Course 2 Unit 6Part a

Teacher Mariska Ronteltap

m.ronteltap@unesco-ihe.org

Introduction to composting

Course 2 Unit 6Introduction to composting

Part A – Fundamentals and design considerationsPart B – Vermicomposting (in separate file)Part C – Engineered composting toilets (in separate file)Part D – Examples and case studies (in separate file)

This unit deals with which part of the sanitation system?

Part E

House-hold toilet

Part A Part B Part C Treatment & storage

Part D

Re-use in Agriculture

Collection & transport

Transport

Household toilets, but can also include showers, bath tubs, sinks

Urine, faeces, greywater transport (road-based vehicles in combination with pipes)

Treatment for faeces and greywater, storage for urine

Transport of sanitised urine and faeces by truck; treated greywater transport by pipes

Sale of fertiliser (sanitised human excreta); irrigation with treated greywater

Crop grown with ecosan products as fertiliser (closing the loop)

The composting process is used to sanitise faeces (either in composting toilets or in a centralised composting system) with the aim to produce an end product suitable for reuse in agriculture Pathogen kill is achieved through the raised temperatures in the compost heap, which are sustained for a certain period of time

Preamble about composting in Europe

Composting is widely used in Europe (Germany being the leader*) to treat organic solid waste, which is collected separately from households in many municipalities – see next slide

There is a vast amount of know-how on composting as a secondary treatment process (semi-centralised or centralised), with using organic solid waste or sewage sludge as an input material

Challenges for “us ecosan people”:- We have to harness this knowledge and apply it to faecal

matter as an input material- Devise simple low-cost processes that can be used at

community level

* In Germany there are currently 485 composting plants with RAL quality assurance, and in total about 800 composting plants which treat organic solid waste (no faeces) - data from Annette Ochs, 23 April 2007

Extent of separate biowaste collection in Europe

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

IT DE FR UK PL ES NL HU BE CZ SE AT PT EE SK DK FIN NO GR IE LT LV SL CY LU MT

MtPotential of source separated biowaste and green waste

EU 25 + NO [ 113 Mio tons ]

Biowaste and green waste separetly collected in 2005 EU 25 + NO [ 24 Mio tons = 21% ]

Germany (DE) has the highest collection level in Europe (“EU 25 + NO” means 25 European member states plus Norway (now there are 27)).Treatment predominantly by composting or anaerobic digestion

How is the “biowaste” (organic kitchen and garden waste) collected? (remember this picture from Course 2 Unit 3 Storage and Transport)

Paper Bin for biowaste (for composting) Other waste

For example at my house in Ede, the Netherlands: kerbside collection (fortnightly for the brown bin)

Amount of biowaste treated in Germany in composting plants (in million tons)

0

1

2

3

4

5

6

Source: Bundesgütegemeinschaft Kompost e.V., 19. Kasseler Abfallforum, April 2007(obtained via Annette Ochs)

Course 2 Unit 6

Development of source separation and composting in Europe

Source: European Compost Network (ECN), http://www.compostnetwork.info/index.php?id=10

Note: the article did not state for which year this situation was (it might have changed by now)

Part A: Fundamentals and design considerations

Course 2 Unit 6

Compost (from www.wikipedia.org)

Note: “compost” is a popular term which is used for all sorts of materials even if they are not really true compost (e.g. Faeces that have been just air-dried) – be careful.

Course 2 Unit 6

What is “compost” and “composting”?

Compost is the aerobically decomposed remnants of organic materials (those with plant and animal origins). Compost is used in gardening and agriculture as a soil amendment, and commercially by the landscaping and container nursery industries. It is also used for erosion control, land/stream reclamation, wetland construction, and as landfill cover (see compost uses). Compost is also used as a seed starting medium generally mixed with a small portion of sand for improved drainage.

Composting is the process of producing compost through aerobic decomposition of biodegradable organic matter. The decomposition is performed primarily by aerobes, although larger creatures such as ants, nematodes, and oligochaete worms also contribute.

