WO1999051522A1

WO1999051522A1 - Nutrient recovery from human urine

Info

Publication number: WO1999051522A1
Application number: PCT/SE1999/000547
Authority: WO
Inventors: Bo B. Lind; Zsofia Ban; Rob H. Hellingwerf; Stefan BYDÉN
Original assignee: A+ Science Invest Ab
Priority date: 1998-04-03
Filing date: 1999-04-01
Publication date: 1999-10-14
Also published as: AU3856999A; SE9801177D0

Abstract

A method for the recovery of nutrients from human urine substantially free of excrements and other debris is described. Said method comprises the following steps: A) the urine is concentrated; B) struvite crystallisation is initiated in the concentrated urine by adding MgO; and C) the struvite crystals are separated from the solution. The method may also comprise a further step, step D), in which nitrogen is recovered from the solution obtained in step C) by ammonia adsorption, preferably by the use of wollastonite or clinoptilolite. The struvite and the ammonium containing adsorbent are suitable for use as fertilizers.

Description

NUTRIENT RECOVERY FROM HUMAN URINE

Field of the invention The present invention relates to a method for the recovery of nutrients from human urine. The invention also relates to use of the thus produced products as plant fertilisers.

Background Eco-cycling of nutrients between urban areas and farmland is a critical step towards achieving ecologically sus- tainable development. Within three decades the world population will be more than eight billion and the subsequent pressure on all types of productive soils will be enormous (McCalla A (1994) Agriculture and Food Needs to 2025: why we should be concerned, Sir John Crowford Memo- rial Lecture, Washington DC, Secretariat, Consultative

Group on International Agricultural Research (CIGAR) c/o The World Bank; Leach G (1995) Global land and food in the 21st century, Trends and issues for sustainability, SEI, Polestar 5, pp 1-90; Olsson L (1997) Miljόrelaterad resursknaphet, In Jervas G (ed) 2000-talets stora utman- ingar -aktuella resurs och miljδproblem I ett kon- fliktperspektiv, SNS-fδrlag, pp 225-310) . With current linear flows most of the nutrients are lost as waste through food production processes, trade and restaurants and as domestic waste and wastewater.

Commercial fertiliser, used intensively in agricul^¬ ture, is produced with high usage of fossil energy and from finite mineral resources, sometimes polluted by cad^¬ mium or radioactive elements such as uranium (Hodge C A and Popovici N N (1994) Pollution Control in Fertilizer Production, Marcel Dekker NY, pp 502) . If all nutrients from domestic waste are recycled, 35-45 % of commercial fertiliser use can be eliminated. The outlet of nitrogen and other nutrients from domestic sewage is currently causing severe problems of eutrophication in lakes and

CONFIRMATION COPY rivers all over the world. Since more than three-quarters of the nitrogen, phosphorous and potassium in toilet wastewater is found in the urine, together with a large volume of micro-nutrients present in balanced concentra- tions, new ideas of eco-cycling based on urine separation have been proposed in order to achieve the maximum recovery and circulation of nutrients not contaminated by hazardous compounds and to reduce eutrophication in freshwater and coastal ecosystems. Urine-separating toilets have been installed in several eco-villages around the world, including different parts of Sweden. The urine collected this way is to some extent used as a fertiliser. The urine in its untreated liquid form is then spread on the field that is to be fertilised. The use of liquid urine is however problematic and controversial with regard to different stages in its management, e.g. storage, transport, spreading and general hygiene considerations (in normal concentrations urine is an excellent medium for bacterial grow because of its high nutrient content) . Urine alone can replace 20-25 % of commercial fertiliser currently used in the production of food for human and animal consumption (Jorgensen S E, Libor 0, Gra- ber K L and Barkacs K (1976) Ammonia removal by use of clinoptilolite. Wat. Res. Vol 10, pp 213-224). Nutrient recovery and recycling from human urine can be an important part of future eco-cycling. Calculations of the nutrient balance show that the food we need and metabolise is in balance with the "waste" we excrete as nutrients during a year (Wolgast M (1993) Rena vatten, Om tankar I kretslopp, Creamon HB Uppsala, pp 1-186) .

