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A research to the removal of phosphate from separately collected urine by means of the precipitation of struvite and the profitability and the social acceptance of separation toilets

Clean Urine

Bonhoeffer College Bruggertstraat,

Enschede, the Netherlands,

17 March 2010

Robert van Houten

Marijn Siemons

Jeroen Wagenaar

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Abstract

Purpose Phosphate in wastewater is removed at a wastewater treatment plant, because even small concentrations of phosphate in water lead to excessive growth of algae, which would extract all oxygen from the surface water. But since the concentration of phosphate is reduced by grey water and rain in the sewers, the phosphate-removal is difficult and costly. Furthermore, phosphate is a limited resource that is generally used in fertilizers. A shortage of phosphate could lead to a major food crisis. Human urine contains 45% of the phosphate in waste water. A solution to remove phosphate more effectively from waste water would be to remove the phosphate from the urine before it reaches the sewers. To achieve this, the urine has to be separated from the faeces and flush water. There are special designed toilets for this purpose, called separation toilets or no-mix toilets. The separation of urine at the source results in very concentrated phosphate, which makes removal much easier. The phosphate can be removed from urine if magnesium-ions are added to the urine. These will precipitate and form the crystal: magnesium ammonium phosphate (MAP), that is also known as struvite. Struvite is a fertilizer which can be used in agriculture and in this way phosphate can be recycled. This essay discusses different aspects of struvite precipitation: the effects of pH-values, different Mg2+-salts, the growth of struvite crystals and the settling speed of struvite. With the results of these researches a reactor design is made for a public building. A small prototype-reactor of this design is build and tested on functionality. This essay also discusses the profitability of separation toilets, which need less water to flush, and the social acceptance of the toilets.

Procedure Several experiments are executed, these procedures are followed:

- To find the ideal pH-value for the precipitation of struvite, the following procedure is followed. Eight measuring cups are filled with a different buffer solution, rising in pH-value. The measuring cups are then filled with equal amounts of struvite and stirred. Then visual observations indicate how much struvite is dissolved.

- The settling speed of struvite measurements involves a measuring cup filled with water and struvite and a video camera. The settling of struvite is monitored for 30 minutes.

- To determine the possible differences between different Mg2+ salts the procedure that is used involves filling 8 measuring cups with urine, adding MgO to the first four, and MgCl2 to the last four. The struvite is filtrated and then measured on a weighing scale.

- The test setup of the growth of the struvite crystals involves a test reactor. In this reactor different currents are produced with air. The struvite crystals are examined with a microscope.

- The prototype of the reactor is tested by measuring the struvite production, with different quantities of MgCl2, different mixing times and with MgO as Mg2+-source.

- The production of urine is estimated in the Bonhoeffer College, by counting the usages of toilets in one toilet section. The information that is gathered is used to make an estimation of the total usages. With that data the urine production per day is estimated.

- A survey about comfort, scent and other subjects, is held under 55 11th grade students and the results are compared to other surveys.

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Results The results are that struvite precipitates better in a basic solution, while it dissolves in acid solutions. MgCl2 forms more struvite then MgO, but is more expensive. The settling speed of struvite is 12mm/min. The growth of the struvite crystals in hard to achieve and is not suitable for a simple batch-reactor in public buildings. The prototype of the reactor works properly, mixing times between 1 and 5 minutes are sufficient. A waterless urinal reaches its breakeven-point after 10.000 flushes and the separation toilets after 5800 flushes. For the Bonhoeffer College Enschede the breakeven-point would be reached after 3,2 years if al toilets were replaced by separation toilets. The urine production at the Bonhoeffer College Enschede is estimated at 70L per day. The rectangle-shape of the separation toilets needs serious reconsideration. Something should be done about the smell of the waterless urinals. 58% of the students would not like to have a separation toilet at their home.

Conclusion To remove the phosphate in a reactor the pH-value should be basic, around 8,5. MgO is considered as a better source for magnesium-ions than MgCl2 , because it is more cost effective. The settling speed is high enough to separate the struvite with settling in a batch reactor. The design that is made works properly and is very suitable for public buildings. Separation toilets are a profitable and an interesting investment for both households and public buildings. But the toilets need much improvements to prevent smell and add more sit comfort. In conclusion, the precipitation of struvite is an easy and cheap way to remove phosphate from urine at the source, which can be easily applied in public buildings or schools.

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Table of contents

Abstract 2

Table of contents 4

Preface 6

Chapter 1 - Separation at source 7

Introduction 8 Materials and Methods 9

Urine flow 9 Economical application 10

Results 11 Urine flow 11 Economical application 12

Discussion 15 Urine flow 15 Economical application 15

Conclusion 16

Chapter 2 – Struvite 16 Introduction 18 Materials and Methods 19

pH-value 19 MgO and MgCl 20 Settling speed 21 Crystal growth 22

Results 23 pH-value 23 MgO and MgCl 23 Settling speed 24 Crystal growth 25

Discussion 26 pH-value 26 MgO and MgCl 26 Settling speed 27 Crystal growth 27

Conclusion 28

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Chapter 3 – Design of a reactor 29 Introduction 30 Reactor Design 31 Separation 31 Reactor type - continue or batch? 32 Supply 33 Mixing 33 Extraction of urine and struvite 33 Scaling 33

Chapter 4 – Test reactor 36 Introduction 37 Reactor 38 Materials and method 39 Blanco test 39 Less magnesium 39 Mixing time 40 Results 41 Discussion 42

Blanco test 42 Less magnesium 42 Mixing time 42 Conclusion 43

Chapter 5 – Social acceptance 44 Introduction 45 Materials and methods 46 Results 47 Discussion 48 Conclusion 50

Acknowledgements 51

References/Bibliography 52

Appendices 53

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Preface

In this report for the O&O (Research & Design) we discuss the possibilities and applications of the removal of phosphate, by means of the precipitation of struvite, from urine, before the urine reaches the sewers. Struvite is a crystal that forms when phosphate precipitates with ammonium and magnesium. Urine already contains these substances, but magnesium in a much smaller degree. Therefore, only a small amount of phosphate precipitates normally. Struvite can be used as a fertilizer. We got involved in this subject because several separation toilets and waterless urinals were installed in our school. These toilets separate the urine at the source from the faeces and flush water. The urine is collected separately in the front part of the toilet, and is removed to a storage tank. The faeces with additional flush water is dumped in the sewer. The waterless urinals are not flushed, the urine flows away automatically and is collected in a storage tank. During this project we got help from several companies and we would like to thank the water board Regge & Dinkel, Norit, Saxion High School Enschede, University of Wageningen, Water Research Lab Wetsus, Waterstromen bv Steenderen and Technasium Overijssel. These parties have provided us with materials and data. Several companies have ongoing researches to the removal of phosphate and the precipitation of struvite, and are therefore specifically interested in our project. Phosphate-removal, by means of struvite-precipitation, and separation toilets definitely have a future. It increases the efficiency of phosphate removal and the separation toilets save water. Moreover, phosphate is a limited resource; there is not an infinite amount of it on earth. According to the Water board Regge & Dinkel, 15% of the total phosphate usage in the Netherlands can be provided with this method. It is also very economical. When removing phosphate at the source, it does not has to be removed at wastewater treatment plants, which saves both space and money. Struvite will also be profitable when it will become an acknowledged fertilizer.

