Discipline: effluent management; Keywords: reduced water intake, waste-water disposal, processing, cleaning processes.
Efficient water use and effluent management by the dairy processing industry is in the national interest as South Africa is a water scarce country and the quality of water is of concern. It is therefore in the interest of the industry to have guidelines to reduce water intake and waste-water disposal. As far back as 1970 an attempt was made to that effect by J.W. Funke in the CSIR Guide K12, with the title: “Industrial water and effluent management in the milk processing industry”. In 1989 the Water Research Commission (WRC) contracted the engineering company Steffen, Robertson and Kirsten Inc to come up with specific guidelines. These were reported in the WRC Project no 145, TT 38/89, the title being: Water and waste-water management in the Dairy Industry. While some of the major findings and targets of this report is discussed here, it is recognized that significant changes have occurred in the industry. The WRC has recognized the need for an update as well and is in the process of commissioning new research.
The report estimated that the dairy processing industry in 1986 used some 4.5 million m3 water. At the time there were more than 150 factories producing a wide range of products such as fresh milk, butter, cheese, yogurt, milk powder, ice cream, condensed milk and various milk-based desserts. These factories discharged large quantities of effluent from the processing and cleaning processes, the ratio being dependent on the particular products made. In the case of pasteurized milk, the effluent discharge was often 85 to 90% of water intake, for butter and cheese 90 to 95%, whereas for milk powder and condensed milk sometimes more than 100%. Major effluent quality contaminants present were oxygen absorbed (OA), chemical oxygen demand, total dissolved solids and suboptimal pH. The final effluent OAs, for example, varied between 200 and 10000 mg per litre.
Based on size, Steffen, Robertson and Kirsten distinguished between three categories: factories that process 1500 m3 raw milkper month or less, or 1500 – 4000 m3, or more than 4000 m3. The mean water intake to raw milk ratio was respectively 4.6, 3.9 and 2.6, indicating that the larger factories in general was more efficient in their water management than the smaller ones. Overall, the range for all dairies investigated was 1.4 to 9.5 with a mean of 3.6; the wide variation suggesting much scope for improvement. The researchers used the average water use for specific products as a point of departure to arrive at targets. These are shown in the table. The units are litre water per litre product unless otherwise indicated.
Product Mean water use Water use target
Pasteurized milk – bulk production 1.6 0.75
Pasteurized milk packed in:
Sachets 1.7 1.1
Cartons 2.2 1.5
Cultured products 10.2 6.3
Fruit juices and mixes 2.7 1.7
Sterilized/UHT products 3.7 2.0
Skim milk 3.6 2.1
Ice cream 2.5 1.9
Products in units of m3/ton:
Milk powder 11.8 8.7
Cheese 23.0 20.0
Butter 1.5 1.3
Condensed milk 4.4 3.5
These targets were presented to the dairy industry as guidelines. To what extent the guidelines are useful is unknown. Hopefully with the update intended by the WRC, with support from the industry, appropriate guidelines for the present situation can be developed.