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2020-08-02 16:37:05

Dairy wastewater treatment and related industries

Dairy wastewater treatment and related industries

Types of wastewater in the dairy industry-Dairy wastewater

Sewage from cleaning

Dairy effluent - mainly due to cleaning of machinery in contact with milk or milk products, leakage of milk and organic products, whey, brine and pressure equipment, cleaning operations in CIP, defective water And even operational errors. This effluent may contain milk, cheese, curd, cream, and dairy water from separators, clarifiers, and stabilizers.

Sanitary sewers

This sewage is usually piped directly to the sewage system. Dairy cleaning water may contain a variety of sterilized agents and different acids and alkaline detergents. Therefore, the pH of the effluent can be significantly dependent on the cleaning strategy used. The most common chemicals used for CIP are caustic soda, nitric acid, phosphoric acid, and sodium hypochlorite, all of which have significant effects on biological oxygen demand (BOD) and chemical oxygen demand (COD). Usually more than 10% of the total BOD concentration in wastewater treatment plants is the share of phosphorus from the use of phosphoric acid and other detergents containing phosphorus. The high volume of water used for cleaning and sanitation (more than 30% of the total discharged water) as well as public concerns due to the impact of biodegradability of detergents and the specific toxicity of this wastewater make it necessary to treat this wastewater and pay attention to environmental standards. Their biology has become.

Dairy wastewater treatment - resulting from processes:

Dairy wastewater is normally produced by an intermittent method, so the flow and characteristics of the effluent can vary between factories depending on the type of product, production and processing methods. Published information on the chemical composition of dairy wastewater is scarce. Milk has about 250 times more BOD than municipal sewage. Therefore, it can be said that the digestion of dairy wastewater by municipal wastewater will cause a relatively high organic overload, with large amounts of lactose, fats and proteins (especially casein) as well as high levels of nitrogen and phosphorus, which are essentially dependent on protein. It is milk. The general specifications of dairy wastewater are as follows:

The COD and BOD of whey are between 35,000-68,000 mg / l and 30,000-60000 mg / l, respectively. Lactose is responsible for 90% of the COD and BOD in these wastewaters.

Dairy wastewater treatment methods

Physical separation
The main purpose of separation in dairy wastewater treatment is to remove large or small particles that cause damage to the pumps and clogging of downstream equipment. It is also recommended that the physical separation of wastewater from the dairy industry be done as quickly as possible to Prevent solids from dissolving.

PH control

There is a great deal of variation in the pH of dairy effluents, which may be directly related to the different treatment strategies used. In general, alkaline detergents used for soap making (to remove fat and protein) will typically have a pH of about 10-14, while pH 1.5-6 can be precipitated with an acidic cleanser used to remove minerals. Or acid-based disinfectants are obtained.

Remove grease, oil and grease

The presence of fats, oils and greases (FOG) in dairy wastewater can cause many problems in on-site biological wastewater treatment systems and municipal wastewater treatment plant facilities. It is therefore essential that FOGs be reduced or eliminated prior to treatment. According to the IDF, milk processing plants such as milk separators, as well as butter and cheese factories, whey separators (such as whey factories) and milk bottle machines, have experienced many problems with FOG. Skim milk processes rarely encounter these problems.

Gravity tanks (traps)

Gravity tank is one of the most effective and safe systems in operation and easy to operate, but it has a high running cost. In these systems, the flow of dairy wastewater passes through a series of cells and the fat mass, which is usually floating above, is removed by getting stuck inside the cells. There are many drawbacks to this system, such as the need for regular monitoring and cleaning to prevent the formation of FOGs, as well as reduced removal efficiencies at pHs above 8.

Air flotation system and soluble air flotation system

Mechanical removal of FOG by dissolved air flotation (DAF) involves aerating part of the recycled wastewater at a pressure of about 400-600 kPa in a pressure chamber and then discharging it into a flotation tank containing untreated dairy wastewater. Dissolved air turns into tiny air bubbles under normal atmospheric pressure conditions in the buoyancy tank. The formed heavy solids settle as air bubbles attach to the fat particles and other suspended matter remaining in the passing effluent. The resulting sludge is removed and will produce an odor if stored in an open tank. These are unstable materials that should preferably be disposed of without mixing with sludge from other biological and chemical treatment processes because they are difficult to lose water. FOG wastes should be disposed of and disposed of in accordance with previous procedures. The DAF system requires regular maintenance and relatively high operating costs. Air flotation is more cost-effective than DAF systems. Air bubbles are introduced directly into the flotation tank containing untreated wastewater using aerators with a propeller. There are various types of air flotation systems on the market, including Robosep Hydrofloat, Vacuum Flotation, Electrofloatation and Zeda. The main problem with DAF is the free FOGs that can be removed. Therefore, in order to increase the efficiency of the separation process, the soluble material and the soluble emulsified FOG must be subjected to a physicochemical treatment when free water is removed and the excess coagulating molecules to form larger masses for easier removal.

