Feed water and effluent treatment in food and drink

Aquabio UF system (part of MBR).
Aquabio UF system (part of MBR).

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Second only to drinking water production (covered in our last issue), the provision of wholesome food and drink ranks high among human needs, and as an industrial sector makes wide and important usage of filtration and sedimentation equipment among its processing activities. Ken Sutherland here reviews the range of applications for this separation equipment, and looks at likely developments in the field that will keep the sector sustainable.

The use of mechanical separation equipment is critical in many of the operations of the food and beverage production sector: partly to assure the required quality in a liquid product, whether this be a thick mayonnaise or a crystal clear drink; partly to keep harmful contaminants out of the materials in process, and especially out of the sector’s products; and increasingly in the recycling of wastes.

Wide variety There is a very wide range of manufacturing steps involving liquids in the food and beverage sector, some with quite high intrinsic values, offering scope for a wide range of filtration processes. There is less opportunity for the use of gas filtration in the processing stages, although considerable need for the use of gas treatment in its protective functions. Almost all the main processing tasks for filtration in this sector involve the treatment of liquid suspensions, with the important requirement of sanitary operation, including clean-in-place and steam sterilisation capability.

As a component of the global market for filtration and other separation equipment, the food and beverage sector is one of the larger, but more particularly, it is also one of the most varied in terms of types of equipment utilised in order to meet its markets’ demands. At the retail level the number of products is huge, with that number multiplied by the need to provide equivalent products to satisfy different religious and ethnic groupings in the same geographical areas – all of which must be supplied by the bulk processing sector. It is estimated that the market in 2014 for all kinds of such equipment, including sales of spares, throughout this sector, will be close to $3.7 billion, which represents about 7.5% of the total world market for all filtration and sedimentation equipment.

In the more traditional of its production processes, which still play an important part in food and beverage processing, this is quite a mature sector, with steady growth close to historical changes in GDP values, but there are some exciting developments as well. New and replacement production lines are regularly being installed in all regions of the world, with strong growth in Asia, especially as the large economies of India and China, and increasingly Indonesia, move quite rapidly towards higher standards of living, with very different dietary requirements.

Expanding populations The need to supply food and beverages for expanding populations, desirous of eating at increasingly higher standards, provides the prime driver for the food and beverage market globally, in turn driving the demand for food and beverage processing equipment, at a rate at least keeping up with the general economic growth of the world, and probably mostly exceeding it.

The search for better quality is a natural part of increasingly higher eating standards, which can be produced by delivering a more attractive product. One of the factors leading to higher added value is the flavour of the product, which should obviously be retained (if not heightened) during the processing activities. Foodstuffs, whether raw materials, or final products, are easily denatured during processing, so that a filtration process is advantageous because it usually occurs at little higher than room temperature.

Higher purity at all stages of food and beverage production is another factor in product quality, which offers further scope for the application of filtration and related equipment. The rise in popularity of organic farming and food production has been promoted by concerns over safety of ‘processed foods’ (although not without some doubts as to the actual reality of benefits with organic products).

Food and beverage industries The full range of processing activities included in the food and beverage sector, is:

• processing of meat, fish and their solid products (excluding animal oils and fats); • processing of fruit and vegetables and their solid products (excluding fruit and vegetable oils, fats, and juices); • processing of oils and fats from animal and vegetable sources; • production of milk and other dairy products (cheese, yoghurt, etc); • milling of grain and corn, and manufacture of cereal and starch products; • production of animal feedstuffs (i.e. food for husbanded animals, and domestic pets); • production of bread, sugar, cocoa and confectionery; • processing of tea and coffee; • production of beverages (alcoholic and non-alcoholic), including fruit and vegetable juices, and other soft drinks; • processing of mineral water.

Of these ten sub-sectors, the process use of filtration and sedimentation is found in all of them, and is very important to some of them. Almost all kinds of separation equipment can be found in use in this sector. (Distinction is made here between process filters, those that are an essential part of the production process, and which are the intended subject of this article, and utility filters, which are involved in services provided to most production processes, such as pneumatic or hydraulic systems, and which are not intentionally covered, because they are very largely the same in whichever industry they are found.) The process filters and centrifuges are used in the preparation of ingredients, in the production process itself, in the purification of products, and in the recycling or treatment of waste streams.