Life cycle assessment studies of conventional as well as urine separating wastewater systems show that a urine separating system have many advantages with respect to factors as emissions and nutrient recovery (Bengtsson, M., Lundin, M and Molander, S. (1997) Life cycle assessment of wastewater systems - case studies of conventional treatment, urine sorting and liquid composting in three Swedish municipalities, Chalmers University of Technology, Technical environmental planning, Report 1997:9, Gδteborg, Sweden, 99 pp) . Also exergy (energy efficiency) analyses of sewage treatment systems show that phospho- rous and nitrogen-recycling efficiency is highest when urine separation techniques are used (Hellstrδm D and Karrman E (1997) Exergy analysis and nutrient flows of various sewerage systems, Wat. Sci. Tech. Vol. 35, No. 9, pp 135-144). However, Life Cycle Assessment (LCA) studies of urine-separation systems show that the transport of large amount of urine, as well as spreading and hygiene, are important obstacles to achieving system efficiency (Jenssen P D and Etnier C (1996) Ecological engineering for wastewater and organic waste treatment in urban ar- eas: an overview, Conference on Water saving Strategies in Urban Areas, Vienna February 1-2; Larsen T A and Gujer W (1996) Separate management of anthropogenic nutrient solutions (human urine), Wat. Sci. Tech. Vol. 34, No. 3- 4, pp 87-94). The main problem regarding efficiency in terms of exergy is related to the management aspects - the storage and transportation of the urine (Hellstrδm D (1998) Exergy Analysis. A comparison of urine separation systems and conventional treatment systems, Wat. Environ. Res.). Another problem connected with urine-separation systems is the loss of nitrogen through ammonia evaporation during storage and spreading (Hanaeus A, Hellstrδm D and Johansson E (1996) Convertion of urea during storage of human urine, Vatten 52, pp 263-270) . Large volumes of urine are needed in order to fertilise for example farm- land, and thus there are problems connected to transportation of these larger quantities. Furthermore, the use of liquid urine as fertiliser is in many countries restricted, e.g. it is only allowed during limited periods of the year. Finally, the intended users of the fertil- iser, i.e. the farmers, need delivery assurances regarding volume and quality. Concentration of the nutrients in the urine and transformation into solid minerals may be the solution to most of the problems connected with urine separation. Handling and storage can be revolutionised, the quality can be controlled, the volume can be reduced dramatically compared with the urine, the loss of nitrogen into the atmosphere can be eliminated, a high level of hygiene can be maintained and spreading on arable land is much more flexible in terms of time and dosage.

Summary of the invention One object of the present invention is to solve the problems with the disposal of domestic wastewater emanating from human urine. Another object is to provide slow- release plant fertilisers, which is easy to handle.

A major advantage of the invention is that it provides possibilities for recycling of practically all important nutrients in human urine, and the problems with storage and transportation of large amounts of fresh urine can thus be eliminated.

Thus, the present invention relates to a method for the recovery of nutrients from human urine substantially free of excrements and other debris characterised in that it comprises the following steps: A) the urine is concentrated

B) struvite crystallisation is initiated in the concentrated urine by adding MgO

C) the struvite crystals are separated from the solution. The invention may also comprise a further step, step D) , wherein nitrogen is recovered from the solution obtained in step C by ammonia adsorption, e.g. by using woUastonite or clinoptilolite.

The invention also relates to use of the struvite and/or the woUastonite or clinoptilolite produced as a fertiliser. The characterising features of the invention will be evident from the following description and the appended claims .

Detailed description of the invention

The reduction of the urine volume in step A) is preferably accomplished by the use of a freezing-thawing process. This can be done in two ways: either the total amount of the urine is freezed until approximately half of it remains liquid, or the total amount of the urine is completely freezed and then thawed until preferably at least 40% of the material can be collected as a liquid. The liquid part remaining after this freezing-thawing process is then treated further according to the follow- ing steps. The solid, frozen part consists mainly of water and nearly all, i.e. 70-80%, of the nutrients are contained in the liquid part. The frozen part can be discarded to the municipal waste water system.

It is possible to repeat the freezing-thawing proc- ess several times in order to further reduce the volume to be treated in the following steps.

