Exploring Wastewater Reclamation and Reuse in the Dairy Industry

The dairy industry is one of the most water-intensive sectors in food processing. From cleaning equipment and pasteurising milk to cooling systems and sanitisation, dairy plants consume enormous volumes of freshwater daily. Much of this water exits the process as wastewater – loaded with organic matter, nutrients, and cleaning chemicals. But what if this wastewater could be treated and put back to use? That’s exactly what wastewater reclamation and reuse is about: turning a costly waste stream into a valuable resource. For the dairy sector, it’s not just an environmental strategy – it’s becoming an operational necessity.

What is wastewater reclamation? 🔗

Wastewater reclamation is the process of treating used water to a quality level that makes it suitable for beneficial purposes again. According to the U.S. Environmental Protection Agency (EPA), water reclamation involves treating and repurposing wastewater for applications such as landscape irrigation, industrial processes, toilet flushing, and even replenishing groundwater basins. The key idea is simple: instead of discharging treated water into rivers or oceans, it gets routed back into productive use.

In the dairy context, reclamation focuses on recovering water from processes like equipment washing, milk cooling, CIP (clean-in-place) systems, and whey processing. This recovered water, once properly treated, can serve various on-site and off-site needs – reducing the plant’s freshwater intake significantly.

Why the dairy industry needs wastewater reclamation 🔗

Dairy processing generates substantial quantities of effluent. Research published in Frontiers in Bioengineering and Biotechnology notes that dairy plants can produce between 0.2 and 10 litres of wastewater for every litre of milk processed. That’s an enormous volume when you consider the scale of modern dairy operations. Moreover, dairy effluent is characterised by high levels of biochemical oxygen demand (BOD), chemical oxygen demand (COD), fats, oils, greases, and nutrients like nitrogen and phosphorus.

Discharging this wastewater without adequate treatment harms aquatic ecosystems, contributes to eutrophication (excessive algae growth in water bodies), and violates environmental regulations. At the same time, freshwater resources are becoming increasingly scarce in many dairy-producing regions. Reclaiming wastewater addresses both problems – it reduces pollutant discharge while conserving precious freshwater supplies.

The growing pressure of water scarcity 🔗

Globally, agriculture already accounts for roughly 70% of freshwater withdrawals. The dairy industry, which uses water not just for production but also extensively for hygiene and sanitation, competes for the same limited supply. In water-stressed regions – parts of India, Australia, the western United States, and southern Europe – dairy operations face real constraints on water availability. Wastewater reclamation offers a practical way to ease this pressure by creating a localised, reliable alternative water source.

Key applications of reclaimed dairy wastewater 🔗

Once treated to the required standards, reclaimed water from dairy operations can serve several purposes. The specific application depends on the level of treatment achieved and local regulatory requirements.

Agricultural irrigation 🔗

Irrigating crops with treated wastewater is one of the most common reuse applications worldwide. According to Environmental Sciences Europe, agriculture holds the largest market share – around 30% – of all reclaimed water use globally. Dairy wastewater, after proper treatment, can be particularly useful for irrigating fodder crops, pastures, and non-food vegetation. The residual nutrients (nitrogen and phosphorus) in treated effluent can actually reduce the need for synthetic fertilisers, providing a dual benefit.

However, irrigation with reclaimed water demands careful quality control. Untreated or poorly treated dairy effluent contains pathogens, cleaning chemical residues, and elevated salt levels that can damage soil structure, contaminate crops, and pose health risks to farmworkers and consumers.

Industrial process reuse 🔗

Within the dairy plant itself, treated wastewater can be reused for purposes that do not require potable-grade water. Common internal reuse applications include cooling tower makeup water, boiler feed (after advanced treatment), floor and yard washing, and initial equipment rinsing. A study published in Chemical Engineering Journal investigated the combination of anaerobic membrane bioreactors with reverse osmosis for dairy wastewater treatment and found that the resulting water quality met standards suitable for use as cooling tower makeup water – at a cost of approximately €0.46 per cubic metre.

Processing water – the condensate generated from milk and whey evaporation – is often the cleanest effluent stream in a dairy plant. With minimal pretreatment, it can be reused for applications that do not involve direct food contact, such as steam generation and membrane cleaning.

