Transcript Disposal Of Dairy Sludge

Disposal Of Dairy Sludge
Joan Gray
Lorraine Mitchell
Waste Management
Michael Broaders
Edel Pierce
How Dairy Sludge Arises
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Wastewater sludge is generated at milk processing facilities after
milk is processed into butter, cheese and other products.
The washings created from cleaning processes (pipes, tanks etc)
sent to WWTP and the main by-product from this treatment process
is sludge.
The dairy industry consumes 2 to 6 m3 of water per tonne of milk
entering the plant.
Over 75,000 tonnes of sludge is generated in Ireland from the
treatment of wastewater from milk processing plants.
This sludge generated is predominantly land spread
Composition of dairy sludge
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Dairy sludge contain valuable nitrogen and phosphate although the
nutrient content of potassium is low compared with conventional
mineral fertilizers.
Dairy sludge contains high levels of N, P,K and organic matter.
Dairy sludge has considerably higher fertilizer value than municipal
sludge.
Differences in the fertilizer value of sludge from different kinds of
dairy plants e.g. cheese factories have 50% more phosphorus than
fresh milk dairies.
Dairy sludge has lower levels of heavy metals or other harmful
components than sewage sludge.
The Various Treatments of Dairy
Sludge
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Anaerobic Digestion
Composting (vermicomposting)
Land Spreading
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Sea Disposal
Land Filling
Incineration
Constructed Wetlands
Lime Stabilization
Anaerobic Digestion
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Anaerobic digestion is the breakdown of organic material by a
microbial population that lives in an oxygen free environment.
AD treats waste by converting putrid organic materials to carbon
dioxide and methane gas (biogas can be used to produce electrical
power and heat).
The conversion of solids to biogas leads to much smaller quantities
of solids that must be disposed.
Anaerobic Digestion cont
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Anaerobic digestion is carried out by a group of bacteria which work
together to convert organic matter to gas and inorganic
constituents.
The soluble organic materials that are produced through hydrolysis
consists of sugars, fatty acids and amino acids are converted to
carbon dioxide.
Other groups of bacteria reduce hydrogen to produce ammonia,
hydrogen sulphide and methane.
A group of methanogens converts acetic acid to methane gas.
Advantages and Disadvantages of Anaerobic Digestion
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Advantages
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Recovery of biogas
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Reduction in the mass and volume of sludge
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Reduced emissions of greenhouse gases
Disadvantages
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Relatively high capital costs
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Long retention times
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High polluted supernatant
Differences Between Composting
and Vermicomosting
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Composting is an accelerated biooxidation of
organic matter passing through a thermophilic
stage (45 to 65°C) where microorganisms
liberate heat, carbon dioxide and water
Vermicomposting is also a biooxidation and
stabilisation process of organic matter that, in
contrast to composting, involves the joint action
of earthworms and micororganisms and does
not involve a thermophilic stage
Composting
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Systems of Composting:
-Windrow
-In-vessel
-Continuous vertical reactors
-Horizontal reactors
Vermicomposting
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Open systems based on beds or windrows on the
ground containing materials up to 18 inches deep
-this is labour intensive, process organic wastes
slowly
Batch reactors are containers raised on legs above
the ground
-these can use manual loading and collection or
completely automated and hydraulically driven
continuous flow reactors
Advantages of Vermicomposting
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Organic wastes can be broken down and fragmented
rapidly by earthworms, resulting in a stable non-toxic
material with good structure which has potentially high
economic value as a soil conditioner for plant growth
Vermicompost is a finely divided peat like materials with
excellent structure, porosity, aeration, drainage and
moisture-holding capacity
Vermicompost supplies a suitable mineral balance &
improves nutrient availability
It provides a great reduction in waste bulk density
Principles of Vemicomposting
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Certain species of earthworms can consume
organic residuals very rapidly and fragment
them into much finer particles by passing them
through their gizzard
Earthworms derive their nourishment from the
micororganisms that grow upon the organic
materials
They have both roles of turning and maintaining
the organics in an aerobic condition
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Vermicomposting systems must be maintained at
temperatures below 35ºC. Exposure to to
temperatures above this, even for short periods, will
kill them.
