Composting

I. References

1. Nordstedt, Using Natural Materials: Composting and Alternative Materials Recovery;

2. Cornell Univ. Composting Website: http://www.cfe.cornell.edu/compost/Composting_Homepage.html

II. Introduction

A. What is Composting?

1. Enhanced natural decomposition of organic wastes to humus-like product

2. Material is collected, valuables removed or extracted, and remaining organic fraction is placed into piles or reactors and mixed or aerated to promote decomposition.

3. Effluent is sold as a soil conditioner or fertilizer or land disposed

B. Why Compost?

1. Reduction in organic matter

2. Stabilized organic matter is free of odor, sand, rodents and other pests.

3. Production of soil conditioner (mainly holds water and promotes aeration)

 

III. Microbiology

A. Mixed undefined mixed culture, including anaerobic and anaerobic bacteria, fungi, protozoa, nematodes, and insects

B. Succession of Steps

1. mesophilic bacteria

2. thermophilic bacteria and fungi

3. concentration of microbes can be as high as 35% (dry wt. basis)

4. Figure showing change in number of bacteria and fungi

C. Actinomycetes and streptomycetes

1. are common and cause earthy odors

2. aerobes that depolymerize cellulose and lignin

D. Microbes are poorly characterized

E. Inoculation

1. speeds up process

2. special organisms or inocula are of dubious value

F. Pathogens

1. Most are killed by high temperatures (>69^oC)

2. Table showing pathogen destruction

IV. Operational Parameters

A. Substrate

1. Biodegradability

2. Particle size

B. Nutrient Balance

1. C/N < 30 is preferred

2. Ammonia

C. Temperature and pH

1. Composting is usually conducted at ambient temperatures

- the exception would be controlled in-vessel systems

2. Compost temperature increases with increase in microbial activity

3. High temperatures kill pathogens and remove moisture

4. pH decreases initially due to anaerobic conditions and then increases as acids are metabolized.

5. Temperature and pH are used to monitor progress of process (See Figure).

6. Heating in actual compost piles

 

D. Aeration

E. Moisture

1. Should be >45%

2. Microbial activity ceases when <12%

3. High levels reduce aeration capacity

4. Influence of moisture content on oxygen demand

V. Process Considerations

A. Sorting

B. Inoculation (solids recycle)

C. Indicators of Completion

1. temperature drop

2. organic reduction

4. drop in oxygen uptake

VI. Reactor Types (design, advantages, and disadvantages)

1. round tank

2. Dano drum

D. Table of advantages and disadvantages.

VII. Use of Compost

A. Soil Conditioner

1. Table of nutrient availability of compost

2. Table of water holding capacity

B. Fertilizer

C. Constraints

D. Public Health (Table showing that hand-sorted MSW has less metals)

E. Regulations

VIII. Applications

1. Figure of Yardwaste facilities in US. (number increased to 3,800 in 1988)