c omposting n.
Skip this Video
Loading SlideShow in 5 Seconds..
C OMPOSTING PowerPoint Presentation
Download Presentation

Loading in 2 Seconds...

play fullscreen
1 / 42

C OMPOSTING - PowerPoint PPT Presentation

  • Uploaded on

C OMPOSTING. David T. Brown Dept. of Tourism and Environment Brock University. Composting: . Composting: . The controlled biological decomposition of organic materials. Composting: .

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about 'C OMPOSTING' - khuyen

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
c omposting


David T. Brown

Dept. of Tourism and Environment

Brock University


The controlled biological decomposition of organic materials

  • natural biological process, but for rapid composting and consistent quality, environmental conditions must be controlled
  • end product (compost) bears little resemblance to original wastes from which the compost was made
  • typically dark brown to black in colour, with crumbly texture and earthy odour
finished compost
Finished compost
  • humus-like, resembling rich topsoil
  • resistant to further microbial decomposition
  • typical volume reductions in excess of 50% of the original volume of the waste; effective & useful waste diversion strategy
  • good compost is devoid of organisms that may be harmful to human health
uses of compost
Uses of compost
  • high organic matter content => valuable soil amendment
  • may be used as low-grade fertilizer to supplement plant nutritional needs
  • may be used to condition heavy clay or mineral soils
  • promotes proper balance between air and water in soils
  • aids water infiltration, absorption, and ion exchange in soils
what can be composted
What can be composted?
  • any waste material with a high organic matter content is a potential candidate
  • used for centuries to stabilize human and animal wastes
  • used more recently for:
    • sewage sludges
    • industrial wastes (e.g. food, pulp & paper)
    • yard and garden wastes
    • municipal solid wastes (up to 70% organic matter by weight)
controlling composting
Controlling composting

To achieve maximum composting for any organic material, certain environmental conditions must be maintained in the compost pile

  • may be classified into interdependent
  • biological conditions
  • physical conditions
  • chemical conditions
the biological environment

Key organisms:

  • bacteria
  • fungi
  • Actinomycetes

- play active role in decomposing organic matter

the biological environment1

Secondary organisms:

    • earthworms
    • insects
    • other soil invertebrates
  • play a less significant role in decomposition process compared to microorganisms
  • more important in mechanical breakdown of wastes (chewing, burrowing, movement, aeration)
fate of organic matter in compost
Fate of organic matter in compost
  • Carbon-containing compounds are consumed by microorganisms and converted to:
        • microbial tissues
        • carbon dioxide
        • water
        • humicbreakdown products
    • Heat is released as a result of microbial metabolic activity => temperature in pile increases
Humic breakdown products resulting from one type of microbial activity may be used as a food and energy source by another generation or type of microbes
  • Chain of succession continues until there is little decomposable organic material remaining



Stable end product composed of:

  • living and dead microbial cells and cell fragments
  • byproducts of microbial decomposition
  • undecomposed particles (organic and inorganic)
microbial succession in compost piles
Microbial successionin compost piles
  • A wide variety of microorganisms naturally present in most nontoxic agricultural wastes, yard wastes, or mixed municipal wastes
  • ==> number and type of available organisms generally not a limiting factor
  • Depending upon environmental conditions, certain microbial groups may predominate at certain stages in the decomposition process
If preferred organic substrate is depleted or unavailable, certain microbes may be reduced in numbers, go dormant, or die off
  • Competition occurs between microbe groups
  • Dominant groups emerge based upon current conditions in the compost pile
  • Succession continues as long as there is adequate decomposable organic matter present
the chemical environment
  • determined largely by the composition of the waste materials to be composted

Important factors influencing the chemical environment for composting:

    • adequate food / energy sources for microorganisms
    • balanced amount of nutrients
    • adequate water content
    • adequate oxygen
    • acceptable pH range
    • lack of toxic substances that could inhibit microbial activity
food energy sources for compost microbes
Food / energy sources for compost microbes
  • microbes rely on organic carbon compounds to meet energy needs
  • Carbon in natural or synthetic organic substances varies in degradability, e.g.:
  • sugars easily metabolized by most microbes
  • lignins in wood or paper degraded more slowly, by fewer groups
  • plastic very resistant to breakdown
food energy sources for compost microbes1
Food / energy sources for compost microbes

