Disposal Of Dairy Sludge Joan Gray Lorraine Mitchell Edel Pierce Waste Management Michael Broaders
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
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.
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.
Anaerobic Digestion cont • Anaerobicdigestion 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 • 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
Differences Between Composting and Vermicomosting • 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 • 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
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
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 • 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
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
Nutrient Management Plans • 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 • The following are not used in Ireland • -Sea disposal-not legal since introduction of EU Urban Wastewater Directive in 1991 • -Incineration • -Landfill
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 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. • 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 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.
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.
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.
Legislation in regard to Disposal of Dairy Wastes • Waste Management Act 1996 • Nitrate Directive. • Urban Wastewater Directive. • Sludge use in agriculture • Water Framework Directive.