Yard Waste Composting

Objectives  Describe the most commonly used composting processes.  Explain basic concepts associated with aerobic and anaerobic degradation.  Explain the environmental factors affecting degradation processes.  Explain the operational techniques used to control composting processes.

Definition Biological decomposition of organic constituents of wastes under controlled conditions (approximately 70% of MSW is decomposable).

Composting Types  Open –Conventional Windrow –Forced Aeration –Static Solids Bed –Forced Aeration –Natural Ventilation  Tower in vessel –Moving Agitated Bed –Moving Packed Bed (Continuous, Intermittent, batch feed)  Horizontal in vessel –Tumbling Solids Bed –Dispersed Flow –Cells in Series –Completely Mixed

Compost Rate Controlling Factors  Moisture Content  Carbon:Nitrogen  Temperature  Particle Size  Pile Geometry  Turning frequency

Chronological Temperature – Windrows

Compost Aeration Air (Oxygen) Heat Rises

Effect of Moisture Content on Temperature - Windrows

pH of Windrows

Compost Turner

Windrow Size and Turning Frequency for Leaf Composting a TECHNOLOGYDIMENSIONSTURNING FREQUENCY Minimal12 feet highOnce per year Low6 feet high3-5 times per year Intermediate5-7 feet high feet wide Once per week (windrow turning machine) High10 feet high 20 feet wide Forced aeration for the first 2-10 weeks then periodic turnings

MATERIALC/N RATIO Activated Sludge6:1 Grass Clippings12-15:1 Mixed Grasses19:1 Sawdust :1 Carbon to Nitrogen Ratios for Various Wastes

Compost Maturity  Appearance and Odor  Length of composting period  Reheating temperature  Reduction of Organic Matter  C:N Ratio < 20  Oxygen Uptake Rate  Germination potential

Chronological % VS – Windrows

Bag Opener

Tub Grinder

Compost Windrow

Compost Turner

Compost Monitoring  Oxygen Content  Temperature

Compost Screening

Finished Compost

Sumter County Compost Facility

Return to Home Page Last updated August 2007 by Dr. Reinhart