DAIRY WASTEWATER COMPOSITION IN RELATION TO ACT REGULATIONS

Environmental regulations and waste management in SA are governed by the National Environmental Management Act (NEMA) and other related legislation. Waste management, including dairy waste, falls under the jurisdiction of the Department of Environment, Forestry, and Fisheries (DEFF) (Government Gazette, 2013). According to the National Water Act 36 of 1998 (NWA) authorization enables the disposal of wastewater from dairy farming activities into on-site or off-site slurry ponds, as well as irrigation with wastewater from slurry ponds if certain conditions are met, such as the slurry pond must be at least 100 meters away from a stream and 500 meters away from a wetland, and irrigation must be at least 500 meters away from a wetland. Water quality guidelines have been established to ensure that the irrigation of dairy waste water does not pose a threat to human health, the environment, or agricultural crops. These guidelines then define the permissible limits of certain contaminants in water. To establish to what extend commercial dairy farms meet these quality guidelines the broad aim of the study cited was (a) to conduct a physico-chemical analysis of wastewater produced by commercial dairy farms, and (b) assess the feasibility of using low cost biological wastewater treatment methods for mitigating the environmental effects of the wastewater. In this report results of (a) are presented.

Dairy effluent was collected from slurry ponds of four dairy farms located in the Midlands of KZN. Electrical conductivity, total dissolved solids, pH, and dissolved oxygen pHmV of the wastewater were analysed using a portable YSI 556 (YSI, Yellow Wood Springs, USA). The total NH₄-N, NO₃-N, COD and TP were also analysed.

There was high electrical conductivity in all the samples tested with an average value of 2163 uS/cm. The total dissolved solids also ranged between 0.665-7.28 g/L indicating high levels of inorganic salt, minerals and heavy metals in the water. The electrical conductivity is higher than the municipality wastewater treatment plants. These results coincided with high NH₄-N ranging between 71.5 and 276 mg/L as well as high COD levels. Although these numbers are within ranges shown in the literature, all samples for COD and NH₄-N are in exceedance of the thresholds as can be seen in Figures 1 and 2, while 10 of the 16 samples exceeded the threshold for EC (Figure 3).                         

These results highlight that better practices are necessary on-farm to bring the wastewater to compliance with the legislated thresholds for irrigation, which necessitates wastewater treatment as envisaged in (b).

Figure 1: