Presentation on theme: "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."— Presentation transcript:
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 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%
Incineration - nutrient transformations N: All is lost – most as N 2, but some as NO x P: Partly fixed – availability probably % of that in chemical fertiliser K: high availability S: lost to air as SO x 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 – 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(NH 2 ) H 2 O 2NH 3 + H 2 CO 3 – NH 4 + +OH - NH 3 (aq)+ H 2 O pKa=9.25 at 25°C – NH 3 (aq) NH 3 (g) – Upon addition pH reach 9 the higher the pH, the more NH 3 (g), the more toxic
Ammonia distribution as %NH 3 The distribution depends on Temperature pH
Ammonia treatment Closed vessel required Temp. >20°C – High effect on all pathogens esp with NH 3 >50mM Temp. <20°C – Low effect on Ascaris and viruses – High effect on bacteria No effect on spore formers
Ammonia treatment - in praxis Lower dosage longer time needed for treatment – 0.6% N-NH 4 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 - nutrient transformations N: left in initial form NH 3 = 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 Urea ammonium/ammonia CO(NH 2 ) H 2 O 2 NH OH - + CO 2 pH 6 – – 9.4 – NH 3/4 pKa=9,25 at 25°C Precipitation as metal phosphates (in pipe and tank) NH 4 + +OH - NH 3 (aq)+ H 2 O NH 3 (aq) NH 3 (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)
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 – n t =n 0 [f l ] 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