Due to its intimate connection with public health, the food industry has had a long history of surveillance of its activities by local, state and federal agencies, so the use of chemicals to treat these waters is more limited in the food industry than in other large water-consuming industries. Data on consumption vary greatly between the different subsectors, also according to the product (s) produced, the processing technology, seasonality, etc. The polluting agents that predominate in these wastewaters are the following:
- Animal and vegetable waste: Meat, bones, hair, vegetable fibers, etc.
- Suspended matter from dragging and washing: Earth, sand, clay, insoluble particles.
- Putrescible products: Fats, sugars, dextrins, proteins, ferments, vegetable water.
- Diverse dissolving materials: Dissolved salts, pesticides in greater or lesser amounts depending on their solubility in water, etc.
Although there are wide variations in production phases in each of these industry sectors, there are a number of common unit operations. The production processes normally consist of the following phases: washing of the raw material, elimination of the inedible part, preparation of the food product and packaging.
Classification of waters
The distribution of water in food processing plants can be classified according to its destination into three categories: sanitary water, cooling water and boilers, and process water. The process water includes all the operations that are carried out on the raw materials to obtain the final product, such as the washing of raw materials and process equipment, dissolution or extraction of compounds; and purification of the final product. The cooling water can be used to operate refrigeration equipment, to condense steam from evaporators or turbines, or to cool process equipment.
The percentage distribution varies considerably from a maximum of about 60% used for process water in the meat and poultry processing industry, to a minimum of 15% in the sugar industry. However, 75% of the water used in the sugar industry is for cooling purposes, while the meat and poultry processing industry only uses 25% for this purpose. The rest, up to 100%, would correspond to sanitary water.
Discharges from the production of food products
The characteristics of discharges from the production of food products are extremely variable. The BOD5 can be between 100 mg / L and 100 g / L. Suspended solids, almost completely absent in some discharge or up to 120 g / L in others. The discharge can be very alkaline (pH 11.0) or very acidic (pH 3.5). There may be mineral nutrients in excess or lack of the necessary ratio to obtain good conditions for biological treatment. Likewise, the volume of discharges can be almost zero in some industries, but reach thousands of cubic meters per day in others.
This type of activity, which operates with products intended basically for human consumption, is characterized by the widespread consumption of large volumes of water and by the high pollutant load of its discharges, basically organic and sometimes mineral. Likewise, the discharges from these industries normally lack toxic products, so their treatment must be based on physicochemical procedures in the first phases, and then on biological systems.