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 FactorsMoisture ContentCarbon:NitrogenTemperatureParticle SizePile GeometryTurning frequency

Chronological Temperature – Windrows

100

120

140

160

180

0 20 40 60 80 100 120 140 160

Time (days)

Tem

p.

(deg

.F)

Compost Aeration

Air (Oxygen)Air (Oxygen)HeatRises

Effect of Moisture Content on Temperature - Windrows

140

150

160

0 50 100

Moisture Content

Max

imu

m

Tem

per

atu

re

pH of Windrows

6.0

6.5

7.0

7.5

8.0

8.5

9.0

0 20 40 60 80 100 120 140 160time (days)

pH

Windrow I Windrow II Windrow III Windrow IV

Compost Turner

Windrow Size and Turning Frequency for Leaf Compostinga

 

TECHNOLOGY DIMENSIONS TURNING FREQUENCY

Minimal 12 feet high Once per year

Low 6 feet high 3-5 times per year

Intermediate 5-7 feet high10-14 feet wide

Once per week(windrow turning

machine)

High 10 feet high20 feet wide

Forced aeration for the first 2-10 weeks

then periodic turnings

MATERIAL C/N RATIO

Activated Sludge 6:1

Grass Clippings 12-15:1

Mixed Grasses 19:1

Sawdust 200-500:1

Carbon to Nitrogen Ratios for Various Wastes

Compost Maturity

Appearance and OdorLength of composting periodReheating temperatureReduction of Organic MatterC:N Ratio < 20Oxygen Uptake RateGermination potential

Chronological % VS – Windrows

40.0

45.0

50.0

55.0

60.0

65.0

70.0

75.0

80.0

0 20 40 60 80 100 120 140 160

time (days)

% V

ola

tile

(d

ry b

asis

)

Bag Opener

Tub Grinder

Compost Windrow

Compost Turner

Compost Monitoring

Oxygen ContentTemperature

Compost Screening

Finished Compost

Sumter County Compost Facility

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Last updated August 2007 by Dr. Reinhart