After crystallisation the struvite is separated from the remaining liquid. This can be made in any known way, such as by filtration. The remaining liquid is purified and can be discarded to the municipal waste water system. However, it is preferable to further treat this remaining according to step D) of the method according to the invention. The solution obtained from step C) is then brought into contact with a suitable ammonium adsorbent, such as an ion exchange resin or other suitable substance. This may be done in any suitable way known to man skilled in the art. For example, the adsorbent may be provided as particles of a suitable size in a column, and the solution is then made to flow through the column. Ac- cording to the invention this ammonium adsorbent is preferably a suitable mineral, and most preferably woUastonite or clinoptilolite, or a combination thereof. WoUastonite (CaSi0₃) often occurs in nature as a common constituent of thermally metamorphosed impure limestone or in contact with calcareous sediments as a result of reaction of quartz and calcite (Deer W A, Howie R A and Zussman J (1997) WoUastonite, In: Single-chain silicates Volume 2A, The Geological Society, London 1997, pp 543-563) .

The most abundant form is the triclinic woUastonite with a fiber-like structure. During the formation of the woUastonite, volatile components as C0₂ create a large number of pores contributing to the porous macrostructure of the mineral. The unbalanced charge within the CaSi0 structure and the large porous macrostructure makes wol- lastonite a good cation adsorbent. In aqueous solutions the cation adsorption is mainly due to electrostatic attraction between electrically charged woUastonite surfaces and cations. This electrostatic adsorption is highly dependent on the ionic strength and the pH. Chemisorption may also occur depend- ing on the chemical composition of the adsorbent. This type of cation bonding is a slow process and may be irreversible (Lifvergren T (1997) Heavy metal leakage and adsorption Part II: Heavy metal adsorption to woUastonite concentrates, Gδteborg University, Dept . of Geology, Pa- per B65, pp 1-33) .

The use of woUastonite for removal of heavy metals from aqueous solutions was thoroughly investigated by Sharma and others (Sharma Y C, Gupta G S, Prasad G and Rupainwar D I (1990) Use of woUastonite in the removal of Ni(II) from aqueous solutions, Water, Air and Soil Pollution 49, pp 69-79) and Lifvergren (Lifvergren T (1997) Heavy metal leakage and adsorption Part II: Heavy metal adsorption to woUastonite concentrates, Gδteborg University, Dept. of Geology, Paper B65, pp 1-33) . WoUastonite as adsorbent for NH₄ ⁺ from human urine was not investigated before.

Clinoptilolite is a zeolite type of mineral of the heu- landite group and its structure consists of a three- dimensional framework of Si0 and A10₄ tetrahedra. The isomorphous replacement of Al³⁺ for Si⁴⁺ raises a negative charge in the lattice. This imbalance in net negative charge of the structure is corrected by exchangeable ca- tions like sodium, calcium or potassium ions. These cations can be exchanged with certain cations in solutions, like metal ions from industrial effluent waters (Curkovic L, Cerjan-Stefanovic S and Filipan T (1997) Metal ion exchange by natural and modified zeolites. Wat. Res. Vol. 31. No. 6, pp 1379-1382; Kayabali K and Kezer H (1998) testing the ability of bentonite-amended natural zeolite (clinoptilolite) to remove heavy metals from liquid waste. Environmental Geology 34 (2/3), pp 95-102) or ammonium from municipal and industrial wastewater (Baykal B B (1998) Clinoptilolite and multipurpose filters for upgrading effluent ammonia quality under peak loads. Wat. Sci. Tech. Vol 37, No. 9, pp 235-242; Baykal B B and Gu- ven D A (1997) Performance of clinoptilolite alone and in combination with sand filters for removal of ammonia peaks from domestic wastewater. Wat. Sci. Tech. Vol. 35. No. 7, pp 47-54; Lahav 0 and Green M (1997) Ammonium removal using ion exchange and biological regeneration. Wat. Res. Vol. 32. No. 7, pp 2019-2028; Oldenburg M and Sekoulov I (1995) Multipurpose filters with ion exchanger for the equalization of ammonia peaks. Wat. Sci. Tech.

