefly explained in this section.

Table 2.1: Impact categories used in this assessment.

Impact category

Characterization factor

Unit Source

Climate change Global warming potential for 100 years (GWP 100)

kg CO ₂ to air (Levasseur, 2015)

Freshwater eutrophication

Freshwater eutrophication potential (FEP)

kg P to water (Henderson, 2015)

Human toxicity, non-cancer

Human toxicity potential (HTP)

kg 1,4-DB to urban air

(Huijbregts et al., 2016)

Marine eutrophication

Marine eutrophication potential (MEP)

kg N to water (Henderson, 2015)

Ozone depletion Ozone depletion potential (ODP)

kg CFC-11 to air

(Lane, 2015)

Terrestrial acidification

Terrestrial acidification potential (TAP)

kg SO 2 to air (van Zelm et al., 2015)

2.5.1 Acidification

Acidification can either be terrestrial or aquatic, in this assessment terrestrial acidification are going to be used since this is used in ReCiPe method. The main contributors to terrestrial acidification are nitrogen and sulfur. This impact category converts data from acids from the LCI into H ⁺ equivalents relative to SO 2 (van Zelm et al., 2015).

2.5.2 Climate Change

Climate change is the warming of the atmosphere, like increased temperatures of oceans and the atmosphere. The main contributor to climate change is GHG due to activities by humans.

This impact category converts data from GHGs from the LCI into CO 2 eq (Levasseur, 2015).

2.5.3 Eutrophication

In ReCiPe freshwater or marine eutrophication can be investigated. Aquatic and terrestrial eutrophication can be investigated with other methods. The main contributors to eutrophication are phosphorus for freshwater and nitrogen for marine (Henderson, 2015).

2.5.4 Human Toxicity

Human toxicological effect can be expressed in either cancerogenic or non-cancerogenic, in

this study the latter will be investigated. This category measures harmful impacts on human

health caused by emissions that are exposed to humans, like inhalation of toxic air. HTP is

measured in kg 1,4-dichlorobenzene equivalents (1,4-DB eq) (Huijbregts et al., 2016).

2.5.5 Ozone Depletion

The stratospheric ozone layer is depleted by emissions of halocarbons, like

chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC), among others. When this

happens, the UVB radiation increases which have a negative impact on both humans and the

ecosystem. Halons from the LCI are converted to CFC-11eq (Lane, 2015).

3 Wastewater Treatment Methods

Wastewater treatment occurs both as mainstream and sidestream. Mainstream is the central part of the treatment process, the core, while a sidestream is a smaller stream that are separated from the mainstream, which can be further treated before it gets recycled back into to mainstream. Sidestream is a liquid stream that is generated when solids and liquids are separated by dewatering, for instance. Some benefits with sidestream treatment are that it can reduce costs, both regarding energy and chemicals (Bowden et al., 2015).

Several methods to treat wastewater exist today. In this chapter we are going through them briefly and finish with a more detailed description of nitrogen removal, of which are used in the sidestream at Himmerfjärdsverkets WWTP.

3.1 Treatment Principles

Water treatment principles can be divided into four main categories: biological, chemical, physical and mechanical. Biological treatment is when microorganisms are used to decompose or transform matter in the wastewater either through aerobic, anaerobic or anoxic degradation. The microorganisms can exist either in a suspended form or as a biological film.

One drawback with biological treatment is that it is sensitive to toxic compounds. This is because toxic compounds blocks active sites of the enzymes in organisms that treat wastewater and thereby lowering the effectiveness on the treatment. Moreover, chemical treatment is the treatment methods that involve chemical reactions (other than those arising from biological treatment methods). For WWT, the most common methods are precipitation, coagulation and flocculation. The first is to reduce phosphorus and the others for separation of particles. Physical treatment on the other hand is for separation of some specific components from the stream either to extract them or recycle them back in. Adsorption is one example of this, which could be used as a pretreatment method to adsorb toxic substances.

The last category is mechanical treatment, which is a method to separate particles by size or density. Screens separate particles by size while sedimentation or settling separates by density differences (Persson, 2011).

