Using algae to treat dairy farm wastewater

Dairy farming contributes significantly to the agriculture waste load because of the high volumes of wastewater generated. Phycoremediation has come to the fore as a promising alternative treatment for dairy farm and dairy processing wastewater, say Mzamo Mnikathi, technical intern, and Jon McCosh, chief scientist at the Institute of Natural Resources.

Using algae to treat dairy farm wastewater
Unchecked wastewater can have a detrimental effect on sensitive aquatic environments. It can also leach into groundwater, potentially contaminating drinking water.
Photo: Supplied
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South Africa’s dairy farming industry is a vital component of the agriculture sector, contributing significantly to the country’s economy. With approximately 360 000 cows being milked daily, South Africa stands out as one of Africa’s leading milk producers.

However, dairy farms are not only known for their economic benefits, they also consume substantial volumes of water and generate considerable volumes of wastewater, primarily in the form of slurry waste from milking parlour operations. This wastewater can pose a significant threat to the environment if not properly managed.

Now, a groundbreaking initiative in South Africa is exploring the use of algae to treat dairy farm wastewater with the aim of protecting our precious water resources.

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Importance of water in dairy farming

Water is crucial for dairy farming, serving various purposes like irrigation, washing cows, removing mud and dung, and cleaning milking equipment.

The milking process generates large volumes of wastewater, which contains both organic pollutants (for example, waste milk, manure, and urine) and inorganic pollutants (cleaning chemicals, disinfectants, medications, and so on).

If this wastewater is not managed responsibly, it can enter rivers and streams and have detrimental effects on sensitive aquatic environments. Moreover, wastewater applied to fields can leach into groundwater, potentially contaminating drinking water sourced from boreholes.

The agriculture sector, including dairy farming, utilises a large percentage of the world’s freshwater supplies, and South Africa is no exception. As the fourth-largest agricultural industry in the country, dairy farming plays a key role in the economy but also contributes significantly to the waste load due to high levels of wastewater generation.

Therefore, effective treatment of dairy farm wastewater is essential for environmental protection and ensuring the sustainability of water resources.

Current methods of treating wastewater

In South Africa, settling ponds are the common method for managing dairy farm wastewater. These ponds allow solids to settle at the bottom, with the remaining water being used for irrigation onto grass pastures that are grazed by dairy cows.

However, this method often falls short of meeting national wastewater standards, leading to environmental concerns. Farmers may also utilise engineered wetlands, which focus on pollution removal, but this approach requires large areas of land that could otherwise be used for grazing.

Additionally, constructed wetlands can present challenges, such as high construction costs and potential pest breeding.

Recognising these issues, Milk South Africa commissioned research in 2021 to produce best-practice guidelines for wetland management on dairy farms. This research highlights the importance of wetland maintenance and the establishment of buffer zones around watercourses, which can enhance biodiversity and mitigate pollution.

However, the effectiveness of a wetland depends on its nature, condition, and placement within the watershed.

Dairy wastewater (DWW) can also be treated through various methods, including mechanical, physiochemical, and biological approaches. Biological treatment methods are particularly cost-effective for removing organic material from DWW due to its easily biodegradable organic contents.

The large volumes of wastewater from a dairy concern can pose a serious environmental threat. A groundbreaking initiative in South Africa is exploring the use of algae to address it.

Anaerobic processes, which require lower energy consumption and produce less sludge, are considered more efficient than other methods.

However, no single treatment method consistently produces wastewater that meets the minimum discharge standards, necessitating a combination of approaches to achieve optimal results.

Over time, a combination of aerobic and anaerobic treatments has been employed, resulting in benefits such as low energy consumption, minimal sludge production, and fewer chemical requirements.

Recently, there has been a paradigm shift in the dairy industry, with an increasing recognition of wastewater as a valuable resource rather than merely waste. Dairy farm waste contains nutrients that can be transformed into economically valuable bioproducts, such as biofuel and biofertiliser, with minimal changes to existing systems.

Research gaps and the need for effective treatment

Despite the advances in wastewater treatment technology, there are significant gaps in research regarding dairy farm wastewater treatment in South Africa. Notably, there is a lack of awareness of the on-site treatment technologies employed by farmers and variations in these technologies among different farms.