Source: www.wikipedia.org

Which materials can be a substrate (input material) for composting?(in order of importance for ecosan concept)

1. Dried faeces (from UDD toilets)*

2. Faecal sludge

3. Organic solid waste (kitchen residue)

4. Animal waste / agricultural waste

5. Sludges from centralised wastewater treatment plants (i.e. this includes faeces)

Materials 3 – 5 are already widely composted; materials 1 and 2 are “ new”

Compost samples from Romanian UDD toilets with secondary composting (displayed by Margriet Samwel from WECF at Ecosan Seminar in Bulgaria, April 2007)

* Moisture content and C/N ratio may have to be adjusted by adding water or wet kitchen waste

Composting and anaerobic digestion (AD) can be competing processes to treat organic solid waste

Composting may be preferred over AD in the following cases:For dry solid input materials, e.g. > 50% d.s.

Some organic matter is more amenable to composting than to AD, e.g. garden clippings, leaves (high lignin content)

When a higher quality soil conditioner is desired fewer pathogens in compost compared to digester residue drier product can be transported more easily; easier to sell but less nitrogen content (nitrogen losses during aeration)

When there is no need or use for biogas (energy) E.G. in Germany, anaerobic digestion appears to be gaining the

upper hand compared to composting because of the desire to produce green energy (climate change issues)

When a system with lower investment costs is desired (less know-how required for construction of composting processes compared to AD)

When some odour emissions are acceptable (population density low) – composting processes are usually not enclosed, although a building could be constructed around it

Applications of composting process in ecosan concept

1. Thermophilic composting (55-65°C) as secondary treatment of faeces (in semi-centralised composting plants) E.g. Co-composting of faeces or faecal sludge with organic

solid waste at semi-centralised level2. Mesophilic composting (35°C) in composting toilets (for

primary treatment of faeces) - see Part C for more details on composting toilets Most of the traditional composting toilets have no urine

diversion (in recent times, urine diversion has been added) Careful: Some people call dehydration toilets also

composting toilets, which can be confusing

See debate on Ecosanres Discussion Forum end of September 2006: Some experts say that composting and dehydration are both occurring at the same time when ash is added as a carbon source to a UDD toilet. Paul Culvert (ecosan pioneer in India) calls his toilet design a “dry composting toilet” (with urine-diversion).

most important

Course 2 Unit 6

2 levels of excreta treatment: primary, secondary

Urine;faeces

Sanitised urine;sanitised faeces

Sanitised urine;partially sanitised faeces

PRIMARY TREATMENT Treatment integrated into individual toilet Usually sufficient when households can

reuse their own products

Examples: Storage and drying in the toilet (double-pit

collection is preferred) Alkaline treatment (addition of ash and lime;

pH >9 during >6 months) Composting (not recommended except for

dedicated users)

SECONDARY TREATMENT Treatment at community / block

level (outside of household) Necessary if project is at

community level, particularly for faeces

Examples: See next slide

primary treatment

secondary treatment

Reminder from Course 2 Unit 1 Part C:

Secondary treatment options for faeces

Type of process

Description Is it common?

Storage One year under tropical conditions (28-30 ºC)

Very common

Composting Thermophilic preferred (> 50 ºC for > 1 week)

Common

Anaerobic digestion Works well in conjunction with animal manure (household biogas plants), but incomplete pathogen removal

Common in some countries (e.g. China, India, Nepal)

Chemical treatment Mixing with urea to achieve pH increase Experimental stage

Incineration Burning, reuse of ash; complete pathogen kill

Not common

based on Schönning and Stenström (2004)

Reminder from Course 2 Unit 1 Part C:

This elevated temperature for an extended time period will achieve pathogen kill (not complete pathogen kill but sufficient to make it safe for reuse (see also Course 3 Unit 1))

Reminder of terms (1): “Indicator organisms” Microorganisms which are easy to quantify and

which exhibit same or greater survival characteristics in the environment as the target pathogen organism for which they are a surrogate

