Managing Organic Wastes By Composting and Vermicomposting

DENR Environmental Education WorkshopNovember 16, 1999Presenter: Craig Coker, Division of Pollution Prevention & Environmental Assistance

PRINCIPLES OFCOMPOSTING

Principles of Composting What Is Compost?

The product resulting from the controlled biological decomposition of organic materials

Sanitized through the generation of heat Stabilized to the point where it is beneficial to plant

growth Provides humus, nutrients, and trace elements to

soils Organic Materials

Landfilled wastes (food, wood, textiles, sludges, etc.) Agricultural wastes (plant or animal) Industrial manufacturing byproducts Yard trimmings Seafood processing wastes In short, anything that can be biodegraded

Why Compost? > 75% of solid waste in NC is organic 12% of landfilled solid waste in NC in 1998

was food wastes/discards Agricultural wastes potential for nutrient

pollution Yard wastes – banned from landfills in 1993 Compost benefits to soil – 25 lbs N, 13 lbs P

(as P2O5), and 7 lbs K (as K2O) per ton of compost

Environmental sustainability

The Composting Process

Biological decomposition in aerobic environment

Decomposition & mineralization by microbes Bacteria, actinomycetes, fungi, protozoans,

nematodes Food source – Nitrogen (biodegradable organic

matter) Energy source – Carbon (bulking agent)

Outputs Heat Water Vapor Carbon Dioxide Nutrients and minerals (compost)

Process occurs naturally, but can be accelerated by controlling essential elements

Composting Essential Elements Nutrients

Carbon/Nitrogen (C/N) – 20:1 to 35:1 Carbon/Phosphorus (C/P) – 100:1 to 150:1

Moisture Content – 50% to 60% (wet basis)

Particle Size – ¼” to ¾” optimum Porosity – 35% to 50% pH – 6.5 to 8.0 Oxygen concentration - >5% Temperature – 130o F. to 150o F. Time – one to four months

Nutrient Balance in Composting

C/N ratio – target is 30:1 > 30:1 – not enough food for microbial population < 30:1 – nitrogen lost as ammonia (odors)

Sources of N & P - Organic wastes, manures, sludges, etc.

Sources of C – wood wastes, woodchips, sawdust Example C/N Ratios:

Food waste 14 – 16 : 1 Refuse/trash 34 –80 : 1 Sewage sludge 5 –16 : 1 Corrugated cardboard 563 : 1 Telephone books 772 : 1

Mixing components needed to optimize C/N ratio

Moisture Content Source of nutrients for microbial protein synthesis

and growth Optimum water content – 50% to 60% (wet weight

basis) < 50% - composting slows due to microbial

dessication >60% - compaction, development of anaerobic

conditions, putrefaction/fermentation (odors) Water may be needed during mixing, composting

Yard wastes – 40 to 60 gallons per cubic yard Typical moisture contents

Food wastes 70% Manures and sludges72% - 84% Sawdust 19% - 65% Corrugated cardboard 8% Newsprint 3% - 8%

Particle Size & Distribution

Critical for balancing: Surface area for growth of microbes (biofilm) Adequate porosity for aeration (35% - 50%)

Larger particles (> 1”) Lower surface area to mass ratio Particle interior doesn’t compost – lack of

oxygen Smaller particles (< 1/8”)

Tend to pack and compact Inhibit air flow through pile

Optimum size very material specific

pH Optimum range 6.5 – 8.0

Bacterial activity dominates Below pH = 6.5

Fungi dominate over bacteria Composting can be inhibited Avoid by keeping O2 > 5%

Above pH – 8.0 Ammonia gas can be generated Microbial populations decline

Porosity and Aeration

Optimum porosity 35% - 50% > 50% - energy lost is greater than heat

produced lower temperatures in compost pile < 35% - anaerobic conditions (odors)

Aeration – controls temperatures, removes moisture and CO2 and provides oxygen Airflow needs directly proportional to biological

activity O2 concentration < 5% - anaerobic conditions

Time and Temperature

Temperature is key process control factor – monitor closely

Optimum temperatures: 130o F. – 150o F. Temperatures above 131o F. (55o C.) will

kill pathogens, fecal coliform & parasites NC Regulations (BYC, small yard waste and

on-farm exempt) Temperatures > 131o F. for 15 days in windrows Temperatures > 131o F. for 3 days in ASP or

invessel Optimum temps achieved by regulating

airflow (turning) and/or pile size

Time and Temperature, cont.Special Olympics/NCSU Composting Project Windrow Temperatures

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Time and Temperature, cont.