3.2 Wastewater Treatment in General

As mentioned in chapter 1, wastewater mainly contains organic materials, suspended solids

and nutrients. The four treatment principles in section 3.1 are used to treat wastewaters from

these pollutants, which is done in different treatment stages where every treatment stage

treats and separates progressively smaller pollutants. The first stage in wastewater treatment

is preliminary treatment, which uses mechanical treatment methods like screens to remove

larger solids from wastewaters to prevent damage and clogging in the forthcoming treatment

steps. Additional methods in this stage could be a grinder that ground solid particles and sand

traps that remove grit and sand. The second stage is primary treatment that also uses

mechanical treatment methods to removes suspended solids, often with settling tanks where

suspended solids settles by gravity. The following stage is secondary treatment whose purpose is to remove BOD, which is done with biological treatment methods that utilize microorganisms. There are essentially two different approaches to choose from when using biological treatment: either activated sludge or trickling filter. In the former the microorganisms are suspended in the wastewater when in the latter they are fixed while water flows past the nutrients (Vesilind et al., 2010; Masters & Ela, 2014). Tertiary treatment is the next stage that treats nutrients, mainly nitrogen and phosphorous. Nitrogen is removed by biological treatment methods that are further described in section 3.3, while phosphorus can be removed by both biological and chemical methods. With biological treatment methods the microorganisms can absorb phosphorus while chemical methods involves addition of metal salts or lime that precipitates phosphorous of which is further removed with mechanical treatment methods, like sedimentation. After this stage the wastewater is purified and can be discharged into the sea or a watercourse (Vesilind et al., 2010).

Sludge is a mixture of particles and water that is removed from the wastewater in the different treatment stages. Sludge is potentially environmental harmful and has an odor that can be treated by stabilize the sludge. This is traditionally done by anaerobic digestion but aerobic digestion or lime could also be used. In anaerobic digestion microorganisms converts organics to CH 4 and CO 2 , so called biogas (Vesilind et al., 2010; Masters & Ela, 2014).

Biogas can be used as a source of energy internally at the plant and it can also be further upgraded to vehicle gas (Syvab, n.d.c). Biodigestate is sludge that remains after digestion, which is dewatered to reduce its volume and is further used as fertilizers or disposed as landfill. The water that is removed by dewatering is reject water. Some treatment plants have an additional treatment step of the reject water before it gets recirculated back into the treatment system (Masters & Ela, 2014).

3.3 Nitrogen Removal Technologies

Different biological treatment technologies for removal of nitrogen have been developed during time for WWTPs application. The main idea is to transform ammonium (NH 4 + ) by oxidation to either nitrite (NO 2 - ) or nitrate (NO 3 - ) by bacteria in aerobic conditions followed by a reduction to nitrogen gas (N 2 ) by bacteria that nourish on some carbon source, often methanol, in anoxic conditions (Bowden et al., 2015; Trela et al., 2015). Three different treatment pathways are shown in figure 3.1 of which are explained in section 3.3.1 to 3.3.3.

Figure 3.1: Three different pathways for nitrogen removal (Modified Trela et al., 2015).

N ₂ NH ₄ ⁺

NO ₂ ^-

NO ₃ ^-

Nitrification/ denitrification

Nitration/ denitration

Deammonification

3.3.1 Nitrification & Denitrification

The most important and fundamental technology when it comes to biological nitrogen removal is nitrification and denitrification, which is a two-stage process. Firstly, autotrophic nitrifying bacteria perform nitration in two-step oxidation of ammonium in aerobic environment. Nitrosomas, which is an aerobic ammonia oxidizing bacteria (AOB), oxidize NH 4 + to NO 2 - (equation 3.1). After that Nitrobacter, an aerobic nitrite oxidizing bacteria (NOB), oxidize NO 2 to NO 3 - (equation 3.2). Secondly, denitrifying bacteria, which is a heterotrophic bacterium, converts NO 3 - to N 2 by oxidizing organic matter with either NO 2 - or NO 3 - in anoxic environment (equation 3.3). Here, organic matter operates as an electron donor that is added from an external source into the wastewater stream (Persson, 2011;

Bowden et al., 2015).