Robert van Houten, Marijn Siemons and Jeroen Wagenaar

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Chapter 1 – Separation at source



Results 10


Discussion 14


Conclusion 15

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Introduction There are two ways to separate urine at the source: with separation toilets and with waterless urinals (figure 1.1). The separation toilets have different looks and workings compared to regular toilets. The separation toilets separate the urine from the faeces and collect the urine in a storage tank. The toilet is divided in two parts, one for collecting urine and one for the faeces and toilet paper. The separation toilets only use 500 ml of flush water(4), and a small amount of the flush water is collected in the front part where the urine is collected. So the separately collected urine is slightly diluted. The waterless urinals do not flush at all, the urine flows away automatically. This results in highly concentrated urine. If separation toilets are to be installed in public buildings it is necessary to give an estimation of the profitability of separation toilets and waterless urinals. For that, the amount of urine produced in a public building is necessary to estimate the urine flow and then it is possible to calculate when it will reach it’s breakeven-point.

Figure 1.1 Separation toilet and waterless urinal

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Materials and Methods

Urine flow

Purpose The purpose of this research is to find out how many times, on average, the toilets are used per day at the Bonhoeffer College Bruggertstraat Enschede, the Netherlands. This information is necessary for an estimation of the urine flow and profitability of the separation toilets and waterless urinals in schools.

Method The number of usages of one toilet section was counted during one school day. As it is not possible to count the amount of the 5th and the 6th class, the amount of the 5th class is assumed to be the average of the previous 4 hours. During the 6th class half of the students have gone home, because of their timetables. Therefore the amount of visitors of the 6th class is assumed to be the half of the average of the first 4 hours. It is also not possible to count how many regular toilets are used at the boys toilet, but it is possible to count the amount of visitors. Therefore, based on own experiences, it is assumed that 10% of the boys who visits the toilet-section make use of the regular toilets and 90% of the urinals. The amount of usages of, the toilet section which was used for the research, is estimated to be 50% of the total usages, because of its position. To calculate the amount of usages of the toilets per year the results of this research is used as an average per day.

Hypothesis Per day about 50 people make use of the toilet section and around 50 people make use of the urinals.

Data For the research we used the following data:

- Everyone produces on average 0,150 L(1) of urine every time they go to the toilet

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Economical application

Purpose The purpose of this research is to find out how economical a separation toilet is compared to a regular

toilet, and to find out after how much time the breakeven-point is reached.

Method It is possible to determine the profit which is made by a separation toilet or waterless urinal compared

to a regular toilet or normal urinal, if the prices of the toilets and water are known. A few calculations

are made with the data that was obtained from the research to the amount of usages on the Bonhoeffer

College in Enschede, the Netherlands.

Hypothesis A separation toilet will reach its breakeven-point after 3 years.

Data For this research the following data was used:

Regular toilet 6 liter flush water(5)

Separation toilet 0,5 liter flush water(4) Regular urinal 2,5 liter flush water(5)

Waterless urinal no flush water

The water in the province Overijssel, the Netherlands, costed €0,026 per liter in 2004(5). These are the prices of the toilets:

All-inclusive costs of separation toilets €1300,- (5)

All-inclusive costs of waterless urinal €1050,- (5) All-inclusive costs of regular toilet €470,- (5) All-inclusive costs of regular urinal €420,- (5)

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Results

Urine flow

Measurements

Girls Boys Teachers (men)

Total Total toilets*

Total urinals*

1st Class 17 11 1 29 19,1 9,9

2nd Class 7 8 3 18 10,8 7,2

1st Break 16 23 2 41 20,3 20,7

3rd Class 11 15 0 26 12,5 13,5

4th Class 22 21 1 44 25,1 18,9

2nd Break 18 18 0 36 19,8 16,2

*It is assumed that 90% of the boys that visit the toilet section make use of the urinal and 10% of the toilet.

Counting during the 5th and 6th class was not possible, so an estimation is made. The figures for the 5th class are the average of the 1st, 2nd, 3rd and 4th class. The figures for the 6th class are half of that.



Total urinals*

5th Class 14,3 13,8 1,3 29,4 17 12,4

6th Class 7,1 6,9 0,6 14,6 5,4 6,2

These estimated values are used to calculate the total urine flow per day.



Total urinals*

Total 112,4 116,7 8,9 29,4 133 105

Toilet usage in the entire school : 133 ∙ 2 ≈ 270 usages per day Urinal usage in the entire school : 105 ∙ 2 ≈ 210 usages per day Urine production in the entire school : (266+210) ∙ 0,150 ≈ 70 L A school year has 200 days Toilet usage per year: 270 ∙ 200 = 54.000 visits Urinal usage per year: 210 ∙ 200 = 42.000 visit

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Economical application

Figure 1.2 Breakeven-point of a separation toilet, regular toilet, waterless urinal and urinal.

From figure 1.2 can be determined: The break even of the separation toilets is at approximately 5.800 flushes. The break even of the waterless urinals is at approximately 10.000 flushes.

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Processing

1. How much money does the school save every year on water costs if all toilets were to be replaced by separation toilets?

Research to the amount of users indicated that every school year about 54.000 people visit the toilet when nature calls, and 42.000 men visit the urinals. The amount of money saved every year can be determined with the water prices. Water consumption per year:

Toilets: 54.000 ∙ 6,0 liter = 320.000 = 3,2 ∙ 105 liter per year Urinals: 42.000 ∙ 2,5 liter = 105.000 = 1,1 ∙ 105 liter per year Separation toilets: 54.000 ∙ 0,5 liter = 27.000 = 2,7 ∙ 104 liter per year Waterless urinals: 42.000 ∙ 0,0 liter = 0 liter per year

Water costs per year:

Toilets: 3,2 ∙ 105 ∙ €0,026 = € 8300,- per year Urinals: 1,1 ∙ 105 ∙ €0,026 = € 2700,-per year Separation toilets: 2.7 ∙ 104 ∙ € 0,026 = €700,- per year Waterless urinals: 0 ∙ € 0,026 0 = €0,- per year

Savings: Separation toilets: €8300,00 - €700 = €7600,- Waterless urinals: € 2700,- With the separation toilets the school saves €7600,- a year and with the waterless urinals €2700,-. With those numbers the school would save approximately €10.300,- in total every year.

