Overview

The food industry is directly dependent on the natural environment for a supply of raw materials to produce contaminant-free products for human consumption. Due to the extensive processing of a great volume of materials, potential impact on the environment is considerable. This is also true of the beverage industry.

Environmental concern with respect to the food industry focuses more on organic pollutant loadings than on the impact of toxic substances. If pollutant loadings are inadequately prevented or controlled, they will strain community pollution control infrastructure or produce negative impacts on local ecosystems. Production techniques that control product losses serve the double function of improving yield and efficiency while at the same time reducing potential waste and pollution problems.

While the availability of potable water is essential, the food-processing industry also requires very large volumes of water for a wide variety of non-consumption uses, such as for initial cleaning of raw material, fluming, blanching, pasteurizing, cleaning of processing equipment and cooling of finished product. Water uses are identified by quality criteria for different applications, with the highest quality uses often requiring separate treatment to assure complete freedom from odour and taste and to ensure uniform conditions.

The processing of very large volumes of material introduces a potentially great solid waste problem in the production phase. Packaging waste has been the subject of increasing concern with regard to the post-consumer phase of a product’s life cycle. In certain branches of the food industry, processing activities are also associated with potential air emissions and odour control problems.

Despite considerable variation among specific industry sub-sectors, approaches to the prevention and control of pollution share many general characteristics.

Water Pollution Control

The food-processing industry has a raw waste effluent before treatment that is extremely high in soluble organic matter. Even small, seasonal plants are likely to have waste loads comparable to those of populations of 15,000 to 25,000, with large plants approximating the population-equivalent waste load of a quarter of a million people. If a stream or waterway receiving effluent is too small and organic waste too large in volume, the organic waste will utilize the dissolved oxygen in the process of being stabilized and will pollute or degrade the water body by reducing the dissolved oxygen value below that required by normal aquatic organisms. In most cases the waste from food-processing plants is amenable to biological treatment.

The strength of wastewater varies considerably according to plant, specific process and raw product characteristics. From an economic point of view, it is normally less costly to treat a high-strength, low-volume waste than a large-volume, diluted waste. For this reason, effluent with a high biological oxygen demand (BOD), such as the blood of chickens or meat, should be kept out of poultry and meatpacking plant sewers to reduce pollution load, and retained in containers for separate disposal in a by-products or rendering plant.

Waste streams with extreme pH (acidity) values should be carefully considered because of their effect on biological treatment. The combination of acid and basic waste streams may result in neutralization, and, where possible, cooperation with adjacent industries may be very beneficial.

The liquid portion of food-processing waste is normally screened or separated after settling, as a preliminary step in any treatment process, so that these wastes can be disposed of as garbage or combined with other solids in a by-products recovery programme.

The treatment of wastewater can be accomplished by a variety of physical, chemical and biological methods. As secondary processes are more expensive, maximum use of primary treatment is critical in reducing loads. Primary treatment includes processes such as settling or plain sedimentation, filtration (single, dual and multi-media), flocculation, flotation, centrifugation ion exchange, reverse osmosis, carbon absorption and chemical precipitation. Settling facilities range from simple settling ponds to sophisticated clarifiers designed specifically for the particular waste stream characteristics.

The use of biological secondary treatment to follow primary treatment is frequently a necessity to reach wastewater effluent standards. As most food and beverage industry wastewaters contain mainly biodegradable organic pollutants, biological processes used as secondary treatment seek to reduce the BOD of the waste stream by mixing higher concentrations of organisms and oxygen in the waste stream to provide rapid oxidation and stabilization of the waste stream prior to their discharge back to the environment.

Techniques and combinations of techniques may be adapted to address specific waste situations. For example, for dairy wastes, anaerobic treatment to remove the major portion of the pollutant load, with aerobic post-treatment to further reduce the residual BOD and chemical oxygen demand (COD) down to low values and remove nutrients biologically, has proven to be effective. The biogas mixture of methane (CH₄) and CO₂ that is produced from anaerobic treatment can be captured and used as an alternative to fossil fuels or as a source for electrical power generation (typically 0.30 m³ biogas per kg of COD removed).

Other secondary methods that are widely used include the activated sludge process, aerobic trickling filters, spray irrigation and the use of a variety of ponds and lagoons. Odour nuisances have been associated with ponds of inadequate depth. Odours from anaerobic processes can be removed by the use of soil filters that can oxidize objectionable polar gases.

Air Pollution Control

Air pollution from the food industry generally revolves around the question of objectionable odours rather than toxic air emissions, with a few exceptions. For this reason, for example, many cities have regulated the location of slaughterhouses under their health codes. Isolation is one obvious way to reduce community complaints about odours. However, this does not remove the odour. Odour control measures such as absorbers or scrubbers may sometimes be necessary.

