COMPOSTING

(Managing Organic Wastes )

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
 Landfill wastes (food, wood, textiles, sludge etc.)
 Agricultural wastes (plant or animal)
 Industrial manufacturing byproducts
 Yard trimmings
 Seafood processing wastes
 In short, anything that can be biodegraded
Why Compost?
 40–85% of solid waste in INDIA is organic (National Solid
Waste Association of India, 2003)
 12% of landfilled solid waste is food wastes / discards
 Agricultural wastes  potential for nutrient pollution
 Yard wastes – banned from landfills

 Compost benefits to soil – 25 lbs N, 13 lbs P (as P 2O5) 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, sludge, 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 sludges 72% - 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

 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 rate is directly proportional to the 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
 Optimum temps achieved by regulating airflow (turning)
and/or pile size
COMPOSTING
TECHNOLOGIES
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
 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
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
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
Overview Of Citizen’ Initiatives For Waste Collection And
Composting In India
 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 Characteristics
Parameter Typical Range Importance
pH 5.0 –8.5 Optimum plant health
Soluble Salts 1 – 10 dS (umhos/cm) Phytotoxicity

Nutrients N (0.5-2.5%), P (0.2- Plant Vitality

2.0%), K (0.3-1.5%) Need for fertilizers
Water Holdng 75 - 200% dry weight Irrigation requirements
Capacity basis
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
Stability Stable – Highly Stable Phytotoxicity
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!
Why Should You Compost????

BECAUSE IT’S ALL ABOUT RESOURCE

CONSERVATION AND WATER QUALITY!