Groundwater recharge 🔗

Treated wastewater can also be directed into the ground to replenish depleted aquifers. This practice, known as groundwater recharge, involves allowing reclaimed water to percolate through soil or injecting it directly into underground formations. The EPA notes that recycled water can be injected into aquifers to protect freshwater supplies from saltwater intrusion and to address land subsidence caused by excessive pumping. For dairy-producing areas that depend heavily on groundwater, this approach helps maintain long-term water security.

Treatment technologies that enable reuse 🔗

Raw dairy wastewater cannot be reused directly. It must undergo multiple stages of treatment to remove contaminants and meet quality standards. The treatment chain typically follows a progression from preliminary to primary, secondary, and then tertiary (advanced) processes.

Preliminary and primary treatment 🔗

The first step is screening – removing large debris like packaging fragments and coarse solids that could damage downstream equipment. This is followed by dissolved air flotation (DAF), a widely used primary treatment method in dairy plants. DAF uses micro-bubbles to separate suspended solids, fats, oils, and greases from the water. The separated material floats to the surface and is skimmed off, producing a substantially clarified effluent. Many dairy operations also use coagulation and flocculation at this stage, where chemical or natural coagulants aggregate fine particles into larger clumps for easier removal.

Secondary biological treatment 🔗

The bulk of organic matter removal happens during secondary treatment, which relies on biological processes. In aerobic systems, microorganisms consume dissolved organic pollutants in the presence of oxygen. Common configurations include activated sludge systems, bio-towers, and moving bed biofilm reactors (MBBR). In anaerobic systems, bacteria break down organic material without oxygen – producing biogas (primarily methane) as a valuable byproduct that can offset energy costs.

Research reviewed by PMC (National Library of Medicine) confirms that dairy wastewater’s high organic content makes it well-suited for biological treatment, though the wide fluctuation in effluent composition across production cycles presents a design challenge for treatment plant operators.

Tertiary and advanced treatment 🔗

For reuse applications – especially those involving potential human or crop contact – tertiary treatment is essential. This stage targets the removal of remaining dissolved solids, nutrients, pathogens, and trace contaminants. Key technologies include:

Membrane filtration: Ultrafiltration (UF) and reverse osmosis (RO) are particularly effective. UF removes fine particles and most microorganisms, while RO strips out dissolved salts, sugars, and remaining organic compounds. The combination of biological treatment followed by membrane filtration can produce water that meets stringent reuse standards.

Disinfection: Chlorination, UV irradiation, or ozonation destroys residual pathogens. This step is critical when reclaimed water will be used for irrigation of food crops or for groundwater recharge.

Advanced oxidation: Techniques like ozone combined with hydrogen peroxide can break down persistent organic pollutants and pharmaceutical residues that conventional treatment may miss.

Water quality monitoring: the non-negotiable requirement 🔗

Reuse is only safe and sustainable when water quality is consistently monitored and maintained. The FAO/WHO Joint Expert Meeting on Microbiological Risk Assessment (JEMRA) has provided specific guidance on safe water reuse in the dairy sector. Their framework emphasises that every reuse scenario – meaning each combination of water source and intended application – must be thoroughly reviewed through hazard analysis and risk assessment. This ensures that reuse does not compromise consumer safety or product quality.

Parameters to monitor 🔗

Effective monitoring of reclaimed dairy wastewater involves tracking several key parameters on a regular basis. BOD and COD levels indicate how much organic matter remains after treatment. Total suspended solids (TSS) reflect the clarity and physical quality of the water. pH must be maintained within acceptable ranges to prevent corrosion of equipment or soil damage during irrigation. Nutrient concentrations – particularly nitrogen and phosphorus – need to be controlled to avoid over-fertilising soils or contaminating groundwater. Pathogen indicators such as E. coli and faecal coliform counts are essential for any reuse involving human exposure. Additionally, electrical conductivity measures dissolved salt content, which affects both plant growth and soil health when water is used for irrigation.