Should be present when faecal contamination is present

Examples: helminth eggs, total coliforms, faecal coliforms, E. coli, Enterococci, MS2 coliphageo Helminth eggs (e.g. Ascaris) is now becoming the norm

as an indicator organism for treatment of faeces in composting since they are very resilient

o Unfortunately, helminth eggs are also expensive to measure

Note: Ova = eggs

Reminder of terms (2): what is “organic”? An organic compound is any member of a large class of chemical

compounds whose molecules contain carbon and hydrogen; therefore, carbides, carbonates, carbon oxides and elementary carbon are not organic (see below for more on the definition controversy for this word). The study of organic compounds is termed organic chemistry, and since it is a vast collection of chemicals (over half of all known chemical compounds), systems have been devised to classify organic compounds.

The name "organic" is a historical name, dating back to 19th century, when it was believed that organic compounds could only be synthesised in living organisms through vitalis - the "life-force". The theory that organic compounds were fundamentally different from those that were "inorganic", that is, not synthesized through a life-force, was disproved with the synthesis of urea, an "organic" compound by definition of its known occurrence only in the urine of living organisms, from potassium cyanate and ammonium sulfate by Friedrich Wöhler in the Wöhler synthesis.

(Source: www.wikipedia.org)

Course 2 Unit 6

Reminder of terms (3): what is “humic acid”?

Humic acid is one of the major components of humic substances which are dark brown and major constituents of soil organic matter humus that contributes to soil chemical and physical quality and are also precursors of some fossil fuels. They can also be found in peat, coal, many upland streams and ocean water.

Humic substances make up a large portion of the dark matter in humus and are complex colloidal supramolecular mixtures (Piccolo, 1996, 2001; MacCarthy, 2001) that have never been separated into pure components.

Source: www.wikipedia.org

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Compost during curing phase after active composting period Substrate: organic solid waste

Composting fundamentals overview Organic material undergoes biological degradation to

a stable end product (the compost) During the decomposition process, the compost heap

heats itself up to temperatures in the pasteurisation range of 50 to 70°C (=self-heating) and enteric pathogenic organisms are destroyed-Note no external heating needs to be applied!- Sometimes an insulation is used (in composting toilets)

Composting is usually carried out under mostly aerobic conditions

When composting is used to treat faecal matter, the recommended indicator organism to measure extent of pathogen kill is helminth eggs

Note: the temperatures in vermi-composting are much lower (under 25ºC – see Part B)

Composting process microbiology

Complex destruction of organic material coupled with the production of humic acid* to produce a stabilised end product The micro-organisms involved are bacteria, actinomycetes

and fungi Interrelationships between microbial populations are not fully

understood Three stages of activity and associated temperatures:

Stage 1: Initial mesophilic stage (40°C) – self-heating Stage 2: Thermophilic range 40-70°C – self-heating Stage 3: Cooling period (stabilisation of pH, completion of

humic acid formation)

* see definition on next slide

Tem

pera

ture

in °

C

(or

CO

2 re

spira

tion)

Mesophilic temperatures

Thermophilic temperatures

High-rate composting

Curing

Stable and mature compost

Source: Metcalf & Eddy (2003), page 1547

Phases during composting as measured by carbon dioxide respiration and temperature

3-4 weeks 1 month or longer

Typical values for aerated static pile composting:

Stage 3Stage 2Stage 1

Isothermal lines in a cross-section of a 14-day-old compost heap

(= in stage 2 of the composting process)

Course 2 Unit 6

If your compost pile is not heating itself up, then you know that something is wrong!

