WASTE WATER MANAGEMENT ON THE DAIRY FARM

As the dairy industry expands to meet demand, there will be a significant increase in the use of scarce water resources and therefore an increased generation of wastewater. The milking parlour is one area where wastewater can be minimised. Here, wastewater is generated through cleaning processes that occur before and after milking. This results in two wastewater streams: 1) wastewater from cleaning, disinfection and sanitation of milking machinery and equipment (i.e. containing water, milk, detergents etc.), and 2) floor washing which generates wastewater containing animal waste in the form of manure and urine, waste milk and dirt. These could be a considerable proportion of the waste burden since dairy wastewater contains a variety of suspended and dissolved solids, nutrients, fats, sulphates, chlorides, trace and soluble organic compounds; and is characterised by a high biological oxygen demand (BOD) and chemical oxygen demand (COD). While the exact composition of dairy wastewater may vary depending on the specific production operation, it must be appropriately treated before being discharged into any aquatic or terrestrial environment.

The dairy industry employs strict standards for milk quality, animal welfare and food safety. Therefore, dairy wastewater treatment is well-managed, the methods which include physico-chemical and biological methods. However, although there are data on the efficacy of these methods, there are no comprehensive guidelines on the application of the biological methods, and limited information on the suitability of applicable technologies such as sequencing batch reactors (SBR) and micro-algae for dairy parlour wastewater treatment. This motivated the Institute of Natural Resources (INR) to partner with the Durban University of Technology’s (DUT) Institute for Water and Wastewater Technology (IWWT) to conduct research into understanding the physico-chemical composition of wastewater produced by commercial dairy farms in South Africa and assessing the feasibility of using cost effective biological wastewater treatment methods for mitigating the environmental effects of the wastewater.

The project has a focus on the KwaZulu-Natal dairy sector, with several dairy farms participating. Through a collaborative learning approach, dairy farmers that are involved in the project benefit directly from the research findings, knowledge transfer and the opportunity to pilot the lab-based technologies on their farms.

Preliminarily investigations have revealed that the common on-farm dairy wastewater treatment method involves the use of gravity fed lagoons or ponds to treat wastewater through sequential settlement of solids and in some cases phyto-extraction (using typical wetland plant species). They are relatively low cost systems, requiring little energy and can reduce the need for chemicals. However, the use of lagoons or ponds come with their own set of problems. They occupy a large area of land, have evaporative water losses (which leads to nutrient/chemical concentration) and may also produce odours and lead to insect pests which impact neighbouring communities. Fertigation, using the nutrient rich wastewater, is common practice due to the rising costs of fertilisers. To counteract these disadvantages, the research team is investigating the potential of creating bio-fertilisers from the wastewater as an environmentally safer alternative. The two-year multi-stakeholder project has already revealed some interesting results, with many farmers standing to benefit should these lab-based solutions prove to be scalable to farm level.