The industry has a number of large companies, with a host of smaller ones. Nestlé is by far the largest of the food producers, the next largest being Unilever, closely followed by Cargill, the largest private company in the USA. This comparison of size is complicated by the other facets of business, as in the case of Unilever, which is also large in the household products business. The leading soft drink companies are Pepsico and Coca Cola, in which the corporate boundaries are further blurred by their being food manufacturers of considerable size. The leading brewer, after much merging activity, is ABInBev, while the merger of Constellation Brands (of the USA) with Hardy (of Australia) has formed the world’s largest wine company.

Giant supermarkets One important characteristic of the food and beverage processing industry is the presence in it of giant supermarkets and other retail groups, such that the third largest global company of all types is a retailer of food and beverage products: namely WalMart. The picture is then further complicated by the movement of many of the large retailers into food processing, and the production of ‘own brand’ foods by major retailers.

One of the fastest growing parts of the whole sector is the mineral water and soft drinks business, which has a sizeable requirement for fine filtration. There is a wide disparity of consumption rates among the major countries (driven, of course by climatic and living standard considerations) - the Italians drink about 155 l per head annually, and the Americans about 90 l, but the British drink only 25 l per head, and the Japanese no more than 10 l. If all countries increased to the Italian level this would be a very exciting market for clarifying and polishing equipment.

Because of its vulnerability to microbial attack, and many other health issues, both during processing and in the post-production storage phase (which can be very long), the food and beverage sector is subject to quite stringent regulation. There are national bodies, such as the Food Standards Agency in the UK and the Food and Drug Administration in the USA, with European standards deriving from EU Directives, as well as the Food Standards Programme of the UN’s FAO/WHO. A major problem for the industry is the resultant plethora of standards, differing in minor (and sometimes major) details. There is a great need for globally applicable standards, and the HACCP (Hazard Analysis & Critical Control Points) programme seems to be achieving that for food safety and hygiene.

Equipment applications The simple definition of the whole food sector is that food processing takes clean, freshly harvested crops or freshly butchered animal products, and uses them to produce attractive, marketable food products, with an adequate shelf-life. Similarly beverage processing takes clean fresh water and, with appropriate admixture of fruit and vegetable components, uses it to make a wide range of drinks products with global appeal.

Separation equipment has two primary functions within these tasks: to keep the processes, food or beverage, as free as possible from harmful micro-organisms, and to prepare the raw ingredients in their best state to produce the right formulation for inclusion in a final product or for subsequent processing. The hygiene task requires similar kinds of equipment to that employed in the pharmaceutical sector, or in medical and health processing: the major problem being to prevent entrance of micro-organisms into the processing zones or packaging areas. The separation equipment used for this purpose will mostly be very fine cartridge filters in HEPA or ULPA grades, or membrane filters.

It follows that one of the most important characteristics of the separation equipment used in the food and beverage industries is the need for it to be able to operate in a state of scrupulous cleanliness. Contact surfaces will normally be of polished stainless steel, and the whole equipment should be easily cleaned, preferably by some kind of clean-in-place process.

The cleaning processes must allow sufficient residence time for the solutions to do their job. Square corners, dead ends and threaded joints should be avoided in contact with process materials, and surfaces should be sloped so that liquids may drain from them. Care must be exercised for process materials that involve salt solutions, as these can attack stainless steel, so glass-lined equipment may be preferred.

To offset this need for high quality materials in food and beverage processing, it is mostly true that equipment for this sector does not have to withstand the severe processing conditions found in some chemical or pharmaceutical operations. Indeed the most severe operating parameters may well be those involved in steam sterilisation or an aggressive clean-in-place solution.

High specification filter media The protective function just described employs relatively simple filters, which rely on high-specification filter media for their performance. By contrast, it is probably true that every possible type of filter, centrifuge or sedimentation system is in use somewhere in the world on some process within the food and beverage sector.

