The content of the food industry is extremely complex, including sugar making, brewing, meat, dairy processing and other production processes. The wastewater discharged contains organic substances, has strong oxygen consumption, and a large number of suspended solids are discharged with the wastewater. The wastewater from animal food processing also contains animal excreta, blood, fur, grease, etc., and may contain bacteria, so the oxygen consumption is very high, which is much more polluting than the wastewater from plant food processing.
The food industry has a wide range of raw materials and products, and the amount and quality of wastewater discharged vary greatly. The main pollutants in the wastewater are (1) solid substances floating in the wastewater, such as vegetable leaves, peel, broken meat, bird feathers, etc; (2) Substances suspended in wastewater include oil, protein, starch, colloidal substances, etc; (3) Acids, alkalis, salts, sugars, etc. dissolved in wastewater: (4) mud and sand and other organic substances carried by raw materials; (5) Pathogenic bacteria, poison, etc. Food industry wastewater is characterized by high content of organic matter and suspended solids, easy to decay, and generally non-toxic. Its harm is mainly to eutrophic the water body, resulting in the death of aquatic animals and fish, and promote the organic matter deposited on the bottom to produce odor, deteriorate the water quality and pollute the environment.
Physical indicators of wastewater
The physical indicators of wastewater mainly include temperature, color, odor and solid content, etc. the two indicators often detected are chromaticity and solid content.
1. Chromaticity food industry wastewater often contains organic or inorganic dyes, biological pigments, inorganic salts, organic additives, etc., but the wastewater is colored, and the color is very dark. In water quality analysis, the index to measure the degree of water color is chromaticity. Generally, the true color after the removal of suspended solids is taken as the standard, and the results are obtained by comparing the color of standard colored solution with known concentration and water sample with unknown chromaticity by colorimetric analysis.
2. Solid content most of the magazines contained in wastewater are solid substances, which exist in water in the form of dissolved and suspended. The two are collectively referred to as total solids, including organic compounds, inorganic compounds and various organisms. In water quality analysis, in addition to measuring the total solid content, several indicators such as suspended solids, volatile suspended solids and dissolved solids should also be measured.
(1) Total solid (TS) refers to the residue after drying a certain amount of water samples at 105~110 ℃ in water quality analysis, which is expressed by weighing.
(2) Suspended solids (SS) or suspended solids are the suspended parts of total solids, which contain organic and inorganic components.
(3) Volatile suspended solids (VSS) is the weight loss of suspended solids under heating and burning at 600 ℃, which represents the organic part of suspended solids. One part is biodegradable suspended solids (bvss) and the other part is non biodegradable (nbvss).
(4) Nonvolatile suspended solids (NVSS) is the residue of suspended solids after burning, also known as ash, which represents the inorganic part of suspended solids.
(5) Dissolved solid (DS) or dissolved matter refers to the part of total solid in dissolved state, which is obtained by drying and weighing the filtrate of a certain amount of water sample.
Selection of food wastewater treatment process
The food industry has a wide range of raw materials and products, and the amount and quality of wastewater discharged vary greatly. But in general, the main pollutants in food wastewater are
(1) Solid substances floating in wastewater, such as vegetable leaves, peel, broken meat, bird feathers, etc
(2) Substances suspended in wastewater include grease, protein, starch, colloidal substances, etc
(3) Acids, alkalis, salts, sugars, etc. dissolved in Wastewater
(4) Mud, sand and other organics carried by raw materials
(5) Deadly germs, etc
Food industry wastewater is generally characterized by high content of organic matter and suspended solids, easy to decay, and generally non-toxic. Its harm is mainly to eutrophic the water body, resulting in the death of aquatic animals and fish, and promote the organic matter deposited on the bottom to produce odor, deteriorate water quality and pollute the environment.
in addition to proper treatment according to the characteristics of water quality, biological treatment is generally suitable for the treatment of food industry wastewater. If the effluent quality is highly required or the organic content in the wastewater is high, two-stage aeration tank or two-stage biological filter, or multi-stage biological rotary table, or the combination of two biological treatment devices, or anaerobic aerobic series biological treatment system can be used.
From the perspective of the selection of polyacrylamide as the dehydrating agent for food wastewater sludge, the medium cation polyacrylamide is generally selected as the dehydrating agent for sludge, which is similar to the treatment of biochemical sludge from domestic sewage treatment plants. We know that the sewage from domestic sewage treatment plants also has a relatively high content of organic matter, and most of the sewage comes from our daily catering wastewater, fecal wastewater, and bathing wastewater. From the analysis of the complexity of the source structure of wastewater, it is very similar to food wastewater.