حالة معالجة مياه الصرف الصحي في المسالخ

1.1 Slaughterhouse Wastewater Water quality analysis

Slaughter wastewater mainly comes from the slaughtering and processing of chickens and fish. A certain amount of wastewater is generated during the slaughtering process, cleaning after slaughtering, dismantling and washing, cleaning of internal organs and washing of the ground, as well as livestock manure. Wastewater contains a large amount of organic matter, the main components of which are: animal feces, blood, animal internal organs, animal hair, broken skin and meat, grease and other organic matter, which are high-concentration organic wastewater. The wastewater is brown-red and has a strong fishy smell. If the fat, protein and other substances in these wastewater are not treated and directly discharged into the water body, they will cause serious eutrophication of the surrounding water bodies, seriously damage the self-destruction ability of the water body, cause the water body to turn black and smelly, and affect the environment and agricultural irrigation.

Slaughterhouse wastewater is a high-concentration organic polluted wastewater with complex components. It has the following characteristics:

1. It has a certain blood red color, which is mainly caused by blood;

2. It has a bloody smell, which is mainly caused by the decomposition of blood and protein;

3. Contains a large amount of suspended matter, mainly composed of animal hair, meat scraps, bone scraps, visceral debris, undigested food and feces;

4. Contains high levels of animal fat;

5. Contains a large amount of E. coli.

The main characteristic pollutants of slaughterhouse wastewater are: COD, BOD, total nitrogen, total phosphorus, pH, etc. Since the indicators of each item in the wastewater are very high, a large part of them are mainly caused by insoluble animal blood, meat scraps, bone scraps, visceral debris, undigested food and feces, etc., and cannot be directly treated biochemically. Therefore, the wastewater needs to take necessary pretreatment and physical and chemical treatment to reduce the above substances entering the biological treatment process as much as possible, and then carry out biochemical treatment to ensure the normal operation of biochemical treatment.

In addition, the oil content in slaughter wastewater is generally high, and the oil adheres to the surface of the biofilm, blocking the contact between the wastewater and the biofilm, which reduces the biochemical removal efficiency. Therefore, the pretreatment of the wastewater must consider the treatment of oil indicators.

1.2 Treatment process selection

According to the above analysis, the main pollutants of this project are conventional biochemical indicators such as COD, BOD, total nitrogen, total phosphorus, pH, etc. Therefore, the main process adopts biochemical treatment, which is the most mature and economical way.

In addition, it is necessary to consider the pretreatment of insoluble animal blood, fat, meat scraps, bone scraps, visceral debris, undigested food and feces before entering the biochemical process.For slaughterhouse wastewater. The pretreatment is usually carried out by using a solid-liquid separator.The solid-liquid separator can separate the above substances from the wastewater and use them directly as fertilizer.

For oil substances, conventional oil separation and dissolved air flotation processes are used for treatment. The DAF device is an advanced flotation system that integrates coagulation, flotation, skimming, sedimentation, and sludge scraping. It is an efficient and energy-saving water purification equipment. It is mainly composed of a pool body, a skimming device, a walking device, a water and air distribution device, a water collection device, and a power collection device.

For wastewater with high COD and BOD concentrations, biochemical treatment needs to first use anaerobic processes to reduce COD and BOD concentrations as much as possible to reduce the load of subsequent treatment. Generally, the anaerobic biochemical process of organic wastewater removes COD by anaerobic fermentation to produce biogas. Commonly used anaerobic biological treatment reactors for slaughterhouse wastewater include UASB reactors.The upflow anaerobic sludge blanket (UASB) reactor has no carrier and is a suspended growth type digester consisting of three parts: reaction zone, sedimentation zone and gas chamber.

The COD, BOD, total nitrogen, total phosphorus and other indicators of wastewater after anaerobic treatment are still high, so it is necessary to choose a biochemical treatment process with good denitrification and phosphorus removal effect. The traditional AAO process is a typical denitrification and phosphorus removal process. Its biological reaction tank consists of three stages: anaerobic, anoxic and aerobic. This is a plug-flow pre-denitrification process.

The process flow is shown in the figure below.