Presentation on theme: "Chapter 4 module 3 Treatment of faeces by composting How should urine and faeces be treated for safe handling and reuse in crop cultivation? How can organic."— Presentation transcript:
Chapter 4 module 3 Treatment of faeces by composting How should urine and faeces be treated for safe handling and reuse in crop cultivation? How can organic material from households be co-treated? Goal: After the lecture the student should know the principles, prerequisites and main characteristics, properties, advantages and disadvantages of composting of faeces of kitchen waste.
What is composting? Oxygen Organics: energy nitrogen (N) phosphorus (P) potassium (K) sulphur (S) etc. Sun shine Compost: nitrogen (N) phosphorus (P) potassium (K) sulphur (S) etc. Gas emissions Carbon dioxide ammonia Odours Heat energy
The compost process? Organics: energy nitrogen (N) phosphorus (P) potassium (K) sulphur (S) etc. Compost: nitrogen (N) phosphorus (P) potassium (K) sulphur (S) etc. Gas emissions Vapour Carbon dioxide Ammonia Odours Heat energy Oxygen Water/ moisture pH Microbes: bacteriar, fungi
Degradation – compost – digestion Composting C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + bacteria E= -3880 KJ/mol Energy – appr. half to heat, half to bacteria Digestion C 6 H 12 O 6 3 CO 2 + 3 CH 4 + few bacteria E= - 405 KJ/mol Energy – almost all remains in the biogas (-3475 KJ/mol sugar)
Optimal conditions – moisture/oxygen Oxygen Water/ moisture Water/oxygen – optimal moisture Water – bacteria thrive in 100% Oxygen – compost bacteria are aerobic (>5% oxygen in pores) Optimal moisture – as squeezed sponge Too much moisture Pores waterlogged – no aeration, anaerobic, acidic, smelly Action – add dry structure material & mix Too little moisture Slow degradation – low temperature Action – add water & mix
Optimal conditions - energy Energy Sources – fast release: Carbohydrates, proteins, fats. Lignin & cellulose slow release Food waste - rich in fast energy, Faeces: less energy, slower release Woody waste slow release Too much fast energy Oxygen – goes easily anaerobic acidic and/or smelly Action – add structure material & mix Too little fast energy Too low temperature Action – add food waste and/or insulate
Optimal conditions – C/N-ratio C/N-ratio Sources of C: the organics of the substrate. Sources of N: both organic nitrogen (protein) and inorganic nitrogen, e.g. NH 4 +, in the substrate C/N > 30 Process – might be slowed down due to lack of N for bacteria Action – add N, e.g. faeces or urine & mix C/N < 15 Process – might smell ammonia – excessive losses of ammonia Action – add C, e.g. park waste & mix
Optimal conditions - pH thermophilic bacteria prefer pH > 6.5 Too high pH (lots of lime) Slow degradation – low activity of bacteria Action – add food waste and/or wait Too low pH (lots of food waste) Slow degradation Action – wait (especially if the compost is small) or add ash/lime
Optimal conditions – temperature Temperature – for sanitation >50ºC, for fastest degradation approx. 55ºC Too low temperature Sanitation not ensured Action – insulate and/or add fast energy
Compost heat & scales Heat production: 20.7 kJ/g degraded Temperature increase - Heat capacity Surface cooling: -temperature difference -insulation Airflow 100% rel. humidity Good sanitation Good insulation needed
Insulation crucial Theoretical heat loss Heat transfer coefficient: – non-insulated: 13 W C -1 m -2 – Insulated 10cm: 0.053 W C -1 m -2 so t he heat resistance was 25 times larger for the insulated box.
Composts – small scale These small composts reach high temperatures, thanks to good insulation
Composts - medium scale These medium size windrow composts reach high temperatures. For good sanitation they ought to be covered by some insulating material, e.g. straw.
Composts - large scale Insulated large scale compost with mechanical aeration
Compost and plant nutrients N: Protein (org. N) + NH 4 + 10-50% loss & of remainder 90-95% is humus (organic N) + a few % NH 4 + + a few % NO 3 - – Usually 10-50% of N is lost to air – Low availability of N left in compost 10% first year and 20-30% in total over the years. K: K+, high availability, water soluble and thus large risk for loss with leachate Composting decreases the amount of N, due to losses, and the remaining N has low availability
Composting - disadvantages Difficult to get the whole compost hot – usually cold at air intake mixing several times needed for sanitation Additional energy rich substrates, e.g. kitchen waste, can be needed to reach above 50°C A large proportion of the nitrogen is lost (often around 50%, more if urine has not been well diverted) Mixing - handling - is needed also before sanitation hygiene risk
Summary - Why compost? To sanitise 50ºC required insulation To eliminate visual contaminants (toilet paper etc) To decrease C/N-ratio - to eliminate risk for N fixing To homogenize – simplifes handling To produce good humus – high doses can be used To decrease the amounts to handle – Organic matter is degraded by 30-60% – Finished compost has a high dry matter content (50-70%)