Nitrification:

2 NH _! ^! + 3 O _! → 2 NO _! ^! + 4 H ^! + 2 H _! O (Eq. 3.1)

2 NO _! ^! + O _! → 2 NO _! ^! (Eq. 3.2)

Denitrification:

Organic matter + 2 NO _! ^! + H _! O → 2.5 CO _! + 2 OH ^! + N _! (Eq. 3.3) Nitrification bacteria are pH sensitive, grows slowly and the organic material content in its surrounding needs to be low. The growth rate is slower in lower temperatures, and thus the solid retention time (SRT) i.e. the time the bacteria spends in the unit, has to be high. This is to keep the amount of bacteria in an adequate quantity.

3.3.2 Nitritation & Denitritation

Since nitrification/denitrification have some disadvantages, other technologies have been developed. One of them is nitritation/denitritation. According to Bowden et al. (2015), with this technology a shortcut is taken in the pathway of transforming ammonium into nitrogen gas. What happens is that AOB oxidize NH 4 + to NO 2 - in a partial nitrification followed by denitritation that reduces NO 2 - to N 2 , see equation 3.4 and 3.5. Overall, this reduces the need for oxygen with 25% and carbon source with 40% compared with the nitrification/denitrification technology. Additionally, energy savings are made because ammonium is only oxidized to nitrite and not the whole way to nitrate (Bassin, 2018).

Nitritation:

NH _! ^! + 1.5 O _! + 2 HCO _! ^! → NO _! ^! + 2 CO _! + 3 H _! O (Eq. 3.4) Denitritation:

3 C + 4 NO _! ^! + 2 H _! O + !" _! → 4 HCO _! ^! + 2 N _! (Eq. 3.5)

3.3.2.1 SHARON

One process, among others, that has nitritation/denitration as a method is Single reactor system for High activity Ammonium Removal Over Nitrite, SHARON. This was the first process were the intermediate was nitrite instead of nitrate and also without the need for retention of biomass, hence the solid retention time equals the hydraulic retention time i.e. the time the liquid spends in the unit (Mulder et al., 2001). The idea is to modify the growth rates between AOB and NOB which is done by temperature and biomass control. To prevent further oxidation of nitrite, NOB has to be minimized (Gustavsson, 2010; Milia et al., 2012).

The working temperature of a SHARON reactor has to be about 30-40 °C, since microorganisms grows faster at higher temperatures. Additionally, AOB grows faster than NOB which makes it possible to optimize hydraulic retention time to wash out NOB before oxidation of nitrite happens and at the same time keep AOB, which is possible since they grow faster and thereby is larger (Mulder et al., 2001).

The ideally implementation of a SHARON reactor is after a digester to treat digester effluent since this effluent flow already have a higher temperature. Because of this, the flow does not need further heating for the treatment to function properly (Bassin, 2018).

3.3.3 Deammonification

A third technology to transform NH 4 + into N 2 is by deammonification. This is a two-step process that starts with partial nitrification, identical to nitritation (equation 3.4), followed by autotrophic bacteria that performs anaerobic ammonium oxidation, known as anammox. An anammox bacterium uses NO 2 - as electron acceptor and, together with NH 4 + , forms N 2

(Bowden et al., 2015; Bassin, 2018). See simplified equation 3.6 (Persson, 2011) below. Note that only a part of the ammonia is converted into nitrate by nitritation, and that nitrate then forms nitrogen gas with the remaining ammonia.

Anammox:

NH _! ^! + NO _! ^! → N _! + 2 H _! O (Eq. 3.6) In contrast to the conventional nitrification/denitrification technology, deammonification reduces the need for oxygen with 60% (Plaza et al., 2015) and carbon source with 89%. No addition of an external carbon source is required; instead the carbon needed is taken solely from CO 2 (Bowden et al., 2015). The organic carbon in the system can be used in a digester to become biogas since no organic carbon is used in the process (Capodaglio et al., 2016).

