There are many types of dairy products, such as pure milk, milk powder, cold drinks, cheese, etc., and the production process of each product is different, and the wastewater produced is also different. In general, dairy wastewater mainly comes from four aspects: (1) recyclable condensation and cooling water in the production process, (2) processing vessels, pipelines, and floor cleaning water, which are the main sources, accounting for more than 70;(%, 3) domestic sewage of employees, and (4) boiler room sewage.
Dairy wastewater is a type of food processing wastewater, which is mainly characterized by a large amount of soluble organic matter and a high concentration. These organic substances mainly include protein, lactose, milk fat, detergents, etc., which can be degraded by microorganisms, and BOD5/COD is usually greater than 0.5, with good biochemical properties. For this reason, we usually adopt a bio-based approach to make dairy wastewater meet the standard discharge.
(1) What are the options for dairy wastewater treatment methods?
The main processes of dairy wastewater treatment include pretreatment, anaerobic biological treatment, aerobic biological treatment and advanced treatment.
1. Pretreatment: Remove animal and plant oils, suspended solids and other pollutants in wastewater through physicochemical treatment process. Specific methods include solid-liquid separation methods such as coarse grids, fine grids, grease traps, etc., as well as coagulation and air flotation devices. These methods are effective in removing not only suspended solids and animal and vegetable oils, but also macromolecular organics such as milk fat and milk protein.
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2. Anaerobic biological treatment: This is one of the important methods for treating industrial wastewater.
Common methods include upflow anaerobic sludge bed reactor (UASB), anaerobic expanded sludge bed reactor (EGSB), anaerobic baffle reactor (ABR), etc. These methods convert organic matter into methane, carbon dioxide, etc., through the adsorption and decomposition of microorganisms.
In a case, the effect of using UASB process to remove COD in dairy wastewater is as follows: the wastewater quality is < 3000mg/L, and the treated effluent is < 600mg/L. UASB reactor has the advantages of high sludge concentration, high organic load, cost saving, three-phase separator, strong impact load resistance, good and stable effluent quality, strong adaptability, low energy consumption and low sludge production, etc., which is an efficient and economical choice for connecting industrial wastewater.
3. Aerobic biological treatment: It is widely used in the field of biological treatment technology, and the common methods include activated sludge method and biofilm method.
Contact oxidation is an aerobic biological treatment in which microorganisms form a biofilm on the surface of the filler by filling the treatment tank with a filler. As wastewater flows through these fillers, microorganisms in the biofilm purify the water by breaking down the organic matter in the water, converting it into harmless carbon dioxide and water. This method combines the advantages of activated sludge method and biofilm method, with high treatment efficiency and stable operation, and is suitable for the treatment of industrial and municipal wastewater containing organic matter.
4. Advanced treatment: Select the appropriate advanced treatment process according to the local discharge standards and the water quality and quantity of wastewater. For example, in a dairy wastewater treatment case, sand filters and multi-media filters were selected as advanced treatment of reclaimed water to reduce wastewater discharge and improve water resource utilization.
(2) Dairy wastewater treatment case
In a dairy wastewater treatment case, the COD concentration of the influent water is 6000mg/L, and the process of "grid + adjusting grease trap + coagulation air flotation + UASB reactor + A/O + secondary sedimentation tank" is used to make the COD concentration of the effluent less than 100mg/L.
In another case, the COD concentration of the influent water was 1500mg/L, and the process of "oil separator sedimentation tank + grid + regulating tank + air flotation tank + hydrolysis acidification tank + biological contact oxidation tank + secondary sedimentation tank" was used to make the COD concentration of the effluent less than 150mg/L.
The dairy industry has a wide range of products, including pure milk, milk powder, cold drinks, cheese, etc., and each product is produced in a different way, so the wastewater generated during the production process is also different. In general, dairy wastewater mainly comes from the following four aspects: first, recyclable condensation and cooling water in the production process, secondly, processing vessels, pipelines, and floor cleaning water, which accounts for a relatively large proportion of more than 70%, third, domestic sewage of employees, and finally boiler room sewage.