Milk and other dairy products are a mixture of fats, proteins, and sugars. Dairy wastes have a very high biochemical oxygen demand (BOD) that requires a considerable amount of effort on the part of microorganisms to break down. Typically, the largest waste stream in the dairy processing sector is wastewater contaminated with dairy. The BOD of dairy processing waste is so great that it is unsafe of to dispose of in conventional sewage. Leakage of dairy wastewater into freshwater ecosystems can be very damaging, depleting the oxygen levels in the water, essential for aquatic life.
The contents of dairy wastewater, like the contents of milk itself, include highly nutritious molecules. Milk contains both soluble and insoluble components. The insoluble components are fats and insoluble milk proteins, known as caseins. The soluble fraction of milk contains the soluble whey proteins and saccharides, including lactose. These nutrients can be provided as food supplementation and nutritional enhancers in food for both people and animals.
Caseins, the large insoluble proteins, have a potential for repurposing as a material for the textile and fashion industry. Gallaith, a polymer manufactured from formaldehyde treated caseins was initially patented at the very end of the 19th century, making it one of the earliest plastics available. Casein plastics were limited by their lack of mouldability, but lauded for their ability to readily adopt colourful patterns, even able to become pearlescent, which was a unique property for polymers at the time. Additionally, it was totally biodegradable, unlike the emerging plastics derived from crude oil fractions. It found most of its functional use in manufacturing small items and rods such as buttons. Its popularity has declined in recent years, aside from in nations such as New Zealand, with considerable milk surpluses.
In recent years, considerable developments have been made to casein polymer technology to make it a more versatile material. This has led to the development of a new generation of milk derived materials, such as the QMILK textiles. QMILK is a company that manufactures biodegradable polymers from renewable milk sources. They cater for fashion and other industries, boasting that the protein creates a naturally silky texture to their cloth. Utilising the proteins from waste milk and dairy wastewater could make a truly circular economy.
In recent years, there have been systems developed, utilising microfiltration techniques to remove organic molecules from dairy wastewater, ensuring it is either fit to be repurposed as fresh cleaning water for manufacturing facility floors or to be treated as normal sewage. One technique, to remove the insoluble component of dairy waste, is to feed the wastewater through filters composed of sodium lignosulfonate. Sodium lignosulfonate can be made cheaply by sulfonating lignin, a large disordered polysaccharide common in woody materials. Filtering the wastewater through sodium lignosulfonate meshes works to remove organic contaminants by selectively trapping hydrophobic molecules, such as fats and casein. A study investigating the efficacy of this process identified a 96% capture rate of fats and, crucially, a 75% decrease in the BOD of the dairy waste water after filtering through the lignosulfonic salt. This is not sufficient to be drained as regular water but is deemed by the authors to be sufficiently clean to be reused as water to wash the factory.
Disappointingly in this filtration system a total protein yield was calculated to be around 46%. However, this can be explained as the system absorbing caseins, but not the other soluble proteins, known as whey.
Another system, that could potentially be run sequentially with the lignosulfonate filters was proposed by another study focusing on the removal of soluble proteins and sugars from dairy wastewater utilising hollow fibre membrane filtration to selectively remove whey proteins and sugars such as lactose. The study yielded a 90% removal rate of lactose from the wastewater and an 80% yield of whey proteins. These extracted materials can then be repurposed for other uses. The whey protein can be utilised as animal feed or protein supplementation for people. The sugars extracted can be used as food additives or building blocks for renewable polymers. Combining these two strategies together could create an in-situ extraction facility that fully utilises the chemicals that are left to decay in fermenters and anaerobic digesters.
IntelliDigest is a biotechnology company specialising in establishing innovative solutions for businesses in the food system, from farm-to-fork, to become more sustainable. Prioritising the elimination of edible food waste and the efficient upcycling of inedible food wastes back into the food system. We draw on our cutting-edge research, consulting, and training capabilities to address the global food sustainability challenges.
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