2. After how many years is the breakeven-point reached? At the school there are 17 toilets and 10 urinals. If all these toilets and urinals are replaced by separation toilets and waterless urinals, the investment would be: 17 ∙ 1300,- + 10 ∙ 1050,- = €32.600,- The school would save € 10.300,- on water costs. The breakeven-point is reached in: 32.600,- / 10.300,- = 3,1 years The breakeven-point would be reached in 3 years and 2 months.

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3. How many people have to visit the separation toilets every day to reach the breakeven-point after 5 years?

For public buildings it is convenient to have a minimum amount of users necessary to reach the breakeven-point after a certain amount of time. After 5800 flushes the break-even of a separation toilet with regards to a regular toilet is reached, for waterless urinals 10.000 flushes. 5 year has 1825 days. To reach breakeven-point after 5 years, the amount of people who have to use the separation toilet on average per day must be: 5800 / 1825 = 3,2 For waterless urinals it is: 10.000 / 1825 = 5,5

This can also be put in a diagram:

Breakeven-point in: Min. Amount of users per day

Year Days Toilets Urinals

1 365 15,9 27,4

5 1825 3,2 5,5

10 3650 1,6 2,7

15 5475 1,1 1,8

20 7300 0,8 1,4

4. When is the breakeven-point in a regular household reached? When taking into account that an average household has 3 inhabitants, which make use of the toilet

4 times per day, this makes a total of 12 usages per day, the breakeven-point can be calculated. It is

also assumed that a regular household has 2 toilets and no urinals.

Cost of the separation toilets: 2 · €1300,- = €2600,-

Water to be saved: €2600 / €0,026 = 100.000 L

A separation toilet saves with every flush 5,5 liters compared to a regular toilet.

Amount of flushes: 100.000 / 5,5 = 18.181,8

Breakeven-point after: 18.181,8 / 12 = 1515.15 days = 4,2 years

The breakeven-point in a regular household is reached after 4,2 years.

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Discussion

Urine flow The expected amount of toilet visits (50 toilet and 50 urinals usages) proved to be quite low with regards to the actual result (133 toilet and 103 urinal usages). As the percentage of visits to the specific toilet section relevantly to the entire school was roughly estimated, the actual outcome of the research may be inaccurate. There is no other research to compare it with. It is virtually impossible to calculate a precise result, because there will always be peaks and drops. A possible improvement to this research would be to count the use of the toilets for a longer period of time at every toilet section. Possibly every day during one to two weeks would be optimal.

Economical application The hypothesis for this research was that the breakeven-point for separation toilets is reached after 3 years at the Bonhoeffer College Bruggertstraat Enschede. The results showed that this point will be reached after 4,2 years, so the estimation was pretty accurate. As the water prices were from 6 years ago, the prices are quite outdated. But as the price of water probably has risen, the separation toilets will only save more money. Of course the accuracy of the research could be improved if more recent prices were used.

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Conclusion The toilets at the Bonhoeffer College Bruggerstraat are used in total 270 times. The urinals are used approximately 210 times. Per school year there are 54.000 toilet users and 42.000 urinal users. An average 70 liters urine is produced per day. The separation toilets save relatively a lot of water, and thus money, compared to a normal toilet. A separation toilet is profitable compared to a regular toilet after 5800 flushes and urinals after 10.000 flushes. If on a school with 1000 students and teachers all toilets would be replaced with separation toilets and waterless urinals, then these would be profitable after 3 years and 2 months. This is relatively fast, because a toilet section lasts longer than 3 years. It is calculated that on average of 3,2 people per day have to make use of the separation toilet in a public building for a period of 5 years to be profitable. For waterless urinals 5,5 people per day on average are needed. In a household it takes only 4,2 years when the breakeven-point is reached. In conclusion, separation toilets save a lot of water and are an interesting investment for both public buildings and households.

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Chapter 2- Struvite



Results 23 pH-value 23 MgO and MgCl 23 Settling speed 24 Crystal growth 25

Discussion 26


Conclusion 28

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Introduction Magnesium precipitates with ammonium and phosphate into a crystal, called MAP or struvite (figure 2.1), according to the following equation:

Mg2+ + NH4+ + PO4

3- + 6H2O MgNH4PO4 · 6H2O

Because this is a precipitation it will react automatically. To remove all phosphate, magnesium has to be added because there is not enough magnesium in urine to react with all the phosphate. Ammonium is in much larger quantities present. If the struvite precipitates completely almost 10 grams is formed in every liter of urine. For more details on the contents of urine and the calculations, see Appendix A.1 and B.2. If the precipitation of struvite is to be used to remove phosphate a reactor is needed. If a reactor has to remove the phosphate as efficiently as possible, certain properties of struvite have to be known. There are two kinds of properties of struvite which are essential: the chemical properties and the physical properties. The chemical properties are the optimal pH-value of the precipitation and the difference in magnesium salts. The physical properties are the settling-speed of struvite and the crystal growth. These properties are needed if a reactor has to be built.

Figure 2.1 Struvite

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Materials and Methods Chemical properties

Optimal pH-value of struvite precipitation

Purpose The purpose of this research is to find out if different pH-values make a difference in the precipitation of struvite.

Hypothesis Struvite precipitates at pH 8 or higher, at lower pH-values struvite does not precipitate.

Method First struvite is made for this research. The struvite in the urine is settled, and the urine is then poured off. After that, distilled water is added to remove any urine left and is again poured off. Several measuring cups are filled with pH-buffers (figure 2.2). After that 4ml of struvite suspension is added to every cup. Because of the high costs of measuring the phosphate concentration, it is decided the effects of the pH-value are determined with visual observation. The following pH-values are used:

pH-value

measuring cup 1 2,8

measuring cup 2 4,4

measuring cup 3 5,2

measuring cup 4 6

measuring cup 5 7

measuring cup 6 8,4

measuring cup 7 9,2

measuring cup 8 10

For the buffer solutions see appendix D.

Figure 2.2 Research pH-values, from high (left) to low pH-values(right).

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Difference in Mg2+-salts

Purpose The Magnesium salts which are not harmful to the environment, are MgO and MgCl2. The purpose of this research is to determine if struvite precipitates different with MgO or MgCl2.

Hypothesis Struvite precipitates equal with different Mg2+-salts, and thus the amount which is expected to be measured is 2,9 g struvite for both Mg2+-salts. See for the calculations Appendix A.

Method There are 2 measuring cups of 0,5 L, which are filled with urine, which has been stored. To determine how much of the PO4

3- has precipitated, the amount of struvite that is formed is measured.