Five basic process steps of technical composting operation (at the large scale)

1. Pre-processing: mixing of faecal matter (or sludge) with an amendment* and/or a bulking agent

2. High-rate decomposition: aerating the compost pile either by addition of air, by mechanical turning, or by both

3. Recovery of the bulking agent*4. Further curing and storage; cooling5. Post-processing; screening

* for explanation see next slide

Amendments and bulking agentsAmendment

= Organic material added to the feed substrate to reduce the bulk weight, reduce moisture content and increase the air voids for proper aeration

Can be used to increase the quantity of degradable organics in the mixture

Examples are sawdust, straw, recycled compost, rice hulls

Bulking agent = Organic or inorganic material that is used to provide

structural support and increase the porosity of the mixture for effective aeration

Wood chips are commonly used (can be recovered and reused)

Main technical methods of large-scale composting (brief summary)

Agitated (see photo on next slide) Periodic agitation to introduce oxygen, control the

temperature and mix the material to obtain uniform product

Composting period is about 21 – 28 days e.g. windrow method

Static Air is blown through the static composting material,

composting period of 21-28 days, and > 30 days for curing period

e.g. aerated static pile method

In-vessel composting systems Composting is accomplished inside an enclosed

container or vessel

Composting in rows (agitated by machine), with organic solid waste as a substrate

Course 2 Unit 6

Example of an agitated composting process

In many countries (rich and poor alike), the process of composting kitchen waste is widely practiced. But not many people add human excreta to their compost heap, even though this would be possible

Example of home composting (static process)

Composting of toilet and kitchen waste (outside)

Compost vessel with lid Worm culture, 24 hours active

Source: Wolfgang Berger (more information on him in Part C)

Design considerations for composting systemsItem Comment

Carbon to nitrogen ratio

Initial C/N ratio should be 20:1 to 35:1 by weight*. The ratio reduces during composting process because of carbon loss and nitrogen accumulation

Air requirements Air with at least 50% oxygen remaining should reach all parts of the composting material

Moisture content Moisture content of the composting mixture should not be > 60% for static pile and windrow composting and not > 65% for in-vessel composting

pH control pH should be 6 to 9; optimally 7 to 7.5

Temperature Temperature should be 50 to 55°C for the first few days and 55-60°C for the remainder of the active composting period

Control of pathogens

To kill all pathogens, temperature must be maintained between 60 and 70°C for 24 hours

Mixing and turning

Material should be mixed or turned on a regular schedule

Source: Metcalf & Eddy (2003), page 1552

* See table slide after next for some example C/N values (be aware that it is not so easy to measure the C/N ratio: you will require access to a laboratory for this)

Possible reasons for process failure (related to the table on the previous slide)

C/N ratio too low add carbon source

Not enough aeration mix more (turn over more) use of bulking agent

Too much moisture reduce water content of input material remove leachate use urine diversion if composting toilet is used

Not enough moisture add water (rainwater harvesting or recirculate leachate or add

urine)

Example C/N ratios for several waste types

Source: Rothenberger et al. (2006), p. 27

Human faeces should be similar

See also Part D for further C/N ratios

Guidelines for design: space requirement

This table and many more design details can be found in the excellent recent publication by Sandec: Rothenberger et al. (2006), p. 50

You can also find it under Assigned Reading

Course 2 Unit 6

Practical points: the impact of ambient temperature

“One has to be aware that as composting is a very nature-connected process things might work differently in different natural environments.

For example in Sweden they say - 'always insulate the composter'. No one ever thinks of insulation in Bulgaria - the summer is so hot that the material will decompose until the next growing season, and who cares to invest money and labor in something that the nature will do it by itself.

In European climate more or less the composting heap/bin has to have a volume of ca 1 m3 - something like 1 x 1 x 1 m. With these dimensions it has good chance to develop enough inside heat (to kill the pathogenes) and still to be manageable for turning over relatively easy.”

Source: Diana Iskreva, Bulgaria, former online course participant (May 2007)

Main indicators for composting process failure

Odour No temperature rise in compost heap (or only

small increase in temperature)

Possible compost prices

€ 7 per ton for compost made from organic solid waste in Germany (personal communication with Annette Ochs) – sometimes the compost also has to be given away for free

€ 22 per ton for compost made from faecal sludge and organic solid waste in Accra, Ghana – predicted value (Vodounhessi and von Münch, 2006)

€ 28 per ton for compost made from organic solid waste (Rothenberger et al., 2006, p. 34 – example from Bangladesh)

How much does compost sell for in your country?