Key to successful vermicomposting lies in adding
materials to the surface of piles or beds in thin,
sucessive layers so that heating does not become
excessive
The processing of organic materials occurs most
rapidly at temperatures between 15-25ºC & moisture
contents of 70-90%
Species of earthworm used: Eisenia fetida, Lumbricus
rubellus, Eudrilus eugeniae, Perionyx excavatus
Landspreading
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The dairy industry consumes 2 to 6m3 of
water per tonne of milk entering the plant
The effluent produced is either spread
directly on agricultural land or treated in an
on-site or local mixed wastewater treatment
plant
Dairy sludge contains high levels of nitrogen,
phosphorus, potassium and organic matter
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In the context of landspreading, the key
elements of groundwater protection are
-groundwater vulnerability
-groundwater resource underlying the
proposed spreadlands
-response to the perceived risk
Groundwater is most at risk where the
subsoils are absent or thin and in areas of
karstic limestone
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Regionally Important Aquifers-must have a
consistent minimum of 2m of soil/subsoil
before landspreading takes place
Locally Important Aquifers & Poor Aquifersmust have a consistent minimum of 1m of
soil/subsoil before landspreading takes place
No landspreading if vulnerability of
groundwater source is classified as Extreme
or High within Inner Protection Area
Buffer Zones for Landspreading of
Organic Waste
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Sensitive buildings-200m
Dwelling houses-100m
Karst features-30m
Lakes and main river channels-20m
Small watercourses-10m
Domestic wells-50m
Public water supplies-300m
Nutrient Management Plans
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The objective of NMP’s is to protect the
quality of water resources by avoiding
pollution from agriculture. The preparation of
a NMP for a REPS scheme involves the
following:
-the planner shall identify current land use & areas of
farm which nutrient application should be restricted
-baseline soil fertility survey of the farm
-sampling areas shall be selected on the basis of such
characteristics as soil type, previous cropping and
fertilising history
Other Methods of Disposal
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The following are not used in Ireland
-Sea disposal-not legal since introduction
of EU Urban Wastewater Directive in 1991
-Incineration
-Landfill
Constructed Wetlands
Constructed Wetlands
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Man-made purpose built wetland
Specially designed to treat wastewater by using various
type of ecosystems and substrate to create the right
biological environment.
Built to treat various types of wastewater such as
Farm run-off, Industrial and Domestic wastes.
How Constructed Wetland work
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Sedimentation: plant stems reduces the flow of the
water allow sediments in wastewater to be deposited in
the marsh.
Bacterial Action: the leaves draw oxygen through the
roots. Oxygen is released which allows micro-organisms
to thrive in the roots zone of the marsh. All microorganisms feed off the wastewater which plays a major
role in the water cleaning process.
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Filtration: soil, roots zone, plant litter help to filter the
pollutants.
Absorption: Attractive forces between particles in
wastewater draws them together and settles to base of
wetland.
Precipcation: of heavy metals to soil and plant
material.
Decompostion:Organic pollutants in the wastewater
are oxidised and reduced in the treatment process.
Advantages & Disadvantages
Advantages
 Low energy cost.
 Provides growth for plant life.
 High level of treatment is achieved.
Disadvantages
 Large area of land is required
 No design and operating criteria in place.
Examples of it use the Dairy Industry Ireland
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Cheese Industry Kilmeaden Co Waterford.
In 2000 Developed a wetland system to treat dairy
wastes produced
The objective of the plan was to create ecological affect
and to reduce various organic pollutants.
Monitoring of the system was done over a 3 year period.
B.O.D,Nitrates,PO4,Ammonia,pH,C.O.D,Conductivity.
Example of Constructed Wetland
Yearly % Reduction in B.O.D
2001
2002
2003
Lagoon 1
32
61
23
Lagoon 2
82
95
73
Lagoon 3
81
93
82
Yearly % Reduction in C.O.D
2001
2002
2003
Lagoon 1
44
63
26
Lagoon 2
82
90
77
Lagoon 3
71
90
86
Other Example of Constructed Wetlands in Ireland
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Tara Mines
objective was to treat water containing sulphate and
metals. Reduce sulphate content by 69%,64% lead &
98% Zinc.
Lime stabislation
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Addition of lime to sludge material,
creates a high pH as a result.
Stabilisation occurs as a result of the
reaction between the lime & water.
Produces a exothermic heat pasteurises
the sludge.
Legislation in regard to Disposal of
Dairy Wastes
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Waste Management Act 1996
Nitrate Directive.
Urban Wastewater Directive.
Sludge use in agriculture
Water Framework Directive.