In one measuring cup 4,3g MgCl2· 5H2O is added and the solution is stirred. In the other measuring cup 0,85g MgO is added and the solution is stirred. The struvite is removed from the urine with filtration (figure 2.3)and the weight of residue is measured. This is repeated 4 times and then the average is calculated. For the calculations see Appendix A.2

Figure 2.3 Filtration of urine with struvite

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Physical properties

Settling-speed

Purpose It is important to know how fast struvite settles, because one can then calculate how tall the settling part of the reactor has to be. One can also determine how long it takes to reach a certain concentration of struvite.

Hypothesis Struvite settles first at a speed of 1 mm/min, after a few minutes it settles much slower. The concentration that can be achieved by settling is estimated at 20%.

Method To make the struvite visible while it settles, it is put in water instead of in urine, because urine is not transparent enough. To make this struvite suitable for this research it was first cleaned. This is done by first making struvite in urine by adding Mg2+, let it settle and then pour off the urine. Distilled water is added to the struvite and the water is poured off again. The struvite is now suitable to use it for this research. The suspension is put in a tall thin measuring cup (figure 2.4). The width of the measuring cup does not influence the settling speed. The measuring cup is placed on a stable and flat surface. Then a bright light is placed behind the measuring cup to make the settling of struvite clearly visible. The settling is then captured by a camera, which records 30 minutes. In this way the settling speed can be easily determined. Previous observations showed that struvite settles fast and that a layer of struvite is formed on the bottom. But after a day this layer had become smaller. To measure this phenomenon this height is measured after 1, 2 and 5 days. This will give an indication how struvite behaves after a long period of settling. It is assume that the maximum concentration is achieved after 5 days. This mass-percent is measured. Because the height is proportional with the concentration, the concentrations after 30 min, 1 and 2 days are then calculated. The results are written down in two tables, one with the information of 30 minutes and one with information over 5 days. After that the concentrations of the different heights are calculated. These data are processed in two diagrams.

Figure 2.4 Research settling speed, a measuring cup with a struvite substance

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Crystal Growth

Purpose To determine if a current increases the size of struvite crystals.

Hypothesis The current will increase the size of struvite crystals and has influence on the shape of the crystals.

Method A test reactor is made of plexiglas of the following dimensions: 25cm x 20cm x 2,5 cm. In the bottom of the test reactor a hole is drilled for the air tube. 2 Triton 2000 cc aquarium pumps were used for the air supply. Two wooden pieces were used to put in the reactor to make a flow possible. These pieces were 9cm x 1cm x 2,5cm. See figures 2.5 and 2.6. Five different experiments are executed, each with other configurations, to test the effect of a current The struvite crystals are examined with a microscope before the experiment and after to determine if the crystal have grown in size.

Airflowtype Conditions

Test 1 1 entrance Struvite in suspension

Test 2 2 entrances Struvite in suspension

Test 3 2 entrances PO43- precipitates with MgCl2 and NH4

+

Test 4 2 entrances PO43= precipitates with MgO and NH4

+

Test 5 2 entrances Suspension of struvite and shell sand

Figure 2.5 Test reactor with one tube Figure 2.6 Test reactor with two tubes

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Results

Chemical properties

Optimal pH-value of struvite precipitation In measuring cup 1 till 4 there was a clear solution visible. In measuring cup 5 struvite was clearly visible. In 6, 7 and 8 there was increasingly more struvite in the measuring cups visible.

Difference in Mg-salts Test 1

Amount of struvite in grams

MgCl2 2,9957

MgO 0,5079*

Test 2


MgCl2 3,6597

MgO 2,414

Test 3

Test 4


MgCl2 0,8721*

MgO 2,0307

Average


MgCl2 3,3277

MgO 1,8974

*These values are inaccurate due to several inconsistencies during research. Therefore, these values are not taken in consideration when calculating the averages.


MgCl2 1,4098*

MgO 1,3808

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Physical property

Settling-speed

Short term data The data of the short term research are put in a diagram (figure 2.7).

Figure 2.7 Settling of struvite

According to the graph the struvite settles evenly in the first 250 seconds. The gradient of the first 250 seconds represents the settling speed of struvite. The program Coach 5 was used to determine the gradient (figure 2.8).

Figure 2.8 Derivative of the settling of struvite of the 250 seconds.

The gradient is: - 0,00021 m/s Then the speed is : 12 mm/min

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Long term data It is assumed that the maximum concentration, which can be acquired through settling, is acquired after 5 days. Of this sample the concentration of dry-struvite is measured. This is done by the Water board Regge & Dinkel. This turned out to be 5,37%. After that the other concentration could be calculated by using the fact that the height is proportionate with concentration. With this done, the following table is achieved:

Time (days) Height struvite (mm) Concentration (%)

0 (30 min) 20 2,95*

1 14 4,22*

2 12 4,92*

5 11 5,37

*Calculated

Crystal growth In all the experiments, with the reactor (figure 2.9) the crystals were of the same size and shape. All

crystals were between 0,2 and 0,5 mm long.

Test Size (mm)

Test 1 0,2-0,5

Test 2 0,2-0,5

Test 3 0,2-0,5

Test 4 0,2-0,5

Test 5 0,2-0,5

Figure 2.9 The test reactor

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Discussion

Chemical properties

Optimal pH-value of struvite precipitation The data from this research matched the hypothesis. Above a pH-value of 8 the struvite precipitated best (figure 2.10), at lower pH-values the struvite did not precipitate at all. Other results of already published data also match the data. The already published data(3) was more accurate than this research and contained at different pH-values the different phosphate-concentrations. The optimal pH-value for the precipitation was 8,5 , according to STOWA and the water board Regge & Dinkel(3). Stored urine already has a pH-value of 8,5(3), so no substances have to be added to precipitate all phosphate. Unfortunately, due to budget, the phosphate-concentrations could not be measured in this research. To improve this research, instruments that measure the phosphate concentration should be used. Also, more different pH-values could be used for research.

Difference in Mg2+-salts In general the amount of struvite, which was measured, turned out to be quite the same. The expected amount was 2,9 g struvite, however with MgCl2 an average of 3,3 g struvite was measured and with MgO 1,9 g struvite. It is slightly more, but this can be explained with the fact that not all of the crystal water has evaporated. According to a research of STOWA(3), struvite precipitates for 90% with MgO, and 99-100% with MgCl2. The amount of MgO that was measured was substantially lower than the amount measured by MgCl2. This matches the research of STOWA. However, it did not matched on the proportions. With MgO, struvite precipitated around 40% less than with MgCl2. But as MgO is much cheaper than MgCl2, it is better to use MgO. MgO is also used in the struvite reactor at Steenderen(9), which removes phosphate from the waste water of a factory. There are a few ways to clarify the fact that the amount of struvite was less than expected. The concentration of phosphate in the urine could be not as high as assumed. Also, the filtration method that was used, could contain some (major) flaws, but this is less likely than the first clarification. To improve this research the phosphate concentration could be measured before and after the precipitation. Then the amount of phosphate could be compared to each other. Again, due to budget, this could not be measured in this research.

