Chapter 4 module 2: Treatment of excreta for safe reuse

How should urine and faeces be treated for safe handling and reuse in crop cultivation? How can

organic material from households be co-treated?

Incineration

Chimney

Removable top, through which faeces are fed into the incinerator

Access door through which the stove is passed and locked inside after firing

• Quick and simple method

• Faeces are applied in the stove

• Require external fuel• Is quick and gives a

product, the treatment of which can be verified by the eye

Incineration - function

• To avoid odour, moisture should not be above 10%

• Large amounts of non-organic material calls for additional fuel

• Very efficient pathogen reduction

• Mass of faeces reduced by more than 90%

Chimney

Removable top, through which faeces are fed into the incinerator

Access door through which the stove is passed and locked inside after firing

Incineration - nutrient transformations

• N: All is lost – most as N2, but some as NOx

• P: Partly fixed – availability probably 30-70% of that in chemical fertiliser

• K: high availability• S: lost to air as SOx

• Ash is a concentrated K fertiliser containing large amounts of P

• Can be reused as amendment in toilet

Storage of faeces

• Biological degradation during storage

• Final product look like soil• Risk for pathogenic

survival• Current recommendation

– >20°C >1 year– <20°V >2 years– Restriction in usage

Ammonia treatment

– Uncharged ammonia is toxic to all organisms

• animals, plants, bacteria, viruses and parasites

– The ammonia distributes by itself through the material

– The ammonia can be added as urea or as ammonia(aq)

Ammonia treatment

– Urea is enzymatic degraded to ammonia

– CO(NH2)2 + 2 H2O 2NH3 + H2CO3

– NH4++OH- NH3(aq)+ H2O

• pKa=9.25 at 25°C

– NH3(aq) NH3(g)

– Upon addition pH reach 9

• the higher the pH, the more NH3(g), the more toxic

Ammonia distribution as %NH3

• The distribution depends on

• Temperature• pH

Ammonia treatment• Closed vessel required • Temp. >20°C

– High effect on all pathogens esp with NH3 >50mM

• Temp. <20°C – Low effect on Ascaris and

viruses– High effect on bacteria

• No effect on spore formers

0

1

2

3

4

5

6

7

8

9

0 10 20 30 40 50 60

Time (days)

Con

cent

ratio

n(lo

g)

PhageE. coliClostridiaEnterococci

Ammonia treatment - in praxis

• Lower dosage longer time needed for treatment– 0.6% N-NH4 Dr-

salmonella=6d• Temperature

– Higher temperature faster die-off

– Main effect on enzymatic activity

• In large scale ammonia cheaper than urea and more efficient

Ammonia treatment - recommendations

• For human consumption– T>20°C

• 2% urea• 8 weeks

– T>30°C• 1.5%urea• 4 weeks

• For fodder/non-food– T<20°C

• 1% urea• 12 weeks

– T>20°C• 1% urea• 1 week

– T>30°C• 1%urea• 1 week

Ammonia treatment - nutrient transformations

• N: left in initial form NH3 = high availability– Buffered in soil to pH~7 = no toxicity

• P: Probably similar to chemical fertiliser• K: high availability• High content of organic substances• Ammonia treatment gives a fertiliser with very

high fertilising value

Ammonia treatment

• Pro– Increases fertilising

value– High content of organics– No mixing necessary

after initial mix– No risk for regrowth

• Con– Corrosive– Smelly– Require closed container– Risk for ammonia

emission at application

Urea treatment in use

• Peepoo– Single use– Biodegradable– Self sanitising toilet

• Contain 4g urea• 4 weeks T>20°C safe to

use• 2 weeks T>30°C safe to

use

Photo: Camilla Wirsen (www.peepoople.com)

Storage of urine

– Approx. 90% of N in fresh urine is urea

– Enzymatic degradation to ammonia

– pH increase from 7 to 9– Pathogens inactivated

by ammonia– Sanitation faster at high

temperature and high concentration.

Storage of urine• Ureaammonium/ammonia• CO(NH2)2 + 3 H2O 2 NH4

+ + 2 OH- + CO2 • pH 6 – 7 8.8 – 9.4

– NH3/4 pKa=9,25 at 25°C

• Precipitation as metal phosphates (in pipe and tank)

• NH4++OH- NH3(aq)+ H2O

• NH3(aq) NH3(g)• Minimum ventilation!!

Urine storage recommended times

• Faecal contamination main source of pathogens

• Storage >20°C 6 month no restrictions in use

• Storage <20°C 2 month not to crop consumed raw

Urine storage - nutrient transformations

• N: Plant availability of N in urine is very high, similar to chemical ammonium fertiliser

• P: Similar availability as chemical fertiliser• K: Similar availability as chemical fertiliser• Urine is a fertiliser with uniquely high

availability for being a biological fertiliser

Hygiene and composting

• Main effect from heat– Require T>50°C– WHO guidelines 1 week

• Other effects– Stablilisation of material

• No easy available organics

• Competing microbiota

• Risk for regrowth

Heat inactivation

• Most common treatment• Only heat, removes all available organisms

– Risk for re-growth of unwanted bacteria. First on site wins

• Combination of heat and stabilisation from removal of available carbon is better

• Moisture result in faster inactivation– Heat transport– Albumin p164 (haug)

Albuminwatercont aprox cog T

50 5625 7615 96

5 1490 165

Rule of thumb – hygiene treatment

• Reactor turn 3 times in high temp• Pile or windrow turn 5 times in high temp• Calculation of ternings for hygiene

– nt=n0[fl]N+1

• Nt= number of surviving organisms• N0=number of initial organisms• Fl= fraction in cold zone• N=number of turnings

Anaerobic digestion

• 1-3 log10 reduction• Longer HRT and MRT

higher reduction• Sedimentation in non-

mixed systems (parasites)

• Additional treatment required– Heat– Ammonia