Aerobic Composting

1
Aerobic Composting
2
Presentation 7The Composting Toolkit

• Funded by the Indiana Department of Environmental
  Management Recycling Grants Program
• Developed by the Indiana Rural Community
  Assistance Program - RCAP

3
So Lets Talk About Composting . . .
4
Compost

• NOUN OR VERB?
• BOTH!
• The verb Composting is the process by which
  microorganisms break down waste and turn it into
  a valuable product.
• The noun This end product is referred to simply
  as compost.

5
Types of CompostingAerobic or Anaerobic?

• We are talking is AEROBIC composting.
• That is, composting in the presence of OXYGEN.
• Microorganisms decompose organics aerobically
  (with oxygen) under carefully controlled
  conditions to produce finished compost.
• Anaerobic decomposition is what occurs in a
  landfill with Carbon Dioxide, Methane, and
  Leachate being three major products.

6
Compost Happens
7
Aerobic Composting

• Composting is part science and part art. There
  is no one correct recipe for aerobic
  composting.
• You will be introduced in this unit to the basics
  of aerobic composting and optimal conditions,
  but you need to always keep in mind that
  flexibility is the key to successful composting.

8
Aerobic Composting Key Components

• Air
• Water
• Compostable Materials
• Carbon to Nitrogen Ratio
• Surface Area
• Temperature
• pH
• Other Variables

9
Aerobic Composting Optimal Composting Conditions

• Oxygen gt5
• Moisture Content 40-60
• Carbon to Nitrogen Ratio 30 to 1
• Shredded Materials Over Chipped Materials To
  Maximize Surface Area
• Temperature 90-140 Degrees F
• pH 6-8
• Other Variables

10
Aerobic Composting

• Air
• Optimal composting when oxygen is greater than 5
• The air we breath is 21 oxygen
• Right picture is testing for oxygen level within
  the compost pile

11
Aerobic Composting

• Air
• The microorganisms that perform the composting
  process require oxygen to survive. Because the
  compost pile provides a plentiful food source for
  these microorganisms they quickly multiply.
• This is beneficial to the composting process, but
  there can become too many microorganisms for
  oxygen supplies within the pile. Oxygen
  statically flowing into the pile will be far less
  than the oxygen being consumed by the
  microorganisms.
• Thus oxygen levels will begin to fall within the
  pile from the 21 oxygen level in the surrounding
  atmosphere. Below 5 oxygen level the
  microorganisms will begin to be impaired
• Regular turning is required of a windrow compost
  pile restores oxygen to the compost pile and
  helps to ensure that oxygen levels do not fall
  below 5

12
Aerobic Composting

• Water
• An ideal moisture content is between 40-60.
• Composting microorganisms need a wet environment.
• gt60 is too wet, water will take up too much pore
  space required for proper air diffusion.
• lt40 is too dry, decomposition rates will
  progressively slow the drier the pile.

13
Aerobic Composting

• Water
• Here in Indiana it is unusual to have a pile that
  is too dry, you are more likely to have a pile
  that is too wet. A pile that is too wet can be
  turned on an increased schedule until moisture
  contents fall back into desired ranges.
• In a case where the pile is too dry water may be
  added or the pile may be reshaped to allow more
  water to enter the pile during the next rainstorm.

14
Aerobic Composting

• Water
• Shaping the compost pile according to moisture
  content needs is clearly an example of the art
  of composting
• A concave shape helps to trap water whereas a
  peak shape helps to shed water.

15
Aerobic Composting

• Carbon to Nitrogen Ratio
• Also commonly called the CN ratio or the brown
  to green ratio
• This is because organics high in carbon tend to
  be brown (wood and old leaves being two examples)
• Organics high in nitrogen tend to be green (grass
  clippings and food waste being two examples)
• An optimal carbon to nitrogen ratio is 301
• Too much carbon slows the composting process
• Too much nitrogen supercharges the composting
  process and runs the risk of going anaerobic or
  off-gassing nitrogen compoundsboth causing
  negative odors

16
Aerobic Composting

• Common Carbon to Nitrogen Ratios
• High Nitrogen Materials
• Activated Sewage Sludge 61
• Humus 101
• Vegetable Food Waste 151
• Digested Sewage Sludge 161
• Grass Clippings 191
• Cow Manure 201
• Horse Manure 251
• Green Leaves lt301

17
Aerobic Composting

• Common Carbon to Nitrogen Ratios
• High Carbon Materials
• Fruit Food Wastes 351
• Typical Brown Leaves 40-801
• Foliage 40-801
• Corn Stalks 601
• Pine Needles 60-1101
• Straw 801
• Bark 100-1301
• Paper 150-2001
• Wood and Sawdust 300-7001

18
Aerobic Composting

• Steaming compost during turning is a sure sign
  that temperatures are being maintained. An
  indicator that the oxygen levels, moisture
  content, and the CN ratio are in balance.