Figure 2.10 Research pH-values, basic solution.

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Physical properties

Settling-speed The settling-speed that was measured turned out to be much higher than expected. The 12 mm/min that was measured is believed to be high enough for a reactor with a height of 1,5 meter to gain a high concentration. There is no research which measured this before, so it cannot be compared. The gradient after 250s is getting smaller, so the struvite settles less fast. This is explained because at a certain moment the struvite particles at the bottom slow down the other struvite particles. The concentration that can be achieved was lower than expected. After 5 days of waiting the concentration that was achieved was 5,37%. A possible error in this research is the start amount of struvite. This amount did not match the amount of struvite in urine, when all the phosphate has precipitated. More research should be done to the effect of the start amount of struvite on the concentration that can be achieved by settling.

Crystal Growth The results do not match the hypothesis at all. None of the crystals were larger in size or had a different shape. The current had no effect on the crystals. Other researches(8) did succeed in creating larger crystals with a certain current speed. Some other ions like Ca2+ were used to make larger crystals. But this is hard to achieve and maybe not suitable for a reactor in public buildings. To improve this research better instruments should be used and more precise measuring equipment. More experiments should also be done in more varied conditions for more results.

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Conclusion Struvite precipitates best in a basic solution, it dissolves in an acid solution. The optimal pH-value for the precipitation is 8,5. Stored urine already has this value, so no substances have to be added. Magnesium oxide should be added to the urine for the precipitation (figure 2.11), because it is cheaper than magnesium chloride and it is not harmful for the environment. The settling speed of struvite is 12mm/min and the concentration that was reached after five days was 5,37%. The growth of struvite-crystals is difficult to achieve and is maybe not suitable for a relatively simple reactor for public buildings.

Figure 2.11 Filtrated urine

29

Chapter 3 – Design of a reactor

Introduction 30 Reactor Design 31 Separation 31 Reactor type - continue or batch? 32 Supply 33 Mixing 33 Extraction of urine and struvite 33 Scaling 33

30

Introduction Now that the properties of struvite are known, it is possible to make a design for a reactor which removes phosphate from urine by means of struvite precipitation. The reactor (figure 3.1) is designed for a public building like a school. There are six issues which are discussed: what type the reactor should be, the supply of urine and magnesium, the mixing of the urine, the separation of the struvite from the urine, the extraction of struvite and scaling, a phenomenon that occurs when struvite attaches to a surface.

Figure 3.1 A possible reactor design

31

Reactor Design A reactor which removes the phosphate needs certain requirements such as the supply of MgO and urine, the mixing, the separation of struvite, etc. The most important requirement is the separation section, because this is defining for the reactor design. This is discussed first. After that the process type is discussed (batch or continue). Then the supply, mixing and extraction are discussed. One of the things that should also be taken in consideration is scaling, this is discussed last. Then the operation of the reactor is explained and the properties of the reactor are given.

Separation The struvite has to be separated from the treated urine. There are a few ways of separation which can be used. To make a decision which method should be used in the reactor, all advantages and disadvantages have to be known. Here they are discussed:

Settling Struvite will settle because it has a higher density than urine. When it has settled down the clean urine can be removed and the remaining struvite will have a higher concentration. Advantages: This is a very simple method. The obtained concentration of struvite is believed

to be sufficient for a fertilizer. Disadvantages: It is time-consuming (maximum concentration appeared to be 5,39 % after five

days). Also the struvite will always contain some urine.

Centrifuge This method is based on the difference in density of both substances. Advantage: A higher concentration of struvite is possible. Disadvantages: Continuous processing is not possible and it is very costly.

Filtration The filtration method is based on the difference in size of the particles. Advantage: This method is quite effective. Using this method a concentration of almost

100% can be obtained. Disadvantage: The struvite must be removed from the filter on a regular basis. This requires

complicated and expensive installations.

Evaporation The evaporation method is based on the difference in boiling point of the components in the solution. Evaporation of the solution also salts from the urine are left as a residue in the struvite. This can be solved by rinsing the solution. Rinsing is done by adding water to the mixture and then drain it by using the settling method. Repeating this process will leave a mixture of struvite and water. Evaporation of this mixture will leave pure struvite. Advantage: Using this method a concentration of 100 % can be obtained. Disadvantage: This process requires a lot of energy to evaporate the water. Rinsing the struvite

takes a lot of time because settling is a slow process. The settling tanks require a lot of space.

Conclusion Settling is, in this case, compared to the other methods the best. It is a simple method that does not require a complicated installation. Therefore it is relatively cheap. All other methods require large and/or expensive installations.

32

Reactor type – Continue or Batch? The best way to separate the struvite of the urine is by means of settling. This settling requires time. In a continuous processing reactor urine is supplied and drained constantly. The struvite is also removed continuously. All these flows effect the settling process of the struvite. This can be seen in figure 3.2.

Figure 3.2 Flows in the settling tank

So with a continuous reactor not al struvite-crystals will settle and struvite-crystals would be drained with the urine and scaling would occur on the pipes. With a batch reactor the struvite could have enough time to settle and the urine could be drained without any struvite-crystals and there would be no scaling. The urine production is not constant, as people do not go to the toilet very often at night, and a public building is closed in the evening. This would mean that a continues reactor needs a buffer tank. A batch reactor would not need one, as the urine that is produced that day could react in the afternoon and the struvite could settle in the night. Then the struvite and urine can be extracted in the morning and the reactor is emptied and ready to process new urine. The reaction and the settling could be done in the same tank. This would make the reactor very simple. From this can be concluded that a batch process is the best option.

33

Supply The reactor should be supplied with magnesium oxide and urine. Magnesium oxide has to be dosed in the right proportions. This can be done easiest when the magnesium is in solution. But magnesium oxide does not dissolve in water, it will settle after some time. So the tank that stores the solution requires a mixer to keep the magnesium oxide in suspension. The urine can be supplied normally with a pump.

Mixing To let all magnesium react with the ammonium and phosphate the solution has to be mixed. This, however, cannot be done by a mixer because then scaling will occur (described below). The urine can also be mixed by means of a current. This current can be established by pumping air in the urine with a flexible tube. Because scaling does not occur on flexible moving objects, the urine is mixed without any additional scaling.

