The canning industry is one of the most important food sectors in Italy. However, it generates a series of non-negligible impacts on the environment, in particular in terms of pollution of water bodies, water consumption and waste production. To achieve the goal of more sustainable canning products, it is important to find solutions that will help prevent or at least reduce environmental impacts, also with an eye to cost savings that are often included in the use of these techniques.
Solution for saving water in washing operations
In the canning industry water consumption is largely justified by the need to sanitize workplaces, machinery and packaging (e.g. bottles, cans, jars). Another process that requires a large amount of water is the washing of the raw material destined to thermal treatments. One of the most common solutions for saving water in the washing operations is backwash. Commonly used by food industries, backwashing can replace parallel tanks systems in the cleaning of facilities and departments. They are multistage systems in which water is used in a given stage of cleaning and then reused in the preceding cleaning step: the water coming from the last washing phase in which clean water is fed into a second tank and reused for intermediate washing. The latter, which is dirtier, is in turn reused for the first wash and then drained. This system requires larger space than other washing solutions but it is able to reduce the consumption of clean water and the volume of draining even by 50%. This system can also be used for washing raw materials, such as tomatoes intended to sauces, etc. The canning companies may also adopt solutions for the containment of water consumption in washing stages for bottles and glass jars, such as the sanitization multistage system that synergistically exploits the use of hot water, chemicals and mechanical cleaning mechanisms. The most important advantages of this technology are related to the reduction of water consumption and therefore the volumes of draining and chemical products with everything that is involved, including storage, use, and contamination of waste water. Energy consumption is also reduced, including energy necessary to the treatment of wastewater. This system can replace the old washing machines present in already existing bottling lines. It is considered affordable if the water consumption per bottle / jar is more than 400ml per unit, with an acceptable ROI time when the water saving amounts at least to 200 ml. Another solution consists in the reuse of the washing solution of glass containers to save caustic soda and water and to limit excessive increase of the pollutant load of wastewater. The cleaning bath can be pumped into a sedimentation tank in which contaminating particles are separated and filtered before using the solution again for a new wash. This system has the disadvantage, however, to increase energy consumption in relation to the operation of pumps and filtering system. Even the pasteurization water of bottles / jars can be reused and conveyed in cooling systems that carry it in functional thermal conditions to a new use. This system is applicable to pasteurization and vacuum pumps.
Solutions to reduce pollution in wastewater
Waste water in the food industry is determined in particular by the activities of sanitizing raw material, work environments, plants and equipment. A common feature of these discharges is the organic content that normally determines high values of suspended solid, B.O.D. and C.O.D. To reduce the wastewater from the washing phase, it is possible to adopt different solutions: pre-wash and dry cleaning of the work area, flow regulators, use of anti-waste valves and injectors. Pollution in the wastewater can also be reduced through foaming of fat from the washing water of containers such as bottles, cans, tins containing foods in oil bath. Suspension oils can be recycled and managed as waste, decreasing the contamination of water discharges and increasing the possibility of reusing the washing solution.
Plant waste recovery in the industry of tomato and other vegetables
The waste produced by the canning industry may represent an economic resource. Studies about the possibilities of recovery have been made especially for tomatoes. It relates to their use as feed, fertilizers or phyto-chemical species (lycopene, tocopherols, tomatina, polyphenols) which are used as supplements in cocktails or in new food products (soups, sauces, etc.) and in the pharmaceutical-cosmetic sector (lycopene, tomatina). The solid-liquid extraction techniques currently in use by companies that need to process large amounts of material are essentially of three different types:
• Maceration: a simple and inexpensive technique, which does not require complex equipment or specialized personnel. The extraction process is generally long (days or weeks). It can be accelerated by increasing temperature or if ultrasonic or microwaves are used. Maceration requires occasional agitation phases to allow the diffusion of extracted substances in the whole mass of the extracting liquid.
• Percolation: it differs from maceration since it occurs in a dynamic manner. Despite the speeding up of the process, high extraction yields are not reached, but it is used because it reduces the time of extraction which is very important for some processing. In addition, treated quantity may reach the order of tons magnitude.
• Extraction with fluids in supercritical phase: it is a solid-liquid extraction technology which is complex and expensive and requires qualified personnel. The extraction process is carried out by putting CO2 under pressure in a closed system; at a specified pressure and temperature, CO2 becomes a supercritical fluid. At the end of the process CO2 is returned to its gaseous state, releasing the extracted substances. Depending on the quantities of produced waste and the type of company that processes tomatoes, it is possible to assess, in economic terms, the use of different extraction technologies.
Maceration and percolation are more economically sustainable for the companies which produce large quantities of waste and therefore need to dispose of large quantities in a short time. It is possible to have an extracted product of lesser purity to be used as a supplement for the enhancement of new food products. The extraction through supercritical fluid delivers a product of higher purity to be used in both food and pharmaceutical-cosmetic sector. It can be used in small to medium-sized factories and can get higher yields of extracted products. It is also possible to increase the degree of extraction of each technique with further purification by chromatography. In each case, the skins or residues resulting from the extraction process are dried up to total loss of contained water; the dry material is shredded and used as animal feed. Another use is the production of fertilizers obtained by enzymatic fermentation and subsequent natural drying.