Some characteristic food and beverage applications include:

• the use of basket centrifuges in the production of table salt; • the separation of cream from milk in a disc centrifuge – for which this type of centrifuge was invented; • the further purification of water by membranes to serve as a food or beverage ingredient; • the use of a rotary vacuum drum filter in the separation of sugar juice from settled-out muds, followed later by a ‘sugar centrifugal’ to recover the pure crystallised product; • the purification of starch in batteries of hydrocyclones, which provides one of the key uses of the hydrocylone; • the refining of vegetable seed oils, after washing with water, in an array of tubular or disc centrifuges, followed, usually, by winterising (de-waxing) in vacuum filters; • among many separation activities in a brewery or a distillery, the dewatering of separated grains in a filter press or decanter centrifuge, and the clarification of the product in a sheet filter;

and, of course, the need in most food and beverage factories for the treatment of often very concentrated liquid wastes, requiring the full gamut of treatment stages, from oil and grease separation (in a lamellar separator), followed by primary settlement (in large sedimentation tanks), then secondary activated treatment (in aerated tanks) with separation of the surplus sludge in a filter or another settlement tank. The process will then finish with tertiary treatment, possibly a biological one, or, increasingly commonly, a membrane micro- or ultrafiltration stage, to deliver recycled water of a similar standard to the fresh ingredient water. The secondary stage is increasingly being undertaken in a membrane bioreactor.

Market developments The main factors driving market growth that have already been mentioned for the basic food and beverage supply sector, include population growth, a search for higher standards of food and beverage supply (especially in the developing countries), and a continual rise in required product purity levels.

Some other developments that are mainly affecting the food and beverage manufacturing sector in developed markets – and therefore can be expected to spread to the whole world in the not too distant future - are:

• the appearance of ‘functional’ foods and ‘energy’ drinks to meet real, or apparent, needs for personal improvement; • the growing realisation that cholesterol accumulation in the body may be caused by an • incorrect diet, as might the onset of Alzheimer’s disease; • the continuing concern over the use of additives whose function is uncertain, but fiercely contested – and are easily added during processing; • the rapid growth in consumption of convenience and snack foods, leading perhaps to obesity in all age groups; and • the equally rapid growth in concern in the marketplace over better diets, especially for children, and the provision of foods to match, such as the current excitement over spelt and quinoa.

An important development in the processing of foodstuffs, which is still not yet fully accepted as the major step it surely will be, is the use of supercritical fluids for the solvent extraction of components from natural materials. In the food and beverage sector the best example of its use is in the removal of caffeine from coffee beans by the use of supercritical carbon dioxide. This is a fairly straightforward application of the technique, with the advantage of replacing the toxic solvents first used for decaffeination by the readily available carbon dioxide, which is easy to remove in a subsequent evaporation step, which can also involve filtration.

Long term prospects In the long term, the arrival of genetically modified food products onto the market may be the largest development in food provision for some time (or its largest problem, depending upon one’s point of view – science has some way to go yet to justify the wilder claims of either view).

A problem that has only recently become apparent is the conflict between the demands for food and fuel crops as resources. This has come from the perceived need to find alternative energy sources to the fossil fuels now accepted as a prime cause of global warming. Among the carbon-neutral systems (i.e. those consuming as much carbon from the atmosphere as will subsequently be released in energy generation), the most obvious is the growing of burnable ‘biomass’ crops for energy production – on land which cannot then be used for food crops. Whilst this problem is currently still largely a matter of political consideration, it will eventually impact on the food sector, perhaps first in requiring better use of processing wastes as fuels.

The question of food wastes has another potential solution: for all of its talk of food shortages, humankind is extremely wasteful of the food that it does produce. It is said that, in the USA, food processing has reached the point where virtually100% of the food produced at the farm finds its way to the consumer’s table, whereas in most of the rest of the world as much as 50% or more never reaches the consumer because it is lost to insects, bacteria, humidity, etc – and probably during processing. If this loss could be halved, then food poverty would be much less of a problem.