Vol. 32. No. 7, pp 199-206; Olah J, Papp J, Meszaros-Kis A, Mucsi Gy and Kallo D (1989) Simultaneous separation of suspended solids, ammonium and phosphate ions from waste water by modified clinoptilolite. Karge H G and Weitkamp J (ed) : Zeolites as catalysts, sorbents and detergent builders 46, Elsevier Amsterdam 1989, pp 711-719; Jorgensen S E, Libor 0, Graber K L and Barkacs K (1976) Ammonia removal by use of clinoptilolite. Wat. Res. Vol 10, pp 213-224) . Clinoptilolite, having high porosity and a very stabile structure with large cation-exchange capacity, is useful in controlling plant nutrients in agricultural systems. NH⁺- and K-saturated clinoptilolite mixed with phosphate rocks provides slow-release of N, P, K and Ca in the soil (Lai T M and Eberl D D (1986) Controlled and renewable release of phosphorus in soils from mixtures of phosphate rock and NH₄-exchanged clinoptilolite, Zeolites Vol. 6, pp 129-132; Barbarick K A, Lai T M and Eberl D D (1990) Exchange fertilizer (phosphate rock plus ammonium- zeolite) effects on Sorghum-Sudangrass, Soil Sci. Soc. Am. J. 54, pp 911-916; Allen E R, Hossner L R, Ming D W and Henninger D L (1993) Solubility and cation exchange in phosphate rock and saturated clinoptilolite mixtures, Soil Sci. Soc. Am. J. 57, pp 1368-1374; Allen E R, Ming D W, Hossner L R and Henninger D L (1995) Modeling transport kinetics in clinoptilolite-phosphate rock systems. Soil Sci. Soc. Am. J. 59, pp 248-255; Dwairi I M (1998) Evaluation of Jordanian zeolite tuff as a controlled slow-release fertilizer for NH₄ ⁺. Environmental Geology 34 (1), pp 1-4; Dwairi I M (1998) Renewable, controlled and environmentally safe phosphorus release in soils from mixtures of NH₄ ⁺-phillipsite tuff and phosphate rocks. Environmental Geology 34 (4), pp 293-296).

The ion exchange process using NH₄ ⁺-selective clinoptilolite, in natural form and pretreated or activated form, was thoroughly investigated by Jorgensen and others (Jorgensen S E, Libor 0, Graber K L and Barkacs K (1976) Ammonia removal by use of clinoptilolite. Wat. Res. Vol 10, pp 213-224), and by Tomazovic and others (Tomazovic B, Ceranic T and Sijaric G (1996) The properties of the NH₄-clinoptilolite, Part 1-2, Zeolites Vol.16 pp 301- 312). Clinoptilolite as mineral sieve for NH₄ ⁺ from separated domestic wastewater streams e.g. human urine was not investigated before.

It is also possible to use other types of suitable zeolites . The method according to the invention is particularly suitable for treatment of human urine, and especially human urine that have been separated from excre- ments and other debris in urine-separating toilets. Urine from urine-separating toilets can either be treated at the location of the toilet or collected and by appropriate means transported to a treatment facility. It is of course also possible for example to perform step a) in connection to the toilet and steps B) and C) , and optionally also step D) , at another location.

The struvite and the nitrogen containing ammonium adsorbent, such as the woUastonite or the clinoptilo- lite, obtained from this method is very suitable for use as a plant fertiliser. In those cases it may be advantageous to formulate the struvite into particles of a suitable form, such as granules.

Struvite (magnesium ammonium phosphate hexahydrate, Mg (K, NH ) P04-6H₂0, also known as guanite, can precipitate as large single crystals, very small crystals, large curds or a gelatinous mass depending on the conditions. Struvite is known since long in the area of waste water treatment where it causes problems in the sludge handling systems at waste water treatment plants due to deposits of struvite on the equipment, said deposits being hard and, once formed, difficult to prevent and/or remove . Struvite is a valuable plant fertiliser since it contains a high percentage of readily available plant nutrients and also because its low solubility and "non-burning" property. Due to the low solubility it is possible to utilise struvite as a slow-release conditioner. It has been tested extensively in the USA and Germany with ex- cellent results. However all artificial struvite production so far has been based on animal dung or waste water sludge.

The invention will now be further explained in the following examples. These examples are only intended to illustrate the invention and should in no way be considered to limit the scope of the invention. 10

Brief description of the drawings In the examples, reference is made to the accompanying drawings on which:

Fig 1 is a graph illustrating an adsorption test per- formed on clinoptilolit (0.5 g) from NH₄C1;

Fig 2 is a graph illustrating an adsorption test performed on woUastonite (0.5 g) from NH₄C1.