Additionally, an anammox bacterium grows slower than both AOB and NOB and thus requires a longer SRT. However, anammox bacteria have a higher affinity towards NH 4 + and NO 2 - compared to AOB (Bowden et al., 2015). The reason why SRT have to be longer is because the growth of the bacteria is slower, a longer SRT means that the bacteria need more time to grow. If ratio of the concentrations COD/BOD is high denitrifying bacteria will grow fast and anammox bacteria cannot compete with them and will in that case decease.

Additionally, anammox bacteria cannot live by themselves since they are dependent on other

organisms that produce nitrite. Because of this, anammox bacteria have to be implemented together with a nitrification process (Syvab, 2016a).

Three different deammonification methods are described in section 3.3.3.1 to 3.3.3.3. The idea behind them is similar, except that they use different reactor types together with different designs for the nitrogen reduction.

3.3.3.1 Anammox

The first method is called Anammox that uses a granular sludge blanket reactor (GSBR).

Here, the anammox bacteria grows in suspended biofilms i.e. activated sludge, where the organisms are suspended in the form of granules that have a mean diameter about 1,4 mm and are red to the color (Bowden et al., 2015), see figure 3.2. Anammox can take place in either two-step or single-step reactor system (Plaza et al., 2015; Bowden et al., 2015).

Two-step Anammox

The two-step system is named SHARON-Anammox process. Like the name implies, the first step is made out of a SHARON reactor that transform about 50% of ammonium in the stream to nitrite. The second step is an Anammox reactor that performs the anammox process described in section 3.3.3. It becomes easier to control the process by having two reactors for the different reactions (Plaza et al., 2015; Bowden et al., 2015).

Single-step Anammox

For the single-step process, both reactions take place in the same reactor. With this, AOB, NOB and anammox bacteria have to be controlled. This is mainly done with pH and dissolved oxygen. Even though the process control is more complicated for single-stage, the system is cheaper to invest in than for two-step since only one reactor is needed. Also, this process needs a lower amount of aeration which give rise to reduced GHG emissions (Plaza et al., 2015).

Figure 3.2: Anammox bacterias in suspended biofilm (© Syvab)

Figure 3.3: Plastic carrier with some biofilm on the interstitial surface

(Pesten, CC BY-SA).

3.3.3.2 DeAmmon

The second deammonification method is DeAmmon, which is a tradename for Deammonification In Biofilms. The reactor is a moving bed biofilm reactor (MBBR). Here, microorganisms exist as biofilms that grows on the interstitial surface at plastic carriers, i.e.

trickling filter, with a diameter of about 1 cm that looks like wagon wheels, see figure 3.3.

Carriers take up about 40-50% of the volume in the reactor (Bowden et al., 2015).

3.3.3.3 DEMON

The third deammonification method, named DEMON, obtained its name from the method

name itself (DEamMONification). This method exploits sequencing batch reactor (SBR)

technique, which is operated in cycles. A cycle is about 8 h long, where 6 h is for filling the

reactor and then letting the reaction happen and the remaining 2 h is for settling and

discharging. During nitritation when reaction occurs, pH is reduced when oxygen is used to

oxidize ammonia. Conversely, pH is rising during the anammox reaction. On account of this,

pH is controlled by aeration in the reactor. When pH gets to high aeration takes place, and

when it gets to low aeration stops (Gonzalez-Martinez et al., 2014; Bassin, 2018). In

DEMON, anammox bacteria, just like the Anammox method, is present as activated sludge

(Bowden et al., 2015).

4 Environmental Impacts: Previous Studies

In this chapter some general cases regarding environmental impacts and LCAs in literature are presented, with a focus on sidestream treatment with deammonification and treatment plants similar to Himmerfjärdsverket. This is followed by two cases where DeAmmon and DEMON has been implemented and impact categories for some WWTPs are presented.

Population equivalents, PE, is a measurement that is used in this chapter. According to European Commission (2019) the definition is: “The organic biodegradable load having a five-day biochemical oxygen demand (BOD5) of 60 g of oxygen per day”. Meaning that 1 PE is the amount of BOD, or organic material, that is emitted to sewage water by one person per day.

