Treatment present stateoftheart and future trends

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The task of minimisation of water usage and minimising wastewater discharge has received considerable attention over the last few years as water has become more and more costly and an environmentally strategic concern. Most of these trends are general and are not limited to food processing.

Smith (2005) summed up the main water usage and water and waste-water minimisation measures as follows.

1 Process changes. These include increasing the number of stages in an extraction processes that use water, changing from wet cooling towers to air coolers, improving energy efficiency to reduce steam demand, increasing condensate return from steam systems, etc. Under 'process changes' we can also add good housekeeping, which includes analysing and measuring water use and wastage, reducing water wastage, cleaning operations, maintenance of equipment and daily work practices. It is also possible to decrease water consumption or replace some of the water-consuming operations, such as hazardous cleaning agents, chemicals and additives. Additionally, 'process changes' also include major process changes driven either by inspection findings or by the process optimisation results of some modern technologies, e.g. process integration/pinch technology. It is possible to adopt new technologies or replace equipment in order to reduce the generation of wastes and increase the efficiency of the process.

2 Reuse. This can occur when waste water is used directly in other operations, but only if the existing pollutants do not disturb the process. Maximum water reuse methodologies and methods to recycle water are discussed in more detail in Chapter 21 of this book, together with the opportunities to use recycled water in food processing.

3 Regeneration reuse. This is defined as the process of purifying waste water and reusing it in another operation or process.

4 Regeneration recycling. This occurs when contaminants from waste water are partly eliminated and the waste water is then returned to the same process afterwards.

A good review of wastewater minimisation has been published by Blomquist and Brown (2004). They looked at a large number of pre-assess-ment and assessment techniques developed during the last few years for, respectively, identifying waste minimisation focus areas (opportunities) or options (solutions) during a waste minimisation audit. They critically reviewed these techniques and assessed their relative merits. The pre-assessment techniques are analysed in terms of their ease and speed of implementation, while the usefulness and applications of the available general assessment techniques are considered.

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