Course 2: TRANSFER AND TREATMENT OF HUMAN EXCRETA AND GREYWATER
Unit 6: Composting
Expected Study Load : 8 hours.
This Unit's presentation is cut up in 4 parts:
A: general introduction
C: Composting toilets
Composting is widely used in Europe to treat organic solid waste. There is a vast amount of know-how on composting as a secondary treatment process (semi-centralised or centralised), but this is mainly focused on organic kitchen waste.
In this Unit, we will discuss how this knowledge can be applied to faecal matter and how to devise simple low-cost processes that can be used at community level.
After completing this unit, you will:
- understand basic principles and design considerations for composting processes
- understand the importance of heat development in conventional composting (for pathogen kill)
- know of possible causes for composting process failure and how to rectify them
- know how to choose between composting and anaerobic digestion for a given sanitation or waste management situation
- be aware of vermicomposting as a possible method for composting faeces and understand process differences to conventional composting (e.g. lower process temperature)
- be aware of the existence of engineered composting toilets on the market and their limitations for use in low-income settings
- know which indicator organism is usually used to indicate pathogen kill in composting of faecal sludge (helminth eggs)
Recommended reading sources on Internet
- SOIL Haiti: http://www.oursoil.org/
- In which countries are composting toilets used for normal houses?
They are used for example in Germany, Sweden, Finland, Austria, Switzerland. Also in many other countries for remote locations, e.g. national parks in Australia, the alps in Austria, Finland, Norway, etc.
- What is the difference between composting and vermicomposting?
Composting is a process that converts organic materials, such as kitchen and garden waste, into humus. The production of humus is carried out by microorganisms which live in the compost heap, mostly under aerobic conditions. For this reason, and to generally produce compost efficiently, conditions such as the humidity, temperature, aeration and carbon/nitrogen content need to be controlled.
In vermicomposting, humus is also an end product, but this time it is produced by microorganisms and by worms. There are several types of worms which can rapidly consume, and thus process, organic waste and turn it into valuable humus. The earthworm species which are most often used are Brandling Worms (Eisenia foetida) or Red Wigglers (Lumbricus rubellus). These species are also called composting worms, and they are specially adapted to digest rotting organic material, such as vegetation, kitchen waste and manure.
The conditions for vermicomposting are similar to "regular" composting, but the most important difference is the operating temperature (vermicomposting does not operate at the very high temperatures as regular composting does).
- What is compost?
Compost is the end product of the process of composting - whereby organic materials are aerobically decomposed. The compost which is produced can be used in gardening and agriculture.
- Are composting toilets the same as dry toilets?
Many people use the term "dry toilet" to mean "composting toilet". But be careful, and check each time (a pit toilet could also be called a "dry toilet" but it is definitely not a composting toilet, even though some partial composting may take place).
- Do composting toilets work better with urine diversion?
The traditional composting toilets were built without urine diversion (note the Arborloo is also without urine diversion). But this can often lead to an excess of moisture. So nowadays, composting toilets are also often offered with urine diversion to reduce this excess moisture problem.
- Is compost a fertiliser or a soil conditioner?
The borders are fluid but it is more of a soil conditioner than a fertiliser, because the important aspect of compost is its organic matter content. Nitrogen content is relatively low (compared to anaerobic digestate) because ammonia is lost during aerobic composting processes.
- Is it better to use composting or anaerobic digestion for secondary treatment of faecal matter?
This depends on a number of factors, mainly the dryness of the material, whether there will be a co-substrate, possible investment costs (AD more expensive than composting), whether biogas is desired, what the end product (compost or digestate) could be used for and so on. For single households, the composting option is generally more common because not much know-how is required. For applications in dense settlements, anaerobic digestion at neighbourhood scale could be more advantageous (enclosed system).
- How do the self-heating activities in a compost heap come about?
The heat development is a by-product of the activities of the microorganisms that are involved in the aerobic composting process. - I have not yet seen an exact description of how the microorganisms do it! (tell me if you find a good description)
- Is a composting toilet better than a UDD toilet?
My rule of thumb is: if you deal with highly educated and very motivated people, then you could consider the sophisticated engineered composting toilets available on the market. But for the average user, a UDD toilet is simpler and easier to operate (more robust). The UDD toilet should be coupled with secondary treatment of faeces, e.g. external composting, especially if the system is beyond just at household scale. If you call the Arborloo a composting toilet, then this is also a simple easy to use system (for rural areas), just like the UDD toilet.
- Can I simply heat up my compost heat to speed up the composting process (e.g. by blowing hot air through it)?
No, this won't help. If the process is not self-heating, then the composting process is not taking place properly, for some reason. What can help though, is to insulate the composting vessel (this is sometimes done in composting toilets).