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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
60
70
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6/26 6/30 7/4 7/8 7/12 7/16 7/20 7/24 7/28 8/1 8/5 8/9 8/13 8/17 8/21 8/25 8/29
Date
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Rainfall Average Windrow Temp. 131 deg. F. Daily High Air Temp
Time and Temperature, cont.
Figure 6Special Olympics/UNC-CH Composting Project Windrow Temperatures
60
80
100
120
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180
6/26 7/1 7/6 7/11 7/16 7/21 7/26 7/31 8/5 8/10 8/15 8/20 8/25 8/30
Date
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Rainfall Average Windrow Temp. Reg. Standard Daily High Air Temp
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!