Pollutant loads of dairy effluent and its potential on pig growth performance.
Sithole, Nhlakanipho Wellcome.
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The broad objective of the study was to determine pollutant loads in dairy effluent and assess its potential in feeding growing pigs. The first specific objective was to assess water utilization and conservation methods used by dairy processing plants. A structured questionnaire was administered to 233 companies and 103 enterprises responded. The idea was to determine water conservation strategies used in dairy processing plants and their level of water consumption. The size of the company on waste water generation and the treatment method used were captured. Water use on different processes was high (P<0.05) in large companies and low (P<0.05) in small companies. Water conservation strategies used were influenced (P<0.05) by period of operation of the company. The size of the company, location and period of operation did not affect (P>0.05) water source and water treatment used by companies. To assess the pollutant loads generated by the different sizes of companies, a total of 150 dairy effluent samples were collected from dairy processing plants. These sample were obtained from small (n = 10); medium (n = 10) and large scale (n = 10) companies. Sources of effluents collected included wash equipment (milk tanks, pasteurizer and vats), effluents from different products (cheese, milk, yoghurt, fruit juices and sour milk), machine cooling effluent, effluent mixture before treating and effluent mixture after treating. The samples were collected from KwaZulu-Natal, Gauteng, Western Cape, Free State and Limpopo provinces using a sterilized 1ℓ plastic bottle and 150 mℓ plastic beaker (for coliform) and stored at 5 ± 1°C. The effluents were analysed for chemical oxygen demand (COD), suspended solids, nitrate/nitrite, chloride, sulphate and fluoride concentrations, colour, dissolved calcium, dissolved magnesium, pH, total dissolved solids (TDS), total hardness, turbidity and total coliform counts. The location of the company did not affect (P>0.05) pollutant loads except for fluorides (P<0.05). The size of company had high impact (P<0.001) on pollutant loads except (P>0.05) in sulphate concentration. Pollutant loads were also highly affected (P<0.001) by the type of product. The pH and concentrations of suspended solids and fluorides were not influenced (P>0.05) by water treatment. Effluent generated from washing equipment, products and pasteurizer cooling machine were affected by size of company and type of products but not the location of the company. The high volumes and concentration of effluents from washing of tanks lead to exploring the potential of using the effluent in feeding growing pigs. Objective 3 was, therefore, designed to compare the growth performance of pigs fed on dairy effluent from washing tanks. Seventy two weaned male Landrace x Large White pigs housed in individual cages were randomly assigned to treatments. Half of the pigs were fed on dairy effluent, while the remainder received regular reservoir water. Average water intake (ADWI) (2.48 ± 1.21 l/d), average daily feed intake (ADFI) (1.03 ± 0.31 kg/d), average daily gain (ADG) (0.53 ± 0.39 kg/d) and feed conversion ratio (FCR) (2.5 ± 0.27) were not affected (P>0.05) by water source. The ratio of water intake (WI) to feed intake (FI) (2.4 ± 0.72) and ratio of water intake (WI) to body weight gain (BWG) (0.8 ± 0.2) was similar between the two treatments (P>0.05). The use of dairy effluent to feeding pigs could, therefore, save fresh water use.