Urine diversion

Question 1

What is the composition of urine?

Answer 1

o Water 95%
o Urea
o Inorganic salts
o Creatine
o Ammonia
o Blood breakdown
o Most relevant: nutrients and organics
o Micropollutants
 Depends on diet and medication
o Pathogens – if cross-contamination

Question 2

Describe the reaction occuring with urea

Answer 2

• Urea is rapidly hydrolyzed to ammonia and carbon dioxide as soon as urine enters the non-sterile environment, leading to the release of ammonia and bicarbonate and causing a pH increase
  o -> precipitation processes -> decrease in phosphorus concentration of around 30% and a nearly complete removal of calcium and magnesium ions

Question 3

Why should we do urine diversion

Answer 3

o Water pollution control – less eutrophication
 Sustainable development goals
o Recycling of nutrients
o Energy recovery (e.g. biogas from less liquid fractions)
o Increases capacity in WWTP – decrease in nutrient load, lowering energy demand and volume needed to be treated
o Food security

Question 4

What are the reasons for stabilisation of urine?

Answer 4

 (i) degrades organic matter, thus preventing malodor, (ii) prevent volatilization of NH3 and (iii) prevent unwanted precipitation, which can result in operational problems such as pipe clogging or membrane fouling

Question 5

How can stabilization of urine be done?

Answer 5

 Biological processes
* Nitrification: biological oxidation of ammonia to nitrate
 Chemical processes
* Acid dosage
* Base dosage
 Electrochemical processes
* Urine stabilization in electrolysis cells (EC)
* Oxidation with free chlorine

Question 6

Describe nitrification of urine

Answer 6

• Nitrification: biological oxidation of ammonia to nitrate
  o Ammonia oxidizing bacteria (AOB) mediate the oxidation of ammonia to nitrite
  o Nitrite oxidizing bacteria (NOB) mediate the oxidation of nitrite to nitrate
  o Reduces pH through nitrification. Removes most organic matter, including malodorous compounds.
  o Slow reaction

Question 7

Describe acid and base dosage of urine

Answer 7

• Chemical stabilization of urea inhibits the enzyme responsible for its degradation and prevents a pH-increase in the first place.
• Acid dosage
  o Neutralization of stored urine requires large amounts of acid due to the high alkalinity of urine after urea hydrolysis.
  o More economic urea stabilization in fresh urine weak acids like acetic acid, citric acid, and vinegar could be used for the inhibition of urea hydrolysis
• Base dosage
  o Chemicals for reaching a pH above 11, necessary for urease inhibition in urine
  o Stability of pH value obtained? CO2 adsorption from the air critical pH decrease

Question 8

Describe the electrochemical processes to stabilize urine

Answer 8

• Used to stabilize urine by removing organic substances, preventing urea hydrolysis or inactivating microorganisms
• Urine stabilization in electrolysis cells (EC)
  o indirect oxidation with chlorine is the main mechanism for removal of organics and nitrogen compounds, and sometimes, NaCl was even added to boost the oxidation process
• Oxidation with free chlorine
  o Fast and efficient removal process for organics, nitrogen compounds, pharmaceuticals and pathogens
  o Chlorinated by-products (CBPs) – hazardous
  o High energy demand

Question 9

How can nutrient recovery be done?

Answer 9

 By volume reduction
* Drying
* Distillation
* Forward osmosis
* Membrane distillation
* Electrodialysis
 Targeted nutrient recovery
* Ammonia stripping
* Struvite precipitation

Question 10

Describe drying, distillation, forward osmosis, membrane distillation and electrodialysis

Answer 10

• Drying:
  o Optimizing high temperatures and air flow rates
  o Alkaline stabilized urea becomes chemically unstable at temperatures above 40°C
• Distillation:
  o Energy recovery is possible
  o Small loss of nitrogen is contained in the distillate and therefore not emitted to the atmosphere
• Forward osmosis
  o The rejection of nitrogen compounds and the water flux increase with increasing concentration of the draw solution
• Membrane distillation
  o the driving force is the vapor pressure difference produced by the temperature difference across a hydrophobic membrane, only volatile compounds can pass
• Electrodialysis
  o Used to produce a concentrated solution of all ions in urine. An electric field and at least one pair of an anion exchange membrane (AEM) and cation-exchange membrane (CEM) is needed
  o Effective removal of micropollutants compared to distillation

Question 11

Describe ammonia stripping

Answer 11

 Removing N in the form of ammonia instead of converting it
 Ammonia has to be present as NH3
 Stored urine with high ammonia concentrations and high pH
 High temperature
 Pushing the acid-base equilibrium towards volatile free ammonia
 Prior P removal to prevent clogging problems
 Large scale of application required

Question 12

Describe struvite precipitation

Answer 12

 Transfer dissolved compounds into a solid phase
 Recovering both ammonia and phosphate (also K) from urine
 Operating pH range is 8.0 to 9.5; process efficiency increases as the pH rises within this interval
 Addition of magnesium oxide to produce the crystal magnesium-ammonium-phosphate (MAP) or struvite.

Question 13

How can nutrient removal be conducted?

Answer 13

 Biological (heterotrophic) denitrification
 Anaerobic ammonium oxidation (Anammox)
 Electrochemical N removal

Question 14

Describe biological (heterotrophic) denitrification

Answer 14

• Denitrification is a microbial facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products
• Biological denitrification requires previous complete nitrification or nitrification
• Electron acceptor is nitrite or nitrate, instead of O2
• Organic substrate needed
• Final product is nitrogen gas (N2)

Question 15

Describe anaerobic ammonium oxidation (Anammox)

Answer 15

• Denitrification
  *Without organic material
• Mediated by a group of chemo-litho-autotrophic bacteria called anammox bacteria (anaerobic ammonium oxidizing bacteria, AMX)
• These bacteria use ammonia as electron donor and nitrite as electron acceptor
• Very specific environmental conditions: slow growth, sensitive to O2, irreversibly inhibited by elevated nitrite concentrations

Question 16

Describe the removal of pathogens and organic micropollutants

Answer 16

 Pathogen inactivation or separation from the nutrients has mainly been reported, or can be assumed, as a side-effect of a main urine treatment process e.g. distillation at high temperatures, alkaline drying
 Unspecific removal of organic micropollutants, e.g. activated carbon, ozonation
 Separation of nutrients from micropollutants, e.g. struvite precipitation, nanofiltration
 Removal of micropollutants, e.g. advanced oxidation processes, adsorption, electrochemical processes

Question 17

Describe treatment technologies - from unready to ready

Answer 17

o Ozonation
o Membranes
o Electro-chemical systems
o Adsorption
o NH3-stripping
o PO4- precipitation
o Nitrification
o Distillation (ready)
o Alkaline dehydration (ready)

Question 18

Describe complete recovery of urine

Answer 18

o Instead of removing nutrients – water is removed and nutrient loss minimized.
o E.g. by distillation
o Urine must be stabilized first – otherwise ammonia volatilizing, causing pollution and odor

Question 19

What is the Vuna process?

Answer 19

o Pilot in Switzerland
o Process
 Nitrification stabilizes the nitrogen in the urine, prevents nutrient losses and malodors
 Distillation separates the water and produces a concentrated nutrient solution
o Complete nutrient recovery
o Instrumentation and process control
o End product: Distillate (3-5% of initial volume) which can be reused for toilet flush water, irrigation, battery water

Question 20

How does the Vuna process system look like?

Answer 20

 1.Urine storage tank: Attenuates fluctuations and ensures complete urea hydrolysis (the nitrifying bacteria require ammonium as a substrate, because they cannot degrade urea).
 2.Nitrification column: An aerated tank containing the nitrifying bacteria mainly on biomass carriers.
 3.Intermediate storage tank: Stores the (partially) nitrified urine before it is distilled.
 4.Vacuum distiller: Concentrates the urine and separates distilled water.
 5.Final product storage and recycling: holds the concentrated nutrient solution and/or distilled water or recycles the water.

Question 21

What is the Sanitation 360 system?

Answer 21

o Dry nutrient rich urine-based fertilizer (Sweden)
o Urine is collected during excretion and diverted into a cassette that contains, treats and concentrates the urine. The toilet can be any urine-diverting toilet (flush or dry).
o Process
 Stabilizing the urine by increasing the pH to >10 by use of alkaline substrate (or anion exchange), retaining: >80% of the nitrogen, 100% of the phosphorus and potassium
 Removing 95% of the mass through convective air-drying at temperatures of 40-60 degrees.
o Substrates
 wood ash, biochar, lime, MgO, Ca(OH)2
o One cassette – 250 L urine.
o End product: Full cassette with dry urine-based fertilizer – for direct use on-site or transport to centralized service station

Question 22

What are some considerations for urine collection, treatment and reuse

Answer 22

o Liquid vs dry fertilisers
 Dry fertiliser needs moisture and heat to break down, but it’s cheaper and it is good for building up the soil
 Liquid fertiliser is ready for application and already set to go, can be applied early in the season when you need to increase the fertility quickly
o Net energy use
o On-site set-up vs larger scale
o Technical challenges
o Users acceptance
o Transport of substances, logistics

Question 23

What are some barriers for implementation of urine diversion?

Answer 23

o Immature technology
o Conventional infrastructure
o Users acceptance
o Weak national advocacy coalition
o Risk aversion
o Difficulties organizing the system
o Strong mixed sewage regime in urban areas
o Recovered nutrients have low economic values

Question 24

How do you choose the nitrogen removal technology?

Answer 24

The choice of a biological nitrogen removal process depends on the availability of
biodegradable organic substrate. Nitritation/anammox is recommended for nitrogen removal from urine and anaerobically digested blackwater, because both solutions have too little organic substrate for complete heterotrophic denitrification.