Disposal Of Dairy Sludge

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 washing.

Dairy sludge contain valuable nitrogen and phosphate although the nutrient content of potassium is low compared with conventional mineral fertilizers.

Dairy sludge has considerably higher fertilizer value than municipal sludge.

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

Anaerobic Digestion Composting (vermicomposting) Land Spreading

Sea Disposal Land Filling Incineration

Constructed Wetlands Lime Stabilization

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.

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

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

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

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

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

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

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

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

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.

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 micro-organisms feed off the wastewater which plays a major role in the water cleaning process.

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.

Precipitation: of heavy metals to soil and plant material.

Decomposition: Organic pollutants in the wastewater are oxidised and reduced in the treatment process.

Advantages & Disadvantages of Wetlands

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.

Example of Constructed Wetland

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.

Lime stablization 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 the sludge.

Legislation in regard to Disposal of Dairy Wastes

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