Example 1 - concentration of the urine (step A) of the process)

In this example human urine from young and middle- aged people was used.

The concentration was performed by two different methods la - bath freezing-melting and lb - column freez- ing-melting.

la - bath freezing-melting

100 ml urine was placed in a beaker and this was then placed in a bath consisting of a saturated NaCl so- lution. The bath functioned as an isolator in a top- freezing process. The urine was frozen during 3.5 hours at -14°C. After this period the beaker contained a solid, frozen phase on top of a liquid phase. The solid phase, which constituted approximately half of the original urine volume, was separated from the liquid phase.

This process was repeated for another 5 samples. The pH and conductivity for the six liquid phases obtained after partial freezing were measured. The results are shown in table 1. Similar results were obtained when the total original urine volume was frozen and then thawed until approximately half of the original volume is liquid. The liquid part was then separated from the frozen part and analysed as above. The results are shown in table 2. 11

Table 1

Start temperature: 2 1°C Freezing temperature: -14 °C Measurement temperature: 21°C

Sample St.art Separated Sepaicated No. Para eters ice phase liquid phase (100 ml) (50 ml) (50 ml) pH ConducpH ConducpH Conductivity tivity tivity (mS/m) (mS/m) (mS/m)

1 7.6 1865.6 8.2 523.7 7.8 2836.6

2 7.6 1865.6 8.3 512.8 7.7 3262.1

3 5.6 2062.0 5.7 218.2 5.4 4604.1

4 5.6 2062.0 5.8 229.1 5.4 4233.1

5 5.7 1680.1 5.7 261.8 5.4 1767.4

6 5.7 1680.1 5.7 207.3 5.4 2171.1

Table 2

Start temperature: 21°C Freezing temperature: - 14 °C Measurement temperature: 21°C

Sample Start Separated Separated

No. Parameters Ice phase liquid phase

(100 ml) (50 ml) (50 ml)

PH ConducpH ConducPH Conductivity tivity tivity (mS/m) (mS/m) (mS/m)

1 7.6 1865.6 8.0 1832.9 7.9 3153.0

2 7.6 1865.6 8.0 1898.4 7.9 3043.9

3 5.6 2062.0 5.6 1189.2 5.4 4505.8

4 5.6 2062.0 5.6 1014.6 5.4 5084.1

5 5.7 1680.1 5.6 693.6 5.4 4036.7

6 5.7 1680.1 5.6 971.0 5.4 4571.3 12 lb - column freezing-melting

The freezing and melting in these experiments were performed and controlled in three vertical plastic columns (column A, column B, and column C) . The purpose was to observe the melting process and collect smaller fractions to analyse the concentration of ionic compounds. 450 ml of urine was used in each column.

In column A the urine was frozen immediately and was then held frozen. In column B the urine was frozen and then crushed into small and substantially homogenous ice grains, which were left to melt during approximately 30 minutes at room temperature (22°C) and were then refrozen. This was repeated twice, resulting in a snow-like sample. In column C the urine was treated in the same way as in column A, i.e. it was frozen immediately and was then held frozen.

The frozen urine in the three columns was then melted simultaneously and the melting processes for the urine frozen by the two different methods were compared. Twenty fractions, each of the volume 20 ml, were collected from column A and from column B during the melting, at 12-15 minutes intervals. The pH and conductivity for the different fractions were then determined. The results are shown in table 3.

From column C fourteen fractions were collected, each of the volume 20 ml, at 12-15 minutes intervals. The pH and the conductivity for the different fractions were then determined. The first, the sixth and the thirteenth fraction was also analysed with regards to total content of N (total N) and P (total P) , respectively. The results are shown in table 4. 13

Table 3

Start parameters : sample volume : 450 ml pH: 5.6

Conductivity (mS/m) : 1931 .1

Temperature ( °C) : 21

Freezing temperature (°C) - 14

Measurement temperature (°C) 22

COLUMN A COLUMN B

Fraction pH Conductivity Fraction pH Conductivity

No. (mS/m) No. (mS/m)

(20 ml (20 ml each) each)

1 5.4 7725.1 1 5.6 3894.6

2 5.4 5559.1 2 5.6 3873.2

3 5.5 4150.6 3 5.6 4182.6

4 5.6 2155.3 4 5.7 2955.6

5 5.7 2016.6 5 5.7 2272.7

6 5.7 2230.0 6 5.7 2390.1

7 5.7 1781.9 7 5.8 1589.8

8 5.7 1579.2 8 5.8 1291.1

9 5.7 1323.1 9 5.8 1056.3

10 5.7 1077.7 10 5.8 832.3

11 5.7 1216.4 11 5.8 629.5

12 5.7 714.9 12 5.7 554.8

13 5.6 586.9 13 5.7 522.8

14 5.5 298.8 14 5.7 234.7

15 5.5 181.4 15 5.7 149.4

16 5.5 160.1 16 5.8 96.0

17 5.7 106.7 17 5.8 21.3

18 5.8 64.0 18 5.7 6.4

19 5.8 53.4 19 5.6 2.1

20 5.8 21.3 20 5.5 1.6 14

Table 4 Start parameters: sample volume: 450 ml pH: 6.1

Conductivity (mS/m) : 1547.2

Temperature (°C) : 22

Freezing temperature (°C) : - 14

Measurement temperature (°C) : 22

COLUMN C

Fraction No. pH Conductivity total P total N (20 ml each) (mS/m) (mg/1) (mg/1)

1 5.6 8834.8 165 2700

2 5.8 6209.9 - -

3 5.9 4716.1 - -

4 5.9 2635.5 - -

5 6.0 1845.9 - -

6 6.0 1547.2 28.5 425

7 6.0 1280.4 - -

8 6.0 1323.1 - -

9 6.0 1035.0 - -

10 6.1 832.3 - -

11 6.1 800.3 - -

12 6.1 565.5 - -

13 5.8 501.5 15.5 230

14^* 5.7 96.0 - - Fraction No. 14 had a total volume of 190 ml because the results from columns A and B showed that the second half of the total volume had very low conductivity values.

The results show that a considerable concentration of the important nutrient compounds can be obtained by freezing and melting of the urine. The results from the bath freezing-melting method show considerable differences in the conductivity values of the ice-bulk part of the sample compared to the liquid part of the sample. 15

Over 75% of the electrolytes, i.e. the nutrients etc., in the urine was comprised in the liquid phase.

In the column freezing-melting experiments a more detailed study was made of the fractionated urine. The results obtained for column A and for column B were similar, although the results could favour the method used for column A since it is easier to handle.

The conductivity values show that the main part of the ionic compounds are collected in the first melt-out or 80 ml from the total volume of 450 ml. More than

70 - 75% of the electrolytes were collected in the first fractions. The nutrients, such as nitrogen and phosphorous, are also mainly concentrated to those fractions. The test results for the total amounts of N and P show very high levels of nitrogen and phosphorous in the first fraction. In the sixth fraction the levels were so low that they were comparable with treated domestic water.

Example 2 - crystallisation of the urine (step B) of the process)

A series of experiments were performed. 98% pure MgO was added to fresh human urine and concentrated urine obtained after freezing-melting according to example 1, respectively, contained in test tubes. The normal pH of human urine is normally such that most of the phosphate in the urine is present as the ions H₂P0₄ ^~ and HP0₄ ^2~. When MgO is added the pH increases and the phosphate equilibrium shifts in the direction of P0₄ ^3~. The P0₄ ^3" ions forms together with Mg²⁺ and NH_⁺ rap- idly small, crystalline, needle shaped structures on the walls of the test tube. The crystals were formed both in the untreated urine and in the concentrated urine. The Mg:N:P ratio for struvite formation is 1.71:1:2.2, based on molar weights, which means that the crystallisation is proportional to the N and the P concentrations. The crystal structures were studied in a scanning electron microscope (SEM) , by electron dispersive spectroscopy (EDS) , 16 and by X-ray crystallography. It was established that the crystals consisted mainly of struvite.

Example 3 - nitrogen uptake by an ammonia adsorbent (step D) of the process)

In order to get well defined concentrations of NH₄, synthetic human urine was prepared according to conven^¬ tional urological research (Griffith D P, Musher D M and Itin C (1976) Urease, the primary cause of infection- induced urinary stones, Investigative Urology Vol 13, No. 5, pp 346-350). Synthetic human urine contains 11 solutes, each in a concentration equivalent to the average concentration found in 24-hr period in the urine of normal healthy men. Two types of experiments were performed, a) adsorp^¬ tion from synthetic urine and b)a combination of struvite precipitation and ammonium uptake by woUastonite or clinoptilolite.