Figure 6Special Olympics/UNC-CH Composting Project Windrow Temperatures

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COMPOSTINGTECHNOLOGIES

Backyard Composting Potential diversion – 400 – 800

lbs/year/household Suitable materials

Yard trimmings (leaves, grass, shrubs) Food wastes (produce, coffee grounds,

eggshells) Newspaper

Unsuitable materials Pet wastes Animal remains (meat, fish, bones, grease,

whole eggs, dairy products) Charcoal ashes Invasive weeds and plants (kudzu, ivy,

Bermudagrass)

Types of BYC Systems

Types of BYC Systems

Backyard Composting – Easy To Do!

Locate in flat area, shielded from sun & wind

Add materials in layers (browns/greens)

Turn pile after 1st week, then 2-3 times over next two months

Backyard Composting, cont.

Can add fresh wastes when turning, but better to start new pile

Compost will be ready to use in 4 – 6 months for

piles started in Spring

6 – 8 months for piles started in Fall

Troubleshooting – see Handout

Vermicomposting Home Wastes

Vermicompost = worm castings + bedding Nutrient Value - 6600 ppm organic

nitrogen, 1300 ppm phosphorus & 1,000 ppm potassium

What to feed worms – Vegetable scraps, breads and grains Fruit rinds and peels Tea bags, coffee grounds, coffee filters, etc.

What not to feed worms – Meat, fish, cheese or butter Greasy, oily foods Animal wastes

Vermicomposting – How To Do It

Bin – wooden, plastic or metal with tight-fitting lid 2’ x 3’ x 1’ – good for 2-3 person household Need drainage holes in bottom and air vents

on top and sides

Vermicomposting – How to do it

Add moist drained bedding to worm bin 1” – 2” strips of

newspaper/cardboard/leaves/peat moss/sawdust

Fill bin with bedding Start with 2 lbs of redworms/lb daily scraps

Eisenia foetida or Lumbricus rubellus Bury food scraps under 4 – 6” bedding

Rotate burial around bin to prevent overloading Harvest vermicompost in 3 – 6 months

Institutional Composting

University dining halls Industrial/government cafeterias Current programs in North Carolina

UNC – Asheville (Earth Tub) UNC – Charlotte (Earth Tub – next year) NIEHS (Worm Wigwam) DENR/Archdale Cafeteria Sampson Correctional Institution (Worm Wigwam) Brown Creek Correctional (Rotary Drum

Composter) Several small schoolroom vermicomposting

systems

Institutional Composting

Worm Wigwam (small)

Worm Wigwam (large)

Institutional Composting

Rotary Drum

Earth Tub

Institutional Composting

Key is efficient source separation of organics

Separate collection containers from regular trash

Training needed to minimize contaminants (non-compostables like plastics, foils, metals)

Commercial Composting

Larger-scale commercial and municipal facilities

Feedstocks: manures, agricultural wastes (I.e. cotton gin trash), industrial and municipal wastewater treatment sludges, food wastes

Technologies used: Windrows Aerated Compost Bins Aerated Static Pile In-Vessel Systems

Produced compost sold for $18 - $20/yd3

Overview Technology in Composting

Materials Handling Biological Process Optimization Odor Control

Capital Cost Increases with technology

Operational Costs Decrease with technology

Footprint (Area Required) Decreases with technology (usually)

Windrow Composting

Materials mixed and formed into windrows Windrows 7’ –8’ wide, 5’ – 6’ tall, varying lengths Compost turned and mixed periodically Aeration by natural/passive air movement Composting time : 3 – 6 months

Windrow Composting, cont.

