Introduction to food wastewater and common treatment methods

Characteristics of food wastewater:

① The amount of wastewater varies. The food industry ranges from small-scale household operations to various large-scale factories. There are many types of products, and their raw materials, processes, scales, etc. vary greatly. The amount of wastewater ranges from several m3/d to thousands of m3/d. For small workshops with a small amount of wastewater, due to practical difficulties in maintenance and management, wastewater treatment facilities that are easy to maintain and manage should be used.

② Production changes with the seasons, and the quality and quantity of wastewater also change with the seasons. For example, in the processing of agricultural products and aquatic products, due to seasonal changes and the input of raw materials, there is a concentration of processing in a certain period. Since the tofu making and catering industries only work for a few hours a day, wastewater is also concentrated during this period.

③ There are many biodegradable components in the food industry wastewater. For the general food industry, since the raw materials are derived from natural organic substances, the components in the wastewater are also mainly natural organic substances (such as protein, fat, sugar, starch) and do not contain toxic substances. substance, so it has good biodegradability. Its BOD5/COD ratio is as high as 0.84.

④ Wastewater contains various microorganisms, including pathogenic microorganisms, and wastewater is prone to corruption and odor.

⑤ There is a lot of high-concentration wastewater. In recent years, from the perspective of saving water resources and reducing costs, water utilization rationalization has been promoted. When the organic matter remains unchanged but the water volume decreases, and when the organic matter increases but the water volume does not increase, these will lead to wastewater The concentration increases. Generally speaking, food industry wastewater has relatively high concentrations, and its BOD value is often above 500 mg/L. It is not uncommon to find concentrations as high as tens of thousands of mg/L.

⑥ Wastewater often contains high nitrogen and phosphorus contents. When meat, beans and animal glue are processed, nitrogen is produced from protein. When aquatic products are processed, fish cakes and other small products are made, and ham and sausages are made, which increase the nitrogen and phosphorus in the wastewater.

Physical indicators of food wastewater:

It mainly includes temperature, color, odor and liquid content, etc. The two indicators that are often tested are colorimetric and liquid content.

1. Color Food industry wastewater often contains organic or inorganic dyes, biological pigments, inorganic salts, organic additives, etc. The wastewater is colored and very dark. In water quality analysis, the indicator to measure the degree of water color is chroma. Generally, the true color after removing suspended solids is used as the standard, and the colorimetric analysis method is used to compare the color of a standard colored solution of known concentration and a water sample of unknown color.

2. Liquid content Most of the chemicals contained in wastewater are liquid substances. These liquid substances exist in the water in molten and floating forms. The two are collectively called the total liquid state, which includes organic compounds, inorganic compounds and various living organisms. During water quality analysis, in addition to measuring the total liquid content, several indicators such as suspended solids, volatile suspended solids and melted liquid content must also be measured.

Food wastewater treatment methods:

At present, food wastewater treatment methods at home and abroad include trickling filter method, activated sludge method, oxidation pond method, etc.

①Trickling filter method: The trickling filter method is a method in which wastewater flows down from a filter paved with gravel, plastic, etc. and comes into contact with a thin layer of biofilm on the surface of the filter material. The advantages are simple structure, small floor space, low maintenance costs, and strong adaptability to changes in water quality and quantity. The disadvantage is that the treatment depth is not as good as the activated sludge method, and there are still some remaining organic matter that need further treatment.

② Activated sludge method: Activated sludge method, also called biochemical aeration method, is the most important method in aerobic treatment. Activated sludge is a flocculent sludge that can adsorb and condense organic matter and other substances in sewage, and oxidize and decompose organic matter through the aerobic microorganisms that constitute the activated sludge.

a. The microorganisms in activated sludge are a group composed of a variety of microorganisms, among which bacteria are the main ones, followed by molds and yeasts, in addition to protozoa and invertebrates.

b. Activated sludge must undergo a period of domestication.

c. The activated sludge treatment system mainly consists of a primary sedimentation tank, an aeration tank, aeration equipment, sludge return equipment, and a secondary sedimentation tank.

③ Oxidation pond method: Natural or artificial ponds that use naturally occurring microorganisms and algae in the water to perform aerobic and anaerobic biological treatment of wastewater.

Process selection and treatment chemicals for food wastewater:

The common characteristics of food industry wastewater are high organic matter and suspended matter content, easy to putrefy, and generally not very toxic. Its main hazards are eutrophication of water bodies, causing the death of aquatic animals and fish, causing organic matter deposited on the bottom of the water to produce odor, deteriorating water quality, and polluting the environment.

In addition to appropriate treatment according to water quality characteristics, food industry wastewater treatment usually uses biological treatment of potassium sulfate. For example, if the water quality recommendations are very high or the organic matter content in the wastewater is very high, you can use a two-stage aeration tank or a two-stage biological filter, or a multi-stage biological knob, or use two biological treatment devices in combination, or you can use anaerobic- Aerobic tandem biological disposal system.

From the perspective of food wastewater sludge dehydration agent polyacrylamide selection, the sludge dehydration agent generally chooses medium cationic polyacrylamide, which is similar to the biochemical sludge used in domestic sewage treatment plants. We know that the sewage in domestic sewage treatment plants The organic matter content is relatively high, and most of the sewage comes from catering wastewater, fecal wastewater, and bathing wastewater from our daily lives. From the analysis of the complexity of the wastewater source structure, it is very similar to food wastewater.