Composition of dairy sludge
The dairy industry generate on an average 2.5-3.0 litres of waste
per litre of milk processed.
Generally this sludge contains large quantities of casein, lactose, fat
and inorganic salts, besides detergents, sanitizers etc. used for
Dairy sludge contain valuable nitrogen and phosphate although the
nutrient content of potassium is low compared with conventional
Dairy sludge has considerably higher fertilizer value than municipal
Cheese factories have 50% more phosphorus than fresh milk
Dairy sludge has lower levels of heavy metals or other harmful
components than sewage sludge.
The Various Treatments of Dairy
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.
Advantages and Disadvantages of Anaerobic Digestion
Reduction in the mass and volume of sludge
Recovery of biogas
Reduced emissions of greenhouse gases
Relatively high capital costs
Long retention times
High polluted supernatant
Composting and Vermicomposting
Composting is an accelerated biooxidation of
organic matter passing through a thermophilic
stage (45 to 65°C) where microorganisms
liberate heat, CO2 and water
Vermicomposting is also a biooxidation and
stabilization process of organic matter that, in
contrast to composting, involves the joint action
of earthworms and micro-organisms and does
not involve a thermophilic stage
Systems of Composting:
-Continuous vertical reactors
Open systems based on beds or windrows on the
ground containing materials up to 18 inches deep
-this is labour intensive, process organic wastes
Batch reactors are containers raised on legs above
-these can use manual loading and collection or
completely automated and hydraulically driven
continuous flow reactors
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
Vermicompost supplies a suitable mineral balance &
improves nutrient availability
It provides a great reduction in waste bulk density
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
Dairy sludge contains high levels of nitrogen,
phosphorus, potassium and organic matter
In the context of landspreading, the key
elements of groundwater protection are
-groundwater resource underlying the
-response to the perceived risk
Groundwater is most at risk where the
subsoils are absent or thin and in areas of
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
Man-made purpose built wetland
Specially designed to treat wastewater by using various
type of ecosystems and substrate to create the right
Built to treat various types of wastewater such as
Farm run-off, Industrial and Domestic wastes.
How Constructed Wetland work
Sedimentation: plant stems reduces the flow of the
water,hence 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.
Filtration: soil, roots zone, plant litter help to filter the
Absorption: Attractive forces between particles in
wastewater draws them together and settles to base of
Precipitation: of heavy metals to soil and plant
Decomposition: Organic pollutants in the wastewater
are oxidised and reduced in the treatment process.
Advantages & Disadvantages of
Low energy cost.
Provides growth for plant life.
High level of treatment is achieved.
Large area of land is required
No design and operating criteria in place.
Example of Constructed Wetlands in Ireland
objective was to treat water containing sulphate and
metals. Reduce sulphate content by 69%,64% lead &
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 pasteurizes
Legislation in regard to Disposal of
Waste Management Act 1996
Urban Wastewater Directive.
Sludge use in agriculture
Water Framework Directive.