Equipment Needed Grinder/Shredder Tractor/FEL Windrow Turner

tractor-pulled self-propelled

Screener One Acre Can Handle

4,000 - 7,000 CY Compost Mix

Aerated Compost Bins

Aerated Compost Bins

Aeration through porous floor plates Composting time : 2 - 3 weeks Curing time : 2 months Durable materials of construction Equipment needed : front end loader Vector/vermin control needed with food

wastes Capacities : 3 - 4 days food waste +

bulking agent per bin

Aerated Static Pile Composting

Mixed materials built on bed with aeration pipes embedded Aeration by mechanical blowers Composting for 21 days, followed by curing for 30 days Often used in biosolids (sludge) composting

Aerated Static Pile

Better suited to larger volumes (landscape debris, sludges)

Shorter processing time than with windrows

May not be suited to wastes that need mixing during composting, like food wastes

Difficult to adjust moisture content during composting if needed

Odor control difficult with positive aeration

Less land area than windrows, still labor intensive

In-Vessel Composting

More mechanically complex More expensive Smaller footprint (area) Relatively high operations & maintenance

costs

In-Vessel Composting

Commercial Composting in NC Brooks Contractors, Goldston, NC

Windrow composting – eggshells, food waste, yard wastes, cardboard

McGill Environmental, Rose Hill, NC Aerated static pile – biosolids, industrial food

processing residues, furniture wastes Progressive Soil Farms, Welcome, NC

Windrow composting – textile wastes, yard wastes

City of Hickory, NC In-vessel composting – biosolids, sawdust

Mountain Organic Materials, Asheville, NC Aerated compost bins – manures and sawmill

wastes Others: Lenoir, Morganton, Shelby

Benefits of Compost Utilization

Compost Benefits

Physical Benefits Improved soil structure, reduced density,

increased permeability (less erosion potential) Resists compaction, increased water holding

capacity Chemical Benefits

Modifies and stabilizes pH Increases cation exchange capacity (enables

soils to retain nutrients longer, reduces nutrient leaching)

Biological Benefits Provides soil biota – healthier soils Suppresses plant diseases

More Compost Benefits

Binds heavy metals and other contaminants, reducing leachability and bioabsorption

Degrades petroleum contaminants in soils Enhances wetlands restoration by simulating

the characteristics of wetland soils Coarser composts used as mulch provide

erosion control Can provide filtration and contaminant

removal of stormwater pollutants Biofiltration of VOC’s in exhaust gases

Typical Compost CharacteristicsParameter Typical Range Importance

pH 5.0 –8.5 Optimum plant health

Soluble Salts 1 – 10 dS (mmhos/cm)

Phytotoxicity

Nutrients N (0.5-2.5%), P (0.2-2.0%), K (0.3-

1.5%)

Plant VitalityNeed for fertilizers

Water Holdng Capacity

75 - 200% dry weight basis

Irrigation requirements

Bulk Density 700 - 1200 lbs/yd3 Handling/Transportation

Moisture Content

30 – 60% Handling/Transportation

Organic Matter 30 –70% Application Rates

Particle Size < 1” screen size Porosity

Trace Elements

40CFR503 Regs Toxicity

Stability Stable – Highly Stable

Phytotoxicity

Compost Utilization Examples

Planting Bed Establishment Apply 3 – 6 yd3 per 1000 sq. feet Rototill to depth of 6 – 8” Mulch and water after plants installed

Turfgrass Establishment Apply 2” – 3” layer of compost to soil Rototill 6 – 8” deep Rake smooth, lay sod or spread seed Apply starter fertilizer and/or water as needed

Compost Used For Bedding Mulch 2” – 3” layer installed before mulching with pine

bark or hardwood bark mulch

Summary

Composting is an effective way to manage organic wastes

Composting promotes environmental sustainability by converting a waste to a value-added product that improves our environment

Composting can be done at home, at school or at work, and by commercial and municipal entities

Composting is a mix of the art of the gardener, the science of horticulture, and the discipline of waste engineering…

COMPOST HAPPENS!