How to treat sewage in catering industry?

The increasingly deteriorating social environment is mostly due to the disorderly discharge of various waste gases and waste water. In the catering industry, not only the hygiene of food needs to be strict, but also the treatment of food residue and waste water also need to comply with strict discharge standards. The equipment of public sewers and sewage treatment plants is easy to be damaged by grease wastewater. Among them, the concentration of animal and vegetable oil is as high as 1000 ~ 8000mg/L, the concentration of suspended particles is as high as 1500 ~ 8000mg/L, and the concentration of COD is as high as 1200 ~ 25000mg/L. If these untreated pollutants are allowed to be discharged directly into the river or into the urban sewage network with sewage, it will cause a series of environmental problems, but also a waste of precious resources.

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1. Pollution of food and beverage wastewater to water bodies

If the sewage of the catering industry is directly discharged into natural water bodies such as rivers and lakes, the original microflora in the water body will multiply wildly due to the large amount of nutrients. The vigorous respiration of the aerobic bacteria in these microorganisms consumes the dissolved oxygen in the water body, and the concentration of dissolved oxygen in the water drops sharply. Aquatic organisms such as fish will die because they cannot get enough oxygen. 

At the same time, the oily substances in the sewage destroy the ecological balance of the water. The oil floats to the water surface and forms a large oil film, which separates sunlight and oxygen from the water body, making it difficult for the already scarce oxygen in the water body to be effectively supplemented from the air. Moreover, the tiny oil particles enter the body through the respiration of aquatic animals such as fish and stick to the digestive tract. The cheeks of fish will be stuck by oil and other dirt, inhibiting respiration. Resulting in disease and death of the aquatic community. When the concentration of pollutants reaches a certain level, the oxygen in the water is almost consumed, and there are almost no aquatic animals in the water body. The anaerobic bacteria in the microorganisms are in absolute advantage, because the anaerobic bacteria can not digest organic matter completely and thoroughly, and produce many intermediate products with odor, such as putrescine, cadaverine and H2S, CH4, NH3 and so on. H2S and other substances can produce black iron sulfide precipitation when they encounter iron. If this situation is not effectively stopped, in a very short time, the water quality of the natural water body will become black and smelly, become stagnant water, not only seriously affect the natural landscape, reduce the quality of life of residents near the water body, but also destroy the ecological balance of the natural water body, reduce the availability of water resources, making the already scarce available fresh water resources further loss. Moreover, various bodies of water eventually discharge into nearby seas, further causing a crisis in Marine ecosystems.

2. The harm of sewage from catering industry to urban pipe network

Urban sewage pipe network is complicated, because of the different drainage time, pipe diameter, pipe material, pipe laying and other conditions, the flow rate of sewage in the pipe network is different. When the sewage from the catering industry is directly discharged into the urban sewage network, the large particles suspended in the sewage, sediment and other substances will be deposited in the pipeline when the flow rate of the pipeline is low or the pipe section of the pipeline is sunk. Grease condenses on these substances, and then adheres to more suspended substances, and more and more, forming a similar "reinforced concrete" structure, resulting in pipe blockage. The annual costs and other indirect losses that municipal departments spend on dredging and replacing urban pipe networks are even more difficult to estimate.

3. Sewage from catering industry cannot be effectively treated by traditional sewage treatment process

After a large number of oils, suspended substances and high concentration of organic matter enter the municipal sewage plant with the sewage, they cannot be removed in the traditional primary treatment units such as grille, sand settling and primary settling. After entering the secondary biological treatment unit, especially the oils will adhere to the microorganisms, preventing the aeration process from transferring oxygen to microorganisms, resulting in lower efficiency of the secondary biological treatment unit. In severe cases, even a large number of bacteria died, and the effluent water quality could not meet the standard. 

4. Sewage from catering industry affects the implementation of sustainable development strategy

Due to the difficulty of sewage treatment in the catering industry and the neglect of sewage treatment in the catering industry for a long time, the catering sewage has caused damage to the environment to a large extent. In the areas where the original river was densely covered, the river surface of the river was often covered with white oil, and the river became black and smelly, resulting in no water available; Due to the blockage of the pipeline, the road is impassable due to the cross flow of sewage. Especially in some sections, when it rains, the water floods the Jinshan Mountain, which seriously affects the daily life of residents and aggravates the contradictions in urban management. The random discharge of sewage and food residues in the catering industry has become a food and breeding ground for rats, flies, mosquitoes, and cockroaches, causing the "four hazards" to flourish and easily causing various infectious diseases. Reports show that the direct discharge of sewage from the catering industry is one of the main culprits of the pollution of several major freshwater systems in China; It is also one of the direct reasons for the frequent outbreak of red tides in offshore waters in recent years. It has been proved that the sewage discharged at will will seriously affect the implementation of sustainable development strategy. Due to loopholes in management and driven by economic benefits, a large amount of grease (commonly known as gutter oil) in catering sewage discharged directly into urban sewers will be partly flushed into the downstream with the water flow, partly mixed with debris and adhering to the pipe wall, and the other part will be deposited in pipe manholes and septic tanks. The extracted "gutter oil" is illegally collected, illegally used, and even reprocessed and packaged into "salad oil" by illegal traders, causing a series of social problems in health, hygiene, safety and other aspects.