4.1 General

In 2002 world’s first full-scale Anammox reactor was implemented in Dokhaven, Rotterdam treatment plant. Today the reactor operates as a two-step SHARON-Anammox (i.e. partial nitration - anammox) and treats 620 400 PE (van der Staar, 2007). The performance of the anammox reactor was investigated between 2007-2008. Results indicated that the nitrogen removal rate was 84% (van Haandel & van der Lubbe, 2012). Hauck et al. (2016) compared three different cases regarding sidestream treatment in a LCA study over the treatment plant in Rotterdam. The first case is the traditional treatment case, were no nitrogen removal took place within the sidestream. The second case is when a SHARON reactor had been implemented and the third case is with a two-step Anammox reactor. Regarding nitrogen removal it became clear that SHARON is better than the traditional case and that Anammox, in turn, is better than SHARON. Moreover, both Anammox and SHARON had an increase of 9% regarding climate change impacts in contrast to the traditional, were more than 75% of this increase was due to GHG and mostly by N 2 O. Marine eutrophication had also a higher difference between the cases; it was reduced with 5% with SHARON and by 16% with Anammox in contrast to the first case. Marine eutrophication is almost solely dependent on the amount of nitrogen emissions, meaning that the reduction is due to lowered nitrogen emissions. For other impact categories the difference was not more than 3% increase for Anammox and somewhat higher for SHARON, mostly due to higher electricity consumption in contrast with the traditional case. Since SHARON reactor need an external carbon source the natural land transformation impact was 10% higher than for the other cases.

In a LCA study conducted by Fenu et al. (2019) they concluded that sidestream treatment

with Anammox reduced nitrogen content in the reject water. On the contrary, implementation

of reject water treatment is at its best neutral in measurements of carbon footprint if not

increased. In the study a full scale WWTP with and without Anammox in the sidestream was

compared with each other. Regarding climate change, the two largest contributors are

electricity followed by emissions of N 2 O for the case without sidestream treatment. For the

other case with Anammox, almost 75% is due to N 2 O emissions. Moreover, for natural land transformation almost 80% is due to electricity for the first case and about 55% for the second. Additionally, about 25% is due to sodium bicarbonate (NaHCO 3 ), which is used as a carbon source for the bacteria in the latter case.

In a report by Tumlin et al. (2014) climate impact for four different sewage treatment plants are investigated. One of these four are Käppalverket, located in Lidingö, Sweden, which is very similar to Himmerfjärdsverket regarding the treatment process and has the same products and handling of the products. The difference is that this plant is larger with 428 000 PE and does not have sidestream treatment for reject water; instead the reject water is directly recirculated into the mainstream. Since the plant produces biogas the environmental impacts decreases because biogas is a substitute to vehicle gas. The three major contributing factors to the environmental impact, in terms of CO 2 eq, is energy consumption, emissions from the treatment process and sludge handling. Their relative percentages of the total climate impact is about 54%, 36% and 6% respectively.

4.2 DeAmmon

World’s first full-scale DeAmmon process was built 2001 in a WWTP at Hattingen, Germany, and was based on laboratory-scale reactors. The DeAmmon process has a MBBR that are filled to 40% with Kaldnes carriers of type K1. The system treats 53 000 PE and was designed to remove 80% of the nitrogen load. However, the maximum nitrogen removal performance is between 70-80% depending on the nitrogen load (Rosenwinkel & Cornelius, 2005; Jardin et al., 2006; Gustavsson, 2010).

According to Bowden et al. (2015), until June 2015 it only exists three treatment plants were DeAmmon has been implemented. Except from Germany, the other two are located in Sweden (Himmerfjärdsverket) and China. Due to small number of plants with this technique, no LCA study in literature has been found regarding DeAmmon.

4.3 DEMON

Before 2004 a municipal WWTP in Strass, Austria, had a two-stage nitrification/denitrification reactor in the mainstream and another nitration/denitration reactor for the reject water in a sidestream. The latter was, in 2004 (Schaubroeck et al., 2015) replaced by the world’s first DEMON reactor (Innerebner et al., 2007). Sludge from the mainstream are digested which results in electricity from the produced biogas and fertilizers to agriculture from sludge (Schaubroeck et al., 2015). The facility treats 200 000 PE (Innerebner et al., 2007) and is energy self-sufficient since they produce their own energy.