As degradable organic compounds are decomposed:

  • small portion of the carbon goes into microbial cells
  • large portion of carbon converted to CO2 and lost to the atmosphere

=> reduction in weight and volume of waste

food energy sources for compost microbes2
Food / energy sources for compost microbes
  • More resistant carbon compounds form the matrix for the physical structure of finished compost.
  • Most municipal, yard, and agricultural wastes have adequate biodegradable carbon to support microbial activity
nutrients for compost microbes
Nutrients for compost microbes
  • nitrogen, phosphorus, and potassium are most important nutrients
  • nitrogen is usually the limiting nutrient


C:N ratio established on the basis of decomposable rather than total carbon
  • ratio lower than 30:1 is desirable
  • higher ratios result in slower decomposition rates
    • adjusted by co-composting with different materials
Typical C:N ratios for waste products:

Manure - 15:1 to 20:1

Yard wastes - 20:1 to 80:1

Municipal wastes - 40:1 to 100:1

Wood chips - 400:1 to 700:1

As composting proceeds:
  • carbon dioxide is lost to the atmosphere
  • C:N ratio narrows

Finished compost has a C:N ratio between 10:1 and 15:1

moisture in compost piles
Moisture in compost piles
  • ideal moisture: 50% to 60% by weight
  • most wastes do not contain enough moisture => composting process slowed down unless water is added
  • excess water causes problems in compost piles: leachate generation, anaerobic conditions, rotting, and obnoxious odours
  • loss of moisture occurs through evaporation => controlled by adjusting the size and shape of the compost pile
oxygen in compost piles
Oxygen in compost piles
  • aerobic decomposition is required for odour-free, rapid composting
  • pile should have enough void space to allow gas exchange with the atmosphere
  • 5% to 15% oxygen concentration is considered adequate
  • piles aerated by mechanical turning, air injection
ph in compost piles
pH in compost piles
  • pH of 6 - 8 considered ideal

Level of acidity / alkalinity affects:

    • nutrient availability
    • solubility of (potentially toxic) heavy metals
    • overall metabolic activity of microbes
ph in compost piles1
pH in compost piles
  • pH may be adjusted upwards by the addition of lime (calcium carbonate), but most organic substances are naturally well-buffered with regard to pH change
  • slight tendency towards acidification as compost matures, due to production of carbonic acid
the physical environment

Includes factors such as:

  • particle size
  • temperature
  • mixing
  • pile size and shape
small particle size promotes rapid decomposition due to increased surface area-to-volume ratio
  • However: if all particles are small, they pack together and create dense, anaerobic compost
  • => particles should have enough surface area to promote microbial activity, but have enough air spaces to permit gas exchange with the atmosphere
co composting
  • used to achieve better balance of particle sizes (e.g. small-particle sewage sludge mixed with large-particle wood chips)
  • Particle size reduction by grinding is occasionally done before composting; sometimes undertaken after composting to improve aesthetic appeal of finished product
temperatures in the compost pile
Temperatures in the compost pile

Different microbes have different optimal temperature ranges:

  • psychrophiles (cool - below 20o C)
  • mesophiles (warm - 20o to 40oC)
  • thermophiles (hot - 40o to 80o C)
  • sub-optimal temperatures interfere with metabolic activity and reproduction of microbes
as temperatures increase above the maximum threshold, cell proteins are destroyed and the microbes die
  • most effective temperature range for efficient composting is 55o to 75o C (thermophile range)
  • promote rapid decomposition
      • destroy pathogens
  • Temperatures in excess of 55o C are required for at least 3 days to ensure pathogen destruction
  • If compost pile is large enough, internal heat will allow composting in subzero conditions
composting techniques

Small-scale home composting:

  • simple compost heaps
composting techniques1

Small-scale home composting:

  • box or barrel composters
composting techniques2

Small-scale home composting:

  • commercial composter units
composting techniques3

Small-scale home composting:

  • digester units
composting techniques4

Commercial composting:

  • windrows
  • aerated static piles
  • in-vessel composting systems
processing of municipal compost
  • Removal of bulky items
  • Particle size reduction (grinders, shear shredders, hammermills)
  • Screening (size requirements)
  • Magnetic separation
  • Moisture addition and mixing
  • Composting (numerous techniques)
  • Postprocessing: screening, curing, storage, marketing, application