19
Aerobic Composting

• Surface Area
• Greater surface area accelerates decomposition.
• There are two primary ways to increase surface
  area
• Smaller particles size
• Shredding materials over chipping materials

20
Aerobic Composting

• Temperature
• Exothermic microorganisms decompose waste and in
  the process give off heat
• An optimal temperature range is 90-140 degrees F
• Below 90 degrees the composting rate slows
  substantially
• Above 140 degrees the microorganisms have
  difficulty functioning and the pile runs the risk
  of spontaneous combustion

21
Aerobic Composting

• Temperature
• A compost piles temperature is a balance of the
  heat produced by the respiration of the
  microorganisms offset by the heat lost through
  surface cooling
• In the winter larger pile sizes may be required
  to offset heat losses
• In the summer more frequent turning and smaller
  pile sizes may be required to offset excess heat

22
Aerobic Composting

• Temperature
• One other important function of maintaining high
  temperatures in a compost pile is weed seed
  destruction and pathogen destruction.
• Example Salmonella destruction requires
• 20 minutes at 140 degrees F
• Or
• 1 hour at 131 degrees F

23
Aerobic Composting

• Temperature Testing temperature within the
  compost pile

24
Aerobic Composting

• pH
• Decomposition occurs most efficiently between pH
  6 and pH 8.
• During the initial stages of decomposition,
  organic acids are formed that, under normal
  conditions, are immediately consumed by
  microorganisms. Without enough oxygen in the
  pile, these acids will not be converted as
  quickly.

25
Aerobic Composting

• Other Variables
• There may be other variables of concern as a
  composting operation is refined to make products
  of a specified composition. These variables,
  which are beyond the scope of this manual,
  include mass balance, rate of respiration of the
  microorganisms, mixing and agitation of the pile,
  nutrient balance, inoculation, wetting agents,
  cation exchange ratio, pathogen destruction, wind
  velocity, and specific elemental composition.

26
Windrow Composting

• Most common method of yard waste composting in
  the United States
• Generally a row of material is composted,
  usually about 10-25 feet wide, 6 feet high, and
  as long as 150 feet.
• Windrow composting has been shown to be highly
  cost effective.

27
Windrow
28
Windrow
29
Windrow Turner
30
Windrows Optimum Composition

• Shredded and screened organics
• Moisture content 40-60
• Balanced 301 Carbon to Nitrogen ratio
• Frequent turning Frequent turning keeps the
  pile aerobic and reduces odor

31
Volume and Weight Reduction

• With optimal composting a volume reduction of up
  to 75 can be achieved and a weight reduction of
  up to 50 can be achieved.
• For high water content materials this volume and
  weight reduction can be as high as 90.

32
Single Biggest Problem ODOR

• Reasons
• 1 Reason is Lack of Oxygen
• Also . . . Out of balance CN Ratio
• And . . . Excessive wetness
• Odor control is discussed in more depth in the
  Ongoing Operations section.

33
Other Problems

• Pathogens destruction
• Litter and contaminants (plastic bags, heavy
  metals, pesticides)
• End product quality

34
Windrow CompostingTrouble Shooting

• Symptom Pile has a bad odor
• Problem Not enough oxygen
• Solution Turn pile daily until odor is gone
• Symptom Center of pile is dry
• Problem Not enough water
• Solution Moisten material while turning pile
• Symptom Compost is damp and warm
• Problem Pile too small or needs more nitrogen
• Solution Collect more material and mix the pile.
  If still not heating add more nitrogen rich
  materials.
• Symptom The pile will not heat up
• Problem Lack of nitrogen
• Solution Mix in a nitrogen source such as grass
  clippings, fresh manure, or fertilizer

35
Windrow Composting - Overall

• Capital costs ? generally low
• Operating costs ? generally low
• Land requirements ? high
• Control of Air ? limited unless forced aeration
  is used
• Operational control ? turning frequency,
  amendment, or compost recycle addition
• Sensitivity to cold or wet weather ? sensitive
  unless in housing
• Control of odors ? depends on feedstock,
  potential large-area source
• Potential operating problems ? susceptible to
  adverse weather

36
Windrow Composting - Conclusion

• Most commonly used composting technique in
  Indiana and Nationally
• Uses aerobic microorganisms to breakdown woody,
  yard waste, and food waste products into a useful
  compost end product
• When compared against the capital costs of other
  MSW management techniques, it is very cost
  effective

37
(No Transcript)
38
QUESTIONS?
39
Thank You!

• Additional Questions, Comments, or You Think You
  Have A Potential Pilot Community
• Please Feel Free to Contact Me
• Mark W. Davis
• Technical Assistance Provider
• Rural Community Assistance Program
• Office 1-800-382-9895
• Wireless [phone]
• E-mail mdavis_at_incap.org