The ammonia adsorbents used in this example were: • Natural clinoptilolite from Mad, Hungary; the chemical composition of this mineral is (weight%)

Component

Si0₂ 62 . 43

A1₂0₃ 10 . 95

Mo0₃ 0 . 11

FeO 0 . 12

MgO 0 . 7 9

CaO 3 . 17

Na₂0 0 . 13

K₂0 2 . 74 17

WoUastonite from Hulta East, Sweden; the chemical composition of this mineral is (weight!):

Component 0. o

Si0₂ 63 . 16

A1₂0₃ 4 . 20

Fe₂0₃ 1 . 12

MnO 0 . 26

CaO 31 . 12

Na₂0 0 . 12

K₂0 2 . 62

P₂0₅ 0 . 01

The adsorbents were not pre-treated or activated in any way, just crushed and sieved for distinctive grain size classifications necessary for the experiments. Grain sizes of 125-250 μm were used. Four different tests were performed for each adsorbent. The contact time between the solution obtained after struvite crystallisation and the adsorbent was either 5 or 10 minutes, as indicated in tables 5 and 6 below.

The results from ammonia adsorption from synthetic human urine after struvite precipitation (b) are given in table 5 for woUastonite and in table 6 for clinoptilo^¬ lite. The NH₄ uptake was determined from the NH content remaining in the solution. The values of the uptake given in the table are weight percentage. From the tables it is evident that natural clinoptilolite as well as woUasto^¬ nite can be used as excellent adsorbents for ammonium from ammonium rich solutions, including human urine. Table 5

Test no. Contact time % NH₄ uptake (min) from solution

1 5 64

2 10 64

3 10 74

4 10 74

Table 6

Test no. Contact time % NH₄ uptake (min) from solution

1 5 67

2 10 75

3 10 79

4 10 80

Additional adsorption experiments were performed with different concentrations of NH₄ using NH₄C1 solutions and different grain size of the two adsorbent, as shown in figures 1 and 2. The results, illustrated in the figures, show similar adsorption as in previous experiments .

The ammonium uptake is a function of grain size, ion concentration and contact time. There is a trend of higher adsorption with smaller grain size and more so at a low ammonium content. The results show an overall good adsorption of ammonium from low concentrated solutions, with 70-80 % uptake for the clinoptilolite, approximately 50 % for the woUastonite and 50-60 % for the mixed zeolite.

In many of the experiments an initial high adsorption was followed by a minimum after a few minutes. The phenomenon is not very important for the total adsorption but a possible explanation could be ion exchange proc- esses du to varying proportions of NH₄ ⁺ and H⁺ .

Claims

19 CLAIMS

1. A method for the recovery of nutrients from human urine substantially free of excrements and other debris and characterised in that it comprises the following steps :

A) the urine is concentrated

B) struvite crystallisation is initiated in the concentrated urine by adding MgO C) the struvite crystals are separated from the solution.

2. A method according to any one of the claim 1, wherein step A) is accomplished by partially freezing the urine and separating the concentrated liquid urine.

3. A method according to claim 1 or 2, wherein step A) is accomplished by first completely freezing the urine, then partially thawing it, and separating the concentrated liquid urine.

4. A method according to any one of claims 1 - 3, wherein step A) is repeated at least once in order to further concentrate the urine.

5. A method according to any one of claims 1 - 4, wherein the urine is human urine collected from urine- separating toilets.

6. A method according to any one of claims 1 - 6, wherein the struvite after separation from the solution in step C) is formulated as granules.

7. A method according to any one of the claims 1 - 6, further comprising a step D) , performed after step C) , wherein nitrogen is recovered from the solution obtained in step C) by ammonia adsorption.

8. A method according to claim 7, wherein the ammonia adsorption is performed through use of woUastonite or clinoptilolite .

9. The use of struvite produced by the method accord- ing to any one of claims 1 - 8 as a fertiliser. 20

10. The use of ammonia containing woUastonite or clinoptilolite obtained according to claim 8 as a fertiliser.