Extraction of struvite and urine Now that all phosphate has precipitated the struvite needs to be extracted. The extraction of the struvite and the draining of the clean urine must be separated. The struvite settles at the bottom of the reactor, where a valve is placed. If all the struvite is settled at the bottom the urine can be pumped away. The pumping should be slow, because it is unwanted that struvite is pumped with the urine. The pumping should be slower then 12mm/min, because the struvite would settle faster than it is drained. The valve which is placed at the bottom remains closed during the precipitation and settling. It opens after the clean urine is pumped away. The struvite will drop in a reservoir through the valve and the valve closes again.

Scaling Scaling is an adverse effect that occurs on the surface of the reactor or tubes. Scaling means that struvite attaches to a surface. Scaling is unwanted and needs to be minimized. There is less scaling when there is a constant current. When there is not a constant current, struvite will stick to a surface. Tubes will get clogged due to this scaling effect. However, on flexible moving objects scaling does not occur. This is already used in a struvite precipitation reactor in Steenderen(9). They make use of flexible tubes to add the magnesium oxide solution to the wastewater and scaling did not occur at all on the flexible tubes. The previous research shows that struvite dissolves in an acid solution, so scaling in the reactor can be removed with acid.

34

Operation reactor The operation of the reactor (figure 3.3) is as follows: the school closes around four o’clock and the toilets will not be used any more. Then the process will start. A suspension of magnesium oxide in water is added and mixed with the urine. It takes about ten minutes for all phosphate to precipitate into struvite. After that the mixing is stopped. The struvite can then settle from 4.30 pm until 7.00 am. The bottom of the reactor will gradually be filled with struvite. This is a period of 14,5 hours. According to previous research, the struvite concentration will be 3,74%. The clean urine will be pumped away when all the struvite has settled. Then the valve opens and the struvite drops in the reservoir. The reactor should be cleaned once in a month with an acid solution to remove any scaling. For more details on all the calculations, see Appendix B.

Figure 3.3 Batch reactor functional design.

35

Reactor size During daytime the urine is collected in the reactor. Previous research showed that 70 liters of urine is produced per day at the Bonhoeffer College. This means that the reactor has to be about 100 liters for peaks. The research about settling speed of struvite showed that struvite settles quite fast. So the height of the reactor does not have much influence on the concentration of struvite that is reached by settling. Therefore a height of 1,5 meters is suitable and the diameter should then be 0,164 meters. The container tank should be about 370 liters if it is emptied once a month. For the calculations see Appendix B.1 and B.4.

Reactor properties The reactor that would be placed at the Bonhoeffer College Enschede has the following properties:

Capacity Reactor 100 L

Height reaction tank 1500 mm

Diameter reaction tank 164,4 mm

MgO usage per liter urine 1,7 g

MgO usage per day 9,8 g

Struvite production per liter urine 119 g

Struvite production per day 690 g

Capacity struvitetank 370 L

The calculations can be found in Appendix B.

36

Chapter 4 – Test-reactor

Introduction 37 Reactor 38 Materials and method 39 Blanco test 39 Less magnesium 39 Mixing time 40 Results 41 Discussion 42

Blanco test 42 Less magnesium 42 Mixing time 42 Conclusion 43

37

Introduction In the previous chapter a design is made for a batch reactor. A small prototype of this reactor is made and tested to see if the design works properly, this is done by filtrating (Figure 4.1) and measuring the amount of struvite. Two tests are done as a blanco test, to see if the reactor works properly. After that, three tests are done to test the influence of the mixing duration on the amount of struvite that is produced.

Figure 4.1 Filtration of struvite

38

Reactor The following prototype (figure 4.2) is used for the tests:

Figure 4.2 Reactor prototype

Capacity De test reactor can contain 4,5L urine.

Urine supply The urine is pumped in the reactor with a Masterflex L/S pump.

Mg-solution supply The magnesium solution is added by hand.

Airflow To produce the airflow, three Triton 2000 CC aquarium air-pumps are used.

Urine extraction The extraction point of the effluent is placed above the level of the settled struvite. In this way, the struvite is not extracted with the urine.

Struvite extraction The struvite is extracted at the bottom where a rubber tube is placed and tightened. To extract the struvite, the rubber tube is untightened and the struvite flows down.

39

Materials and Method

Blanco test

Purpose The purpose of this experiment is to determine if the reactor works properly and produces sufficient struvite. Major questions are: Does the struvite extract well through a rubber tube and is there any struvite extracted with the urine?

Hypothesis 26,1g struvite will be produced in the reactor.

Method 4,5L of urine is pumped in the reactor. The pH of the urine is measured. De urine consists of 50% male and 50% female urine. After that, 38,6g MgCl2∙5H20, which is dissolved in water, is added (See Appendix C.1). The urine is mixed for 15 min, it is believed that is enough. The struvite settles for 15 hours and then the urine is extracted. After that, the rubber tube is untightened and the struvite is extracted and collected in a measuring cub. The struvite is filtrated and measured on a balance. This is repeated for 2 times.

Less magnesium

Purpose In the blanco test less struvite was produced than expected. The purpose of this experiment is to determine if the same amount of struvite is produced when less magnesium is added.

Hypothesis Female urine is diluted with a factor of 4. This means the 50% female contains 4 times less phosphate and only 24,1g MgCl2∙5H2O has to be added (See for calculations Appendix C.2). But in the blanco tests around 7,9g was produced. This suggests only 11,7g MgCl2∙5H2O has to be added (See for calculations Appendix C.3). If with 11,7 MgCl2 around 7,9g struvite is produced, then is that the correct amount.

Method The same method as the blanco test is used, but now only 24,1g and 11,7g is added.

40

Mixing time

Purpose To determine if a shorter mixing time, or none at all, will produce the same amount of struvite (figure 4.3). Hypothesis No mixing will result in less struvite, because the magnesium-ions will not be spread out evenly in the solution. Not all the phosphate and ammonium will be able to react with the magnesium. A shorter mixing time than 15 minutes can be sufficient.

Method The same method is used with as the previous experiment. But now the mixing time is variable: no mixing at all, 1 minute and 5 minutes. The results are compared to the blanco test, to determine if it had any effect.

Figure 4.3 Filtrated struvite with 5 min mixing time

41

Results

Blanco pH Mixing time (min) MgCl2··5H2O added (g) Struvite (g)

Test 1 9 15 38,53 7,19

Test 2 9 15 38,53 8,4698

Less Magnesium

Test 1 9 15 24,096 8,1203

Test 2 9 15 11,697 8,7974

Mixing Test

No mixing 9 0 24,096 5,3716

1 minute mixing 9 1 24,096 7,9645

5 minute mixing 9 5 24,096 8,8385

42

Discussion

Blanco Test Less struvite is produced than expected, this can be explained in two ways. The urine consists of 50% male and 50% female urine. The female urine is diluted with water, which means that there is less phosphate in the urine than expected. The other possibility would be that the mixing time was too short. More tests should be executed to make sure 15 minutes is long enough to mix the solution. The struvite extraction works properly, but some flushing with water is needed to extract all struvite, but the loss is not significant. There is also no struvite in the urine effluent, which is also good. This experiment could be improved if more tests were executed to provide a more reliable result.