Excess energy that is not consumed at the facility is fed to the grid (Nowak et al., 2011). In

2005, Jardin et al. (2006) investigated the performance of the DEMON reactor. Results

indicated that the nitrogen removal rate was 85,6% with a margin of error about ± 4,93%.

Moreover, Schaubroeck et al. (2015) pointed out that there is a problem regarding how environmentally friendly WWTPs really are. Because of this, they did a LCA over the treatment plant in Strass using the ReCiPe method. It could be concluded that today it is not possible to consider this plant as environmentally friendly. This is mainly because LCA as a tool gives many outcomes regarding different impact categories, and it is impossible to weight these against each other in a rational way. Overall, the implementation of DEMON in the sidestream instead of nitration/denitration reduced the need for natural resources, mainly electricity since the need for aeration is lowered. On the other hand, the N 2 O emissions increased which have a negative effect on human health. Moreover, when conventional fertilizers are replaced with digestate it not only lowers resource extraction, but also the loss of diversity. A backdraw is however that the digestate contains heavy metals to the degree that it has a total higher environmental impact than for conventional fertilizers.

4.4 Impact Category Results for WWTP

Some impact category results for five different WWTPs are presented in table 4.1, together with each method used for the LCIA. The FU is treatment of 1 m ³ wastewater influent for all of the cases and they are therefore comparable with each other. They are however conducted with different methods, meaning that the distribution of environmental impacts can differ within the same impact category, even though they are expressed in the same unit (Merchan

& Agathe, 2014)

Table 4.1: Impact categories for five WWTPs (Hauck et al., 2016; Schaubroeck et al., 2015;

Rodriguez-Garcia et al., 2011; Arnell et al., 2017; Pasqualino et al., 2009).

Unit

kg eq /FU Rotterdam Strass Spain Sweden

(Käppalaverket) Tarragona

LCIA Method ReCiPe ReCiPe CML CML CML

Impact category

Acidification SO ₂ 8,0 E-4 4,4 E-4 4,9 E-4 1,7 E-3

Climate change CO ₂ 2.3 0,1–0,7 0,15 0,11 0,12

Eutrophication PO 4 1,8–9,7 E-2 2,4 E-3 2,2 E-3 1,4 E-3

Freshwater eutrophication

P 1,1 E-3

Marine

eutrophication

N 1,5 E-1 -4,5 E-2

Human toxicity 1.4-DB 9,9 E-1

Ozone depletion CFC-11 1,2 E-7 7,4 E-8 2,0 E-10 9.2 E-10 4,8 E-8

Rotterdam & Strass

Information about Rotterdam and Strass can be found section 4.1 and 4.3 respectively.

Spain

Rodriguez-Garcia et al. (2011) evaluates the performance of 24 Spanish WWTPs regarding GWP and eutrophication potential. Only the lowest and the highest numbers from all of the 24 plants are presented in table 4.1

Sweden, Käppala

A LCA study over Käppala WWTP was conducted by Arnell et al. (2017) where two cases were compared. Case 1 is the current situation and case 2 is if implementation of enhanced primary treatment occurs. Käppala WWTP is located in Sweden.

Tarragona

In a LCA over a WWTP in Tarragona, Spain, water line, sludge line, transportation and final disposal of waste are taken into consideration. Biogas is also produced which are used for heat and electricity internally. Infrastructure such as buildings and equipment, along with demolition are not investigated due to its long lifetime.

4.4.1 Impact Category Results for Biogas & Sludge

Biogas is often a product that is produced in WWTPs. It affects the outcome of a LCA depending on how it is used. Pasqualino et al. (2009) compared four different cases regarding biogas: burned in torch, produce electricity, produce electricity and heat or for replacement of natural gas and compared them with respect to seven impact categories. The worst scenario in an environmental perspective is to just burn it. To replace natural gas with it does not have any major effect except for abiotic resource depletion that will be reduced. To use biogas for production of electricity or electricity and heat are the best options among the four alternatives. Both have avoidance of burden in terms of acidification, climate change and abiotic resource depletion together with major reduction in ecotoxicity and photochemical oxidation. The same study also investigates options for handling of sludge. Between landfill, use it in agriculture or incineration, the first option is the worst in several impact categories followed by incineration. Incineration can however give rise to heat that can be utilized.