Biological treatment

Biodegradation is a promising option for the removal of organic matter from dairy wastewater. However, sludge formation, especially during the aerobic biodegradation process, can lead to serious problems and disposal costs. These problems can be exacerbated by the ability to absorb certain organic compounds as well as toxic heavy metals. However, biological systems have advantages such as the microbial evolution of complex organic matter and the possibility of absorption of heavy metals by suitable microbes. Biological processes are still relatively simple and have the potential to combine different types of biological designs to remove selective compounds.

Aerobic biological systems

Depending on the growth of microorganisms in an oxygen-rich environment, aerobic biological treatment methods oxidize organic matter to carbon dioxide, water, and cellular material. For example, the operating temperature should be maintained at around 35 to 37 ° C for an efficient process. It is also very important to maintain the pH in the range of 7, and consequently methane generators are very sensitive to pH. Ammonia nitrogen is not removed in an anaerobic system and is discharged with digestive effluent, which increases the oxygen demand of the receiving water. At this stage, a complementary treatment is required to reach acceptable discharge standards.

Anaerobic biological systems

Anaerobic digestion (AD) are biological processes performed by a group of active microbes in a system without the presence of an electron oxygen acceptor. More than 95% of organic loads in a sewage stream can be converted to biogas (methane, carbon dioxide) and the rest is used for cell growth and maintenance.

Disadvantages of anaerobic systems are high investment, long start-up period, precise control of operating conditions, high sensitivity to load change and organic shocks, as well as the presence of toxic compounds.

Electrochemical coagulation method for dairy wastewater treatment

The application of electrochemical technologies in the water and wastewater industry is very diverse. This technique has been used in various situations and industries to remove a wide range of pollutants. Applications of this technique in the water and wastewater industry include water treatment, breaking down fat and oil emulsions in water, removal of natural organic matter from water, fluoridation, removal of sulfated compounds, treatment of municipal and restaurant wastewater, removal of heavy metals, removal Arsenic mentioned the removal of phenolic compounds, wastewater treatment of dairy industry and chips production, wastewater treatment of yeast and sourdough industries, wastewater treatment of metal polishing industries, laundry and textile industries, as well as radioactive wastewater treatment. Electrochemical methods include: electrocoagulation, electrofluculation and electroflotation. The electrochemical method of electrocoagulation provides the unstable agents that cause the neutralization necessary to separate the contaminants. Electrofluctuation also produces factors that promote particle bridging or coagulation. Electroflotation is a method in which contaminants such as fats and oils are attacked by gas bubbles formed on the surface of the electrode (H2, O2) and are transported to the solution surface with these bubbles. In this way, the removal of contaminants from the system can be achieved by performing soaking.

Electrocoagulation and flotation using sacrificial anodes have been extensively studied for the removal of particulate matter, organic compounds, dyes, metal ions and inorganic anions, and various combinations of water and wastewater.

The process consists of 3 steps which are:

Coagulant formation by dissolution of metal ions from the reactive anode electrode;
Stabilization of contaminants, suspended particles and breaking of emulsions;
Accumulation of unstable phases and clot formation.
The general mechanism of coagulation and electrical buoyancy is a combination of the functions of different mechanisms simultaneously that intensify each other's performance in a chain. The main mechanism in the process may act as dynamic reactions through dynamic processes and change according to the type of pollutant and environmental and operational parameters.
Small oxygen bubbles that are naturally produced on the surface of iron or aluminum anodes are powerful oxidants that can oxidize organic matter molecules and turn them into smaller biodegradable particles. Hydrogen bubbles produced at the cathode can modify highly stable organic molecules and reduce their resistance to oxidation. Also, hydrogen and oxygen gases from electrolysis reactions can be very effective in better purification of pollutants. The hydrogen gas produced helps the mixture to mix and float as well as possible. When a clot is formed, the electrolytic gases produced attach to the clot and produce an immersion force, causing it to float and remove contaminants from the liquid surface.

Advantages of electric coagulation and flotation over other dairy wastewater treatment methods

Production of effluents with the least soluble solids (TDS) compared to chemical methods, in addition, the costs required to reuse such effluents are low.
Simple equipment and easy operation as well as minimal operation problems during the process compared to chemical and biological methods.
The effluent from the coagulation and flotation process is clear, colorless and odorless.
The sludge from the process is easily precipitated and dewatered from it, because most of the sludge is composed of metal hydroxides.
The clots formed in this process are larger than the clots resulting from the chemical coagulation process, and the amount of water in the clot junctions is lower, the resistance to acid is higher and more stable, and as a result it can be separated by faster filtration.
 The space required to install the equipment and set up the system is very small.
No need to buy and consume chemicals on a daily basis
No need for a specialized operator to set up
Having the minimum current costs in the matter of liquidation
Fixing the odor problem of factory effluent using electric coagulation method
System installation in the shortest possible time