The success rates and efficiencies of these treatment methods concerning the specific chemical properties of each farm’s wastewater have not been adequately documented. This lack of data is concerning because farmer-based innovations that are not included in the existing literature may yield interesting and valuable results.

Characterising DWW across various farms and processing plants is critical in the South African context, particularly before and after on-site treatment. Additionally, exploring biological treatment technologies could yield positive results, as they are generally viewed as effective for treating dairy wastewater.

Given the diminishing freshwater reserves and rising costs of nitrogen-phosphorus-potassium-based fertilisers, research into optimal treatment methods for nutrient-rich dairy wastewater is crucial for both environmental sustainability and economic viability.

Emerging from the literature review, a process to audit DWW was developed, allowing farmers to self-report on a series of questions related to on-farm practices and wastewater management.

Notably, all farmers indicated that they did not monitor wastewater quality, nor did any report water quality issues associated with their DWW. This lack of monitoring highlights a significant gap in knowledge and practice that needs to be addressed.

A breakthrough solution

To tackle the challenges associated with dairy farm wastewater, scientists from the Institute of Natural Resources in Pietermaritzburg and the Durban University of Technology, KwaZulu-Natal, have collaborated to explore a low-cost, innovative solution called phycoremediation.

This technique utilises algae to clean wastewater, leveraging the algae’s natural ability to absorb nutrients and pollutants from the water. Algae, tiny green organisms that thrive in aquatic environments, use sunlight and carbon dioxide for growth, effectively acting as nature’s sponge.

Laboratory experiments have demonstrated that certain strains of microalgae can effectively clean dairy farm wastewater, removing more than 90% of harmful pollutants. This success underscores the potential of algae as a sustainable solution for treating dairy wastewater.

Advantages of algae

The benefits of using algae for wastewater treatment are as follows:

  • Water conservation. By cleaning and reusing wastewater, dairy farms can reduce their consumption of fresh water, which is crucial in water-scarce regions like South Africa.
  • Environmental protection. Clean water contributes to healthier rivers, lakes, and other ecosystems, protecting wildlife and ensuring safe water for communities.
  • Cost-effectiveness. Algae are relatively easy to grow and maintain, making this treatment method affordable for dairy farms. It reduces the need for expensive chemical treatments and complex wastewater systems.

However, challenges remain. High concentrations of nutrients from waste milk, manure, and urine can create a cloudy, oxygen-poor environment that hinders algae’s effectiveness.

While diluting the wastewater can help, further research is necessary to optimise the process and improve efficiency. Field trials are being initiated to test phycoremediation in selected dairy processing facilities, with the aim of refining the treatment process.

The bigger picture

This innovative approach not only helps protect the environment but will also help to support the sustainability of dairy farms, ensuring that natural resources are not further depleted or wasted, allowing future generations to benefit.

By using algae to treat wastewater, dairy farms can continue producing milk and other dairy products without negatively impacting the environment.

Phycoremediation presents a promising treatment alternative for both dairy farm wastewater and dairy processing wastewater.

Nonetheless, the high chemical oxygen demand levels in processing wastewater require dilution to achieve optimal nutrient removal.

Turbidity in dairy farm wastewater also interferes with light penetration, impacting the growth of photosynthetic algae and the efficiency of pollutant removal.

Research findings indicate that nutrient removal is optimal at 60% concentration of both dairy farm wastewater and dairy processing wastewater . However, some farms exhibited low nutrient removal rates due to high turbidity, which limited algal growth.

Conversely, facilities with favourable conditions for algal growth showed satisfactory nutrient removal rates.

Dairy farming is essential for providing us with the delicious milk products we enjoy every day, but it also comes with environmental challenges. The innovative work of scientists using algae offers a promising solution to effectively treat dairy farm wastewater while at the same time protecting our water resources.

By embracing sustainable practices and supporting clean water initiatives, we can all play a part in ensuring a healthy and vibrant environment for generations to come.

Email Mzamo Mnikathi at [email protected] za, Jon McCosh at [email protected], or the Institute of Natural Resources at [email protected].

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