Characterisation of selected dairy processing waste streams from Victoria, Australia

Twenty-six waste samples from eight factories in the Goulburn Valley and south-west Victoria were characterised to determine their suitability for a range of potential uses. The waste streams were found to be diverse in nature and composition. They included sludges and product rejects, such as cheeses, powders and ice-cream solids. The nutrient quality of many dairy processing wastes make them ideal for direct land application, but little information is available about their public health, agronomic and environmental impacts when they are applied to land. The moisture content of the sludges ranged from 21-97% (w/w wet basis). On a dry basis, the total nitrogen, total phosphorus and total potassium of these wastes ranged from 0.7-8.9% (w/w), 913-21,349 mg/kg and 205-19,673 mg/kg, respectively. Waste streams from cheese and/or ice-cream production were commonly recycled as stock feed. The digestibility for the stock feeds ranged from (w/w d.m.) 76.6-94.1%, and there was wide variation in carbohydrate (1.4-92%), protein (4.5-82.1%) and fat (0.4-78.9%) contents between samples. Waste streams that were recycled as tallow had fat contents ranging from (w/w d.m.) 75.3% to more than 95%, but only two of these were close to meeting the specifications for technical tallow production. Three high-fat (>44% w/w d.m.) waste streams were also composted, including two grease trap wastes. High-fat waste streams could possibly be used as boiler fuel, or for bio-diesel production, but at current waste volumes, these applications are probably not yet economically viable. Variability in the composition of dairy processing waste streams is probably not a major concern for the continuing low-level utilisation of these waste streams, such as for land application, composting and stock feed. However, a better understanding of this variability is needed if higher value uses are to be considered for dairy-processing waste streams.