Overview of selected case studies

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Various case studies have been published covering food processing technologies that require water and produce waste water. These include, among others, sugar production, beer brewing and fruit juice production.

Process optimisation to minimise water use in food processing 101 5.3.1 Sugar plant case studies

Zbontar Zver and Glavic (2005) presented a case study of a sugar plant processing approximately 4300 t of beet in a 24-h period. The beet processing season or campaign lasts approximately 3 months, from October until January. The objective of sugar beet processing is to extract pure sugar from the beet while separating pulp and non-sugars such as minerals and water.

The sugar industry is one of the major water users and wastewater producers. Gutteck (1989) assumed that processing of 1 t sugar beet would require around 20 m3 of fresh water, supposing that for each stage fresh water would be used. A large sugar plant processing 10 000 t/day of beet therefore requires 2500-4000 m3/year of fresh water and discharges an even larger stream of waste water (including water contained in the processed beet). Water-saving measures such as water reuse, regeneration and recycling are well known and are widely applied in the sugar industry, see, for example, Grabowski et al. (2002) and Urbaniec and Wernik (2002). The present trend in modern sugar plants is to reduce water consumption towards 'zero', implying that all the needs for water in the process are covered by the water contained in the sugar beet (0.75 t of water per 1 t of sugar beet), except for the water required for the boiler house. Grabowski et al. (2002) suggested that the water and energy use minimisation in the sugar industry 'caused' - as a result of the process changes - a novel sugar manufacturing process to be established.

The case study results presented by Zbontar Zver and Glavic (2005) have shown the possibility of reducing freshwater consumption during the beet processing season by at least by 54.23 m3/h, i.e. 69% of all the water consumed, with a payback period of 5 days. This very economically attractive result clearly demonstrates that there is still huge scope in the food processing industry for rapid improvements. The study evaluated several actions, many of which can serve as inspiration to other similar processing plants:

• good housekeeping and regular maintenance (diminished costs on one side and prevention of unnecessary water losses on the other);

• division of wastewater streams with different quality in order to enable more possibilities for water reuse, regeneration reuse or recycling reuse;

• reuse of less contaminated waste water in cooling systems, for pump packing, for equipment cleaning, production area washing, etc.;

• mixing of waste water with fresh water in order to equilibrate contaminant concentration and temperature;

• reuse of steam condensate in boiler house or other process operations;

• wastewater regeneration with less complicated procedures (disinfection, neutralisation, etc.) that do not raise operation expenses considerably, and reuse of the regenerated water in systems that allow such level of water contamination.

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