One major health concern in the food industries is leaks of ammonia gas from refrigeration units. Ammonia is a severe eye and respiratory irritant, and a major leak into the environment could require evacuation of local residents. A leak control plan and emergency procedures are necessary.

Food processes that use solvents (e.g., edible oil processing) may emit solvent vapours into the atmosphere. Closed systems and recycling of solvents is the best method of control. Industries such as sugar-cane refining, which use sulphuric acid and other acids, may release sulphur oxides and other contaminants into the atmosphere. Controls such as scrubbers should be used.

Solid Waste Management

Solid waste can be quite considerable. Tomato waste for canning, for example, may represent 15 to 30% of total quantity of product processed; with peas and corn, waste is in excess of 75%. By isolating solid wastes, the concentration of soluble organics in wastewater may be reduced and the drier solid wastes may be more easily used for by-product or feeding purposes and as fuel.

Utilization of process by-products in a manner that provides income will reduce the total cost of waste treatment and eventually the cost of the final product. Waste solids should be evaluated as sources of food for plants and animals. A growing emphasis has been devoted to the development of markets for by-products or for the compost produced by converting waste organic materials to an innocuous humus. Table 1 provides examples of uses for by-products from the food industry.

Table 1. Examples of uses for by-products from the food industry

Source: Adapted from Merlo and Rose 1992.

Water Reuse and Effluent Reduction

Extensive dependence on water by food-processing industries has encouraged the development of conservation and reuse programmes, especially in locations of water scarcity. Reuse of process water can provide substantial reductions in both water consumption and waste load, with reuse in many lower-quality applications not requiring biological treatment. However, any potential for anaerobic fermentation of organic solids must be avoided so that corrosive, odourous decomposition products do not affect equipment, work environment or product quality. Bacterial growth can be controlled by disinfection and by changing environmental factors such as pH and temperature.

Table 2 presents typical water reuse ratios. Factors such as the location of sprays, water temperature and pressure are key factors influencing the volume of water required for processing operations. For example, water used as a cooling medium to cool cans and for air conditioning may later be used for primary washing of vegetables and other products. The same water later may be used for fluming waste material, and finally a portion of it may be used to cool ashes in the powerhouse.

Table 2. Typical water reuse ratios for different industry sub-sectors

Water conservation techniques and waste prevention techniques include the use of high-pressure sprays for clean-up, elimination of excessive overflow from washing and soaking tanks, substitution of mechanical conveyors for water flumes, use of automatic shut-off valves on water hoses, separation of can cooling water from the composite waste flow and recirculation of can cooling water.

Pollution loads at processing plants can be reduced through modified processing methods. For example, most pollution load generated from fruit and vegetable processing originates in the peeling and blanching operations. By moving from conventional water or steam blanching to a hot gas blanching process, pollution loads can be reduced by as much as 99.9%. Similarly, dry caustic peeling can cut BOD by more than 90% in comparison to conventional peeling processes.

Energy Conservation

Energy needs have risen with the increased sophistication of the food industry. Energy is required for a wide a variety of equipment such as gas-fired ovens; dryers; steam boilers; electrical motors; refrigeration units; and heating, ventilation and air-conditioning systems.

As the cost of energy has risen, there has been a trend to install heat recovery equipment to conserve energy and to investigate the feasibility of alternative energy sources in various food-processing situations such as cheese processing, food dehydration and water heating. Energy conservation, waste minimization and water conservation are all mutually supportive strategies.

Consumer Health Issues

The increasing separation of the consumer from the food- production sector that has accompanied urbanization globally has resulted in a loss of the traditional means used by the consumer to ensure the quality and safety of food, making the consumer dependent on a functional and responsible food-processing industry. Increased dependence on food processing has created the possibility of exposure to pathogen-contaminated food from a single production facility. To provide protection from this threat, extensive regulatory structures have been established, especially in the industrialized countries, to protect public health and to regulate the use of additives and other chemicals. Harmonization of regulations and standards across borders is emerging as an issue to ensure the free flow of food among all the world’s countries.

Dairy industry wastewater treatment

The dairy industry is made up of a large number of relatively small plants supplying products such as milk, cheese, cottage cheese, sour cream, ice cream, whey solids and lactose.

The dairy industry has long been a proponent of aerobic biological wastewater treatment. Many dairy plants have invested heavily in activated sludge, biotower, sequencing batch reactor and package treatment systems. Interest in water and energy conservation has led many dairy facilities to reduce water consumption. This trend, with the presence of normally high-strength wastewater streams in dairy plants, has resulted in the design and construction of numerous anaerobic wastewater treatment systems.

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