Chapter 4 module 2 Treatment of excreta for safe reuse

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Chapter 4 module 2  Treatment of excreta for safe reuse Powered By Docstoc
					      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
                                      • Quick and simple
                                        method
   Chimney                            • Faeces are applied in
                                        the stove
                                      • Require external fuel
                                      • Is quick and gives a
Removable top, through which faeces
are fed into the incinerator


                                        product, the treatment
  Access door through which the stove is
  passed and locked inside after firing
                                        of which can be
                                        verified by the eye
           Incineration - function
• To avoid odour,
  moisture should not be
  above 10%
• Large amounts of non-
                                   Chimney




  organic material calls
  for additional fuel           Removable top, through which faeces


• Very efficient pathogen
                                are fed into the incinerator




  reduction                       Access door through which the stove is


• Mass of faeces reduced
                                  passed and locked inside after firing




  by more than 90%
Incineration - nutrient transformations
• N: All is lost – most as    • Ash is a concentrated K
  N2, but some as NOx           fertiliser containing
• P: Partly fixed –             large amounts of P
  availability probably 30-   • Can be reused as
  70% of that in chemical       amendment in toilet
  fertiliser
• K: high availability
• S: lost to air as SOx
                  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
                                                  9
                                                  8

    pathogens esp with NH3                        7




                             Concentration(log)
                                                  6
    >50mM                                         5
                                                                                                 Phage
                                                                                                 E. coli
                                                                                                 Clostridia
• Temp. <20°C
                                                  4
                                                                                                 Enterococci
                                                  3


  – Low effect on Ascaris and
                                                  2
                                                  1

    viruses                                       0
                                                      0   10   20       30        40   50   60

  – High effect on bacteria                                         Time (days)



• No effect on spore formers
      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            • For fodder/non-food
  consumption            – T<20°C
  – T>20°C                  • 1% urea
     • 2% urea              • 12 weeks
     • 8 weeks           – T>20°C
  – T>30°C                  • 1% urea
     • 1.5%urea             • 1 week
     • 4 weeks           – 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                          • Con
  – Increases fertilising        –   Corrosive
    value                        –   Smelly
  – High content of organics     –   Require closed container
  – No mixing necessary          –   Risk for ammonia
    after initial mix                emission at application
  – No risk for regrowth
           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
• Ureaammonium/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
                          Albumin
  – Heat transport        watercont aprox cog T
                                 50          56
  – Albumin p164 (haug)          25          76
                                 15          96
                                  5         149
                                  0         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

				
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posted:9/15/2012
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