Less Magnesium The hypothesis was correct, less MgCl2∙5H2O produced the same amount of struvite. Thus the dilution of the urine must be taken in consideration to determine the amount of MgCl2∙5H2O. This research can be improved if more tests were executed. The exact amount can also be determined if more experiments were done with different amounts of MgCl2∙5H2O or by measuring the PO4

3- concentration.

Mixing Time The results match the hypothesis. No mixing results in considerably less struvite (5 grams). 1 minute mixing produces around 8g struvite. 5 minutes produces more than 1 minute mixing, but also more as the blanco test. This suggests that 1 minute of mixing is enough, more tests should be done to explain the higher amount of struvite with 5 min mixing. This experiment could be improved if more tests were executed and more different mixing times were tested.

43

Conclusion Overall, the reactor works properly but does not produce the amount of struvite expected. This is explained because the female urine is diluted. The reactor produces an average of 8,2g struvite. The struvite is extracted well through the rubber tube, but some struvite remains in the reactor. There is no struvite in the urine. 11,7g of MgCl2 ∙ 5H2O is enough to form the maximum amount of struvite. The urine is best mixed when it is mixed for 5 minutes. This short mixing time reduces the scaling in the reactor.

44

Chapter 5 – Application in society

Introduction 45

Materials and methods 46

Results 47

Discussion 48

Conclusion 50

45

Introduction It is important to make it attractive for people to install separation toilets, because at the moment

people are not aware of the existence of the separation toilets. A survey is held under 55 11th grade

students. They answered questions about comfort, scent and their ideas about separation at source. The

results are compared to other surveys about the acceptance of separation toilets. The acceptance of

separation at source is import to efficiently apply struvite as a fertilizer in agriculture (figure 5.1).

Figure 5.1 Application of struvite in agriculture

46

Materials and Methods

Survey

Purpose

The purpose of this research is to find out what the social acceptation of separation toilets are, which is

vital information for the separation toilets to succeed in society.

Hypothesis

The females are expected to be quite unsatisfied, due to the distinct smell of the separation toilets.

Males are expected to be neutral, since it wouldn’t matter much to them.

Method

A survey was held under 55 11th grade students of the Bonhoeffer College, to find the customer’s

opinion on separation toilets. These students had been using separation toilets on the school for roughly

a year at the time the survey was held.

47

Results

Survey

This survey is held under 55 11th grade VWO students. There were 24 boys and 31 girls.

48

Discussion

Survey According to this survey, the design of the separation toilets needs serious reconsideration. The rectangle shape of the toilet seat is uncomfortable and therefore it discourages people to use the separation toilet. The waterless urinals tend to smell more than regular urinals, since the urine is not flushed away with water. A solution has to be found to get rid of the foul smell of urine. These problems have to be solved in order to apply waterless urinals and separation toilets on a large scale. A lot of research to the social acceptance of separation toilets and waterless urinals has been done in Switzerland by the Swiss Federal Institute of Aquatic Science and Technology (EAWAG). [6][7] According to their first questionnaire in 2003[6] among a focus group of citizens, generally the separation toilets and the “urine-fertilized” were very well received (figure 5.2). 80% of the participants liked the thought behind separation toilets, and 60% were willing to purchase a toilet in their own household, which is significantly more than in the questionnaire that was held among the Bonhoeffer College Bruggertstraat students. Although most participants indicated that separation toilets would be more feasible in public buildings. The participants were very positive about urine-based fertilizers as well, 80% of the participants replied that they would have vegetables made with urine fertilizers rather than with artificial fertilizers, although, before full implementation, an in-depth research needs to be done to the possible human health risks with such fertilizers.

Figure 5.2 Answers to the question (A) Could you imagine purchasing a NoMix toilet? (B) Could you

imagine moving into an apartment with a NoMix toilet? The percentages are given on the top of each bar. Results from Eawag research in 2003. [6]

49

Another research was done by Eawag in 2006, a survey among young adults to sound out their opinion on separation toilets and urine-based fertilizers[7]. The participants were divided in a group of long-term users and a group who are new to the concept. Especially the long-time users were positive about the concept, 70% of these participants find the concept of separation toilets convincing, whereas 10% gave a negative response and 20% had no opinion. Again, a significant difference with the students at the Bonhoeffer College. Another surprising result of this survey was that women were far more positive than men, which, again, is a difference between the Dutch survey. An interesting result is that, even though the willingness to pay more for such toilets, the overall acceptance is quite high (figure 5.3), making the application of separation toilets in the society in the future very likely.

Figure 5.3 Answers to: “How do you judge the NoMix toilet compared to a conventional one?” As asked

in an Eawag questionnaire held in 2006. [7]

50

Conclusion In order to let people accept separation at source, more research needs to be done in the possible health risks of using urine-based fertilizers for growing vegetables. Participants of surveys indicated they prefer vegetables grown with urine-based fertilizers rather than those with artificial fertilizers, if health risks can be prevented. The design and comfort of separation toilets needs to be improved according to several surveys that were held. A good way to stimulate people to use separation toilets and waterless urinals would be by means of a subsidy. This subsidy could be distributed by the local government. Subsidy for separation toilets could come in different forms. One way is to make it more attractive by lowering the water taxes for households or organisations that have separation toilets. Not only would the customer save on water costs, due to the low water usage of these toilets, the price of water itself would be lowered as well. Another possible form of stimulation could be to subsidize the purchase of separation toilets. The government would pay a part of the purchase price, making the purchase cheaper for the customer and thus making it more attractive.

51

Acknowledgements

During this project we got aid from several people and companies. Our special thanks goes to our Physics teacher and project supervisor Benno Berendsen and our Chemistry teacher Gerard Kransen. We would also like to thank Mathijs Oosterhuis of water board Regge & Dinkel, professor International Water Technology Harry Futselaar of Norit Nederland BV, Michiel Beukers, student at the Saxion Hogeschool Enschede and Philipp Kuntke, researcher at Water Research Lab Wetsus, for their continuing support and material help.

52

References/Bibliography

1Waterschap Regge & Dinkel. “Schone Urine/Clean Urine,” Technasium Project, Dec. 2008.

2Kuntke, Philipp. “Recovery of Nutrients and Energy from Source Separated Urine,” Wetsus results

2008, Apr. 2009.

3Wilsenach, Jac. Stowa. “Stowa-Desar; options for separate treatment of urine,” 2005.

4Mels, Adriaan. Zeeman, Grietje. Bisschops, Iemke. Stowa. “Stowa; Brongerichte inzameling en

lokale behandeling van afvalwater,” 2005.

