Disposal Of Dairy Sludge

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Disposal Of Dairy Sludge

• Joan Gray Lorraine Mitchell Edel Pierce

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How Dairy Sludge Arises

• 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

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Composition of dairy sludge

• 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.

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The Various Treatments of Dairy Sludge

• Anaerobic Digestion
• Composting (vermicomposting)
• Land Spreading
• Sea Disposal
• Land Filling
• Incineration
• Constructed Wetlands
• Lime Stabilization

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Anaerobic Digestion

• 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.

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Anaerobic Digestion cont

• 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.

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Advantages and Disadvantages of Anaerobic
Digestion

• Advantages
• Recovery of biogas
• Reduction in the mass and volume of sludge
• Reduced emissions of greenhouse gases
• Disadvantages
• Relatively high capital costs
• Long retention times
• High polluted supernatant

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Differences Between Composting and Vermicomosting

• Composting is an accelerated biooxidation of
  organic matter passing through a thermophilic
  stage (45 to 65C) 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

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Composting

• Systems of Composting
• -Windrow
• -In-vessel
• -Continuous vertical reactors
• -Horizontal reactors

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Vermicomposting

• 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

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Advantages of Vermicomposting

• 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

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Principles of Vemicomposting

• 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

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Landspreading

• 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 Aquifers-must
  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

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Buffer Zones for Landspreading of Organic Waste

• 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

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Nutrient Management Plans

• The objective of NMPs 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

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Other Methods of Disposal

• The following are not used in Ireland
• -Sea disposal-not legal since introduction of EU
  Urban Wastewater Directive in 1991
• -Incineration
• -Landfill

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Constructed Wetlands
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Constructed Wetlands

• 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.

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How Constructed Wetland work

• 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 micro-organisms 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.
• DecompostionOrganic pollutants in the wastewater
  are oxidised and reduced in the treatment process.

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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.

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Examples of it use the Dairy Industry Ireland

• 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,Conductivi
  ty.

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Example of Constructed Wetland
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Yearly Reduction in B.O.D
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Yearly Reduction in C.O.D
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Other Example of Constructed Wetlands in Ireland

• Tara Mines
• objective was to treat water containing
  sulphate and metals. Reduce sulphate content by
  69,64 lead 98 Zinc.

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Lime stabislation

• 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.

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Legislation in regard to Disposal of Dairy Wastes

• Waste Management Act 1996
• Nitrate Directive.
• Urban Wastewater Directive.
• Sludge use in agriculture
• Water Framework Directive.