Aerobic Composting

Presentation 7: The Composting Toolkit Funded by the Indiana Department of Environmental Management Recycling Grants Program Developed by the Indiana Rural Community Assistance Program - RCAP

So Let’s Talk About Composting...

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

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

Compost Happens

Aerobic Composting Composting is part science and part art. There is no one “correct” recipe for 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. 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.

Aerobic Composting: Key Components Air Air Water Water Compostable Materials Compostable Materials Carbon to Nitrogen Ratio Carbon to Nitrogen Ratio Surface Area Surface Area Temperature Temperature pH pH Other Variables Other Variables

Aerobic Composting: Optimal Composting Conditions Oxygen: >5% Oxygen: >5% Moisture Content: 40-60% Moisture Content: 40-60% Carbon to Nitrogen Ratio: 30 to 1 Carbon to Nitrogen Ratio: 30 to 1 Shredded Materials Over Chipped Materials To Maximize Surface Area Shredded Materials Over Chipped Materials To Maximize Surface Area Temperature: Degrees F Temperature: Degrees F pH: 6-8 pH: 6-8 Other Variables Other Variables

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

Aerobic Composting Air: 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. 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. 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 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% 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%

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

Aerobic Composting Water: 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. 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. 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.

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

Aerobic Composting Carbon to Nitrogen Ratio Carbon to Nitrogen Ratio Also commonly called the C:N ratio or the brown to green ratio Also commonly called the C:N 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) 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) Organics high in nitrogen tend to be green (grass clippings and food waste being two examples) An optimal carbon to nitrogen ratio is 30:1 An optimal carbon to nitrogen ratio is 30:1 Too much carbon slows the composting process 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 compounds—both causing negative odors Too much nitrogen “supercharges” the composting process and runs the risk of going anaerobic or off-gassing nitrogen compounds—both causing negative odors

Aerobic Composting Common Carbon to Nitrogen Ratios: Common Carbon to Nitrogen Ratios: High Nitrogen Materials: High Nitrogen Materials: Activated Sewage Sludge: 6:1 Activated Sewage Sludge: 6:1 Humus: 10:1 Humus: 10:1 Vegetable Food Waste: 15:1 Vegetable Food Waste: 15:1 Digested Sewage Sludge: 16:1 Digested Sewage Sludge: 16:1 Grass Clippings: 19:1 Grass Clippings: 19:1 Cow Manure: 20:1 Cow Manure: 20:1 Horse Manure: 25:1 Horse Manure: 25:1 Green Leaves: <30:1 Green Leaves: <30:1

Aerobic Composting Common Carbon to Nitrogen Ratios: Common Carbon to Nitrogen Ratios: High Carbon Materials: High Carbon Materials: Fruit Food Wastes: 35:1 Fruit Food Wastes: 35:1 Typical Brown Leaves: 40-80:1 Typical Brown Leaves: 40-80:1 Foliage: 40-80:1 Foliage: 40-80:1 Corn Stalks: 60:1 Corn Stalks: 60:1 Pine Needles: :1 Pine Needles: :1 Straw: 80:1 Straw: 80:1 Bark: :1 Bark: :1 Paper: :1 Paper: :1 Wood and Sawdust: :1 Wood and Sawdust: :1

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

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

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

Aerobic Composting Temperature: Temperature: A compost pile’s temperature is a balance of the heat produced by the respiration of the microorganisms offset by the heat lost through surface cooling A compost pile’s 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 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 In the summer more frequent turning and smaller pile sizes may be required to offset excess heat

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

Aerobic Composting Temperature: Testing temperature within the compost pile Temperature: Testing temperature within the compost pile

Aerobic Composting pH pH Decomposition occurs most efficiently between pH 6 and pH 8. 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. 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.

Aerobic Composting Other Variables: 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. 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.

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

Windrow

Windrow

Windrow Turner

Windrows – Optimum Composition Shredded and screened organics Shredded and screened organics Moisture content: 40-60% Moisture content: 40-60% Balanced 30:1 Carbon to Nitrogen ratio Balanced 30:1 Carbon to Nitrogen ratio Frequent turning: Frequent turning keeps the pile aerobic and reduces odor Frequent turning: Frequent turning keeps the pile aerobic and reduces odor

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. 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%. For high water content materials this volume and weight reduction can be as high as 90%.

Single Biggest Problem: ODOR Reasons #1 Reason is Lack of Oxygen Also... Out of balance C:N Ratio And... Excessive wetness Odor control is discussed in more depth in the “Ongoing Operations” section.

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

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

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

Windrow Composting - Conclusion Most commonly used composting technique in Indiana and Nationally 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 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 When compared against the capital costs of other MSW management techniques, it is very cost effective

QUESTIONS?

Thank You! Additional Questions, Comments, or You Think You Have A Potential Pilot Community Additional Questions, Comments, or You Think You Have A Potential Pilot Community Please Feel Free to Contact Me: Please Feel Free to Contact Me: Mark W. Davis Technical Assistance Provider Rural Community Assistance Program Office: Wireless: (812)