5School records, Bonhoeffer College Bruggertstraat, Enschede, the Netherlands 2009

6Eawag, “Investigating consumer attitudes towards the new technology of urine separation,” Water

Science and Technology Vol 48 No 1, 2003.

7Eawag, “Young users accept NoMix toilets,” Water Science & Technology Vol 54, 2006.

8 Faculty of Chemistry, Wroclaw University of Technology, “Nucleation and Crystal Growth Rates of Struvite in DTM Type Crystallizer with a Jet-Pump of Descending Suspension Flow in a Mixing Chamber,” American Journal of Agricultural and Biological Sciences, 2007. 9Waterstromen BV, Steenderen, Postbus 8; 7241 JD Lochem.

53

Appendices

A. Contents of urine This is an overview of the contents of stored urine(2):

A.1 The optimal ratio Urine does not contain a perfect ratio of nitrogen, phosphate and magnesium to make al phosphate to precipitate into struvite. There is more nitrogen in urine than phosphate and magnesium. The amount of magnesium can be neglected. If one wants to get the maximum amount of struvite, one should add magnesium ions to make the equation correct. Molar mass N: 14,01 u Amount of mole N: 7,4 / 14,01 = 5,3 ∙ 10-1 moles per liter Molar mass P04: 94,97 u Amount of moles P04: 4,0/ 94,97 = 4,2 ∙ 10-2 moles per liter Because the equation says that the ratio phosphate : magnesium is 1:1, is the amount of magnesium equal to the amount of phosphate. Molar mass Mg: 24,31 u Amount of Mg needed: 4,2 ∙ 10-2 moles per liter Struvite: Amount of moles MgNH4PO4 ∙ 6H20: 4,2 ∙ 10-2 moles Molar mass: 245,418 u Amount of gram MgNH4PO4 ∙ 6H204: 4,2 ∙ 10-2 ∙ 245,418 = 10,3 grams Amount of gram MgNH4PO4: 4,2 ∙ 10-2 ∙ 137,298 = 5,77 grams

Matter gram per liter

Total-N 7,4

Cl- 4,4

Na+

3,0

K+

2,0

PO4 3- 4,0

Mg2+ 0,1

SO42- 3,0

pH-value 8,5

54

A.2 MgO and MgCl2 ∙ 5H2O For 1 liter: Molar mass MgCl2 ∙ 5H2O 204,34 u Amount of grammes MgCl2 ∙ 5H2O 8,6 grams per liter Molar mass MgO 40,32 Amount of grammes MgO 1,7 grams per liter For 0,5 liter: Amount of grams MgCl2 ∙ 5H2O for 0,5L 8,6 / 2 = 4,3 grams Amount of grams MgO 1,7 / 2 = 0,85 grams

55

B. Reactor calculations

B.1 Calculations – Reaction tank 100 L = 100 dm3

Surface bottom = 100 / 15 = 66700 mm² Radius bottom = √(6,67) / π = 82,2 mm Diameter reactor = 0,822 ∙ 100 ∙ 2 = 164,4 mm

B.2 Calculations - Struvite Values - Molecule mass struvite = 233,322 u - 70 L urine produced per day - 4g PO4

3- 4,2 ∙ 10-2 M Calculations 1 L urine contains:

4,2 ∙ 10-2 ∙ 245,418 = 10,3 g struvite The amount of struvite that is precipitated per day:

10,3 ∙ 70 (L) = 721 g struvite

B.3 Calculations – Struvite concentration Settling time from 4.30 PM until 07.00 AM is 14½ hours Settling speed of struvite is 12 mm/min Struvite concentration after 30 min is 2,95% and after 1 day it is 4,22% Calculations The distance struvite settles in that time is:

14½ ∙ 12 = 10,440 m The struvite concentration after 15 hours of settling:

15/24 ∙ (4,22-2,95) = 3,74%

56

B.4 Calculations – Volume reservoir It is assumed that the space 1 gram of struvite occupies 1 ml of space. According to the previous calculations the following values can be noted down: The concentration after 15 hours of settling us 3,74% In the reactor the maximum amount of formed struvite every day is 690 gram. Calculations The volume of the reservoir is: 20 ∙ 721 ∙ 10-3 ∙ (100/3,74) ≈ 386L

57

C. Magnesium

C.1 MgO and MgCl2 in urine Amount of moles PO4

3- per liter 4,2 ∙ 10 -2 moles Amount of moles PO4

3- per 4,5 liter 1,89 ∙ 10 -1 moles Amount of moles Mg2+ per 4,5 liter needed 1,89 ∙ 10 -1 moles Molar mass MgCl2 ∙ 5H2O 204,34 u Amount of grammes MgCl2 ∙ 5H2O needed 1,89 ∙ 10 -1 ∙ 204,34 = 38,6 g

C. 2 Struvite in diluted urine 4g PO4

3- per liter urine In 4,5L 4 ∙ 4,5 = 18g PO4

3-

Molar mass PO43- 94,97 u

Amount of moles in 4,5L 18 / 94,97 = 0,190 moles PO43-

Molar mass struvite 137,412 u Amount of grams struvite in 4,5L 0,190 ∙ 137,412 = 137,412g MgNH4PO4

50%/50% male/female in urine 4,5 / 2 = 2,25L Male urine 4g PO4

3- per liter 2,25 ∙ 4 = 9g PO43-

Female urine 1g PO43- per liter 2,25 ∙ 1 = 2,25g PO4

3-

Total grams PO43- 9 + 2,25 = 11,25

Molar mass PO43-- 94,97 u

Total moles PO43- 11,25 / 94,97 = 0,1185

Molar mass struvite 137,412 u Total struvite 0,1185 ∙ 137,412 = 16,3 g MgNH4PO4

C.3 MgCl2 ∙ 5H2O in 7,9 grammes of struvite Molar mass struvite 137,412 u Amount of moles struvite in 7,9g 7,9 / 137,412 = 0,0575 moles MgNH4PO4

Molar mass MgCl2 ∙ 5H2O 204,34 u Amount of grams MgCl2 ∙ 5H2O 0,0575 ∙ 204,34 = 11,69g MgCl2 ∙ 5H2O

58

D. Buffer solutions

Amount in

percents Amounts in ml

pH 0,2 M K2HPO4 0,1 M Citric acid 0,2 M K2HPO4 0,1 M Citric acid

2,8 15 85 12 68

3,6 20 70 24 56

4,4 45 55 36 44

5,2 55 45 44 36

6,0 65 35 52 28

6,8 75 25 60 20

7,6 95 5 76 4

0,2 M Boric acid 0,2 M NaOH 0,2 M Boric acid 0,2 M NaOH

8,4 85 15 68 12

9,2 65 35 52 28

10,0 50 50 40 40

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