Regulatory frameworks 🔗

Regulations governing wastewater reuse vary significantly by country and region. The EU introduced minimum requirements for water reuse in agricultural irrigation in June 2023, specifying limits for E. coli, BOD, TSS, turbidity, and other biological indicators depending on the crop type and irrigation method. In the United States, individual states set their own treatment standards and permitted uses. India’s Central Pollution Control Board (CPCB) also sets discharge and reuse standards that dairy operations must comply with. The common thread across all frameworks is the principle of fit-for-purpose treatment – the quality of reclaimed water must match its intended use.

Environmental and health risks to consider 🔗

While the benefits of wastewater reclamation are clear, the risks cannot be overlooked. Poorly treated effluent used for irrigation can introduce pathogens – including bacteria, viruses, and parasites – into the food chain. A review published in Environmental Health Perspectives (PMC) found that the reuse of inadequately treated wastewater for agriculture has been linked to diarrheal diseases, parasitic infections, and skin conditions among farmworkers and nearby communities.

Chemical risks are also significant. Dairy effluent may contain residues from cleaning agents (acids, alkalis, detergents), antibiotics used in animal health, and emerging organic contaminants that conventional treatment processes may not fully remove. These compounds can accumulate in soils, leach into groundwater, and potentially enter the food chain through crop uptake.

Salinisation is another concern, especially with prolonged irrigation using reclaimed water. Elevated levels of sodium and chloride in treated effluent can degrade soil structure over time, reducing its productivity. Regular soil and water testing is the primary safeguard against this.

Resource recovery: turning waste into value 🔗

Modern approaches to dairy wastewater reclamation go beyond simply cleaning the water. They aim to recover valuable resources from the waste stream itself. Biogas production through anaerobic digestion converts organic matter into methane, which can be used to generate electricity or heat for the dairy facility. Nutrient recovery captures nitrogen and phosphorus for use as agricultural fertilisers – turning a pollution risk into a commercial product. Some facilities even recover dairy sludge rich in nutrients for land application, as research from the Journal of Cleaner Production has demonstrated that dairy processing sludge generally has very low heavy metal content compared to EU standards, making it suitable for agricultural recycling.

This circular approach – where water is treated for reuse, energy is captured from organic waste, and nutrients are returned to farmland – transforms the dairy wastewater challenge from a cost centre into a source of economic and environmental value.

Challenges in implementation 🔗

Despite its promise, scaling up wastewater reclamation in the dairy industry faces several practical hurdles. The high variability in dairy effluent composition – which changes with every production cycle, product type, and season – makes it difficult to design and operate treatment systems at a consistent level. Capital costs for advanced treatment technologies like membrane systems and reverse osmosis can be significant, particularly for small and medium-scale dairy processors. There is also the matter of public and regulatory acceptance: even when treated water meets all quality standards, there can be resistance to its use, especially for food crop irrigation or any application close to the human food chain.

Operational expertise is another gap. Running a multi-stage wastewater treatment plant requires trained personnel who can monitor performance, adjust processes, and respond to upsets. Many dairy operations, especially in developing regions, lack this capacity. Bridging this gap through training, technology standardisation, and supportive policy frameworks is critical for widespread adoption.

The path forward 🔗

Wastewater reclamation is not optional for the dairy industry – it is becoming a fundamental component of sustainable operations. As freshwater resources tighten and environmental regulations grow stricter, dairy processors who invest in treatment and reuse infrastructure will gain a competitive and operational advantage. Innovations like integrated anaerobic membrane bioreactor systems, microalgae-based treatment, and microbial consortium approaches are making reclamation more efficient and cost-effective. The goal is a closed-loop system where water, energy, and nutrients cycle continuously within and around the dairy operation – minimising waste, reducing costs, and protecting the environment.

What do you think? How can smaller dairy operations, particularly in developing countries, be supported in adopting wastewater reclamation practices? And should treated dairy wastewater be permitted for irrigating food crops – or should its use remain restricted to non-food applications?

References

1. https://www.epa.gov/waterreuse/basic-information-about-water-reuse
2. https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2024.1425933/full
3. https://enveurope.springeropen.com/articles/10.1186/s12302-019-0283-0
4. https://www.sciencedirect.com/science/article/abs/pii/S1385894725071839
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC5434364/
6. https://www.who.int/publications/i/item/9789240066588
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC6292135/
8. https://www.sciencedirect.com/science/article/abs/pii/S0959652619315410