Operating costs for semi-centralised composting processes

It depends on the composting technology used and the scale of the process

In developing countries it may cost only € 15 per ton of input material

in Germany the costs are around € 60 per ton (in comparison: anaerobic digestion: ~ € 120 per ton)

Composting cannot be financed by sale of product alone (in most cases) but mostly via a waste disposal fee

Source: Annette Ochs (April 2007)

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Compost marketing hierarchy indicating market prices (in €/ton or €/m3)

The absolute cost values in this graph are not so important, but note that different applications can result in different compost prices (and different quality requirements)

Source: European Compost Network (ECN), http://www.compostnetwork.info/index.php?id=10

Possible compost yields

0.1 ton compost per m3 faecal sludge if faecal sludge is co-composted with organic solid waste (Source: Vodounhessi and von Münch (2006))

0.3 ton compost per ton of organic solid waste (personal communication with Annette Ochs)

Types of compost end products according to German standardisation

• “Fresh compost”– Hygienised, suitable for further intensive rotting, separated

material for improvement of soil and fertilisation

• “Complete compost”– Hygienised, biologically stable and separated compost for

improvement of soil

• “Substrate compost”– Complete compost with limited content of soluble plant

nutrients and salts, useable as mixed component for use in public gardens (soil covering and fertilising)

• “Mulch compost”– Hygienised, separated compost without fine particles for land

covering

Course 2 Unit 6

The benefits of compost application in agriculture will be dealt with in Course 3 Unit 1

Remember: Hygienised = sanitised = minimal pathogens

Explanations on different compost types and effects on plants“Fresh compost” or “immatured compost”: this compost is not yet

utilisable by the plants (you can test this with the cress test) - but you can easily work it in the top layer of the soil as mulch.

Matured compost is compost that can be utilised by plants. This compost does not have to be soil-like, it can still contain partially-composted parts of plants (or organic matter). Matured compost is rich in soil organisms which can accelerate the decomposition process, and they do not harm the soil or plants.

Complete compost is compost where the decomposition process is totally complete - it ist often called "compost soil". This is the so-called commercial compost - it is less relevant for enriching the soil life (soil microorganisms); often it is amended with nutrients to also have a specific fertilising effect.

Source: Wolfgang Berger (composting specialist) personal communication, May 2007

These compost names have been translated from the German literature on composting – that’s why the names in English seem a bit unclear sometimes (at least for me)

An experience with compost

“Now I know what went wrong with my basil seeds when I sow them in fresh compost substrate; it was probably immature and killed the poor seeds. I guessed already then that there was something not right with the compost. I made another trial with 'older' compost and the plants grew well.”

Source: Ulrike Lipkow, GTZ Philippines, former online course participant, May 2007

Question: “Is compost a soil conditioner or a fertiliser?”

Answer: “The border between soil conditioners and fertiliser is fluid.

Normally, compost is called both. Final clarification about the fertiliser effect of compost can only be obtained with an analysis. Either way it is important to know whether the soil has already an excess of nturients or a shortage of nutrients and what nutrient requirements the respective plant has.”

Source: Wolfgang Berger (composting specialist) personal communication, May 2007

Course 2 Unit 6

Standardised methods for compost analysis

Standard methods "TMECC (Test Methods for Examination of Composting and Compost)" jointly published by USDA and US Composting Council

Swedish Standard method for soil Methods published in Germany (sorry, in German):

BGK (1994) Bundesgütegemeinschaft Kompost e.V: Methodenbuch zur Analyse von Kompost

LAGA (1995) Qualitätskriterien und Anwendungsempfehlungen für Kompost aus Müll und Müllklärschlamm/ Mitteilung der Länderarbeitsgemeinschaft Abfall 8, Merkblatt 10. Erich-Schmidt- Verlag (Quality criteria and application recommendations for compost obtained from refuse and refuse/sludge, Pamphlet M10). Federal German Department of Environment.