Agriculture applications will however have the highest impact for eutrophication due to its

emissions to soil.

5 Himmerfjärdsverkets WWTP

Himmerfjärdsverket is Sweden’s fifth largest WWTP, that today produces, except for treated wastewater, both biogas and biodigestate. It was built in 1974 in Grödinge, located in Botkyrka, Sweden. The southwest Stockholm region's WWT company, Syvab, has owned the plant since then (Syvab, 2018a). Today Syvab, in turn, is owned by the municipalities Botkyrka, Nykvarn and Salem together with Stockholm Vatten AB and Telge AB (Syvab, n.d.a).

Sewage arrives to the plant by tunnels, that have a total length of 55 km. Connected municipals are, except for the three already mentioned, southwest of Stockholm, the majority of Södertälje and parts of Huddinge (Syvab, 2018a). In 2018, this could be compared to a total of 334 440 connected people (Syvab, 2019a). In most of the parts of the tunnel, the sewage travels by gravity. However, in a few places the sewage needs to travel in pressurized pipelines that are driven by two pumping stations (Syvab, 2018a). The extent of the tunnel system and its two pumping stations can be seen in figure 5.1.

Figure 5.1: The tunnel system that moves the water from the connected municipalities to the plant. Dotted lines are pressurized pipelines and pumping stations are located in Eolshäll and Pilkrog (© Syvab).

In this chapter all the treatment steps for the incoming sewage is explained.

5.1 Wastewater Treatment

The process for treating sewage takes about 20 hours. The treated wastewater is then released at a depth of 25 m, 1 600 m from shore into Himmerfjärden, that merge with the Baltic Sea.

This plant treats and removes about 85% of incoming nitrogen, 95% of phosphorus and 97%

of BOD (Syvab, 2018a). An overview of the plant can be seen in figure 5.2 of which the

mechanical and biological treatment units are market along with filtration step. Connections

between the different units in the treatment steps are shown in figure 1.1 and a more detailed flowchart in figure A1.1 (in appendix).

Figure 5.2: Overview of Himmerfjärdverket treatment plant. The arrows show the direction of the water, M is for mechanical treatment, B for biological treatment and F for filtration (© Syvab).

5.1.1 Mechanical Treatment

The first treatment stage is mechanical cleaning which separates solid particles from the incoming water and takes about two to three hours. This treatment step can be divided into sub-steps where each sub-step filtrates even smaller particles and hence prevents the system to be clogged and interrupted later on (Persson, 2011; Stockholm Vatten, 2015). Firstly, the influent passes through a grinder that grounds solid particles like cotton swabs, tampons, condoms, paper towels and similar. A coarse bar screen with 20 mm gap width is also located here for further separation. Moreover, dissolved phosphorus is being precipitated by addition of iron chloride to the wastewater after the screens (Syvab, 2018a).

The next step is to pump the wastewater up to ground level where further separation of the

grounded particles occurs by passing a fine screen with a gap of 6 mm. The collected

particles are washed and later transported in containers, as well as for waste from the coarse

bar screen, to an incineration plant for district heating. The following step is a sand trap. A

sand trap is a 30 m long basin that separates gravel and sand by letting those heavier particles

sink to the bottom while the lighter particles remains in the suspension by air that is blown

through the water. The sunken particles are scraped away and transferred to a sand washer

were organic materials are removed. The water used in the washer is purified process water

that is, after being used in the sand washer, returned to the main wastewater stream. The

separated and cleaned sand are seen as a product that can, for instance, be used during the

winter against icy roads (Syvab, 2018a). By removing sand and larger particles both

accumulation and wear on equipment is prevented in the oncoming biological treatment steps